Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems.
By
LINETTE FERREIRA
DISSERTATION
Submitted in Fulfilment of the Requirements for the Degree
MASTER OF SCIENCE
in
AQUATIC HEALTH
in the
FACULTY OF SCIENCE
at the
UNIVERSITY OF JOHANNESBURG
Supervisor: Professor Victor Wepener
December 2008
Table of Contents
LIST OF TABLES………………………………………………………………………………………… v
LIST OF FIGURES……………………………………………………………………………………….. viii
ACKNOWLEDGEMENTS……………………………………………………………………………….. xii
SUMMARY………………………………………………………………………………………………… xiii
OPSOMMING……………………………………………………………………………………………... xvi
CHAPTER 1: INTRODUCTION ……………………………………………………………………….. 1
1.1. Motivation for the Study...... 1 1.2. The Use of Biota as Indicators of Ecological Integrity...... 2 1.2.1. Diatoms ...... 3 1.2.2. Macroinvertebrates...... 4 1.2.3. Riparian Vegetation...... 4 1.3. The Influence of Agricultural Practices on Ecosystem Health...... 5 1.3.1. Sediment Loads...... 5 1.3.2. Nutrient Enrichment...... 6 1.3.3. Pesticides...... 7 1.3.4. Salinization...... 8 1.4. Study Area………………………………………………………………….. 9 1.5. Main Research Question...... 10 1.6. Hypothesis...... 10 1.7. Aims...... 11 1.8. Objectives...... 11 1.9. Brief Dissertation Outline...... 12
CHAPTER 2: STUDY AREA…………………………………………………………………………… 13
2.1. Introduction...... 13 2.2. Site Selection...... 16 2.3. Study Sites...... 17
CHAPTER 3: DIATOMS………………………………………………………………………………… 23
3.1. Introduction...... 23 3.1.1. The Use of Diatoms in Biomonitoring...... 23 3.1.2. Land Use and Diatom Community Structure...... 24 3.1.3. Diatom Responses to Agricultural Land Use Practices...... 24 3.1.4. Problem Statement...... 25 3.1.5. Aims...... 26 3.1.6. Objectives...... 26 3.2. Materials and Methods...... 26 3.2.1. Study Sites...... 26 3.2.2. Water Quality...... 26 3.2.2.1. Statistical Analysis...... 27 3.2.3. Diatoms...... 27
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. ii
3.2.3.1. Field Collection, Laboratory Analysis and Indices...... 27 3.2.3.2. Statistical Analysis...... 31 3.3. Results...... 32 3.3.1. Water Quality...... 32 3.3.1.1. Temporal Variation...... 35 3.3.1.2. Spatial Variation...... 36 3.3.2. Diatom Community Structure...... 38 3.3.2.1. Temporal Variation...... 38 3.3.2.2. Spatial Variation...... 39 3.3.3. Diatom Index Scores...... 45 3.3.3.1. Low Flow...... 45 3.3.3.2. High Flow...... 47 3.4. Discussion...... 48 3.4.1. Relationship between Water Quality and Land Use...... 48 3.4.1.1. Temporal Variation...... 48 3.4.1.2. Spatial Variation...... 50 3.4.2. Diatom Community Structure in Relation to Land Use...... 52 3.4.3. Diatom Community Integrity and Ecological Description...... 58 3.5. Summary and Conclusion...... 60
CHAPTER 4: MACROINVERTEBRATES……………………………………………………………. 61
4.1. Introduction...... 61 4.1.1. Macroinvertebrates as Biological Indicators...... 61 4.1.2. Land Use and Macroinvertebrate Community Structure...... 62 4.1.3. Macroinvertebrate Response in Relation to Agricultural Land Use...... 62 4.1.4. Aims...... 64 4.1.5. Objectives...... 64 4.2. Materials and Methods...... 65 4.2.1. Study Sites...... 65 4.2.2. Habitat...... 65 4.2.3. Macroinvertebrate Community Composition...... 65 4.2.3.1. Collection, Preservation and Enumeration...... 65 4.2.4. Functional Feeding Groups………………………………………………. 67 4.2.5. Statistical Analyses of Macroinvertebrate Community Data and FFGs 68 4.3. Results...... 69 4.3.1. Habitat...... 69 4.3.2. Macroinvertebrate Indices...... 71 4.3.3. Macroinvertebrate Diversity...... 72 4.3.4. Macroinvertebrate Community Composition...... 74 4.3.4.1. Temporal Variation...... 74 4.3.4.2. Spatial Variation...... 76 4.3.5. Functional Feeding Groups...... 83 4.3.5.1. Temporal Variation...... 83 4.3.5.2. Spatial Variation...... 84 4.4. Discussion...... 87 4.4.1. Macroinvertebrate Community Structure in Relation to Land Use...... 87 4.4.2. Functional Feeding Groups in Relation to Land Use...... 94 4.5. Summary and Conclusion...... 96
CHAPTER 5: RIPARIAN VEGETATION INTEGRITY AND MACROINVERTEBRATES………. 97
5.1. Introduction...... 97
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. iii
5.1.1. Riparian Vegetation and Macroinvertebrate Integrity...... 97 5.1.2. Aims...... 98 5.1.3. Objectives...... 98 5.2. Materials and Methods...... 99 5.2.1. Study Sites...... 99 5.2.2. Field Survey...... 99 5.2.3. Riparian Index...... 99 5.2.4. Statistical Analysis...... 100 5.3. Results...... 100 5.3.1. Riparian Vegetation Community Composition...... 100 5.3.2. Riparian Vegetation and Macroinvertebrate Community Composition. 102 5.3.3. Riparian Vegetation and FFGs...... 103 5.4. Discussion...... 104 5.4.1. Riparian Vegetation Integrity...... 104 5.4.2. Riparian Vegetation, Macroinvertebrate Composition and FFGs...... 106 5.5. Summary and Conclusion...... 109
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS……………………………………… 110
6.1. Introduction...... 110 6.2. Relationship between Agricultural Land Use Practices and Aquatic Communities...... 110 6.3. Recommendations...... 115
CHAPTER 7: REFERENCES………………………………………………………………………….. 118
APPENDIX A: SITE AERIAL PHOTOS………………………………………………………………. 139
APPENDIX B: WATER QUALITY AND DIATOMS…………………………………………………. 143
APPENDIX C: MACROINVERTEBRATES………………………………………………………… 154
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. iv
List of Tables
Table
2.1 The abbreviation and the position of each of the sites selected...... 16
3.1 Diatom indices, their abbreviations and reason for selection and use in the present study...... 30
3.2 Limit values for diatom indices in the evaluation of water quality classes and trophic state...... 31
3.3 Physico-chemical water quality properties of each site sampled during the low- (L) and high (H) flow periods. Target water quality guidelines for the aquatic ecosystem (DWAF, 1996) are also provided...... 34
3.4 Diatom index scores and classes for sites on the Harts- and Vaal Rivers during the low (L) flow period...... 45
3.5 Diatom ecological descriptors for sites on the Harts- and Vaal Rivers during the low (L) flow period...... 46
3.6 Diatom index scores and classes for sites on the Harts- and Vaal Rivers during the high (H) flow period...... 47
3.7 Diatom ecological descriptors for sites on the Harts- and Vaal Rivers during high (H) flow...... 48
4.1 The interpretation of IHAS scores presented as categories, category descriptions and percentage integrity...... 65
4.2 Categories and category descriptions for the interpretation of the SASS5 data...... 66
4.3 Macroinvertebrate families and their respective FFGs per family...... 67
4.4 The IHAS index scores, indicating integrity scores and classes for habitat components and overall habitat during low- (L) and high (H) flow periods. .... 70
4.5 The SASS5 scores, number of taxa, ASPT and EC during low- (L) and high (H) flow periods...... 72
5.1 Generic ecological categories for EcoStatus components (modified from Kleynhans et al., 2006)...... 100
5.2 Integrity scores (VEGRAI) for marginal, non-marginal, total intactness (%) and ECs for riparian vegetation at sites on the Harts- and Vaal Rivers during the high (H) flow period...... 101
5.3 The dominant plant species found at sites on the Harts- and Vaal Rivers during the high (H) flow period...... 101
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. v
B1 Historical water quality data for the relative reference site HR 1...... 148
B2 Historical water quality data for the agricultural site HR 3...... 148
B3 Historical water quality data for the agricultural site HR 3...... 148
B4 Species list for low (L) flow indicating species abundances, names and acronyms taken from OMNIDIA database...... 149
B5 Species list for high (H) flow indicating species abundances, names and acronyms taken from OMNIDIA database...... 151
B6 Diatom ecological descriptions (taken from Van Dam et al., 1994)...... 153
C1 Macroinvertebrate family abundance data for the low (L) flow period...... 155
C2 Macroinvertebrate family abundance data for the high (H) flow period...... 156
C3 Historical macroinvertebrate SASS5 data for the relative reference site HR 1 during the low flow period...... 157
C4 Historical macroinvertebrate SASS5 data for the relative reference site HR 1 during the high flow period...... 157
C5 Historical macroinvertebrate SASS5 data for the relative reference site HR 1 during the high flow period...... 157
C6 Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during the high flow period...... 157
C7 Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during the low flow period...... 157
C8 Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during the high flow period...... 158
C9 Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during high flow...... 158
C10 Historical macroinvertebrate family data for the relative reference site HR 1 during the low flow period...... 159
C11 Historical macroinvertebrate family data for the relative reference site HR 1 during the high flow period...... 159
C12 Historical macroinvertebrate family data for the agricultural site HR 3 during the low flow period...... 160
C13 Historical macroinvertebrate family data for the agricultural site HR 3 during the high flow period...... 160
C14 Historical macroinvertebrate family data for the agricultural site HR 3 during the high flow period...... 161
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. vi
C15 Macroinvertebrate FFG abundance data for the low (L) flow period...... 162
C16 Macroinvertebrate FFG abundance data for the high (H) flow period...... 162
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. vii
List of Figures
Figure
2.1 Geographical extent of the Lower Vaal WMA with the positioning of the study sites: 1= Harts River site 1; 2= Harts River site 2; 3= Harts River site 3; 4= Harts River site 4; 5= Harts River site 5; 6= Vaal River site 1; 7= Vaal River site 2 (DWAF, 2008a)...... 13
2.2 Harts River site 1 (relative reference site). (a) Pool area with bridge crossing river. (b) Pool area turns into flowing stream with a lot of cobble substrate. (c) Faster flowing stream flows into another pool area. (d) Rural settlement situated on either side of river...... 17
2.3 Harts River site 2 (HR 2). (a) Upstream of weir - this area consists of a pool area with some cobble substrate, as well as mud. Farm animals are present. (b-d) Downstream of weir - this area consists of a faster flowing area with noticeable cobble substrate, as well as muddy substrate. Bank erosion is visible...... 18
2.4 Harts River site 3 (HR 3). (a) Weir- and (b) bridge crossing the river. (c) Slower moving water; pool area. (d) Faster flowing water (with a lot of cobbles and bedrock) due to the weir stopping two thirds of the way across the river...... 19
2.5 Harts River site 4 (HR 4). (a) This site consists of good riparian vegetation, but poor water quality (turbidity) with high abundances of aquatic macrophytes. (b) The presence of cattle and canalisation...... 20
2.6 Harts River site 5 (HR 5). (a) Bridge crossing river. (b) Presence of weir. (c) Sand piles and aquatic macrophytes. (d) Poor riparian vegetation, bank erosion and presence of cattle...... 20
2.7 Vaal River site 1 (VR 1). (a) Construction created an additional biotope (stones) through the construction of a dirt road. (b) Lush aquatic vegetation and strong flowing cobble region. (c) Slower flowing cobble; gravel, sand and mud area. (d) Removal of riparian vegetation by construction practices...... 21
2.8 Vaal River site 2 (VR 2). (a) Easily accessible site; aquatic vegetation present. (b) Good riparian cover and marginal vegetation...... 22
3.1 Water quality physico-chemical properties for sites on the Harts- and Vaal Rivers during low- (L) and high (H) flow periods...... 35
3.2 Water quality physico-chemical properties for sites on the Harts- and Vaal Rivers during the low (L) flow period...... 36
3.3 Water quality physico-chemical properties for sites on the Harts- and Vaal Rivers during the high (H) flow period...... 37
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. viii
3.4 RDA bi-plot showing the relationship between measured environmental variables and diatom community structures for sites on the Harts- and Vaal Rivers during low- (L) and high (H) flow periods. An explanation of the acronyms is provided in Appendix B, Tables B4 and B5...... 38
3.5 CCA bi-plot showing the relationship between measured environmental variables and diatom community structures for sites on the Harts- and Vaal Rivers during the low (L) flow period. An explanation of the acronyms is provided in Appendix B, Table B4...... 40
3.6 Ranked species K-dominance plot for diatom community structures at low (L) flow for sites on the Harts- and Vaal Rivers, utilising abundance to indicate cumulative dominance...... 42
3.7 RDA bi-plot showing the relationship between measured environmental variables and diatom community structures for sites on the Harts- and Vaal Rivers during high (H) flow. An explanation of the acronyms is provided in Appendix B, Table B5...... 43
3.8 Ranked species K-dominance plot for diatom communities at high (H) flow for sites on the Harts- and Vaal Rivers, utilising abundances to indicate cumulative dominance...... 44
4.1 Univariate diversity index values for macroinvertebrates during both seasons (a) Total Species (S); (b) Total Individuals (N); (c) Margalef’s Species Richness (d); (d) Pielou’s Evenness (J’); and (e) Shannon-Weiner Diversity Index (H’ (loge)) for sites on Harts- and Vaal Rivers...... 73
4.2 RDA bi-plot showing the relationship between macroinvertebrate communities and selected environmental variables during both seasons for sites on the Harts- and Vaal Rivers...... 75
4.3 RDA bi-plot showing the relationship between selected environmental variables and macroinvertebrate community structures during the low (L) flow period for sites on the Harts- and Vaal Rivers...... 76
4.4 RDA bi-plot of the IHAS scores in relation to macroinvertebrate community structures for sites on the Harts- and Vaal Rivers during the low (L) flow period. SIC= stones-in-current; SC= stream condition; Veg= vegetation; OH= other habitat...... 78
4.5 Ranked species K-dominance plot for macroinvertebrate communities at low (L) flow for sites on the Harts- and Vaal Rivers, using abundances to indicate cumulative dominance...... 78
4.6 RDA bi-plot showing the relationship between selected environmental variables and macroinvertebrate community structures during the high (H) flow season for sites on the Harts- and Vaal Rivers...... 79
4.7 RDA bi-plot of the IHAS scores in relation to macroinvertebrate community structures for sites on the Harts- and Vaal Rivers during the high (H) flow period. SIC= stones-in-current; SC= stream condition; Veg= vegetation; OH= other habitat...... 80
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. ix
4.8 Ranked species K-dominance plot for macroinvertebrate communities at high (H) flow for sites on the Harts- and Vaal Rivers, using abundances to indicate cumulative dominance...... 81
4.9 RDA bi-plot showing the relationship between selected environmental variables and macroinvertebrate FFGs during both seasons for sites on the Harts- and Vaal Rivers...... 84
4.10 RDA bi-plot showing relationship between selected environmental variables and macroinvertebrate FFGs for sites on the Harts- and Vaal Rivers during the low (L) flow season...... 85
4.11 RDA bi-plot showing the relationship between selected environmental variables and macroinvertebrate FFGs during the high (H) flow season for sites on the Harts- and Vaal Rivers...... 86
5.1 RDA bi-plot of the relationship between riparian vegetation and macroinvertebrate community structures for sites on the Harts- and Vaal Rivers...... 103
5.2 RDA bi-plot of the riparian vegetation integrity in relation to macroinvertebrate FFGs for sites on the Harts- and Vaal Rivers...... 104
6.1 Summary of the results for water quality and indicator diatoms in relation to land use...... 111
6.2 Summary of the results for habitat, macroinvertebrate index, community structures and FFGs...... 112
6.3 Summary of the results for riparian integrity and macroinvertebrate community structures and FFGs...... 114
A1 Aerial photo of the relative reference site HR 1 (Google Earth, 2008)...... 140
A2 Aerial photo of the agricultural site HR 2 (Google Earth, 2008)...... 140
A3 Aerial photo of the agricultural site HR 3 (Google Earth, 2008)...... 141
A4 Aerial photo of the agricultural site HR 4 (Google Earth, 2008)...... 141
A5 Aerial photo of the agricultural site HR 5 (Google Earth, 2008)...... 142
A6 Aerial photo of the relative reference site VR 1 and the agricultural site VR 2 (Google Earth, 2008)...... 142
B1 Historical water quality graph of available water quality data for the Harts River downstream of Taung Dam, in the vicinity of the relative reference site HR 1 (DWAF, 2008b)...... 144
B2 Historical water quality graph of available water quality data for the Harts River at Espagsdrift, in the vicinity of the agricultural site HR 4 (DWAF, 2008b)...... 145
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. x
B3 Historical water quality graph of available water quality data for the Harts River at the confluence with the Vaal River, in the vicinity of the agricultural site HR 5 (DWAF, 2008b)...... 146
B4 Historical water quality graph of water quality data for the Vaal River upstream of the Harts confluence, downstream of the relative reference site VR 1 (DWAF, 2008b)...... 147
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xi
Acknowledgements
I would like to express my sincere gratitude to the following people and institutions:
Prof. Victor Wepener for his excellent guidance, support, patience, availability and insight.
Dr. Jonathan Taylor (North-West University) for his time, knowledge and guidance with regard to the diatom identification and enumeration.
Mr. Andrew Hankey (Walter Sisulu National Botanical Garden) for his time and knowledge regarding the identification of the riparian vegetation.
The National Research Foundation (NRF) for their financial support throughout the duration of my study.
Gina Walsh for her mentorship and friendship.
To my fellow students and friends Martin Ferreira, Wynand Malherbe, Leanie Graham, Arno de Klerk and Zola Scholtz, for their support in the field and in the laboratory, as well as for their emotional and moral support.
On a more personal note, I would like to express my love and gratitude to:
My mother Louise, father Willem and my brother Quinton for their support and unconditional love.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xii
Summary
Water resources in South Africa are scarce and need to be protected and managed in a sustainable way for future generations. Food supply is a great priority worldwide and the pressure to produce enough food has resulted in the expansion of irrigation and the steadily increasing use of fertilizers and pesticides to achieve higher yields. Rivers are impacted by agriculture through increased suspended sediment loads (which affects primary production, habitat reduction and introduction of absorbed pollutants), elevated nutrient inputs (which may increase the abundances of algae and aquatic plants), salinization and pesticide runoff (which eliminates species intolerant to these conditions and therefore impacts on the normal production of the river system). Aquatic biota plays an integral part in the functioning of aquatic ecosystems. Biological monitoring is used to assess ecosystem health and integrity. Biological communities reflect the overall integrity of the river ecosystem by integrating various stressors and therefore provide a broad measure of their synergistic effects.
The research area falls within the Lower Vaal Water Management Area (WMA), which lies in the North-West and Northern Cape Provinces. The lower Vaal River and the Harts River (one of the tributaries of the Vaal) are the river systems under investigation in this study. Farming activities ranges from extensive livestock production and rain fed cultivation to intensive irrigation enterprises at Vaalharts (such as maize, cotton and groundnuts). The Vaalharts is the largest irrigation scheme in South Africa. Salinity is of concern in the lower reaches of the Harts- and Vaal Rivers, due to saline leachate from the Vaalharts irrigation scheme. Agricultural inputs are known to affect aquatic communities and chemicals (e.g. pesticides, herbicides, fertilizers) are extensively used in the Vaalharts irrigation scheme. At present there are no data on the effect of these chemicals on the aquatic biota of the lower Harts- and Vaal Rivers. The aims of this study were to assess the diatom- and macroinvertebrate community structures, ecosystem integrity and macroinvertebrate feeding traits (functional feeding groups – FFGs) in relation to land use.
Study sites were selected above, adjacent to, and below agricultural activities. Diatom- and macroinvertebrate community data were obtained using standardised sampling techniques. Organisms were identified, enumerated and different indices (diatom, e.g. Generic Diatom Index - GDI, Specific Pollution sensitivity Index - SPI, Eutrophication Pollution Index - EPI, Biological Diatom Index - BDI and Percentage Pollution Tolerant Valves - %PTV and macroinvertebrate e.g. South African Scoring System - SASS5) were applied. Additional habitat indices (Integrated Habitat Assessment System - IHAS and Riparian Vegetation
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xiii
Response Assessment Index - VEGRAI) and water quality analyses were undertaken to determine which environmental drivers contributed towards the community structure data. Principal Component Analysis (PCA) was undertaken on the water quality data to elucidate the spatial and temporal trends in relation to land use. Multivariate and univariate analyses were conducted on the water quality, habitat, macroinvertebrate (community structure and FFG), diatom (community structure) and riparian vegetation data to determine the spatial and temporal trends in the community structures and associated environmental influences.
Diatom- and macroinvertebrate community structures were found to change in relation to land use. Communities with higher abundances of sensitive taxa were recorded at the relative reference sites, whereas tolerant taxa dominated the community structure at the agricultural sites. Diatom indicators included the motile genera Navicula and Nitzschia species (indicators of sedimentation and organic pollution), Nitzschia frustulum (high phosphates) and Tabularia fasciculata (turbidity and conductivity) found at the agricultural sites. The macroinvertebrate indicator species were Simuliidae (regulated flow and nutrients), Chironomidae, Oligochaeta, molluscs (nutrient loads), Hydropsychidae (sedimentation) and Atyidae (salinization).
The macroinvertebrate FFGs could not be used to distinguish between different land uses. However, they did indicate that fine particulate organic matter (FPOM) was the main available food source in the Harts- and Vaal River systems. Collector-filterers, collector- gatherers, predators and scrapers were found to be the dominant FFGs.
Riparian integrity had a secondary effect on the structuring of the macroinvertebrate communities and FFGs. The moderately to largely impacted riparian vegetation resulted in changes in instream habitat integrity due to increased sedimentation, decreased litterfall and impaired flow. These in turn were the result of anthropogenic activities e.g. livestock trampling, dams, sedimentation from upland areas and the introduction of alien and invasive plants.
The use of biotic indices was useful to indicate deteriorating conditions due to human impacts, but the community structure data proved to be more reliable indicators of changing integrity due to land use. It was concluded that diatom- and macroinvertebrate community structures could differentiate between differing land uses and were therefore regarded as reliable indicators of water quality and habitat integrity. Diatom communities, however, were a better indicator of land use activities when compared to the macroinvertebrate structure.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xiv
Key words: Land use, diatoms, macroinvertebrates, FFGs, water quality, habitat integrity, riparian vegetation integrity, Harts River, Vaal River.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xv
Opsomming
Waterbronne in Suid-Afrika is skaars en dit is daarom van groot belang dat dit bewaar en op ‘n volhoubare wyse bestuur word om vir toekomstige geslagte behoue te bly. Voedselvoorsiening is ‘n belangrike, wêreldwye prioriteit. Die druk op landbou om genoeg voedsel te produseer het tot die uitbreiding van besproeiingskemas en ‘n toename in die gebruik van kunsmisstowwe en pestisiedes om groter opbrengste te lewer, gelei. Die impak van landboubedrywighede op riviersisteme word deur ‘n aantal veranderinge in die water en habitatkwaliteit gekenmerk. Hierdie impakte sluit o.a. toenames in gesuspendeerde sedimentladings (wat primêre produksie beïnvloed, afname in beskikbaarheid van habitat en toenames in geabsorbeerde besoedelstowwe), verhoogde nutriëntladings (wat die welige groei van alge en akwatiese plante tot gevolg het), toenames in saliniteit en pestisiedafloop (wat sensitiewe spesies elimineer en sodoende die normale produksie van die riviersisteem impakteer) in. Akwatiese biota maak ‘n belangrike deel van akwatiese ekosisteme, asook hulle normale funksionering uit. Biologiese monitering word gebruik om ekosisteem integriteit en derhalwe gesondheid te monitor. Biologiese gemeenskappe reflekteer die algehele integriteit van rivierekosisteme aangesien die aan- of afwesigheid van spesies ‘n geïntegreerde maatstaf van omgewingsfaktore weergee.
Die studie area is binne die Laer Vaal Waterbestuursarea (WBA) in die Noord-Wes en Noord-Kaap provinsies geleë. Die laer Vaal- en Hartsriviere (een van die sytakke van die Vaalrivier) word intensief as waterbronne vir lanbou gebruik en is die riviersisteme wat in hierdie studie ondersoek word. Landbou aktiwiteite wissel van veeboerdery en saaigewasse tot intensiewe besproeiingsondernemings (bv. koring, katoen en grondbone) in die Vaalharts omgewing. Die Vaalharts besproeiingskema is die grootste in Suid-Afrika. Toenames in saliniteit is die grootste waterkwaliteitsprobleem in die laer dele van die Harts- en Vaalriviere. Dit is as gevolg van die souterige afvalwater wat vanaf die Vaalharts besproeiingskema afkomstig is. Landbou besoedelstowwe affekteer akwatiese gemeenskappe en chemikalië (bv. pestisiede en kunsmis) word grootskaals in die Vaalharts besproeiingskema gebruik. Tans is daar geen data oor die effekte van hierdie chemikalië op die akwatiese biota in die laer Harts- en Vaalriviere beskikbaar nie. Die doelwitte van hierdie studie was om die invloed van verskillende grondgebruike (landbou en verstedeliking) op die ekosisteem integriteit (soos voorgestel deur die diatoom- en makroinvertebraatdiversiteit) te bepaal.
Versamellokaliteite is gekies om toestande bokant, aangrensend en onder landbou aktiwiteite te bepaal. Diatoom- en makroinvertebraat gemeenskapsdata was verkry deur
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xvi
van gestandaardiseerde versamelingstegnieke gebruik te maak. Die spesies diversiteit en oorvloed data is in diatoom (GDI, SPI, EPI, BDI, asook %PTV) en makroinvertebraat (SASS5) indekse toegepas. Addisionele habitat indekse (IHAS en VEGRAI) en water kwaliteitsanalises was by dieselfe lokaliteite uitgevoer om sodoende te bepaal watter omgewingsfaktore tot die gemeenskapsamestelling se groeperings kon bydra. Hoofkomponent analise (PCA) was gebruik om die tyd-ruimtelike patrone in die waterkwaliteit in verhouding tot grondgebruik te verklaar. Parametriese en nie-parametriese statistiese analise was op die waterkwaliteit, habitat, makroinvertebraat (gemeenskapsamestelling en funksionele voedingsgroepe), diatoom gemeenskapsamestelling, asook rivieroewer plantegroei uitgevoer om die tyd-ruimtelike verwantskappe te bepaal.
Diatoom- en makroinvertebraat gemeenskapsamestellings het ‘n duidelike verwantskap met grondgebruik getoon. Gemeenskappe wat uit meer sensitiewe taksa bestaan het, is by die verwysingslokaliteite stroom-op van die landbou bedrywighede gevind. Gemeenskappe met meer geharde taksa is by die lokaliteite wat onder die invloed van landbougebiede was, gevind. Die volgende diatome is as indikatorspesies geïdentifiseer: Navicula en Nitzschia spesies (indikatore van sedimentasie en organiese besoedeling), Nitzschia frustulum (hoë fosfate) en Tabularia fasciculata (turbiditeit en konduktiwiteit) wat almal in die nabyheid van landbou aktiwiteite gevind is. Die invertebraat indikatore was as Simuliidae (gereguleerde vloei en nutriënte), Chironomidae, Oligochaeta, molluske (nutriëntladings), Hydropsychidae (sedimentasie) en Atyidae (saliniteit) geïdentifiseer.
Die makroinvertebraat funksionele voedingsgroepe het nie enige verwantskappe tussen grondgebruike uitgewys nie, maar het wel die teenwoordigheid van fyn organiese materiaal as die hoof voedingsbron in die Harts- en Vaalriviersisteme uitgewys. Versamel-filtreerders, versamel-opgaarders, predatore en skrapers was as die dominante funksionele voedingsgroepe uitgewys.
Rivieroewer plantegroei integriteit het ‘n sekondêre effek op die makroinvertebraat gemeenskappe en funksionele voedingsgroepe gehad. Die geïmpakteerde rivieroewer plantegroei het tot veranderinge in die stroomhabitat integriteit gelei. Dit is deur verhoogde sedimentasie, verlaagde toevoeging van organiese materiaal in die vorm van blare en veranderinge in vloei veroorsaak. Die genoemde impakte is deur ‘n aantal aktiwiteite onder meer vertrapping van plantegroei deur vee, damme, erosie en die voorkoms van eksotiese en indringerplante veroorsaak.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xvii
Die gebruik van biotiese indekse was effektief toegepas om die veranderde omgewingstoestande wat deur menslike aktiwiteite veroorsaak is, uit te wys. Die gemeenskapstrukture was op hul beurt beter aanduiers van veranderinge met betrekking tot grondgebruik praktyke. Van die twee indikatorgroepe was die diatoom gemeenskappe meer sensitief en ‘n beter aanduiding van omgewingsveranderinge met betrekking tot grondgebruike.
Sleutel woorde: Grondgebruike, diatome, makroinvertebrate, funksionele voedingsgroepe, waterkwaliteit, habitat integriteit, rivieroewer plantegroei, Hartsrivier, Vaalrivier.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. xviii
Chapter 1: Introduction
1.1. Motivation for the Study: Water is an indispensable natural resource that is relatively scarce and unevenly distributed in South Africa. It is an essential part for life, the environment, food production, hygiene, and economic development (DWAF, 2004a). Human activities have severely affected the condition of freshwater ecosystems. The demand for water increases with human population pressure and economic development. As a result rivers will continue to deteriorate unless they are utilised and managed in a sustainable way (Deksissa et al., 2003).
It is important to protect the quality of the nation’s water resources in order to keep these ecosystems in a healthy, functioning condition and to ensure sustainability of these water resources in the interests of all water users (Baron et al., 2003). Aquatic biota forms an integral part of this goal (critical to sustaining freshwater ecosystems, since they are responsible for water purification, decomposition and nutrient cycling) (Baron et al., 2003) and therefore need to be protected. Aquatic biota, particularly the detritivores and microbes, break down complex organic matter into simple organic molecules and in this way cleanse river ecosystems of nutrient-rich organic waste. This cleansing process is, however, impossible where toxic substances change the chemical nature of the water thereby killing even those organisms that are tolerant enough to withstand gross organic pollution and initiate the cleansing process. The physical alteration of river systems will also result in a decline or loss of aquatic biota (Davies and Day, 1998). Aquatic biota also provide a valuable food source for larger animals, both aquatic and terrestrial.
In order to manage water resources in South Africa, the following legislation has been implemented to protect the country’s water resources: the Water Services Act (WSA, Act 108 of 1997, RSA, 1997), the National Water Act (NWA, Act 36 of 1998, RSA, 1998a) and the National Environmental Management Act (NEMA, Act 107 of 1998, RSA, 1998b). The Department of Water Affairs and Forestry (DWAF) has developed the National Water Policy (NWP, DWAF, 1997), as well as the National Water Resource Strategy (NWRS, DWAF, 2004a), which is the implementation strategy for the NWA. The NWRS sets out policies, strategies, objectives, plans etc. for the protection, use, development, conservation, management and control of the country’s water resources (DWAF, 2004a).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 1
Introduction
Access to food supply is the second greatest priority in South Africa (only to availability of drinking water). The pressure to produce enough food has had a worldwide impact on agricultural practices: 1) expansion into marginal lands; 2) expansion of irrigation, and 3) increasing use of fertilizers and pesticides in order to achieve and sustain higher yields (Ongley, 1996).
It is important to study the effects of agricultural inputs (e.g. pesticides, fertilizers, sediment loads) on aquatic ecosystems in order to fully understand the processes involved of these stresses on aquatic ecosystems (Wendt-Rasch et al., 2003). Generally, the amount of pesticide impinging on target pests is an extremely small percentage of the amount applied. Often, less than 0.1% of pesticides applied to crops reach target pests (Pimentel and Levitan, 1986). Chemicals used in agriculture may find their way into aquatic systems by spray drift, leaching, runoff and accidental spills. Many aquatic species are taxonomically related to the target organisms of pesticides and will be negatively affected by these chemicals either by mortality, reduced recruitment and reduced diversity, among countless others (Cairns, 2003).
1.2. The Use of Biota as Indicators of Ecological Integrity Biological monitoring techniques have been introduced as part of routine monitoring programmes, because of certain shortcomings in standard physical and chemical methods (e.g. it is very expensive and difficult to analyse every potential pollutant in a sample of water) (Eekhout et al., 1996). The monitoring of biota is an easy, rapid and cost effective way of monitoring ecosystem health. The main advantage of a biological approach is that it examines organisms whose exposure to pollutants is continuous, in other words the aquatic biota reflect both the present and past history of the water quality of a particular river ecosystem. Therefore, biological communities are a valuable means of monitoring the overall ecological integrity of an ecosystem, because they integrate and reflect the synergistic impacts of various stressors on that ecosystem (Chutter, 1998; De la Rey et al., 2004). Benthic macroinvertebrates have been shown to be reliable indicators of ecosystem health (e.g. Lenat and Crawford, 1994; Smith et al., 1999; Sandin and Johnson, 2000; Capítulo et al., 2001; Weigel et al., 2002). However, no single group of organisms is always best suited for detecting the diversity of anthropogenic perturbations. Fish, invertebrates and diatoms represent different trophic levels and are therefore expected to be affected differently by different types of disturbance (Allen et al., 1999). The use of diatoms as indicators of ecosystem health has also been proven to be a valuable means of
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 2
Introduction
biomonitoring (e.g. De la Rey et al., 2004; Harding et al., 2005; Taylor et al., 2007a,b). Diatoms indicate specific changes in water quality (Kwandrans et al., 1998; De la Rey et al., 2004), whereas invertebrate assemblages better reflect the impact of changes in the physical habitat in addition to certain chemical changes (McCormick and Cairns, 1994).
1.2.1. Diatoms Diatoms are unicellular and eukaryotic micro-organisms that form an important component of the aquatic ecosystem. Diatoms are protists belonging to the class Bacillariophyceae (Dixit et al., 1992). Diatoms provide relatively unique information concerning ecosystem condition, because of their nutritional needs and their position at the base of aquatic food webs (role as primary producers and transformers of inorganic nutrients into organic forms useable by other organisms) (McCormick and Cairns, 1994). Diatoms stabilise the substrate and create mats that are used by fish and invertebrates as habitat; some invertebrates use algae to construct cases (Bott, 1996 cited in Fore and Grafe, 2002).
Diatoms occur in nearly all aquatic environments (lakes, rivers, wetlands) and are abundant in most (Round, 1993 cited in Reid et al., 1995). They have short cell cycles and rapidly colonize new habitats (Round, 1991). Therefore, changes in diatom community structures represent rapid response to environmental change. For example, diatoms that are attached to a substratum use nutrients as food source and thus respond directly to fluctuations in nutrient levels, stressors and physical conditions in the water (Kriel, 2008). The ecological requirements (optima and tolerances) of many species are well known; so that accurate deductions can be made about the quality of the water (physical and chemical properties) they inhabit (Hall and Smol, 1992; Fritz et al., 1993). Changes in diatom assemblages also correspond closely to shifts in other biotic communities such as other algae, zooplankton, aquatic macrophytes and fish. Diatom communities can also provide insight on what the historical water quality was for a particular water body (McCormick and Cairns, 1994). Hence, water quality conditions can be reconstructed from fossil diatom assemblages, representing periods before human impacts on aquatic ecosystems (Hall and Smol, 1992). Diatoms colonize substrate types such as rocks, macrophytes, silt and sand and therefore appear to have no strong habitat preferences (Round, 1991). They are regarded as cosmopolitan or ‘sub-cosmopolitan’ in distribution and therefore use can be made of taxonomic and ecological studies conducted in other parts of the world (Round, 1993 cited in Reid et al., 1995). The taxonomy of diatoms is generally well-documented and species identifications are largely based on frustule morphology (e.g. Krammer and Lange-Bertalot, 1986, 1988, 1991a,b). The microscope slides prepared for analysis are permanent and
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 3
Introduction
therefore don’t need to be analysed immediately and can also be re-checked or compared in later studies (Round, 1993 cited in Reid et al., 1995).
Plafkin et al. (1989 cited in Pan et al., 1996) stated that species-rich diatom assemblages can integrate temporal variability of environmental conditions and the aggregate influence of different environmental factors. Changes in the abundance and diversity of benthic diatoms are commonly used to survey water quality (e.g. Jüttner et al., 2003). By using changes in diatom species composition, changes in physico-chemical conditions of surface waters can also be detected (Stevenson, 1984). Therefore, diatoms can be used as quantitative indicators of ecological conditions.
1.2.2. Macroinvertebrates Macroinvertebrates are used in biomonitoring, because they are sensitive indicators of environmental changes in streams (Rosenberg and Resh, 1993; Barbour et al., 1996). They also play an important role in the processing of transported organic matter, serve in purifying river water and provide a valuable food source for larger animals.
Macroinvertebrates offer many advantages in biomonitoring. They are ubiquitous, in other words, they can be affected by environmental perturbations in many different types of aquatic systems and in habitats within those waters. They allow for effective analyses of spatial (because of their sedentary nature) and temporal (they have long life cycles) changes caused by perturbations. Macroinvertebrates therefore act as continuous monitors of the water they inhabit (Rosenberg and Resh, 1993), which enable long-term analyses of both regular and intermittent discharges, variable concentrations of pollutants, single or multiple pollutants, and even synergistic or antagonistic effects (Rosenberg and Resh, 1993).
1.2.3. Riparian Vegetation Riparian vegetation performs an important role in structuring a riverine ecosystem, one of which is to provide food and shelter for the faunal components of the system. The riparian vegetation found along rivers is determined by differences in flow patterns and differences in substrate types (e.g. soil texture, pH). Vegetation therefore serves as an important indicator of river characteristics and changes in flow patterns (Boucher, 1999). One of the ways in which the riparian zone influences an adjacent waterway is through its vegetation. According to Gregory et al. (1991) riparian vegetation plays an important role in modifying solar inputs and influencing stream temperatures; controlling the flux of nutrients from
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 4
Introduction
watersheds; controlling the quantity and type of terrestrially derived organic matter and also seasonal patterns of litter inputs; affects the aquatic primary producers, and therefore indirectly affect aquatic invertebrates and vertebrates. Riparian zones also have the ability to trap sediments amassed in upslope areas (Osborne and Kovacic, 1993; Gilliam, 1994), as well as preventing erosion by putting down roots that stabilize the streambank.
Because of their physical location between uplands and aquatic systems, riparian zones are in an ideal position to modify, incorporate, dilute or concentrate substances in ground water before they enter waterways (Osborne and Kovacic, 1993). Riparian zones have the capacity to act as ‘buffer’ zones and because of this capacity, an interest in their preservation has become widespread, particularly in agricultural settings where farm management practices have become increasingly intensified (Martin et al., 1999).
1.3. The Influence of Agricultural Practices on Ecosystem Health
Agriculture uses two-thirds of the world’s water and has been shown to be a chief contributor to water quality degradation (Robertson, 2006). South Africa has a total surface area of 122 million ha. of which 18 million ha. is potential land for cultivation (Dennis and Nell, 2002). The irrigation sector uses approximately 50% of the water used in South Africa. Groundwater irrigates 24% of the irrigable land, compared to surface water which irrigates 76% (Van Tonder and Dennis, 2000 cited in Dennis and Nell, 2002). South Africa has three major rivers (Vaal, Orange and Limpopo) and irrigation schemes were developed near the riverbanks of these rivers. Other irrigation schemes further away are also supplied with water from these rivers (Dennis and Nell, 2002). Rivers are impacted by agriculture through increased suspended sediment loads, elevated nutrient inputs, pesticide runoff and salinization.
1.3.1. Sediment Loads Soil erosion and sedimentation causes substantial waterway damages and water quality degradation. Increased sediment loads caused by agricultural activities may impact stream communities through a variety of direct and indirect processes (Oschwald, 1972 cited in Lenat et al., 1981) that includes reduced light penetration (which affects primary production), habitat reduction and the introduction of absorbed pollutants (e.g. pesticides, metals, nutrients). An increase of suspended sediment levels may increase drift in fauna and is also known to interfere with reproduction, growth and survival (e.g. smothering) of aquatic organisms, which ultimately compromises biotic integrity (Cooper, 1993; Waters, 1995;
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 5
Introduction
Stone et al., 2005). Suspended sediment can alter the water chemistry and cause temperature decreases and turbidity increases.
Lenat et al. (1981) studied the effects of sediment inputs on the macroinvertebrate community structure in two piedmont streams. They found that the macroinvertebrates responded to the sediment additions in two different ways: 1) under high flow conditions the fauna occurred mainly on rocky substrates. As sediment was added to the streams, the area of available rock habitat decreased, which resulted in a decrease in benthic density. However, little change in community structure was detected when compared to the control site (i.e. not impacted upon by sediment inputs). 2) Under low flow conditions, a stable- sand community developed, which was qualitatively different from the community associated with rocky substrates. This sand community was composed of small grazing organisms capable of rapid colonization and reproduction. Thus, sediment addition resulted in the reduction of available habitat (rocky habitats were reduced to stable sand areas). The density of the macroinvertebrates in these sandy areas was found to be much greater than the density in control areas and therefore a distinct change in community structure had occurred.
1.3.2. Nutrient Enrichment Pollution by nutrients from agriculture causes many problems in the environment, one of the main sources being fertilizers. Rivers collect water from the hydrological basin and concentrate substances containing nutrients and trace elements as it makes its way through soil, rocks etc. Kremser and Schnug (2002) stated that ‘rivers are not fertilized, but there is a strong indirect impact of fertilization to the ecosystem i.e. not the fertilizer itself but the effects caused by it are the reason for the impairment’. Inorganic nitrogen and phosphorus compounds may cause nitrification oxygen demand, because of the microbial oxidation of ammonia; intensification of the primary production of plankton, macrophyta and other water plants by increased availability and use of nutrients; and finally the formation of toxic ammonia (NH3) (Kremser and Schnug, 2002).
Globally, more nutrients are added as fertilizers than are removed as produce. Beaton et al. (1995 cited in Carpenter et al., 1998) found that there is a net transport of phosphorus and nitrogen from sites of fertilizer manufacture to sites of fertilizer deposition and manure production. A nutrient surplus is therefore created on agricultural lands, which is the underlying cause of non-point pollution from agriculture. The most common effects of increased nitrogen and phosphorus supplies on aquatic ecosystems are increases in the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 6
Introduction
abundances of algae (Lohman et al., 1991; Welch et al., 1992; McGarrigle, 1993; Basu and Pick, 1996; Smith et al., 1999) and aquatic plants. The degradation of water resources by eutrophication can also result in losses of their component species, as well as losses of the services that these systems provide (Carpenter et al., 1998).
Elwood et al. (1981 cited in Smith et al., 1999) demonstrated the effects of excessive nutrient inputs. Two reaches of a shaded oligotrophic Tennessee stream were enriched for 95 days with inorganic phosphorus. Stream water phosphorus concentrations were increased by over an order of magnitude, which resulted in a significantly increased benthic algal biomass, increased rates of detritus decomposition and increased abundances of macroinvertebrate consumers. Other authors have found similar results (e.g. Horner et al., 1990; Smith et al., 1999). An indirect effect of eutrophication is a rise in water level caused by an excessive growth of macrophyta in conjunction with increasing friction. The ecosystems in the water course as well as at the banks may be affected, too (Kremser and Schnug, 2002).
1.3.3. Pesticides Pesticides can alter an ecosystem’s structure and function by eliminating a certain number of species (reducing their populations). Pesticides may therefore impact producer-herbivore or herbivore-carnivore interactions. Reducing species richness and altering an ecosystem’s structure may then in turn change its stability (e.g. elimination of a certain population’s natural enemy). Pesticides that directly affect plants and one or many decomposer organisms may significantly alter the productivity of ecosystems (Pimental and Levitan, 1986).
In most agricultural catchments, pollutants probably enter as pulses of various strengths and intensities, as was found in two watersheds in Vermont. Gruessner and Watzin (1995) found that six common herbicides entered streams in pulses that usually dissipated within a few days after a rain event. The authors found that the concentration of herbicide in the water varied depending on rainfall intensity and duration; the location of the sampling site within the watershed (upstream sites showed higher concentrations, but a shorter duration of contamination); and the intensity of agriculture surrounding the sites. The authors simulated the pulse exposure of atrazine in laboratory microcosms and found no effects on chlorophyll a or benthic macroinvertebrate community composition, but did found significantly earlier emergence of insects in the atrazine exposures. Alexander et al. (2008) examined the effects of 12 hour pulse and 20 day press (continuous) exposures of the agricultural
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 7
Introduction
insecticide imidacloprid on nymph abundance, emergence patterns and adult body size of Epeorus species (Heptageniidae) and Baetis species (Baetidae). The authors found that in the press exposures, reduced nymph density was driven by reduced survivorship, and in the pulse exposures reduced nymph density was reflected by increased emergence, because of stress. The insecticide imidacloprid resulted in reduced head length in Baetis and thorax length in Epeorus. Body size was linked to male success or fitness and can therefore affect population dynamics. It was found that sub-lethal doses of imidacloprid have the potential to reduce the reproductive success of mayfly populations.
1.3.4. Salinization Salinization refers to an increased concentration in water, or in soil, of naturally occurring mineral ions such as sodium, chloride and sulphate. Agricultural activities are a devastating form of salt pollution, especially in dryland environments. Long-term irrigation, especially in the form of spraying, carried out in dry areas and/or areas where the rocks or soils have high mineral concentrations, results in secondary salinization of soils and water (Davies and Day, 1998). Secondary salinization occurs due to the sinking of some of the irrigation water into the soil. However, some of it evaporates, leaving behind the salts it contained. If this process continues over long periods, especially if the irrigation water was saline to begin with, salts build up in the soil. In dry areas, salts accumulate in the soil during dry periods and are flushed out by rain, thus rivers are characterized in having increased salt concentrations particularly after rain (Davies and Day, 1998).
Salinization of rivers is recognised as one of the major threats to South Africa’s water resources, particularly the Great Berg- and Breede Rivers in the south-western Cape and the Sundays- and Fish Rivers in the Eastern Cape. The water quality of these rivers is rapidly declining as a result of irrigation-induced salinization (Davies and Day, 1998).
Some biotic groups are more tolerant of salinity than others. Freshwater diatoms and aquatic plants appear to be less tolerant of increased salt. Field observations indicate that as salinity increases, diatoms decrease in both abundance and richness (Blinn, 1993; Blinn and Bailey, 2001). Aquatic plants show adverse affects at salinities above 1,000mg/l. Reduced growth rates and reduced development of roots and leaves, the suppression of sexual and asexual reproduction (James and Hart, 1993; Warwick and Bailey, 1997, 1998 cited in Nielsen et al., 2003), as well as decreased germination (Baskin and Baskin, 1998 cited in Nielsen et al., 2003), are some of the effects attributed to increased salinities on aquatic plants. The macroinvertebrate fauna of rivers appear to be tolerant and relatively
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 8
Introduction
resilient to increasing salinity (Williams et al., 1991). The groups most sensitive to increasing salt are insect larvae and molluscs (Hart et al., 1991). Acute 72 hour toxicity tests
(LC50) of 59 macroinvertebrate taxa indicated that the salinity tolerance ranged from 5,000 up to 50,000mg/l, with baetid mayflies the least tolerant (LC50 = 5,500mg/l) and macrocrustaceans the most tolerant (LC50 = 38,000mg/l) (Kefford et al., 2003a cited in Nielsen et al., 2003). According to Nielsen et al. (2003) little is known of the effects of elevated salinity on modifications to egg development or early instar and juvenile development.
1.4. Study Area The research area falls within the Lower Vaal Water Management Area (WMA), which lies in the North-western part of South Africa and borders on Botswana in the north. The Lower Vaal WMA is located downstream of Bloemhof Dam and upstream of Douglas Weir. It extends to the headwaters of the Harts-, Molopo-, and Kuruman Rivers in the north and the Vaal River downstream of Bloemhof in the south. The Lower Vaal WMA covers an area of 51,543km2 (DWAF, 2004b).
Agricultural activities are a major source of diffuse water contamination in the Lower Vaal WMA. The Vaalharts irrigation scheme was developed in 1933 to reduce the unemployment problem in South Africa (Strauss, 1991 cited in Dennis and Nell, 2002). The Vaalharts irrigation scheme is one of the largest irrigation schemes in the world and is managed by Vaalharts Water. The irrigation water for the Vaalharts irrigation scheme is supplied by a channel from the Vaal River. Farmers at Vaalharts receive a water quota of 7,700m2/ha/year (Strauss, 1991 cited in Dennis and Nell, 2002). The quality of surface water in the Harts- and Vaal Rivers is highly impacted upon by irrigation return-flows, as well as by water usage in the Upper- and Middle Vaal WMAs (DWAF, 2004b).
Intensive irrigation practices are undertaken at Vaalharts, with crops such as maize, groundnuts, lucern, as well as cotton being planted and harvested. Salinity is of special concern (DWAF, 2004b) and one wonders how long the irrigation programme will support agriculture before salinization renders the soil incapable of bearing crops. According to the Lower Vaal WMA overview of water resources availability report (DWAF, 2003 cited in DWAF, 2004b), ‘over 90% of the requirements for irrigation are in the Harts sub-area, mainly at the Vaalharts irrigation scheme, with the balance being along the Vaal River’. The result of salt additions to croplands by irrigation farming practices along the lower Vaal River
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 9
Introduction
system and the impact thereof on the osmotic potential of soils over the long-term were estimated with the aid of salt-balance models in the study by Van Rensburg et al. (2008). The authors found that salt-induced water stress could reduce the yield of maize and even wheat in future if appropriate precautionary measures are not introduced. Over 70 different chemicals (active ingredients) are used in more than 140 pesticide products sold in the Vaalharts area, which amounts to approximately 120,000kg of pesticides released annually (Raschke and Burger, 1997). According to Des Puttick (Pers. Comm. 1) and Freek de Lange (Pers. Comm.2) some of the commonly used pesticides used by farmers within the Vaalharts area are the following: aldicarb, asetochlor, atrazine, deltamethrine and parathion. Raschke and Burger (1997) provide a list of pesticides supplied by some companies in their study on risk assessment as a tool to assess the effect of pesticide use in the Vaalharts irrigation scheme. Dennis and Nell (2002) studied precision irrigation in the Vaalharts area in order to convey the importance of precision irrigation in protecting South Africa’s scarce water resources and to assist the South African irrigation farmers to farm sustainably. It was found by the authors that precision irrigation is an efficient way to manage irrigation crop production in South Africa, which could optimise farm profit and minimise the impact of agriculture on the environment.
The lower Vaal River and the Harts River (one of the tributaries of the Vaal River) are the river systems under investigation in this study. It is thought that these river systems are impacted upon by agricultural practices within this WMA. Therefore, use will be made of diatom- and macroinvertebrate community structures, as well as riparian vegetation to assess the ecological integrity of these river systems.
1.5. Main Research Question Are the community structures of aquatic diatoms and macroinvertebrates in the study area being impacted upon or modified by agricultural practices along the lower Harts River?
1.6. Hypothesis The aquatic ecosystem in the lower Harts/Vaal River systems is impacted or modified by the intensive agricultural practices along the lower Harts River in comparison to the ecosystem upstream of these practices.
1 Mr. Des Puttick, Farmer in Vaalharts area, North-West Province, Hartswater, May 2007. 2 Mr. Freek de Lange, Pesticide Supplier, Wenkem S.A., North-West Province, Hartswater, May 2007.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 10
Introduction
1.7. Aims The aims of the study were as follows: To determine whether the community structures of aquatic diatoms and macroinvertebrates change along a longitudinal gradient of agricultural practices compared to the relative reference site, which is situated upstream of these practices. To determine whether the aquatic macroinvertebrates found at the agriculturally impacted sites will show different ecological traits, i.e. functional feeding groups (FFGs) compared to sites upstream of agricultural activities. To select appropriate bioindicators of ecosystem health to elucidate the impacts of agricultural activities at Vaalharts on the lower Harts- and Vaal River systems.
1.8. Objectives To achieve the aims listed in the previous section the following objectives were set: To determine the diatom- and macroinvertebrate community structures of the seven sites located in the Lower Vaal WMA. To characterize spatial (agriculturally impacted sites vs. relative reference sites) and temporal (low- and high flow seasons) trends in diatom- and macroinvertebrate community structures. To compare the FFGs of macroinvertebrates collected from agriculturally impacted sites to those of the macroinvertebrates collected at relative reference sites. To assess the abiotic drivers responsible for the changes in these community structures. Assess the riparian vegetation as an additional means of determining the ecological integrity of these river systems and to elucidate whether the riparian structure interact with agricultural inputs that may cause a change in these communities.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 11
Introduction
1.9. Brief Dissertation Outline Chapter 2 is an introduction to the study sites that were selected for water quality, riparian vegetation, macroinvertebrates and diatom monitoring in the present study.
Chapter 3 focuses on the water quality and diatom community structures in relation to land use practises along the Harts River.
Chapter 4 focuses on macroinvertebrate communities, their community integrity, feeding traits, as well as instream habitat in relation to adjacent land use practices.
Chapter 5 shows the relationship between riparian vegetation integrity, macroinvertebrate community structures and FFGs in the study area.
Chapter 6 contains a summary of all the important factors discussed in chapters 2 to 5 and includes the conclusions and recommendations drawn from the present study.
Chapter 7 entails a list of all the references used in chapters 1 to 6.
Finally, the appendices contain site aerial photos, as well as water quality, diatom and macroinvertebrate data sheets.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 12
Chapter 2: Study Area
2.1. Introduction The study area falls within the Lower Vaal WMA, which lies in the North-West and Northern Cape Provinces, with the south-eastern corner in the Free State and borders on Botswana in the north (DWAF, 2004b). The geographical extent of this WMA is shown in Figure 2.1, as well as land use practices within this WMA and the position of the selected study sites.
WMA 10: Lower Vaal - Land Use
1 2 3 4
5 7 6
Figure 2.1: Geographical extent of the Lower Vaal WMA with the positioning of the study sites: 1= Harts River site 1; 2= Harts River site 2; 3= Harts River site 3; 4= Harts River site 4; 5= Harts River site 5; 6= Vaal River site 1; 7= Vaal River site 2 (DWAF, 2008a).
The Lower Vaal WMA is dependent on water releases from the Middle Vaal WMA in order to meet the bulk of water requirements by the urban, mining and industrial sectors. Local resources are mainly used for irrigation and smaller towns. The water quality of the Lower Vaal is strongly influenced by management practices and usage in the Upper- and Middle Vaal WMAs (DWAF, 2004b).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 13
Study Area
Irrigation dominates water requirements in the Lower Vaal WMA and represents 80% of total water use. All of this use is concentrated in the Vaalharts irrigation scheme. This scheme relies on Vaal River water transferred from the Upper- and Middle Vaal WMAs. The scheme serves merely to utilise lower quality water discharged from the Upper- and Middle Vaal WMAs. However, the return flows are of poor quality due to the poor quality water that is received and used for irrigation. Bloemhof Dam blends the poor quality water received from the Middle Vaal with better quality water from this WMA, thus resulting in marginally improved salinity levels (DWAF, 2004b).
Water in the Harts River downstream of the Vaalharts irrigation scheme is of exceptional high salinity as a result of saline leachate from irrigation fields. According to DWAF (2004b) the lower reaches of the Vaal River is also impacted upon by irrigation return-flows from the Harts River, as well as from the Riet/Modder Rivers further downstream.
Agricultural activities are also a major source of diffuse groundwater contamination. The contribution of each farm on a local scale is often fairly small. Feedlots contribute to the organic nitrates in the groundwater. Other contaminants such as pesticides and herbicides are also of concern (DWAF, 2004b).
A study by Ellington (2003) to determine the impact of the irrigation on the aquifer underlying the Vaalharts irrigation scheme, found that the total dissolved solids (TDS) of groundwater has increased at a rate of 13mg/l/annum in the Vaalharts area. It was also found that the increase in leaching of approximately 100,000t/annum was the main source of this TDS increase. Another contributor to the salt load within the Vaalharts irrigation scheme was found to be the incoming canal water from the Vaal River at Warrenton. Fertilizers were found to contribute 50,000t/annum, whereas the incoming Vaal River contributes 130,000t/annum of salts. These salts are moving towards the Harts River at a rate of approximately 5 million t/annum.
Topography: Most of the terrain within the WMA is relatively flat. Vegetation over the WMA is sparse as a result of the generally arid climate, consisting mainly of grassland and some thorn trees (notably camel thorns) (DWAF, 2004b).
Geology and soils: The geology in the area consists predominantly of Ventersdorp lavas and other volcanic intrusive rocks; Black Reef and dolomite series; Dwyka shales and tillites, calcretes and gravels; and Kalahari sands (Gombar and Erasmus, 1976).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 14
Study Area
Climate: The mean annual temperature across this WMA ranges between 18.3°C in the east to 17.4°C in the west. Maximum temperatures occur in January and minimum temperatures in July. Frost occurs throughout the WMA in winter, typically over the period mid-May to late August (DWAF, 2004b).
Rainfall is strongly seasonal with most rain occurring in the summer months October to April, with the peak rainfall months being December and January. The mean annual precipitation (MAP) for the entire WMA ranges from 100mm to 500mm. Humidity is generally highest in February and lowest in August (DWAF, 2004b). The annual rainfall for the Vaalharts area is approximately 430mm/annum. The average gross potential mean annual evaporation in the Lower Vaal WMA ranges from 2,646mm to 2,690mm, with the highest evaporation occurring in December (300mm to 380mm).
Demography, land use and development: The total urban and rural population in this WMA is approximately 1,282,000 of which about 718,000 live in urban centres (DWAF, 2004b). There are large rural populations in the lower Vaal, especially in the areas west of Mafikeng, around Kuruman, Pampierstad and Lichtenberg. The Harts sub-catchment comprises of 19.0km2 of urban area with a population of 111,100. The rural population within this sub-catchment area comprises 121,000. The Vaalharts sub-catchment consists of 36km2 of urban area (urban population of 51,700 and rural population of 89,110). The Vaal sub-catchment downstream of Bloemhof Dam comprises an urban area of 171km2 with a population of 286,900, with the rural population being 58,930 (DWAF, 2004b).
The dominant land use practise in the Lower Vaal WMA is stock farming. The largest irrigation scheme is the Vaalharts water scheme. The scheduled area of this scheme is 39,147ha. This scheme’s water use is in the order of 500 million m3/annum, including losses. The Harts sub-catchment has an irrigation field area of 1km2 and alien vegetation of 12.5km2. Vaalharts has an irrigation field area of 336km2. Alien vegetation is spread over an area of 0.3km2. The Vaal sub-catchment downstream of Bloemhof Dam comprises of an irrigation field area of 118km2 and alien vegetation of 27.9km2 (DWAF, 2004b).
Economic characterisation of the WMA: The most important economic activities of the WMA are the following: mining (23%), government (16%), trade (15%) and agriculture (14%). The main agricultural activities include livestock (beef and dairy cattle, goats, non- wooled sheep, pigs and ostriches) and dryland cropping (mainly maize, but also sunflower, cotton, groundnuts and vegetables) (DWAF, 2004b).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 15
Study Area
2.2. Site Selection A reconnaissance trip was undertaken from 7 - 11 May 2007, and five sites on the lower Harts (HR) and two sites on the Vaal (VR) Rivers were selected. The abbreviations and position (coordinates, province and ecoregion) of the study sites are given in Table 2.1 and their position is demonstrated in Figure 2.1, as well as in Appendix A (site aerial photos).
Table 2.1: The abbreviation and the position of each of the sites selected. Study Sites Coordinates Province Ecoregion Harts River 1 (HR 1) 27°32’25.9”S 24°49’29.2”E North-West 29.02 Harts River 2 (HR 2) 27°40’25.98”S 24°41’02.47”E North-West 29.02 Harts River 3 (HR 3) 27°47’12.7”S 24°42’20.1”E North-West 29.02 Harts River 4 (HR 4) 27°54’09”S 24°36’52.1”E North-West 29.02 Harts River 5 (HR 5) 28°22’42.8”S 24°18’09.06”E Northern Cape 29.02 Vaal River 1 (VR 1) 28°25’42.8”S 24°17’26.85”E Northern Cape 29.02 Vaal River 2 (VR 2) 28°24’45.52”S 24°16’10.59”E Northern Cape 29.02
The reference site on the Harts River (HR 1), which is not impacted upon by agricultural inputs, will be compared to the monitoring sites (HR 2 to HR 5; and VR 2), which are impacted upon by agricultural land use activities at Vaalharts. The Vaal River study site 2 (VR 2) will be compared to the upper Vaal River site (VR 1), which is impacted upon by a combination of activities upstream (mining, industry, agriculture). Since relatively few studies have sampled biological communities upstream and downstream of agricultural practices, as well as adjacent to them, sampling in different locations during this study can help to determine the severity and extent of agricultural impacts (Allan et al., 1997; Vinson and Hawkins, 1998; Stewart et al., 2001; Dovciak and Perry, 2002).
Sampling was undertaken in July 2007 (low flow season) and in January 2008 (high flow season) to determine if the impacts of the agricultural activities at Vaalharts have a worsening effect on the Harts- and Vaal River systems after pesticide application and irrigation practices that are undertaken during the summer months.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 16
Study Area
2.3. Study Sites Harts River site 1 (HR 1) This site is chosen as the reference site for this study, because it is located upstream of most agricultural activities within the study area. It is also situated just below Taung Dam (Torangstad Road) (Figure 2.2). This site is also used as a River Health Programme (RHP) site. This site is not a true unimpacted reference site but is affected by other activities (urban and rural settlements, as well as flow regulation and other inputs from Taung Dam). Hence, this site is referred to as a relative reference site. The site is also readily accessible, with a road bridge crossing the river. The site consists of relatively good riparian vegetation cover, but poor marginal and aquatic vegetation (Figure 2.2).
(a) (b)
(c) (d)
Figure 2.2: Harts River site 1 (relative reference site). (a) Pool area with bridge crossing river. (b) Pool area turns into flowing stream with a lot of cobble substrate. (c) Faster flowing stream flows into another pool area. (d) Rural settlement situated on either side of river.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 17
Study Area
Harts River site 2 (HR 2) This site is located downstream of the reference site at Hartswater, approximately 15km downstream of where the Vaalharts irrigation scheme begins. The site is situated near farmland, which makes it a bit more accessible. A road crosses this stretch of river, which also impedes the flow of the river. It is also used by cattle and other farm animals for drinking water. The site consists of poor to moderate riparian vegetation cover, with poor marginal and aquatic vegetation (Figure 2.3).
(a) (b)
(c) (d)
Figure 2.3: Harts River site 2 (HR 2). (a) Upstream of weir - this area consists of a pool area with some cobble substrate, as well as mud. Farm animals are present. (b-d) Downstream of weir - this area consists of a faster flowing area with noticeable cobble substrate, as well as muddy substrate. Bank erosion is visible.
Harts River site 3 (HR 3) This site is situated at Pampierstad, which is below the Vaalharts irrigation scheme canal in the vicinity of Hartswater. The site is easily accessible and is one of the RHP monitoring sites. The site is also located in the vicinity of an informal and urban settlement. The site’s water is used as drinking water for cattle, as well as for domestic purposes by some of the residents in the area. A weir, as well as a bridge, crosses the river. This site consists of good riparian vegetation cover, as well as marginal and aquatic vegetation (Figure 2.4).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 18
Study Area
(a) (b)
(c) (d)
Figure 2.4: Harts River site 3 (HR 3). (a) Weir- and (b) bridge crossing the river. (c) Slower moving water; pool area. (d) Faster flowing water (with a lot of cobbles and bedrock) due to the weir stopping two thirds of the way across the river.
Harts River site 4 (HR 4) This site is located at Espagsdrift, just below the greater part of the Vaalharts irrigation scheme and upstream of Spitskop Dam (approximately 15km from Spitskop Dam). A weir runs across the river. This site is also used as drinking water for cattle. Relatively good riparian vegetation cover and aquatic vegetation are found at this site, however, poor marginal vegetation (Figure 2.5).
Harts River site 5 (HR 5) This site is located on the Harts River below Spitskop Dam (approximately 50km from Spitskop Dam) just before the Harts River’s confluence with the Vaal River. The site is easily accessible, with a bridge and weir crossing the river. The site is also used by cattle for drinking water. The site has poor riparian and marginal vegetation, with the presence of aquatic macrophytes (Figure 2.6).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 19
Study Area
(a) (b)
Figure 2.5: Harts River site 4 (HR 4). (a) This site consists of good riparian vegetation, but poor water quality (turbidity) with high abundances of aquatic macrophytes. (b) The presence of cattle and canalisation.
(a) (b)
(c) (d)
Figure 2.6: Harts River site 5 (HR 5). (a) Bridge crossing river. (b) Presence of weir. (c) Sand piles and aquatic macrophytes. (d) Poor riparian vegetation, bank erosion and presence of cattle.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 20
Study Area
Vaal River site 1 (VR 1) This site is situated on the Vaal River in Delportshoop, just before the confluence of the Harts River with the Vaal River (approximately 4km from confluence). The site is moderately modified by human activities (an extra biotope was created for sampling, namely stones). A dirt road crosses the river. The river stretch consists of good riparian cover, as well as marginal and aquatic vegetation (Figure 2.7). This site will serve as a relative reference site for the Vaal River before it is affected by the inputs from the Harts River.
(a) (b)
(c) (d)
Figure 2.7: Vaal River site 1 (VR 1). (a) Construction created an additional biotope (stones) through the construction of a dirt road. (b) Lush aquatic vegetation and strong flowing cobble region. (c) Slower flowing cobble; gravel, sand and mud area. (d) Removal of riparian vegetation by construction practices.
Vaal River site 2 (VR 2) This site is located downstream (approximately 2km) of the Harts River’s confluence with the Vaal River. Thus, the cumulative water quality impacts from the Upper- and Middle Vaal WMAs (VR 1), as well as impacts from agricultural practices on the Harts River, can now be
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 21
Study Area
assessed in the lower Vaal River (VR 2). This site is characterized by relatively good riparian vegetation cover, as well as aquatic and marginal vegetation (Figure 2.8). The site is easily accessible. It was noticed that this site is also used as an angling spot by some of the residents in the area.
(a) (b)
Figure 2.8: Vaal River site 2 (VR 2). (a) Easily accessible site; aquatic vegetation present. (b) Good riparian cover and marginal vegetation.
The agricultural sites (HR 2 to HR 5; VR 2) are potentially impacted upon by irrigation return- flows, which may result in secondary salinization, nutrient loads, pesticide pollution; fertilizer leachate (e.g. nitrogen and phosphorus) and sedimentation. Weirs and dams are likely to cause disruption of the hydrologic regime of these systems.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 22
Chapter 3: Diatoms
3.1. Introduction 3.1.1. The Use of Diatoms in Biomonitoring Diatoms have been extensively studied in South African river systems since the early 1950s (e.g. Cholnoky, 1953; Cholnoky, 1968). Hancock (1973) studied the effects of mineral matter and acid runoff from sanddumps and slimes dams on the ecology of the diatoms of the Klip River. More recently, the potential of diatom indices for monitoring water quality in rivers and streams in South Africa has been explored by authors such as Bate et al. (2002), De la Rey et al. (2004) and Taylor et al. (2007a,b). Diatoms have been used as indicators of water quality in the assessment of the state of the rivers in the Crocodile West and Marico WMA (RHP, 2005). Furthermore, De la Rey et al. (2008) made use of diatom-based biological monitoring in the Marico-Molopo River catchment to evaluate two types of indices by establishing how well they reflect changes in water quality. Only internationally developed diatom indices have been used and tested in South Africa. The latter is possible because of the cosmopolitan distribution of many common diatoms. Taylor et al. (2007a) have found for example that most species (98%) of benthic diatoms present in the Vaal River in central South Africa were cosmopolitan.
A lot of effort has gone into the understanding and determination of the preferences of diatoms. Van Dam et al. (1994) provide extensive information on the water quality preferences of hundreds of diatom species. Recent studies have applied various techniques to gain a better understanding of patterns and to develop indices. The use of diatoms as indicators of water quality (organic pollution, eutrophication, acidification, metal pollution, as well as general water quality such as pH, phosphorus and nitrogen) has been extensively studied with the aid of diatom-based indices (Pederson and Vaultonburg, 1996; Kwandrans et al., 1998; Rott et al., 1998; Almeida, 2001; Hirst et al., 2004; Bellinger et al., 2006). Some of these indices include the Generic Diatom Index (GDI, Coste and Ayphassorho, 1991), Specific Pollution sensitivity Index (SPI, CEMAGREF, 1982) and the Trophic Diatom Index (TDI, Kelly and Whitton, 1995). Chessman (1986) used a variety of ordination techniques in the La Trobe River (Victoria) to assess downstream changes in water quality. Indices that make use of species data and include relative abundance (e.g. Watanabe et al., 1988 cited in Reid et al., 1995) have also been applied. Early methodology using diatoms as indicators of water quality largely originated from Europe (i.e. Saprobic
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 23
Diatoms
system). Diatoms are used as bioindicators in Europe (Kelly et al., 1998), Australia (Chessman et al., 1999), America (Dixit and Smol, 1994; Lobo et al., 2004) and Asia (Jüttner et al., 2003).
3.1.2. Land Use and Diatom Community Structure Many studies have linked changes in diatom community structure to changes in water chemistry; an example being, when nutrient enrichment results from agriculture (Pan et al., 1996). Other studies have evaluated algal response to more direct measures of human disturbance such as catchment land cover/use and riparian disturbance (Kutka and Richards, 1996; Chessman et al., 1999; Pan et al., 1999; Carpenter and Waite, 2000; Hill et al., 2000; Leland and Porter, 2000). In the study by Leland (1995) benthic-algal distributions in the Yakima River, draining forested areas; where timber harvest and grazing were the dominant land use, varied with dominant rock type (reflecting chemical weathering), whereas differences in community structure in agricultural areas were based on the degree of enrichment of inorganic nitrogen and dissolved solids from irrigation return-flows and subsurface drainage.
3.1.3. Diatom Responses to Agricultural Land Use Practices The effects of certain environmental factors, related to agriculture, on diatom community structure have been demonstrated in a number of studies. Leland et al. (2001) studied the taxonomic composition and biomass of the phytoplankton and the taxonomic composition of the phytobenthos of the San Joaquin River and its major tributaries in relation to water chemistry, habitat and flow regime. Agricultural drainage and subsurface flow contributed to a complex gradient of salinity and nutrients in this eutrophic, ‘lowland type’ river. They found that the phytoplankton was dominated in summer by centric diatoms (e.g. Thalassiosirales), species both tolerant of variable salinity and widely distributed in the San Joaquin River. Centric diatoms were more abundant (in biomass) during the winter, spring and summer periods (e.g. Cyclotella meneghiniana Kützing, Cyclostephanos invisitatus Stoermer and Hakans). The authors found that light and flow regime rather than nutrient supply contributed to the patterns in the abundance of species. The phytobenthos was found to be dominated by larger, more slowly reproducing pennate diatoms (e.g. Navicula recens Lange- Bertalot, Amphora veneta Kützing, Gomphonema parvulum Kützing). The authors also found that substantial interaction between salinity and inorganic nitrogen as constraints on the structure of the benthic-algal communities of the San Joaquin River basin exists, via a weighted-averaging regression model.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 24
Diatoms
Winter and Duthie (2000) investigated the effects of agricultural inputs from tile outlets in a stream draining a cultivated field on benthic algal community structure. The authors were able to distinguish the site upstream of agricultural inputs from sites downstream of the tile outlets in the stream draining the cultivated field with the aid of diatoms and algae. An increase in the cover of Cladophora glomerata and other green algae was noted at downstream sites, as well as a reduction in the cover of diatoms and crusts dominated by Oscillatoriaceae.
Munn et al. (2002) studied the response of benthic algae to environmental gradients in an agriculturally dominated landscape (Central Columbia Plateau, Washington). They found that the agricultural sites were dominated by diatom taxa such as Nitzschia frustulum perminuta and Nitzschia palea (Kützing) Smith, which are both nitrogen-heterotrophs. The dominant variables explaining the community composition included agriculture (%), precipitation, water velocity, discharge of nitrogen and phosphorus, as well as conductivity.
Rott et al. (1998) did a study to discriminate between the impacts of treated urban wastewaters and diffuse nutrient sources from farmland on the river water quality of the Grand River, Ontario. The authors used two diatom indices to evaluate the effects of organic pollution and to determine the trophic levels of the Grand River. The indices showed a clear differentiation among the ten sites sampled over a distance of 214km. The sites in the central reaches that were influenced by both urban discharges and agricultural runoff had the lowest water quality. It was found that the water of the river was well buffered and alkaline. There were indications of nutrient pulses after heavy rains and nutrient peaks paralleled high turbidity. There was a clear increase in nitrogen compounds from the middle part of the river downstream, caused by runoff from the intensively cultivated areas. The largest portion of the observed variability in species composition was explained by a seasonal gradient related to temperature and by longitudinal gradients of nitrate-nitrogen, conductivity and chloride. The study was compared to a study conducted in the 1960s. There were clear signs of increased eutrophication in this study compared to the study in the 1960s. The largest portion of the taxa was indicators of eutrophic conditions.
3.1.4. Problem Statement At present there are no data on the effect of pesticides or other agricultural activities and inputs on the diatom communities of the lower Harts- and Vaal Rivers.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 25
Diatoms
3.1.5. Aims The aims of this chapter are as follows: To determine whether the diatom community composition changes along a longitudinal gradient of agricultural activities compared to the relative reference site, which is situated upstream of these practices. To determine whether diatoms are useful bioindicators of ecosystem health to elucidate the impacts of agricultural practices at Vaalharts on the lower Harts- and Vaal Rivers.
3.1.6. Objectives In order to achieve the aims listed above, the following objectives were set: To determine the diatom community structures at seven study sites located on the lower Harts- and Vaal Rivers (Lower Vaal WMA). To characterize spatial and temporal trends in diatom community structures. To assess the abiotic drivers responsible for changes in the diatom community composition of these river systems.
3.2. Materials and Methods 3.2.1. Study Sites The study sites described in Chapter 2 were used in the diatom assessment.
3.2.2. Water Quality Instream water quality measurements for pH, dissolved oxygen (mg/l and %), electrical conductivity (uS/cm) as well as temperature (°C) were done at each site by means of Eutech Cyberscan instruments (Eutech pH 110 RS232C; Eutech DO6 dissolved oxygen meter and a Eutech CON 110 RS232C conductivity and temperature meter). Subsurface water samples were taken at every site using pre-cleanded polypropylene containers. The water samples were frozen until water quality analyses were undertaken. The following variables - formed part of the analyses: nitrite (as NO2-N); nitrate (as NO3-N); chloride (Cl ); sulphate -2 (SO4 ); ammonium (as NH4-N); phosphate (as PO4-P); alkalinity (as CaCO3); calcium (Ca); turbidity; and chemical oxygen demand (COD). These variables were analysed using the appropriate test kits, and read on the Merck Spectroquant Photometer SQ 118.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 26
Diatoms
3.2.2.1. Statistical Analysis The software package PRIMER version 6.0 (Clarke and Gorley, 2006) was used to elucidate the spatial and temporal patterns in the measured water quality variables in relation to land use (agricultural sites). Principal Component Analysis (PCA) was carried out on log- transformed water quality data. A resemblance matrix was created based on Euclidean distance between samples. This resultant resemblance matrix was subjected to two- dimensional Non-metric Multi-Dimensional Scaling (NMDS). The BIOENV (Biota and/or Environment matching) procedure using BEST matching, based on Spearman’s correlation was used to identify the environmental variables that best explained the ordination of the study sites.
3.2.3. Diatoms 3.2.3.1. Field Collection, Laboratory Analysis and Indices Diatoms were collected, prepared and enumerated according to the protocol of Taylor et al. (2005a, 2007c). A summary of the protocols are presented below.
Collection Epilithic diatoms were sampled in the Harts River system, because this is the community of preference for most diatom indices and because rocks were available for sampling at all of the sites on the Harts River system. Epilithic diatoms also yield the best coefficients when multiple regressions are performed with water quality variables (Hodgkiss and Law, 1985 cited in De la Rey et al., 2008). Epiphytic diatoms were sampled from the water reeds Cyperus marginatus and Schoenoplectus brachyceras in the lower Vaal River system, since rocks were absent at the lower most site (VR 2) and water reeds were present at both VR 1 and VR 2.
Five cobbles (HR 1, HR 2, HR 3, HR 4 and HR 5) and ten macrophyte stems (VR 1 and VR 2) were collected at each site. Sampling from rocks was carried out as follows. The rocks were rinsed in the river and placed in a sampling tray on the riverbank. Diatoms were removed from the rocks by scrubbing the upper surface of the substratum with a toothbrush, which was then rinsed in the sampling tray with water. The resulting diatom suspension was poured into a labelled plastic sample bottle. To avoid contamination between sites, the toothbrush and tray were rinsed in the river, both before and after taking the diatom sample.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 27
Diatoms
Sampling from macrophytes was achieved as follows. The emergent macrophyte (water reed) stem was cut with a knife above the water line. A plastic bottle was inverted over the remainder of the stem and the stem was cut slightly above the point from where it emerged from the sediment. The sampling bottle was then inverted and brought to the bank. This procedure was repeated until ten stems were collected. The scrubbing and removal of the diatom communities were carried out in a similar fashion as to that described for the sampling of rocks. After collection the diatom samples were fixed with ethanol (20%) to prevent cell division.
Preparation of Diatom Samples - Cleaning Techniques
The hot hydrochloric acid and potassium permanganate (HCl and KMnO4) method was followed, since it yields good results with samples taken from throughout South Africa (Round et al., 1990; Taylor et al., 2005a, 2007c). This cleaning method was carried out as follows.
The diatom samples were allowed to settle. The supernatant liquid was carefully decanted from the sample bottle taking care not to loose any of the diatom material. Two cleaning techniques within the HCl and KMnO4 method can be followed: the beaker method and the test tube method. The test tube method was used, since the diatom concentration in some of the samples was small. Three to five ml of sample was transferred to the test tube, followed by an equal volume of saturated KMnO4. The sample was mixed and allowed to stand for 24 hours. Hydrochloric acid (HCl 32%) was added to the test tube and the acidified sample was mixed using a vortex. The test tubes containing the sample were transferred to a beaker containing water on a hotplate for one to two hours. The sample was allowed to clear. An additional amount of HCl was added to the sample, if it didn’t clear. The sample was allowed to cool and an equal amount of distilled water was added, after which the sample was allowed to settle for 12 hours. The settled sample was carefully decanted not to loose any diatoms. The sample was mixed and the precipitate transferred to a centrifuge tube. The sample was washed and diluted with distilled water using five cycles of centrifugation at 20°C, 2500rpm for ten minutes. In between each cycle the pellet was resuspended with a jet of distilled water.
Preparation of Diatom Slides The centrifuged pellet was resuspended with a jet of distilled water using a vortex. Cover slips were cleaned with ethanol. A small amount of diatom suspension was transferred to the test tube with a pipette. The cleaned diatom suspension was then diluted until it
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 28
Diatoms
appeared slightly cloudy to the naked eye. Ammonium chloride (one to two drops) was added to the suspension to neutralise electrostatic charges on the suspended particles and to reduce aggregation. The suspension was mixed using a vortex. The suspension (one to two ml depending on the size of the cover slip) was transferred to the cleaned cover slip and allowed to air dry. An inverted beaker was placed over the cover slip in order to prevent contamination. After the water had evaporated, the diatom-coated cover slips were placed on a hot plate for approximately two minutes to drive off the excess moisture and to sublimate the residual ammonium chloride. The diatom-coated cover slips were allowed to cool. One or two drops of mountant (Pleurax) were placed onto the cover slips. The previously-cleaned (cleaned with ethanol) microscope slide was lowered onto the cover slip, inverted, and then placed on a hotplate until the mounting medium started to boil and all the solvent evaporated (approximately two to five minutes). The hot slide was removed from the hotplate and laid on the workbench. The cover slip was then manoeuvred into position and the excess mountant removed with ethanol. The slides were labelled (i.e. location, date of collection, substratum, collector, and mounting medium).
Enumeration The diatom communities were then analysed by counting between 400 and 450 valves. The illustrated guide to some common diatom species from South Africa composed by Taylor et al. (2007d) was consulted to identify the samples. The suggested rules of the Comité Européen de Normalisation (CEN, 2004) were used for counting the diatoms. A Zeiss photomicroscope I with differential interference contrast optics (DIC) was used for identification and enumeration. A magnification of 100 x 1.3 N.A (oil immersion objective) was used in this regard. The microscope was attached to a JVC video camera consisting of a frame grabber, and the images were captured using Automontage software.
Diatom Index Calculation To relate changes in diatom community structure to agricultural land use impacts, multiple endpoints were used (i.e. species assemblages, aut-ecological metrics and diatom indices). The diatom indices used in this study, as well as the reasons for their selection are listed in Table 3.1.
The community counts were entered into the diatom database and index calculation tool OMNIDIA version 3.1 (Lecointe et al., 1993) and several diatom indices were calculated. The
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 29
Diatoms
diatom indices (excluding the %PTV) were based on the weighted average equation of Zelinka and Marvan (1961 cited in De la Rey et al., 2004) which has the basic form:
n a j s jv j 1 j index n a jv j 1 j
where aj= abundance of species j in sample, vj= indicator value and sj= pollution sensitivity of species j.
The diatom indices used in the present study function in the following manner: the most dominant taxa present in a sample would be a reflection of that particular taxon’s optimum water quality requirements. A taxon that is found frequently in a sample, therefore, has more influence on the results than one that is rare. An ‘indicator value’ is included, which gives greater weight to those taxa that are good indicators of particular environmental conditions. A list of the taxa present in a sample, along with their abundances is made. The diatom indices are expressed as the mean of the optima of the taxa in the sample, weighted by the abundance of each taxon. The influence of certain species is increased by the indicator value (Kelly, 1998).
Table 3.1: Diatom indices, their abbreviations and reason for selection and use in the present study. Diatom Index Abbr. Reason for selection Generic Diatom Index GDI Is a relatively simple diatom index to (Coste and Ayphassorho, 1991) use; allows for the determination of water quality at a particular site, based on genus level identification. Specific Pollution sensitivity Index SPI This index is based on a larger (CEMAGREF, 1982) number of taxa, compared to the other indices. Biological Diatom Index BDI This index best reflects water quality (Lenoir and Coste, 1996) problems, since it incorporates 14 water quality parameters. Eutrophication/Pollution Index EPI Indicates whether eutrophication and (Dell’Uomo, 1996) pollution exist at a site. Percentage Pollution Tolerant Valves %PTV Indicates organic pollution. (Kelly and Whitton, 1995)
For the GDI, SPI, BDI and EPI indices a score below 17 indicates an increasing level of pollution. The %PTV index, however, has a maximum score of 100, where a score above 20 indicates possible impact of organic pollution (Taylor et al., 2005b) and below means nutrient enrichment (if any) originating from inorganic sources.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 30
Diatoms
Limit values for the indices SPI, GDI, BDI and EPI for the evaluation of the ecological water quality classes and trophic levels, are indicated in Table 3.2 (Eloranta & Soininen, 2002). These values were used in the present study for the interpretation of the various index scores obtained.
Table 3.2: Limit values for diatom indices in the evaluation of water quality classes and trophic state. Index scores Classes Trophy >17 High Quality Oligotrophy 15 to 17 Good Quality Oligo-mesotrophy 12 to 15 Moderate Quality Mesotrophy 9 to 12 Poor Quality Meso-eutrophy <9 Bad Quality Eutrophy
The diatom ecological descriptions were obtained from the OMNIDIA software based on the calculation by Van Dam et al. (1994) and the descriptor limits and interpretation are addressed in Appendix B (Table B6).
3.2.3.2. Statistical Analysis Multivariate analyses were initially carried out using the computer package PRIMER version 6.0 (Clarke and Gorley, 2006) to assess changes in diatom communities between study sites and seasons. Correspondence Analysis (CA) using CANOCO for Windows version 4.5 (Ter Braak and Šmilauer, 2002) was used to assess how these communities changed between sites and seasons in relation to environmental variables. Since similar ordinations were obtained between sites and seasons using both these software packages, it was decided to use the CA results, because they provided a better visualisation of the diatom community structures in relation to land use (i.e. water quality variables). K-dominance plots were included using PRIMER version 6.0 to indicate sites that have an increased dominance of a particular specie relative to the other study sites and seasons (PRIMER analysis was carried out on log-transformed data). One-way Analysis of Similarity Percentages (SIMPER) was carried out on log-transformed data using PRIMER version 6.0 to identify the diatom species that contributed the most to the diatom communities found at certain study sites.
De-trended Canonical Correspondence Analysis (DCCA) with de-trending by segments and log transformation was performed using CANOCO for Windows 4.5 to obtain the gradient length of the taxa in the environmental space. When the diatom species gradient was < 3
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 31
Diatoms
standard deviations a linear response was assumed and a Redundancy Analysis (RDA) was used. When this species gradient was > 4 standard deviations, a Canonical Correspondence Analysis (CCA) was carried out. Thus, both CCA (low flow data) as well as RDA (high and low flow data; high flow data) were carried out using the computer package CANOCO version 4.5 to indicate the relationship between diatom communities and the environmental variables at both a temporal and spatial scale for sites on the Harts- and Vaal Rivers. Data were log-transformed and the significance of CCA and RDA axes were tested using unrestricted Monte Carlo permutation tests (499 permutations, P ≤ 0.05).
3.3. Results 3.3.1. Water Quality Water quality data, including system variables and nutrients for low- and high flow, are shown in Table 3.3. These tables indicate that variables were generally within target water quality guideline range for aquatic ecosystems (DWAF, 1996), except for dissolved oxygen (HR 1, HR 2, HR 3, HR 4, HR 5H, VR 1H, and VR 2H), pH (HR 1L, HR 2L, HR 3L, HR 4, VR 1, and VR 2) and nitrate (HR 3).
From the tables the following can be deduced: Turbidity levels showed a marked decrease during January 2008 (high flow) when compared to the levels in July 2007 (low flow) for both the Harts- and Vaal Rivers sites. Oxygen levels (mg/l and saturation) were higher during high flow than during low flow. Conductivity levels were higher for agriculturally impacted sites during both seasons. pH levels were higher during the low flow period than during high flow, with the agriculturally impacted sites having a higher pH than the reference site HR 1. During low flow, nitrites were higher at the agriculturally impacted sites (HR 2 to HR 5) compared to the reference site HR 1. Nitrite levels were higher for the reference site HR 1 and the agriculturally impacted site HR 3 during high flow when compared to the low flow period. Nitrates were higher at the agriculturally impacted sites (HR 3 and HR 4) when compared to the reference site HR 1 during low flow. During high flow, however, the nitrate concentration was lower than the low flow concentration for the reference site. The agriculturally impacted sites (HR 2, HR 3 and HR 4) were higher than the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 32
Diatoms
reference site HR 1 during high flow. These sites also show an increase in nitrate concentration, together with VR 2, when compared to their low flow levels. Chloride levels remained fairly constant for both seasons. Sulphate levels were higher for the agriculturally impacted sites when compared to the reference site HR 1 for both seasons. The agriculturally impacted sites on the Harts River (HR 2, HR 3, HR 4, and HR 5) had higher ammonium concentrations than the reference site HR 1 during low flow. The reference site HR 1, as well as the agricultural sites HR 2 and HR 3, showed an increase in ammonium levels during the high flow period. During the low flow period, the agricultural sites HR 3 (which had the highest concentration), HR 4, and HR 5 showed higher phosphate concentrations when compared to the reference site HR 1. During high flow, the reference site HR 1, as well as the agricultural sites HR 2, HR 3 and HR 4, showed an increase in phosphate levels compared to the low flow period.
Alkalinity (as CaCO3) and calcium levels were much higher during the low flow period.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 33
Diatoms
Table 3.3: Physico-chemical water quality properties of each site sampled during the low- (L) and high (H) flow periods. Target water quality guidelines (WQG) for the aquatic ecosystem (DWAF, 1996) are also provided.
Temp Turb DO DO Cond pH NO2-N NO3-N Cl SO4 NH4-N PO4-P COD CaCO3 Ca (°C) (NTU) (mg/l) (%) (μS/cm) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) (as O2,(mg/l) (mol/m3) (mg/l) HR 1L 11.4 44 8.54 89.6 378 8.73 0.01 1.3 8 29.5 0.02 0.01 0.5 0.16 6 HR 1H 26.9 2 7.05 105.3 348 7.71 0.02 0.36 8 6 0.07 0.01 0.5 0.05 2.5 HR 2L 11.5 37 7.39 78.5 859 8.61 0.01 0.8 14 168 0.03 0.01 0.5 0.43 17 HR 2H 28.6 2 7.17 104 870 7.99 0.03 1.75 14 191 0.04 0.01 0.5 0.065 2.5 HR 3L 9.6 35 7.09 71.8 1166 9.26 0.05 2.52 19 253 0.09 0.11 0.5 0.81 29 HR 3H 25.4 2 5.2 73.3 1423 7.96 0.06 3.14 17 259 0.15 0.11 0.5 0.04 2.5 HR 4L 11.3 42 10.5 105.9 1173 8.93 0.02 2.16 18 250 0.03 0.03 0.5 0.51 20 HR 4H 26.6 2 7.28 103 1333 8.4 0.01 2.48 17 229 0.02 0.04 0.5 0.065 2.5 HR 5L 11 47 9.22 96 1778 9.22 0.01 0.4 26 195 0.04 0.02 1 0.88 31 HR 5H 26.9 3 7.67 108.4 849 8.54 0.005 0.29 18 149 0.01 0.01 0.5 0.065 2.5 VR 1L 13.8 38 9.85 106.2 608 8.87 0.005 1.44 14 171 0.01 0.01 0.5 0.36 15 VR 1H 27.2 4 7.43 106.9 660 8.65 0.005 0.22 14 127 0.01 0.01 0.5 0.03 2.5 VR 2L 11 34 9.51 97.5 758 8.58 0.005 0.125 20 224 0.02 0.01 0.5 0.5 19 VR 2H 27.2 4 7.74 110.5 743 8.8 0.005 0.37 15 146 0.01 0.01 0.5 0.09 2.5 WQG - - 9.09-12.77 80-120 - 6.0-8.0 <0.5-2.5 <0.5-2.5 - - <0.5-2.5 <5-2.5 - - - Temp= temperature; Turb= turbidity; DO= dissolved oxygen; Cond= conductivity.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 34 Diatoms
3.3.1.1. Temporal Variation A PCA ordination plot was used to indicate (dis)similarities amongst the study sites on the Harts- and Vaal Rivers due to their water quality characteristics during both flow periods (Figure 3.1). This PCA bi-plot describes 92.9% of the variation in water quality data, where the first axis (PC1) displays 72.9% of the variation and the second axis (PC2) 20.1%.
2
HR 3H SO4 HR 4H HR 2H HR 5H HRHR 4L 3L VR 2H HR 5L 0 VR 1H Cond VR 2L VRHR 1L 2L NO3-NCl Temp
2 NO2-NNH4-N PO4-PpHCODCaCO3 C P O% O2 Ca Turb -2 HR 1L
HR 1H
-4 -4 -2 0 2 4 PC1 Figure 3.1: Water quality physico-chemical properties for sites on the Harts- and Vaal Rivers during low- (L) and high (H) flow periods.
The reference site HR 1 was separated from the agricultural sites along the PC1 axis for both low- and high flow periods, indicating a clear dissimilarity in its water quality variables compared to the agriculturally impacted sites. There was a definite degree of temporal variation and some degree of spatial variation for the impacted sites on the Harts- and Vaal Rivers, with the Harts River sites grouping together and the Vaal River sites grouping together on the PC2 axis. The water quality variables that best described the variation amongst the study sites according to BIOENV (BEST) matching were turbidity, conductivity, nitrate, sulphate and calcium. Turbidity and calcium showed a stronger correlation towards the sites on the Harts- and Vaal Rivers during the low flow season. Sulphate, conductivity, chloride and nitrate were more positively correlated with the agriculturally impacted sites compared to the reference site HR 1 for both seasons.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 35 Diatoms
3.3.1.2. Spatial Variation A PCA ordination bi-plot of the water quality variables for sites on the Harts- and Vaal Rivers during the low flow season is given in Figure 3.2. The bi-plot describes 86.3% of the variation in the data, with the first axis (PC1) describing 71.7% of the variation in the water quality data and the second axis (PC2) 14.6%.
1
NO3-N
HR 3L HR 4L
SO4 VR 1L
PO4-P 2 Ca NO2-NNH4-NpH C 0 HR 2L P CaCO3 Temp Cond O2 O%Turb HR 1L Cl COD
VR 2L HR 5L
-1
-1 0 1 2 3 PC1
Figure 3.2: Water quality physico-chemical properties for sites on the Harts- and Vaal Rivers during the low (L) flow period.
The reference site HR 1 was separated from the rest of the study sites on the Harts- and Vaal Rivers (PC1), indicating a clear dissimilarity with regard to its water quality variables compared to the agricultural sites (Figure 3.2). The agriculturally impacted sites HR 3 and HR 4 tended to be more similar, with VR 1 and HR 2 grouping together, and VR 2 grouping with HR 5. Nitrate was the main cause for the separation of the sites HR 2, HR 3, HR 4 and VR 1 (with concentrations being higher at these sites) from the rest of the impacted sites (HR 5 and VR 2). The upper Vaal River site VR 1, which is impacted upon by other activities upstream, differed from the agriculturally impacted sites regarding sulphate, calcium, conductivity and chloride levels being higher at the agricultural sites (Figure 3.2). The water quality variables that best described the variation amongst the study sites during the low flow season according to BIOENV (BEST) matching were conductivity, nitrate, sulphate, chemical oxygen demand and calcium.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 36 Diatoms
The PCA ordination plot indicated by Figure 3.3 shows (dis)similarities of the water quality variables for sites on the Harts- and Vaal Rivers during the high flow season. The ordination bi-plot describes 98.1% of the variation in the water quality data, with the first axis (PC1) displaying 85.0% of the variation and the second axis (PC2) 13.1%.
1
NO3-N HR 3H
HR 1H HR 4H Cond HR 2H NH4-NPO4-P
2 NO2-N
C 0 Ca
P CaCO3Temp COD pHCl O%O2 SO4 Turb HR 5H VR 2H VR 1H
-1 -3 -2 -1 0 1 2 PC1
Figure 3.3: Water quality physico-chemical properties for sites on the Harts- and Vaal Rivers during the high (H) flow period.
The reference site HR 1 was separated from the agriculturally impacted sites (PC2), indicating that a clear dissimilarity existed between the water quality variables of the reference site HR 1 and the impacted sites (PC1) of the Harts- and Vaal Rivers (Figure 3.3). The agricultural sites HR 2, HR 3 and HR 4 appeared to be different from the other impacted sites (HR 5, VR 1 and VR 2) regarding their water quality variables, however, one also could observe a spatial trend, with the Harts River sites grouping together and the Vaal River sites grouping together (Figure 3.3). Nitrate, conductivity, sulphate and turbidity were higher at the impacted sites compared to the reference site HR 1 (Figure 3.3). The water quality variables that best explained the variation amongst the study sites during the high flow season according to BIOENV (BEST) matching were turbidity, dissolved oxygen saturation, conductivity, nitrate and sulphate.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 37 Diatoms
3.3.2. Diatom Community Structure 3.3.2.1. Temporal Variation
Redundancy Analysis was used to indicate how the diatom community structure changed with relation to changes in water quality due to land use practices within the study area (i.e. agriculture) during low- and high flow periods. The RDA tri-plot indicated by Figure 3.4 describes 42.4% of the variation in species data, with the first axis describing 29.4% of the variation in the data and the second axis 13.0%. Species-environmental correlations for the first and second axes were 0.986 and 0.992, respectively, and explained 34.2% and 15.2% of the species-environment variation, indicating a strong relationship between the diatom community structure and the environmental (water quality) variables selected.
Figure 3.4: RDA tri-plot showing the relationship between measured environmental variables and diatom community structures for sites on the Harts- and Vaal Rivers during low- (L) and high (H) flow periods. An explanation of the acronyms is provided in Appendix B, Tables B4 and B5.
The RDA tri-plot clearly shows a temporal (low flow sites and high flow sites are separated) and spatial (Harts River sites are grouped together, as well as the Vaal River sites) trend in the diatom community data for the study sites on the Harts- and Vaal Rivers (Figure 3.4). By superimposing the water quality variables on the diatom community data it is clear that the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 38 Diatoms
community structure during the low flow season (characterized by high levels of nitrate, pH, turbidity and calcium) differed from the community structure during the high flow period. Increased levels of sulphate, conductivity and chloride contributed to the change in community structure during the high flow season when compared to the low flow season. Taxa typical of cleaner, less impacted waters ordinated out on the left hand side of the diagram (HR 1L, HR 2L, VR 1L, VR 1H, VR 2L and VR 2H) e.g. Achnanthidium minutissimum (Kützing) Czarnecki, Encyonopsis microcephala (Grunow) Krammer, Fragilaria tenera (W.Smith) Lange-Bertalot and Cymbella hustedtii Krasske (Taylor et al., 2007d). The more impacted sites (HR 1H, HR 2H, HR 3L, HR 3H, HR 4L, HR 4H, HR 5L and HR 5H) were associated with an increase of taxa typical of poor water quality e.g. Eolimna subminuscula (Manguin) Lange-Bertalot and Metzeltin, Nitzschia frustulum (Kützing) Grunow, Diatoma vulgaris Bory, Navicula gregaria Donkin, Amphora pediculus (Kützing) Grunow, G. parvulum, C. meneghiniana and Pleurosigma salinarum (Grunow) Cleve and Grunow (Taylor et al., 2007d).
3.3.2.2. Spatial Variation
Canonical Correspondence Analysis was used to determine the relationship between diatom assemblages and measured environmental variables for the reference site HR 1 and agriculturally impacted sites during the low flow period. The CCA tri-plot indicated by Figure 3.5 describes 52.8% of the variation in species data, with the first axis describing 31.8% of the species data variation and the second axis 21.0%. Species-environmental correlations for the first and second axes were 1.000 and 1.000, respectively, and explained 31.8% and 21.0% of the species-environment variation. Thus, indicating a strong relationship between the diatom community structure and the environmental (water quality) variables selected.
The CCA tri-plot (Figure 3.5) shows a clear separation between the reference site HR 1 and the impacted sites. A pollution gradient can be depicted, from HR 1 towards the confluence of the Harts with the Vaal (VR 2). The reference site HR 1 and agricultural site HR 2 showed a similar diatom community structure in relation to the selected water quality variables. The taxa that contributed the most to this similarity (54.29%) were: E. microcephala, Achnanthidium species, Navicula cryptotenella Lange-Bertalot and Cymbella kappii Cholnoky.
The agricultural sites HR 3 and HR 4 showed a similar community structure in relation to the measured water quality variables (Figure 3.5). Amphora pediculus , N. frustulum, N.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 39 Diatoms
gregaria, N. cryptotenella, Surirella brebissonii Krammer and Lange-Bertalot, Cocconeis placentula var. euglypta (Ehrenberg) Grunow and E. subminuscula contributed the most to the similarity between these two agriculturally impacted sites (55.2% similarity).
The agricultural site HR 5, and multi-impacted sites VR 1 and VR 2 tended to ordinate together on the upper right hand side of the CCA tri-plot (Figure 3.5) despite the fact that only epilithic diatoms were sampled at HR 5 and epiphytic diatoms at the Vaal River sites. Encyonopsis microcephala, Achnanthidium species and G. parvulum contributed the most to the similarity in their community structure in relation to the measured water quality variables.
Figure 3.5: CCA tri-plot showing the relationship between measured environmental variables and diatom community structures for sites on the Harts- and Vaal Rivers during the low (L) flow period. An explanation of the acronyms is provided in Appendix B, Table B4.
The diatom E. microcephala (present in high abundances) was associated with the reference site HR 1, agricultural sites HR 2 and HR 5, as well as the multi-impacted sites on the Vaal
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 40 Diatoms
River (VR 1 and VR 2). This diatom species is known to inhabit cleaner, less impacted waters (Taylor et al., 2007b). It is also clear from the CCA tri-plot (Figure 3.5) that the higher levels of chloride, sulphate, calcium, phosphate, nitrite, nitrate and ammonium contributed to the change in the diatom community structures found at HR 3 and HR 4 compared to the relative reference site HR 1 (indicating that these sites were more polluted than the rest of the study sites).
The Relative Reference Sites The reference site on the Harts River consisted mainly of taxa that are typical of cleaner, less impacted waters such as Achnanthidium eutrophilum Lange-Bertalot, A. minutissimum, C. kappii, E. microcephala and N. cryptotenella (Taylor et al., 2007d). The eutraphentic taxon Navicula capitatoradiata Germain was also present at this site, which indicates that this site may have underlying nutrient problems (Van Dam et al., 1994).
The relative reference site VR 1 was characterized by high abundances of the following taxa: Achnanthidium species, C. kappii, Cocconeis placentula Ehrenberg, E. microcephala, Fragilaria capucina var. vaucheriae (Kützing) Lange-Bertalot, Gomphonema affine Kützing, G. parvulum and Pseudostaurosira brevistriata Williams and Round (Appendix B – Table B4). This site was separated from the other sites due to the presence of Gomphonema laticollum Reichardt and Navicula cryptotenelloides Lange-Bertalot (Figure 3.5).
The Agricultural Sites The agricultural site HR 2 differed from the reference site HR 1 in having higher abundances of more tolerant meso-eutraphentic taxa such as C. invisitatus, F. capucina var. vaucheriae, G. parvulum, Fragilaria biceps (Kützing) Lange-Bertalot and Nitzschia species (e.g. Nitzschia dissipata Kützing Grunow).
Rhoicosphenia abbreviata (Agardh) Lange-Bertalot (indicator of critically polluted waters), N. recens and C. invisitatus are taxa that were found in high abundances at HR 3 (Figure 3.5). This site also contained taxa present in low abundance, which were also indicators of critical to very heavily polluted waters e.g. A. veneta, and Tryblionella hungarica (Grunow) Mann.
Tryblionella apiculata Gregory, which is an indicator of strongly polluted waters, as well as taxa typical of brackish, electrolyte-rich waters such as Melosira varians Agardh, Nitzschia sigma (Kützing) Smith and Staurosira elliptica (Schumann) Williams and Round also
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 41 Diatoms
dominated the agricultural site HR 4 (Figure 3.5). Nitzschia linearis (Agardh) Smith, which is associated with circumneutral, oxygen-rich waters of moderate to high electrolyte content, was also found at this site.
Cocconeis pediculus Ehrenberg dominated VR 2 (Figure 3.6), which is an indication that moderate to high electrolyte conditions, perhaps even brackish waters were present at this site. Encyonopsis microcephala, Reimeria uniseriata Sala Guerrero and Ferrario and Tabularia fasciculata (Agardh) Williams and Round also dominated this site. Stephanodiscus agassizensis Hakansson and Kling, which is an indicator of eutrophic waters with elevated electrolyte concentrations, as well as turbidity was present at this site. This taxon also seems to ordinate close to the chloride and conductivity water quality variables as shown in Figure 3.5.
The Vaal River site 2 (VR 2) showed similarities with the reference Vaal River site (VR 1) regarding its community structure, as well as the environmental variables that contributed to this similarity (Figure 3.5). However, this site ordinated more towards the agriculturally impacted sites on the Harts River, which showed that this site was different from the upper Vaal River site VR 1, and thus were impacted upon, to some degree, by the agricultural activities along the Harts River. This site also had the highest abundances of Epithemia sorex Kützing compared to the other study sites.
100 HR 1L HR 2L HR 3L HR 4L 80 HR 5L
VR 1L
% e
c VR 2L
n a
n 60
i
m
o
D
e
v
i
t a
l 40
u
m
u C
20
0 1 10 100 Species rank
Figure 3.6: Ranked species K-dominance plot for diatom community structures at low (L) flow for sites on the Harts- and Vaal Rivers, utilising abundance to indicate cumulative dominance.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 42 Diatoms
Redundancy Analysis was used to determine the relationship between diatom assemblages and measured environmental variables for the reference site HR 1 and agriculturally impacted sites during the high flow period. The RDA tri-plot indicated by Figure 3.7 describes 60.1% of the variation in species data, with the first axis describing 41.8% of the species data variation and the second axis 18.3%. Species-environmental correlations for the first and second axes were 1.000 and 1.000, respectively, and explained 41.8% and 18.3% of the species-environment variation. The latter indicates that a strong relationship between the diatom community structure and the selected environmental (water quality) variables existed.
Figure 3.7: RDA tri-plot showing the relationship between measured environmental variables and diatom community structures for sites on the Harts- and Vaal Rivers during high (H) flow. An explanation of the acronyms is provided in Appendix B, Table B5.
A clear spatial trend is indicated by the RDA tri-plot in Figure 3.7 (the Harts River sites are grouped together and separated from the Vaal River sites, which are grouped together). There is also a longitudinal trend of agricultural pollution from the relative reference site HR
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 43 Diatoms
1 towards the confluence with the Vaal (VR 2). The reference site HR 1 showed a different community structure compared to the other study sites and was associated with meso- eutraphentic and eutraphentic taxa such as Cymbella tumida (Brebisson) Van Heurck, F. capucina var. vaucheriae and G. parvulum. There was a clear difference between the diatom community structure found during the low flow period, compared to this more tolerant group of taxa during the high flow season, indicating decreased water quality at HR 1.
The agricultural sites, HR 2, HR 3, HR 4 and HR 5, had a different diatom community structure compared to the Vaal River sites (VR 1 and VR 2), because the diatoms sampled at the Harts River sites consisted of epilithic diatoms, whereas the Vaal River sites contained epiphytic diatoms. The water quality variables conductivity, phosphate, nitrite, nitrate and ammonium contributed to this arrangement of diatoms amongst these sites. The agricultural sites HR 2 to HR 5 were characterized by tolerant taxa such as Navicula species Bory, P. salinarum, N. frustulum, R. uniseriata, A. pediculus, C. placentula, G. parvulum and C. meneghiniana. These taxa contributed the most to the similarity amongst these sites (50.02%) in relation to the water quality variables mentioned above.
100 HR 1H HR 2H HR 3H HR 4H 80 HR 5H
VR 1H %
e
c VR 2H
n a
n 60
i m
o
D
e
v
i
t a
l 40
u m
u C
20
0 1 10 100 Species rank
Figure 3.8: Ranked species K-dominance plot for diatom communities at high (H) flow for sites on the Harts- and Vaal Rivers, utilising abundances to indicate cumulative dominance.
The Vaal River sites (VR 1 and VR 2) appeared to have better water quality compared to the agriculturally impacted Harts River sites (Figure 3.7) . Water quality variables such as
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 44 Diatoms
dissolved oxygen, alkalinity and pH contributed to the difference in the diatom community structures at these sites. Diatoms such as Mastogloia smithii Thwaites, P. brevistriata, S. elliptica, Achnanthidium species, C. placentula, C. tumida, E. sorex and Encyonopsis subminuta Krammer and Reichardt contributed to these sites’ diatom community structures (47.83%).
Figure 3.8 shows the ranked species K-dominance for the diatom communities at the study sites during the high flow period. The site where there was a clear dominance of a particular specie (M. smithii) was VR 2.
3.3.3. Diatom Index Scores 3.3.3.1. Low Flow The diatom index scores, as well as their classes for the study sites on the Harts- and Vaal Rivers during the low flow period are shown in Table 3.4. The diatom index scores are presented as values from 0 to 17, where a lower score indicates poor to bad water quality (increasing level of pollution). A %PTV above 20 usually is an indication of organic pollution.
Table 3.4: Diatom index scores and classes for sites on the Harts- and Vaal Rivers during the low (L) flow period. SITE DIATOM INDEX SCORES AND CLASSES OVERALL CLASS
BDI SPI EPI GDI %PTV
HR 1L 12.9 14.8 14.6 17.7 0.2 Good/Moderate HR 2L 13 13.8 13.5 15.2 5.5 Moderate HR 3L 9.3 9.5 6.7 9.2 32.7 Poor/Bad HR 4L 10 10.3 8.2 8.9 34.8 Poor/Bad HR 5L 10.7 14.9 11.1 13.1 0.7 Moderate/Poor VR 1L 12.5 14.6 15.1 15.9 3.7 Good/Moderate VR 2L 12.4 14.4 13.3 17.1 0.7 Good/Moderate
The diatom index scores for the reference site HR 1 and the agriculturally impacted site HR 2, as well as the Vaal River sites (VR 1 and VR 2) seemed to be in an overall better ecological health class (high to moderate integrity) than the rest of the agriculturally impacted sites on the Harts River (moderate to poor integrity) during the low flow season (Table 3.4). The agricultural sites HR 3 and HR 4 showed the lowest scores for BDI, SPI and GDI, as well as an increased tolerance to organic pollution (low EPI score and a %PTV above 20).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 45 Diatoms
The diatom ecological descriptors in Table 3.5 indicate that the reference site HR 1 and the agricultural site HR 2 on the Harts River, as well as the Vaal River sites (VR 1 and VR 2) were in a meso-eutrophic and oligosaprobous state. The diatom communities found at these sites were made up of species that had a fairly high oxygen demand and that could only tolerate very small concentrations of organically bound nitrogen. The agricultural sites HR 3, HR 4 and HR 5 were in a eutrophic state and showed that the diatom communities at these sites were made up of species that could tolerate elevated concentrations of organically bound nitrogen. The agricultural site HR 3 was in a α-meso-polysaprobous (very heavily polluted) state, with a low dissolved oxygen requirement, indicating impairment of the diatom community due to changes in water quality. The agricultural site HR 5 was β-mesosaprobous (moderately polluted) and consisted of a community with continuously high oxygen requirements. The diatom community showed that the salinity was tending towards brackish-fresh, which would infer that there was an increase in the presence of halophilous species at this site (HR 5).
Table 3.5: Diatom ecological descriptors for sites on the Harts- and Vaal Rivers during the low (L) flow period. Site pH Salinity Nitrogen Oxygen Saprobity Trophic uptake requirements state mechanism Nitrogen HR 1L Fresh- Meso- Alkaliphilous autotrophic Fairly High Oligosaprobous brackish eutrophic sensitive Nitrogen HR 2L Fresh- Meso- Alkaliphilous autotrophic Fairly High Oligosaprobous brackish eutrophic sensitive Nitrogen HR 3L Fresh- α-meso- Alkaliphilous autotrophic Low Eutrophic brackish polysaprobous tolerant Nitrogen HR 4L Fresh- Alkaliphilous autotrophic Moderate β-mesosaprobous Eutrophic brackish tolerant Nitrogen HR 5L Brackish- Continuously Alkaliphilous autotrophic β-mesosaprobous Eutrophic fresh high tolerant Nitrogen VR 1L Fresh- Meso- Alkaliphilous autotrophic Fairly High Oligosaprobous brackish eutrophic sensitive Nitrogen VR 2L Fresh- Meso- Alkaliphilous autotrophic Fairly High Oligosaprobous brackish eutrophic sensitive
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 46 Diatoms
3.3.3.2. High Flow The diatom index scores, as well as their classes for the study sites on the Harts- and Vaal Rivers during the high flow period are shown in Table 3.6.
Table 3.6: Diatom index scores and classes for sites on the Harts- and Vaal Rivers during the high (H) flow period. SITE DIATOM INDEX SCORES AND CLASSES OVERALL CLASS
BDI SPI EPI GDI %PTV
HR 1H 10.7 11.4 11.7 12.9 16.4 Poor HR 2H 10.8 10.4 12.6 10.3 9.3 Poor HR 3H 9.7 8.5 8.7 9.3 13.9 Poor/Bad HR 4H 11.4 11.3 11.5 9.1 25.1 Poor HR 5H 6.2 7.4 7.7 7.2 8.9 Bad VR 1H 11.1 13.8 10.5 16.7 0.2 Moderate/Poor VR 2H 9 9.2 6.4 11.6 4.6 Poor/Bad
The reference site HR 1, as well as the agricultural sites on the Harts River were in a poor to bad overall state (Table 3.6) during the high flow season. The upper Vaal River site VR 1 was in a moderate to poor overall state and the downstream Vaal River site VR 2 was in a poor to bad overall state according to the selected diatom indices. The agricultural sites HR 3 and HR 5, as well as the Vaal River site VR 2 downstream of the confluence were characterised in having lower BDI, SPI and EPI scores compared to the rest of the study sites. The agricultural site HR 4 showed species with an increased tolerance to organic pollution (%PTV above 20), whereas the other sites showed an increase in inorganic nutrients (%PTV below 20).
The diatom ecological descriptors in Table 3.7 show that the study sites on the Harts River were in a eutrophic state. The agricultural sites HR 3 and HR 4 were α-meso-polysaprobous (very heavily polluted) with a diatom community dominant in species that have a moderate dissolved oxygen requirement and that can tolerate elevated levels of organically bound nitrogen. The diatom community structures at the agricultural sites HR 4 and HR 5 and the Vaal River site VR 2 showed that there was an increase in salinity (brackish-fresh to brackish water) at these sites.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 47 Diatoms
Table 3.7: Diatom ecological descriptors for sites on the Harts- and Vaal Rivers during high (H) flow. Site pH Salinity Nitrogen Oxygen Saprobity Trophic uptake requirements state mechanism Nitrogen HR 1H Fresh- Continuously Alkaliphilous autotrophic β-mesosaprobous Eutrophic brackish High tolerant Nitrogen HR 2H Fresh- Continuously Alkaliphilous autotrophic Oligosaprobous Eutrophic brackish High tolerant Nitrogen HR 3H Fresh- α-meso- Alkaliphilous autotrophic Moderate Eutrophic brackish polysaprobous tolerant Nitrogen HR 4H Brackish- α-meso- Alkaliphilous autotrophic Moderate Eutrophic fresh polysaprobous tolerant HR 5H Nitrogen Alkaliphilous Brackish autotrophic Fairly High Oligosaprobous Eutrophic sensitive Nitrogen VR 1H Fresh- Meso- Alkaliphilous autotrophic Fairly High Oligosaprobous brackish eutrophic sensitive VR 2H Nitrogen Alkaliphilous Brackish autotrophic Fairly High β-mesosaprobous Eutrophic sensitive
3.4. Discussion 3.4.1. Relationship between Water Quality and Land Use 3.4.1.1. Temporal Variation As can be expected, the temperature was higher during the high flow period (January) than the low flow period (July) (Table 3.3). Water bodies undergo temperature variations along with normal climatic fluctuations. The temperature of surface waters is influenced by many factors. These include latitude, altitude, season, time of day, air circulation, cloud cover, as well as the flow and depth of the water body (Chapman and Kimstach, 1996). Physical, chemical and biological processes are affected by temperature in water bodies. As water temperature increases, the rate of chemical reactions generally increases together with the evaporation and volatilisation of substances from the water. As the temperature increases, the solubility of gases in the water decreases. The metabolic rate of aquatic organisms is also related to temperature (Chapman and Kimstach, 1996). In warm waters, respiration rates increase leading to increased oxygen consumption and increased decomposition of organic matter. With increasing temperature, growth rates also increase, which can result in increased water turbidity, macrophyte growth and algal blooms when nutrient conditions are suitable. Macrophyte growth and algal growth were highest at the agricultural site HR 3 where high nutrient conditions (Table 3.3) were found. Surface waters usually fall within the temperature range 0°C to 30°C (Chapman and Kimstach, 1996). These temperatures
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 48 Diatoms
fluctuate seasonally with minima occurring during winter and maxima in the summer (Chapman and Kimstach, 1996). Thus, it can be concluded that the temperature range of all sites during low- and high flow periods were within this range. Therefore, the temperature is adequate for the aquatic biota inhabiting these river systems.
The oxygen content of natural waters varies with temperature, salinity, turbulence, the photosynthetic activity of algae and plants and atmospheric pressure (Chapman and Kimstach, 1996). The measurement of dissolved oxygen can be used to indicate the degree of pollution by organic matter, the destruction of organic substances and the levels of self- purification of the water (Chapman and Kimstach, 1996). All of the sites sampled were well oxygenated (above 5mg/l) during both seasons (Table 3.3), with oxygen concentrations being higher during the high flow period compared to the low flow period. The high percentage saturated dissolved oxygen recorded at all of the study sites during both seasons confirm that all of the study sites contained adequate oxygen to sustain aquatic biota, although the saturation at some of the study sites (HR 2L, HR 3L, HR 3H) was below the water quality guidelines set out by DWAF (1996).
Most of the pH results for the high flow period were between 6.0 and 8.5 (Table 3.3), which is within the range of most natural waters (Chapman and Kimstach, 1996). pH values were higher during the low flow period (which were found to be higher than the natural levels) compared to the high flow period. Lower values can occur in dilute waters high in organic content and higher values in eutrophic waters (Chapman and Kimstach, 1996).
Turbidity, alkalinity and calcium levels were remarkably higher during the low flow season compared to the high flow season for all sites on the Harts River, as well as the Vaal River (Figure 3.1). Usually during winter (low rainfall-runoff conditions) the rivers should be less turbid. Agricultural practices impact rivers through sedimentation. Thus, it is thought that the reason for the high turbidity during the winter, low flow period, may be the result of winter ploughing. Bank erosion was evident at most of the sites and thus was also a contributor of sediment to the river systems. Another natural occurrence which could have contributed to the high turbidity measured during low flow, could be moisture deficit (drought, seasonality and drainage aspect). At the upper Vaal River site (VR 1) construction practises were found, which also could have contributed to the high turbidity measured. Since cattle and other domestic animals (donkeys, goats) were observed at most of the sites, it can also be assumed that their grazing up to the riverbanks might have caused bank instability. It is also thought that releases from Taung and Spitskop Dams could also have increased the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 49 Diatoms
turbidity and suspended solid levels during the low flow period. During the high flow period, a decrease in conductivity levels was detected at HR 1 and HR 5, which are situated below these dams, compared to the low flow period. It is thought that the presence of these dams also serve as a sediment trap. Bate et al. (2002) found a decrease in conductivity at two study sites on the Sundays River, which were situated below the Darlington Dam, which was found to retain sediment. The input of nutrients, for example, fertilizers and livestock faeces could also have contributed to the high turbidity observed. The lower turbidity measured during the summer, high flow period, could mean that the river systems were able to flush out the suspended and deposited material.
3.4.1.2. Spatial Variation The reference site HR 1 was impacted by human activities, when this site’s water quality variables are compared to historic water quality data collected by DWAF (2008b) from 2001 to 2006 (Appendix B – Figure B1). Nutrient inputs were higher in this study compared to the DWAF data (Appendix B – Figure B1). Sewage spills and domestic animal faecal matter from the rural settlement adjacent to HR 1 may have induced eutrophic conditions at this relative reference site.
A pollution gradient existed (Figures 3.2 and 3.3) from HR 1 to HR 5 and VR 1 to VR 2. Nutrients showed an increase at the agricultural sites compared to the relative reference site HR 1, which may cause eutrophic conditions to arise. Natural sources of nitrate to surface waters include igneous rocks, land drainage and plant and animal debris. Natural concentrations seldom exceed 0.1mg/l (NO3-N) (Chapman and Kimstach, 1996). The agricultural site HR 3 had concentrations much higher compared to the natural (as well as the water quality guidelines set out by DWAF, 1996), contributing further to the eutrophic conditions at this site by stimulating algal growth. Nitrite concentrations in freshwaters are usually very low, 0.001mg/l NO2-N, and rarely higher than 1mg/l NO2-N (Chapman and Kimstach, 1996). The agricultural site HR 3 falls within this range, concerning nitrite levels, but nitrate plus nitrite in surface waters gives a general indication of the nutrient status and level of organic pollution in a water body, which seems to be the highest at this agricultural site during both seasons. Organic pollution in streams can lead to oxygen depletion and stressful conditions for aquatic organisms (Dostine, 2002). The agricultural site HR 3 was the only site with low dissolved oxygen (5.2mg/l) during the high flow period, indicating possible organic pollution at this site. However, when this value is compared to historic RHP data (DWAF, 2007) for January 2005 (Appendix B – Table B3), there was an increase in
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 50 Diatoms
dissolved oxygen levels in the present study, indicating possible reduction in organic pollution or increased flow at this site compared to historic data.
Conductivity was one of the water quality variables that contributed to the variation amongst the study sites (Figures 3.2 and 3.3). According to Biggs (1996 cited in Munn et al., 2002) ‘conductivity is a strong indicator of nutrient enrichment and not influenced by biological processes’. Therefore, although conductivity may reflect the relative degree of nutrient supply, it may also be more closely related to land use than to actual concentrations of nutrients (Biggs, 1995). Leland (1995) found that when agricultural lands are decoupled from other land uses, conductivity becomes a useful indicator of agricultural intensity. As can be deduced from the results outlined above, conductivity levels were higher for the agricultural sites (HR 2 to HR 5), as well as VR 2, which set these agriculturally impacted sites apart from the less impacted HR 1 and VR 1 during both seasons (Table 3.3). The conductivity of most freshwaters ranges from 10 to 1000μS/cm, but may exceed 1000μS/cm, especially in polluted waters, or those receiving large quantities of land runoff (Chapman and Kimstach, 1996) (Table 3.3 – conductivity of agricultural sites higher than 1000μS/cm).
The agricultural sites HR 3 and HR 4 had the highest sulphate levels during both seasons (Table 3.3). These values were lower than the ones measured by DWAF (2008b), and may be the result of fertilizer usage within the Vaalharts area. Sulphates are commonly associated with fertilizers such as potassium sulphate (K2SO4) and ammonium sulphate 2 [(NH4) SO4]. These high sulphate levels may also be attributed to the sulphates in the Vaal River water being used for irrigation i.e. irrigation return-flows. According to Chapman and Kimstach (1996) sulphate concentrations in natural waters are usually between 2 and 80mg/l. High sulphate concentrations can occur in arid regions where sulphate minerals, such as gypsum, are present. Thus, the high sulphate concentrations at the study sites on the Harts- and Vaal Rivers may also be as a result of their geology.
Chloride levels were higher at the agricultural site HR 5 during both seasons, compared to the rest of the study sites (Table 3.3). Usually in pristine freshwaters, chloride concentrations are lower than 10mg/l; sometimes even less than 2mg/l (Chapman and Kimstach, 1996). Higher concentrations can occur near irrigation drains and in arid areas. Turbidity levels were the highest at this site during the low flow period compared to the turbidity levels measured at the rest of the study sites. Normal values usually range from 1 to 1000NTU (Chapman and Kimstach, 1996). These levels can be increased by the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 51 Diatoms
introduction of organic matter pollution, other effluents, or runoff with high suspended matter content (e.g. from Spitskop Dam).
Leland et al. (1995) found that the degree of enrichment of streamwater with irrigation return- flows and subsurface drainage contributed to the site groupings found in their study, with agricultural sites being influenced by high total dissolved solids, nitrogen, phosphorus and turbidity levels. Salinization of irrigation schemes has become a major problem in many parts of the world, including South Africa. Research has shown that from a total irrigation area of 12,556ha. in the Orange-Vaal Water Users Association, 23% is either slightly (13%) or severely (10%) affected by salinity problems (Van Heerden et al., 2001). Since conductivity has been shown to play an important role in distinquishing between land use types, it can be concluded that irrigation return-flows in the Vaalharts area are a major cause of salinization in the Harts River. Phosphorus and nitrate are affected by the extent of runoff and soil erosion. Turbidity (suspended solids) could also be linked to phosphorus and nitrate, since erosion, which is responsible for high turbidity, can lead to a loss in soil and nutrient-rich organic matter (Lavoie et al., 2004). Lavoie et al. (2004) concluded that pH, conductivity and suspended solid measurements were better integrative guides of water quality in the agriculturally impacted systems in their study than specific nutrient variables.
3.4.2. Diatom Community Structure in Relation to Land Use Thus far in this chapter it was demonstrated that the water quality variables of the Harts River, as well as the lower Vaal River (VR 2) are impacted upon by agricultural practises along the Harts River. This section of the chapter will attempt to provide an outline of how the community structures of diatoms change in relation to water quality variables and if these changes can be attributed to the agricultural practises along the Harts River.
According to Stevenson’s (1997) hierarchical framework, intermediate factors (e.g. sediment, nutrient loading and hydrology) are regulated by ultimate factors (e.g. geology, climate and land use) which affect proximate (direct) factors. Proximate factors include abiotic factors such as pH, salinity, toxic substances and temperature, as well as biotic factors such as competition and predation. These factors affect the structure and function of benthic algal communities in a direct or indirect manner e.g. sedimentation can affect benthic algae negatively by reducing light availability or positively by increasing phosphorus availability (Burkholder and Cuker, 1991). Thus, after the initiation of a stress, communities adapt by immigration and reproduction of taxa that are tolerant to the specific stressors. The
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 52 Diatoms
assemblages may then recover function and some structural attributes (biomass and diversity), but assemblage composition changes.
From the above mentioned results it can be assumed that the agricultural sites are impacted upon by proximate factors such as salinity, conductivity and to a lesser degree, nutrients, during both flow periods. The diatom community structures changed with regard to increases in these variables during the high flow period compared to the low flow period, indicating increasing disturbance by intermediate factors such as land use.
The water quality variables pH, turbidity and calcium (alkalinity) contributed to the change in the diatom community structure during the low flow period compared to the high flow period, which was characterized by higher levels of conductivity, chloride and nutrients. A strong temporal and spatial trend was depicted in Figure 3.4.
The low flow diatom community structure differed from the high flow diatom community structure in having higher abundances of taxa tolerant of high alkalinity, pH and turbidity. More sensitive taxa were also associated with the low flow period, which seemed to ordinate more towards the reference site HR 1L, the agricultural site HR 2L and the Vaal River reference site VR 1L (e.g. A. minutissimum, E. microcephala, F. tenera and C. hustedtii). Taylor et al. (2007b) found A. minutissimum and E. microcephala at sites on the Crocodile River with cleaner, less impacted waters. Walsh (2008) also found A. minutissimum at a relative reference site on the Magalies River. Encyonopsis microcephala, however, occurred at the agricultural sites as well in this study, which seems to indicate that the water quality is still of a high enough standard to support sensitive species.
Potapova and Charles (2003) found the genus Cymbella Agardh to have the highest affinity towards calcium, as well as the genus Gomphonema Ehrenberg. It was, however, also - 2- shown that these calciphilous taxa also had a high optima for [HCO3 and CO3 ], which makes it difficult to distinguish the effect of that factor from the effect of calcium. The relative reference sites, as well as the agricultural sites showed relative high calcium levels during the low flow period (Table 3.3) and were associated with Gomphonema species.
Cocconeis pediculus was dominant at the agricultural site HR 5 during the low flow period (Figure 3.6) and dominated by T. fasciculata during the high flow period. Therefore, the dominance shifted from C. pediculus to T. fasciculata at this agricultural site from low to high
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 53 Diatoms
flow. According to Jonathan Taylor (Pers. Comm.1) C. pediculus is a strongly seasonal taxon. Cocconeis pediculus and T. fasciculata are known to be dominant in moderate to high electrolyte content, with these taxa also extending into brackish waters (Table 3.7) (Potapova and Charles, 2003; Taylor et al., 2007d). Tabularia fasciculata has also been reported from critically polluted industrial wastewater (Taylor et al., 2007d). Potapova and Charles (2003) found in their study that the highest optima for chloride were observed in species with a high conductivity optima e.g. N. recens and T. fasciculata, which is also the case in this study (Figure 3.4). Agricultural sites on the Crocodile River (Walsh, 2008) were characterised by A. pediculus, C. pediculus, C. placentula var euglypta and N. gregaria. These taxa were also found at agricultural sites in this study. It was found that these taxa were associated with major problems related to eutrophication (Walsh, 2008). Lavoie et al. (2004) found C. placentula, C. pediculus and S. brebissonii at agriculturally influenced sites, with conductivity, nutrients, suspended solids and turbidity as factors that were markedly and significantly lower at the reference sites. Reimeria uniseriata was also associated with the agricultural site HR 5, which is an indication that conditions of reduced light penetration was present at this site, since this taxon is able to grow in high turbidity conditions (Taylor et al., 2007d).
Both sample sets were dominated by motile taxa, especially at the agricultural sites HR 2 to HR 5, such as Navicula and Nitzschia Hassall. Surirella, which is also a motile genus, also occurred during both seasons, but not in high abundance. Motility is an essential adaptation to prevent burial by siltation and most motile species tend to display a greater tolerance to organic pollutants (Fore and Grafe, 2002; Kelly, 2003). Kutka and Richards (1996), Pan et al. (1996) and Detenbeck et al. (2000) also found more diatom valves belonging to motile genera at sites with high levels of fine sediment. Therefore, the presence of these motile taxa, indicates that factors other than water quality (such as sedimentation) may be influencing the diatom assemblages. Walsh (2008) also found two motile species belonging to the genus Navicula (i.e. Navicula tripunctata Bory and N. cryptotenella) dominating at an agricultural site on the Magalies River.
Alkaliphilic taxa were dominant at all of the sites during both seasons. This is a result of the high pH found at all of the sites (Table 3.3). Alkaliphilic taxa prefer a pH range over 7.0 (Appendix B – Table B6). Potapova and Charles (2002) found that the arid areas of the western part of the United States supported a diatom flora rich in alkaliphilic taxa. The
1 Dr. J.C. Taylor, School of Environmental Science and Development, Division of Botany, North-West University, Potchefstroom, May 2008.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 54 Diatoms
authors also concluded that at smaller spatial scales, bedrock type, land use and watershed size become more important than the environmental factor climate. As pH is partly regulated by the water buffering capacity or amount of alkaline metals, it is also influenced by all of the above-mentioned factors. The relative importance of a parameter in explaining variation among diatom assemblages also strongly depends on its range of variation in the data set (Potapova and Charles, 2002). The range of the pH data in the present study ranged from 8.58 to 9.26 during the low flow period and 7.71 to 8.8 (Table 3.3) during the high flow period. Although high, the pH range measured during this study was not as high as those measured in streams in the Appalachian Mountains (Pan et al., 1996). It was found that high pH in the study by Pan et al. (1996) stemmed from watershed geology and pH elevation due to land use such as liming and agriculture-induced nutrient enrichment.
According to Potapova and Charles (2002) polluted rivers are often not only rich in nutrients, but in other ions too, so it is difficult to conclude that diatom communities respond primarily to pH variation. An environmental variable such as pH highly influences patterns in diatom communities, often resulting in a strong relationship between diatom distributions and that variable (e.g. Dixit et al., 1991). Many studies have shown that diatom communities vary along gradients of ionic concentration (Sabater and Roca, 1992). Reavie et al. (1995) found that conductivity exerted the strongest influence on diatom distributions. The strong influence of conductivity and salinity on diatoms has been known for a long time (e.g. Cumming and Smol, 1993; Wilson et al., 1994). It is found that most often the increase in ionic content is accompanied by nutrient enrichment (Leland and Porter, 2000). Leira and Sabater (2005) also found downstream enrichment with dissolved salts and nutrients in their study. Turbidity levels ordinated out towards the Vaal River sites (Figure 3.7) and showed a negative correlation with conductivity during the high flow period. Janse van Vuuren (2001 cited in Janse van Vuuren and Pieterse, 2005) found that the influence of turbidity on the Vaal River water is probably of primary importance in controlling phytoplankton dynamics, as compared to the influence of nutrients, which may only play a secondary role. Janse van Vuuren and Pieterse (2005) regarded turbidity as one of the most important variables influencing not only phytoplankton, but also other physical and chemical variables in the Vaal River system. It was also clear that during the high flow period (Figure 3.7) only few species favoured high turbidities. Nitzschia frustulum and A. granulata are important diatom indicators of high phosphorus environments in streams throughout Australia, whereas M. smithii is associated with streams with low phosphorus concentrations (Blinn and Bailey, 2001). From Figure 3.7 this trend is also evident, with N. frustulum and A. granulata ordinating out towards high phosphates and M. smithii ordinating out in the opposite
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 55 Diatoms
direction. Mastogloia smithii was shown to be dominant at VR 2 during the high flow period (Figure 3.8). In the study by Blinn and Bailey (2001), habitats in regions with high agricultural activity (secondary salinization) had high specific conductance and high nutrients, which showed strong positive loadings with the diatom taxon N. frustulum, as is the case in this study (Figure 3.7). Nitzschia frustulum and A. granulata were also present at the agricultural sites on the Crocodile River (Walsh, 2008), which were linked to increased salts, caused by runoff from the highly cultivated areas. Potapova and Charles (2003) also found an overriding effect of conductivity and nutrients on the composition of diatom communities. Potapova and Charles (2002, 2003) suggest that in these circumstances care must be taken not to confuse the effect of ionic content with that of nutrient enrichment. Carpenter and Waite (2000) reported that agricultural stream sites and forested stream sites were separated along a conductivity gradient in the Willamette Valley. Leland (1995) and Munn et al. (2002) found that conductivity was one of the key explanatory variables for lotic periphyton species assemblages in the Columbia Plateau, Washington, an agriculturally dominated region. Increases in ionic strength in streams may reflect changes in land use and increases in surface runoff. Philibert et al. (2006) also found that of the non-spatial variables measured in the Australian landscape, conductivity appeared to influence the diatom assemblages the most. It is therefore thought that above a particular salinity threshold, salinity is the dominant water quality influence on diatom composition. The narrower range of phosphorus variables (Table 3.3) may explain why diatoms appear to be more responsive to nitrogen variables (Figures 3.5 and 3.7). Philibert et al. (2006) also indicate that diatoms may be robust nutrient bioindicators only in waters of lower conductivity and within a limited pH range. Thus, it is thought that high conductivity (salinity) at the agricultural sites, might be masking the effects of nutrients in the present study.
Diatom species are known to respond to seasonal changes in water temperature (Moore, 1977a,b cited in Potapova and Charles, 2002). However, single measurements of water temperature provide a poor assessment of temperature regime in rivers because of large diurnal and day-to-day oscillations (Potapova and Charles, 2002). Water temperature would have had a stronger relationship with the diatom communities of this study if it was estimated in a more accurate way, for example, if it was monitored constantly during a period preceding diatom sampling. Potapova and Charles (2002) also expected a better response to the water temperature measured at the time of algal sampling than to average annual air temperature. Pienitz et al. (1995) and Rosén et al. (2000) used diatom assemblages to infer water temperature in lakes. However, temperature is rarely found as an important environmental variable in regional data sets. The reason for this statement is, because it is
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 56 Diatoms
rare for temperature to vary in a region more than any other factor (Potapova and Charles, 2002). Another reason may be that it correlates with other environmental factors and their effects are difficult to separate (Anderson, 2000). Figure 3.4 shows how the diatom Epithemia adnata (Kützing) Brebisson is ordinated towards the high flow period where all of the sites had high water temperatures (25.4 to 28.6°C), as well as the Vaal River site VR 2L. This taxon is known to tolerate elevated temperatures (Taylor et al., 2007d). Luticola kotschyi Grunow also ordinated towards the high flow season, but occurred in very small abundance. This taxon is known to prefer thermal waters, as well as waters with elevated electrolyte content (Taylor et al., 2007d). In the study conducted by Janse van Vuuren and Pieterse (2005) it was found that A. granulata (with maximum abundances during summer) was positively correlated with temperature, with this taxon’s optimal temperature being above 20°C. It is, however, evident from Figure 3.7 that Aulacoseira granulata var. angustissima (Ehrenberg) Simonsen ordinated out towards the Vaal River sites where higher temperature levels were noted, but not A. granulata. According to Jonathan Taylor (Pers.Comm.1) A. granulata is planktonic and thus not common in the benthos except under specific conditions.
Since there was spatial variation in the dataset (Figures 3.4, 3.5 and 3.7) it can be assumed that some part of this spatial variation is the result of unmeasured environmental parameters or because of the fact that epiphytic diatoms were sampled at the Vaal River sites, compared to the epilithic diatom communities sampled at the Harts River. Because of this fact the sites on the Harts River will be slightly different regarding their diatom community composition compared to that of the Vaal River. Winter and Duthie (2000) identified no clear habitat preferences, nor seasonality among stream epilithic, epipelic and epiphytic diatoms. Soininen (2004) also found similar results. Species significantly confined to plant surfaces were more or less similar to typical epilithic species, except C. placentula (Soininen, 2004), which according to the authors Krammer and Lange-Bertalot (1986, 1988, 1991a,b) is generally assumed to grow preferentially on plants or other algae. Cocconeis placentula was found at some of the Harts River sites and not just at the Vaal River sites where epiphytic diatoms were sampled. Spatial variation also existed between the Harts River sites (HR 1 to HR 5) and those of the Vaal River sites (VR 1 to VR 2). The analysis of this study shows, however, that at any spatial scale, there were species with patchy distributions, which are not easily explained by environmental factors. Some proportion of this ‘spatial’
1 Dr. J.C. Taylor, School of Environmental Science and Development, Division of Botany, North-West University, Potchefstroom, 2009.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 57 Diatoms
variation can be related to unmeasured environmental parameters that were spatially structured. Another reason for these patchy distributions may be due to spatial autocorrelation, or the tendency of geographically close sites to have similar flora (Jongman et al., 1995 cited in Potapova and Charles, 2002). Rare species can be important in community ecology and bioassessment in detecting primary or secondary environmental gradients or impacts (Cao et al., 1998). Soininen (2004) found that species which tend to occur locally in low abundance, tend also to be more narrowly distributed, thus increasing the spatial structure or variation of the data. Thus, rare species are an important part of biological communities, as is also shown in the present study.
3.4.3. Diatom Community Integrity and Ecological Description The general water quality indices (BDI, SPI and GDI) showed decreased water quality at the agricultural sites compared to the relative reference sites HR 1 and VR 1 during the low flow period (Table 3.4). The agricultural site HR 5 showed a recovery during the low flow period (Table 3.4), but a remarkable decrease in general water quality compared to the rest of the study sites during the high flow period (Table 3.6). The EPI index, which is designed to show amongst others the presence of nutrient pollution, shows the same trend as the general water quality indices for the agricultural site HR 5 (Tables 3.4 and 3.6). It is therefore thought that during the low flow period when irrigation practices ceased, and the presence of Spitskop Dam, which acts as a sink for nutrients and sediment from agricultural practices upstream, resulted in better water quality at this agricultural site during the dry season. During the wet season it is then thought that irrigation return-flows from agricultural practices above this site, as well as livestock related runoff, increased at this site during the wet season. It is also thought that water released from Spitskop Dam, which contains water from the other agricultural sites and the additional impacts from the agricultural practices below the dam, degraded the water quality at this site and that increased nutrients rather than sedimentation and salinization (conductivity levels were lower at this site during the wet season compared to the other agricultural sites) contributed to this decrease in general water quality.
Van Dam et al. (1994) listed attributes for diatom species related to tolerance of salt, inorganic nutrients (nitrogen uptake mechanism, trophic status), saprobic conditions and high or low levels of pH and oxygen concentration. It was found in the study by Fore and Grafe (2002) that diatoms that tolerate salt and alkaliphilic diatoms increased with agriculture and livestock grazing. In the present study, alkaliphilic taxa; taxa typical of brackish-fresh and brackish waters, as well as eutraphentic taxa dominated at the agricultural sites HR 4,
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 58 Diatoms
HR 5 and VR 2 during the high flow period (Table 3.7). Evaporation of irrigation water from agricultural fields can leach salt and alkaline residue into the rivers by precipitation or irrigation return-flows. Fertilization and erosion can also increase soil alkalinity (Fore and Grafe, 2002).
Trophic state refers to the presence of inorganic nutrients such as nitrogen, phosphorus, silica and carbon. Saprobity on the other hand refers to the presence of biodegradable organic matter and low oxygen concentrations (Van Dam et al., 1994). In the study by Fore and Grafe (2002) eutrophic and polysaprobic diatoms increased with disturbance. In the present study, the agricultural sites HR 3 and HR 4 showed an increase in α-meso- polysaprobous diatoms, as well as diatoms that indicated eutrophic conditions during the high flow period (Table 3.7). These taxa usually increase if inorganic or organic nutrients are present in large amounts. The EPI index showed increased nutrient loads at the agricultural sites HR 3 and HR 4 during the low flow period (Table 3.4) and at HR 3, HR 5 and VR 2 during the wet season (Table 3.6). Since the %PTV gives an indication of the percentage diatom taxa that are tolerant to organic pollution, and it was shown that the agricultural sites HR 3 and HR 4 were impacted upon by organic pollution during the dry season (Table 3.4), runoff from livestock and sewage inputs from Pampierstad and Espagsdrift are assumed to be the causes. The agricultural site HR 4 was the only site impacted by organic pollution during the high flow period (Table 3.6) and it is therefore assumed that irrigation return-flows (fertilizer) and livestock excrement and wastewater return-flow (Fore and Grafe, 2002) from Espagsdrift were greatest at this site during the wet season. Inorganic sources of nutrients (irrigation return-flows) were mostly the cause of increased nutrient inputs at HR 3, HR 5 and VR 2 during the wet season. Walsh (2008) found that a study site on the Crocodile River was impacted upon by organic pollution (which was likely due to sewage inputs). This site on the Crocodile River received urban and agricultural impacts. It was found that the cumulative organic inputs from urban and agriculture had synergistic effects on the water quality of the site on the Crocodile River, which caused severe impacts on the primary producer communities (Walsh, 2008).
Nitrogen autotrophs were dominant in the present study (Tables 3.5 and 3.7), whereas nitrogen heterotrophs were present in the studies by Leland (1995), Fore and Grafe (2002) and Munn et al. (2002). According to Fore and Grafe (2002) should nitrogen fixers decline and nitrogen heterotrophs increase with disturbance that cause increased organic nitrogen. This was, however, not the case in the present study. The rest of the study sites during both seasons were classified as oligosaprobous and β-mesosaprobous (Tables 3.5 and 3.7),
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 59 Diatoms
which is an indication of low to moderately polluted waters (Appendix B – Table B6). Walsh (2008) also found β-mesosaprobous taxa at agricultural and urban impacted sites on the Crocodile River.
3.5. Summary and Conclusion Diatom community structures did show differences in relation to land use, from communities with higher abundances of taxa typical of cleaner, less impacted waters (e.g. E. microcephala) found at the relative reference sites, to communities dominated by taxa typical of more impacted waters (e.g. various Nitzschia and Navicula species) found at the agricultural sites. Temporal trends were also depicted, with the high flow period indicating a decreased water quality at all of the study sites according to the diatom community structures, indices and ecological descriptors. Conductivity and turbidity levels were increased by salinization and sedimentation. Nutrients, particularly from inorganic (irrigation return-flows) and organic (sewage and livestock inputs) sources, also played a role in the structuring of the particular diatom community found at the agricultural sites. It is, however, thought that conductivity masked the effects of nutrients on the diatom community composition.
Biological monitoring techniques are considered to be a more holistic approach to monitor river ecosystem health, compared to standard physical and chemical methods, therefore, both the present and past history of the water quality in river ecosystems can be assessed using biological communities. The use of diatoms as biological indicators in the present study showed to be reliable indicators of specific water quality problems such as organic pollution at the agricultural sites HR 3 and HR 4, as well as general water quality (SPI, BDI and GDI).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 60
Chapter 4: Macroinvertebrates
4.1. Introduction 4.1.1. Macroinvertebrates as Biological Indicators Macroinvertebrates are the most commonly used group of freshwater organisms for the monitoring of rivers and streams. Many techniques, protocols and indices have been developed to monitor stream quality (e.g. Lenat, 1993; Growns et al., 1997; Haase and Nolte, 2008). These monitoring techniques, protocols and indices make use of changes in species composition (e.g. Castillo et al., 2006), diversity and functional organization (e.g. Delong and Brusven, 1998) of macroinvertebrates to monitor stream health. According to Rosenberg and Resh (1993) are these changes a valuable means of detecting stream alteration as a result of human-induced disturbances.
Numerous indices are currently in use in South Africa that incorporate macroinvertebrate community structure. These include the use of diversity indices such as the Shannon- Weiner index (Wilhm and Dorris, 1968), Margalef’s species richness (Margalef, 1951 cited in Dallas and Day, 1993) and Pielou’s evenness (Pielou, 1966). Biotic indices such as the South African Scoring System Version 5 (SASS5, Dickens and Graham, 2002) and the Macroinvertebrate Response Assessment Index (MIRAI, Thirion, 2007) are also used to monitor ecosystem health in Southern Africa. The use of functional organization (e.g. FFGs) of macroinvertebrates as water quality indicators is also used. According to Vannote et al. (1980) FFGs are a reflection of resource distribution and use and that these groups also facilitate the understanding of organic matter processing in streams.
The question of whether FFGs reflect macroinvertebrate responses to physico-chemical variables were tested by Palmer et al. (1996) using the Buffalo River, South Africa, as an example. The authors, however, concluded that FFG classifications were not a useful indicator of the water quality conditions in the Buffalo River. The use of FFG classifications are therefore to monitor stream resources, as stream systems are also controlled by mechanisms other than water quality contamination, which includes alterations of food resource availability (trophic base), modification of habitat quality and availability, and influences on biotic interactions through species introduction or extirpation (Karr, 1991, 1993). Macroinvertebrates are therefore useful indicators not only of water quality, but also reflect habitat integrity of aquatic ecosystems.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 61 Macroinvertebrates
4.1.2. Land Use and Macroinvertebrate Community Structure An example of how land use affects aquatic macroinvertebrates was illustrated in a study where the effects of forested, agricultural, and urban land use were determined on water quality and aquatic biota on three streams in the piedmont ecoregion of North Carolina (Lenat and Crawford, 1994). The authors found that invertebrate taxa richness, a biotic index, and the number of unique invertebrate species (found at only one site) indicated moderate stress at the agricultural site and severe stress at the urban site. At the agricultural site, declines in taxa richness within intolerant groups were partially offset by increases within tolerant groups. The agricultural stream had the highest abundance values, indicating enrichment. The urban site was, however, characterized by low species richness for most groups and very low abundance values. Analysis of seasonal patterns indicated that detritus was the most important food source for invertebrates in the forested stream, while in the agricultural stream it was found that periphyton was the most important food source. Dominant macroinvertebrate groups shifted from Ephemeroptera at the forested site, to Chironomidae at the agricultural site, and Oligochaeta at the urban site. Land use was found to have strongly influenced the invertebrate community. The authors also found that macroinvertebrate community structure consistently indicated strong between-site differences in water and habitat quality.
4.1.3. Macroinvertebrate Response in Relation to Agricultural Land Use
The responses of macroinvertebrate communities to agricultural activities were demonstrated by Kay et al. (2001). They investigated the distribution patterns of aquatic macroinvertebrates in an agricultural zone in south-western Australia, as well as the environmental variables that influenced those patterns. The authors found that the macroinvertebrate communities consisted of families that tolerated a broad range of environmental conditions such as high salinities. The most significant environmental factors that influenced the macroinvertebrate distribution in the region were rainfall, salinity, land use and instream habitat.
A field study on the Lourens River, South Africa, was undertaken by Thiere and Schulz (2004) to assess the potential impact of agricultural pollution on the aquatic macroinvertebrate fauna. The upper regions of the Lourens River were free of contamination, whereas subsequent stretches flowing through a 400ha. orchard area received transient insecticide peaks. Seven out of 17 investigated taxa occurred in significantly reduced numbers or were even absent at the downstream site. The SASS5
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 62 Macroinvertebrates
showed a significantly less sensitive community structure at the downstream site, indicating continuously lower water quality. It was concluded that the Lourens River macroinvertebrate communities were affected by agricultural pollution, with pesticides and increased turbidity as the most important stressors.
The Pomahaka River in southern New Zealand has a long history of agricultural development. Harding et al. (1999) sampled 15 sites along a 119km stretch of this river, where headwater sites were surrounded by low-intensity sheep farming, and high-intensity pasture and dairying occurring in the mid-reach and lower reaches. It was found that water clarity decreased significantly from the headwaters to the lower reaches. Benthic sediment levels increased significantly downriver, as well as periphyton levels, nitrogen and phosphorus concentrations. The authors found that macroinvertebrate species richness did not change significantly, but that the species composition did with Ephemeroptera and to a lesser degree, Plecoptera and Trichoptera dominating the headwater sites (high water clarity, low nutrient and periphyton levels) and molluscs, oligochaetes and chironomids dominating the downriver sites. Canonical Correspondence Analysis showed that agricultural activity (e.g. high turbidity and temperature) was strongly associated with the assemblage compositions at the different downriver sites.
Shieh and Yang (2000) investigated changes in stream water- and habitat quality of the agriculturally impacted Chichiawan stream in Taiwan, using community structure and functional organization of aquatic insects at four sites in 1985-1986 and 1995-1996. Water quality in 1995-1996 had not degraded as compared with data in 1987-1988. It was found that the number of taxa and number of individuals per sample unit were higher in 1985-1986 compared to 1995-1996 at the four sites. Substrate quality of the stream had deteriorated at sites located in agricultural areas. Site four was situated downstream of the confluence between Chichiawan Stream and Yousheng Stream where the steam watershed has been developed for agricultural land use. It was found that the community structure and functional organization of aquatic insects at sites one and two in 1995-1996 were similar to those at site four in 1985-1986, therefore indicating that the habitat quality at sites one and two in 1995-1996 had degraded during the ten year period. The analyses of community structure and FFGs of aquatic insects therefore suggested; although no water quality degradation based on physico-chemical data between the two sampling dates occurred; changes in stream substrates, which resulted from increased soil erosion and suspended sediment inputs to the stream.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 63 Macroinvertebrates
Anderson et al. (2003) found that the densities of certain species of midges and mayflies, as well as blackfly larvae (genera found at their reference station) had declined downstream of the drain input of pesticides in the Salinas River. The authors suggested that the pesticides may have influenced the macroinvertebrate community structure through behavioural or indirect mechanisms, which include sublethal influences on drift and predator-avoidance behaviour.
4.1.4. Aims The aims of this chapter are as follows: To determine whether the macroinvertebrate community structures change along a longitudinal gradient of agricultural practices compared to the reference site, which is situated upstream of these activities. To determine whether the macroinvertebrates found at the agriculturally impacted sites will show different FFGs compared to the relative reference sites. To determine whether macroinvertebrates are useful bioindicators of the ecosystem health of the Harts- and Vaal River systems.
4.1.5. Objectives In order to achieve the aims listed above, the following objectives were set: To determine the macroinvertebrate community structures of the seven study sites located in the Lower Vaal WMA. To characterize the spatial and temporal trends in the macroinvertebrate community structures. To compare the FFGs of macroinvertebrates collected from agriculturally impacted sites to those of the relative reference sites. To assess the abiotic drivers responsible for the changes in the macroinvertebrate community structures.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 64 Macroinvertebrates
4.2. Materials and Methods 4.2.1. Study Sites The sites described in Chapter 2 were used in the macroinvertebrate assessment.
4.2.2. Habitat The Integrated Habitat Assessment System (IHAS) was used (McMillan, 1998) in association with SASS5 (the macroinvertebrate index) to measure the availability and quality of aquatic habitats (i.e. instream integrity) present at the Harts- and Vaal River sites during both seasons. Each biotope is expressed as a percentage, where a score of 100% represents natural or ideal habitat availability and quality. Table 4.1 indicates the categories, their description and integrity scores (expressed in percentage) used in the present study as a measure of habitat integrity.
Table 4.1: The interpretation of IHAS scores presented as categories, category descriptions and percentage integrity. Category Category Description Integrity Score (%)
A Natural 90-100 B Largely Natural 80-89 C Moderately Modified 60-79 D Largely Modified 40-59 E Seriously Modified 20-39 F Critically Modified <20
4.2.3. Macroinvertebrate Community Composition 4.2.3.1. Collection, Preservation and Enumeration Aquatic macroinvertebrates were collected using the SASS5 methodology as set out in Dickens and Graham (2002) during two sampling periods: low flow (July 2007) and high flow (January 2008).
Three biotopes were sampled using a standardized SASS net (1000μm mesh with 300 x 300mm square opening) at sites HR 1, HR 2, HR 3, HR 4, HR 5 and VR 1 (stones; vegetation; gravel, sand and mud). Only two biotopes were sampled at site VR 2 (vegetation; and mud), since no stones were available for sampling at this site. These biotopes were sampled according to Dickens and Graham (2002).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 65 Macroinvertebrates
Handpicking of specimens that may have been missed by the sampling procedure was carried out and specimens observed were also added to the SASS5 sheet under the biotope with which they were the most associated. The samples collected were placed into three separate white identification trays, one for each of the biotopes sampled. The identification of the macroinvertebrates took place for a maximum of 15 minutes, for each of the biotopes sampled. The macroinvertebrates were identified using field guides composed by Gerber and Gabriel (2002). This data were then also added to the SASS5 sheet, which includes the following information: the biotope SASS5 scores, total SASS5 scores, the number of taxa and the Average Score Per Taxon (ASPT).
The SASS5 categories were assigned according to a modified method of Dallas and Day (2007) where biological bands for SASS5 scores and ASPT values were determined for the different ecoregions. Since the study area falls within the Southern Kalahari ecoregion, the biological bands for this ecoregion were used in the calculation of the ecological categories (ECs) of the study sites (Dallas, 2007). The ecological categories assigned to each site and their descriptions are given in Table 4.2.
Table 4.2: Categories and category descriptions for the interpretation of the SASS5 data. Category Ecological Category Name Description
A Natural Unmodified natural B Largely Natural Largely natural with few modifications C Moderately Modified Moderately modified D Largely Modified Largely modified E Seriously Modified Seriously modified F Critically Modified Critically or extremely modified The ecological categories and their descriptions were taken from Dallas (2007).
After the samples were examined in the field, the samples were preserved with 10% formalin (to which the vital stain, Rose Bengal was added). The sample bottles were labelled with the necessary information (i.e. date of collection, site name and biotope sampled).
Back in the laboratory, the samples were sorted and enumerated (all of the specimens in each sample were counted i.e. no sub-sampling) to family level. Specimens were placed in storage bottles and preserved in 70% ethanol.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 66 Macroinvertebrates
4.2.4. Functional Feeding Groups Literature from Merritt et al. (1996 cited in Todd, 2000) and Barbour et al. (1999) were used to assign FFGs to the macroinvertebrate families collected. From Table 4.3 it can be noted that most of the families are assigned to more than one FFG. This is because a family is made up of different species that have different mouthparts and therefore different feeding habits. In these cases, the abundance value for these taxa was divided by the number of FFGs that are representative of that particular taxon in an attempt to compensate for the presence of those species. Table 4.3 shows the macroinvertebrate families collected during both seasons, with their respective FFGs as assigned by the above mentioned authors.
Table 4.3: Macroinvertebrate families and their respective FFGs per family. Taxa FFGs Turbellaria PR Oligochaeta DT, COG, COF Hirudinea PR Potamonautidae (Crabs) SHO Atyidae COG Baetidae COG, SC Caenidae COG Heptageniidae SC, COG Leptophlebiidae COG, SC Tricorythidae COG Chlorocyphidae PR Coenagrionidae PR Gomphidae PR Libellulidae PR Pyralidae SH Belostomatidae PRP Corixidae PIH, PR, PRP, SC Naucoridae PRP Veliidae PRP Ecnomidae COF Hydropsychidae COF, PR Hydroptilidae PIH, SC, COG
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 67 Macroinvertebrates
Table 4.3 (cont.): Macroinvertebrate families and their respective FFGs per family. Taxa FFGs Dytiscidae PR Elmidae SHH, COG, SC Gyrinidae PR, SCS Helodidae SC, COG, SHH, PIH Hydrophilidae PR Ceratopogonidae PR, COG Chironomidae COF, PR, PRP, COG Culicidae COF, COG Muscidae PRP Simuliidae COF, COG Tabanidae PRP Tipulidae SHD, COG Ancylidae SC Lymnaeidae SC Physidae SC Planorbidae SC Corbiculidae COF Thiaridae SC
COF= collector-filterers; COG= collector-gatherers; DT= detritivores; PIH= piercer-herbivores; PR= predators; PRP= predator-piercers; SC= scrapers; SH= shredders; SHH= shredder-herbivores; SHD= shredder-detritivores; SHO= shredder-omnivores; SCS= surface-film-scavengers.
4.2.5. Statistical Analyses of Macroinvertebrate Community Data and FFGs Univariate and multivariate analyses were used to assess changes in macroinvertebrate community structures at temporal and spatial scales for sites on the Harts- and Vaal Rivers. The software package PRIMER version 6.0 (Clarke and Gorley, 2006) was used to describe macroinvertebrate species-abundance relations via univariate diversity and evenness indices. Univariate analyses included the Margalef’s index (d) (Margalef, 1951 cited in Dallas and Day, 1993), Shannon-Weiner diversity index (H’) (Wilhm and Dorris, 1968) and Pielou’s evenness index (J’) (Pielou, 1966).
Multivariate analyses were carried out to determine the relationship between macroinvertebrate community structures and the selected environmental variables using the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 68 Macroinvertebrates
computer package CANOCO version 4.5 (Ter Braak and Šmilauer, 2002), as well as to assess changes in macroinvertebrate FFGs at a temporal and spatial scale. Redundancy analyses were performed on both macroinvertebrate community and FFG data, and water quality data collected for both seasons to determine 5 water quality variables that best explained the variation amongst the study sites. These variables were then added to a new environmental data sheet; which included the 5 water quality variables selected, Total IHAS and ASPT Scores (SASS5); for the different seasons, respectively. Redundancy analyses were used to indicate the relationship between macroinvertebrate communities and their FFGs, and the selected environmental variables at a temporal and spatial scale for sites on the Harts- and Vaal Rivers. Data were log-transformed and the significance of the RDA axes was tested using unrestricted Monte Carlo permutation tests (499 permutations). Significance was taken as a probability level of P ≤ 0.05.
Multivariate analyses were also carried out using the computer package PRIMER version 6.0 to assess changes in macroinvertebrate communities and FFGs between sites and seasons. Similar ordination patterns were observed using PRIMER version 6.0 and CANOCO version 4.5. Thus, for the purposes of visually illustrating the relationship between macroinvertebrate community data and environmental variables, the results obtained using CANOCO version 4.5 are shown. K-dominance plots were included to indicate sites that have an increased dominance of a particular family relative to the other study sites and seasons (PRIMER version 6.0 – log-transformed data).
4.3. Results The results for habitat integrity (IHAS), macroinvertebrate integrity (SASS5 and macroinvertebrate community composition) and macroinvertebrate FFGs are presented in the following section. It is important to note that the Vaal River site VR 2 index scores are based on only two biotopes that were sampled, in comparison to the three biotopes sampled at the other study sites.
4.3.1. Habitat The IHAS index scores, indicating the quality and availability of the instream habitat for sites on the Harts- and Vaal Rivers at both seasons, are shown in Table 4.4. The overall habitat integrity at the sites didn’t change temporally. The majority of the sites showed, however, an increase in habitat integrity from low- to high flow.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 69 Macroinvertebrates
According to the integrity classes given in Table 4.4 the reference site HR 1, agricultural sites HR 3, HR 4 and the Vaal River reference site VR 1, were moderately impacted during the low flow period. The agricultural sites HR 2 and HR 5, as well as the downstream Vaal River site VR 2 were in a largely modified to seriously modified state.
The agricultural site HR 2 showed a slight improvement (moderately modified) in its integrity class during the high flow period (Table 4.4). The agricultural site HR 5 remained in a seriously modified class, whereas VR 2 showed an improvement from a seriously modified class to a largely modified class.
Table 4.4: The IHAS index scores, indicating integrity scores and classes for habitat components and overall habitat during low- (L) and high (H) flow periods. IHAS HR 1L HR 2L HR 3L HR 4L HR 5L VR 1L VR 2L Stones-in-current score (20) 16 13 20 18 13 20 0 Vegetation (15) 8 5 14 9 3 5 8 Other habitats (20) 14 10 14 10 12 13 14 Stream Condition (45) 29 31 29 33 23 35 15 Total IHAS (100) 67 59 77 70 51 73 37 Category C D C C D C E IHAS HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H Stones-in-current score (20) 13 11 17 16 11 20 0 Vegetation (15) 8 5 12 9 7 5 12 Other habitats (20) 12 13 16 13 14 12 9 Stream Condition (45) 29 31 29 33 23 35 20 Total IHAS (100) 62 60 74 71 55 72 41 Category C C C C D C D
The Relative Reference Sites The relative reference site HR 1 consisted of lengthy cobble beds situated in slow (runs and pools) and fast flowing water (riffles). Gravel, sand and mud biotopes were sampled, with mud being the dominant of the three. Sand was mostly found under the cobbles. Marginal vegetation was in a poor state and aquatic vegetation wasn’t present. There was some presence of algae, mostly occurring on rocks. Land use impacts were mostly urban, with rural/urban settlements situated adjacent to the river.
The relative reference site VR 1 also consisted of lengthy cobble beds situated in slow (pool) and fast flowing water (riffles and rapids). This stone habitat was present as a result of construction practices (also presence of sand road/weir) along side this river stretch and therefore not natural. The presence of the weir impeded the natural flow of this lowland river, as well as its depth where this stone habitat was created. Marginal and aquatic
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 70 Macroinvertebrates
vegetation were present. Sand, gravel and mud were available for sampling. Riparian vegetation was impacted upon by construction practices and some clearing of this vegetation was noted.
The Agricultural Sites The Vaal River site VR 2 had poor IHAS scores during both seasons (Table 4.4). This was, however, due to the absence of stone habitats at this lowland site. The agricultural site HR 2 consisted of less stones-in-current habitats and mostly consisted of muddy substrate. Poor marginal vegetation was also noted at this site and aquatic plants were non existent. The Harts River site HR 5 also showed less stones-in-current habitats, as well as poor marginal vegetation (Table 4.4). Aquatic grass was evident in the run areas in this stretch of the river. Overall stream condition also showed to be more impacted upon compared to HR 1.
The agricultural sites HR 3 and HR 4 showed better habitat quality compared to the reference site HR 1 (Table 4.4). This was mostly due to better vegetation availability at HR 3 and stones-in-current habitats. The Harts River site HR 3 showed more different stones-in- current habitats, and therefore more time was spent sampling these habitats compared to HR 1. The average stone sizes were also larger compared to HR 1. This site (HR 3) also consisted of good marginal, as well as aquatic vegetation in both riffle, run and pool areas. The Harts River site HR 4 also had larger stone sizes, with most consisting of bedrock. More time was also spent sampling this biotope compared to HR 1.
4.3.2. Macroinvertebrate Indices The SASS5 scores, number of taxa, ASPT and ECs for sites on the Harts- and Vaal Rivers at both seasons, are indicated in Table 4.5. According to the results shown in Table 4.5, the SASS5 scores almost follow the same trend as the taxonomic richness results (Figure 4.1a), with the high flow period showing higher SASS5 scores (except for HR 5) compared to the low flow period. During the low flow period, no trends were noted between the SASS5 scores obtained and land use. During the high flow period some trend between the SASS5 scores obtained and land use was present, with the agricultural sites (except HR 3) showing decreased SASS5 scores compared to the reference site HR 1.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 71 Macroinvertebrates
Table 4.5: The SASS5 scores, number of taxa, ASPT and EC during low- (L) and high (H) flow periods. SASS5 HR 1L HR 2L HR 3L HR 4L HR 5L VR 1L VR 2L SASS5 Score 51 59 64 35 96 76 30 No. of Taxa 9 13 15 9 21 13 8 ASPT 5.67 4.54 4.27 3.89 4.57 5.85 3.75 Ecological Category (EC) A D D/C E/F B A E/F SASS5 HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H SASS5 Score 95 69 102 76 72 127 35 No. of Taxa 20 16 22 13 17 21 8 ASPT 4.75 4.31 4.64 5.85 4.24 6.05 4.38 Ecological Category (EC) B C/B A A B A D
During the low flow season, a trend between ASPT and land use was noted, with decreasing ASPT scores at the agricultural sites (longitudinal gradient). A recovery can be noted at HR 5, which is situated downstream of Spitskop Dam. During high flow, the ASPT scores showed a change in relation to land use, with decreasing ASPT scores at the agricultural sites (except for HR 4) compared to the reference site HR 1. The agricultural site HR 5 showed a decreased ASPT score compared to HR 4, which is situated above Spitskop Dam.
The agricultural sites showed a lower ecological category (which ranged from good to critically modified) compared to the reference site HR 1 during the low flow period and followed the same trend as the ASPT scores. The same is evident for the high flow period where better ecological categories were noted compared to the low flow period. Ecological categories ranged from good to moderately impacted for sites on the Harts River during the high flow period, but these categories didn’t show any relation regarding land use.
4.3.3. Macroinvertebrate Diversity The univariate diversity indices are shown in Figure 4.1a to 4.1e. A total of 40 macroinvertebrate families were identified from the study sites in the present study (Appendix C – Tables C1 and C2). The high flow period had a higher species richness (Figure 4.1a), with only the agricultural site HR 3 having a higher taxonomic richness than the Harts references site HR 1. Macroinvertebrate abundances showed a decrease from the low flow period to the high flow period (Figure 4.1b), with the agricultural site HR 3 having the highest total individuals during low- (approximately 10,000) and high (approximately 7,000) flow seasons. The Vaal River site VR 2 had low total individuals and taxonomic richness during both seasons compared to the other study sites. The reason being that only two biotopes were sampled compared to the three biotopes sampled at the other study sites.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 72 Macroinvertebrates
Margalef’s species richness (Figure 4.1c) was very similar to total species (Figure 4.1a) with regards to a higher species richness occurring during the high flow period compared to the low flow period.
30 12000
25 10000
20 8000
15 6000
10 4000 Total Total Species (S)
5 Total Individuals (N) 2000
0 0 HR 1 HR 2 HR 3 HR 4 HR 5 VR 1 VR 2 HR 1 HR 2 HR 3 HR 4 HR 5 VR 1 VR 2 Sample sites Sample Sites
(a) (b)
0.9 4 0.8 3.5 0.7 3 0.6 2.5 0.5 2 (d) 0.4 1.5 0.3 1 0.2
0.5 Pielou's (J') Evenness 0.1
0 0 Margalef's Species Richness Richness Species Margalef's HR 1 HR 2 HR 3 HR 4 HR 5 VR 1 VR 2 HR 1 HR 2 HR 3 HR 4 HR 5 VR 1 VR 2 Sample Sites Sample Sites
(c) (d)
3
2.5 Low Flow
2
1.5 1 High Flow
Index (loge)) (H' 0.5
Shannon-Wiener Diversity 0 HR 1 HR 2 HR 3 HR 4 HR 5 VR 1 VR 2 Sample Sites
(e)
Figure 4.1: Univariate diversity index values for macroinvertebrates during both seasons (a) Total Species (S); (b) Total Individuals (N); (c) Margalef’s Species Richness (d); (d) Pielou’s Evenness (J’); and (e) Shannon-Weiner Diversity Index (H’ (loge)) for sites on the Harts- and Vaal Rivers.
Pielou’s evenness (Figure 4.1d) is a measure of how the macroinvertebrates are spread over the sites. The agricultural sites HR 2 and HR 3 showed less evenness compared to the other study sites during the low flow period, with HR 3 also showing less evenness during the high flow period, which is indicative that certain perturbations exist at these sites.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 73 Macroinvertebrates
The Shannon-Weiner index (Figure 4.1e) is a measure of the species richness and abundances of the macroinvertebrates present at each site. This index showed higher species richness rather than abundances for all sites during the high flow period compared to the low flow period, which indicates a seasonal trend. A marked reduction in species richness and to a lesser degree, abundance at the agricultural sites HR 2 and HR 3 during the low flow period can be depicted in Figure 4.1e. A reduction in species richness was noted at HR 3 during the high flow period compared to the other study sites.
4.3.4. Macroinvertebrate Community Composition
4.3.4.1. Temporal Variation
Redundancy Analysis was used to indicate how the macroinvertebrate community structure changed with relation to changes in water quality and instream habitat due to land use practices within the Vaalharts area (i.e. agriculture) during both seasons. The RDA tri-plot illustrated in Figure 4.2 describes 48.2% of the variation in species data, with the first axis describing 29.8% of the variation in the data and the second axis 18.7%. Species- environmental correlations for the first and second axes were 0.936 and 0.939, respectively, and explained 41.6% and 25.6% of the species-environment variation. The latter thus indicates a strong relationship between the macroinvertebrate community structures and the selected environmental variables. The macroinvertebrate community structures indicated in Figure 4.2 showed a significant linear correlation with the explanatory axes in the RDA diagram (P = 0.004).
A strong seasonal trend can be depicted from the RDA tri-plot in Figure 4.2 regarding the ordination of the sites and their associated community structures. Of the water quality variables tested, nutrients (i.e. ammonium, nitrite and phosphate), dissolved oxygen and pH were the variables that best explained (dis)similarities amongst the study sites regarding their community structure. Since macroinvertebrates are good indicators of both water quality and habitat, the environmental variables IHAS (measure of habitat integrity), as well as ASPT (which is a measure of general water quality) were also added together with the other water quality parameters to get an indication of which environmental factors can best explain the temporal changes found at the study sites.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 74 Macroinvertebrates
Figure 4.2: RDA tri-plot showing the relationship between macroinvertebrate communities and selected environmental variables during both seasons for sites on the Harts- and Vaal Rivers.
Nutrients showed to be the driving factors that contributed to community structures found at the high flow sites on the Harts River. Average Score Per Taxon showed a stronger correlation with the Vaal River reference site VR 1 during both seasons. From this RDA tri- plot (Figure 4.2) it is also evident that the Vaal River sites’ community structures didn’t change that profoundly over the two seasons.
The Harts River reference site HR 1 is not clearly separated from the agriculturally impacted sites, which makes it difficult to conclude that these sites are indeed impacted upon by agriculture. However, some spatial trend is evident from Figure 4.2. According to Figure 4.2 the more sensitive taxa ordinated out towards the sites sampled during the low flow period, more specifically the Vaal River reference site VR 1L. This site (VR 1) consisted of a good IHAS score, as well as the highest ASPT score during both seasons as outlined in sections 4.3.1 and 4.3.2. Hydropsychidae, Pyralidae, Baetidae, Heptageniidae, Leptophlebiidae, Elmidae and Tricorythidae ordinated out towards the Vaal River site VR 1. Higher abundances of the more tolerant molluscs (Lymnaeidae, Corbiculidae, Thiaridae and Physidae), Turbellaria, Hirudinea and Oligochaeta were found at the high flow period sites,
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 75 Macroinvertebrates
which is an indication of deteriorating conditions present during this period compared to the low flow period. It is clear from Figure 4.2 that increased nutrients during the wet season contributed to the temporal variation, especially at HR 1H, HR 2H, HR 3H and HR 4H.
4.3.4.2. Spatial Variation The relationship between the macroinvertebrate community structures and the selected environmental variables for all of the study sites during the two seasons are illustrated in Figures 4.3, 4.4, 4.6 and 4.7. The RDA tri-plot (Figure 4.3) describes 64.4% of the variation in species, as well as species-environment data, with the first axis describing 45.6% of the variation and the second axis 18.8%. A strong relationship between the macroinvertebrate community structures and the selected environmental variables therefore existed. The macroinvertebrate community structures did, however, not show a significant linear correlation with the explanatory variables indicated in Figure 4.3 (P = 1.000).
Figure 4.3: RDA tri-plot showing the relationship between selected environmental variables and macroinvertebrate community structures during the low (L) flow period for sites on the Harts- and Vaal Rivers.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 76 Macroinvertebrates
The Harts River sites (HR 1, HR 2 and HR 4) showed an average similarity of 73.42% in their macroinvertebrate community structure during the low flow period. The taxa that contributed to the similarity between these sites were: Simuliidae, Chironomidae, Hydropsychidae, Baetidae, Oligochaeta, Corbiculidae, Ancylidae, Potamonautidae, Ceratopogonidae, Muscidae and Caenidae. The study sites HR 3, HR 5 and VR 1 showed an average similarity of 68.86% in their community structure. The taxa Simuliidae, Chironomidae, Baetidae, Hydropsychidae, Coenagrionidae, Physidae, Gyrinidae, Ancylidae, Caenidae, Ecnomidae, Corbiculidae, Oligochaeta, Hydroptilidae and Muscidae contributed to the similarity in these sites’ community structure.
The environmental variables indicated in Figure 4.3 all ordinated towards the Harts River sites on the left hand side of the RDA plot. The Vaal River site VR 1 ordinated towards the Harts reference site HR 1 and the agricultural site HR 4. High Total IHAS and ASPT scores were the driving factors for this type of ordination. Nutrients showed a stronger correlation with the agricultural sites, in particular HR 3 and HR 5. Therefore, taxa more tolerant to increased nutrient inputs ordinated towards the agricultural sites on the upper left hand side of the RDA tri-plot (Figure 4.3).
The RDA tri-plot in Figure 4.4 describes 54.9% of the variation in species data (with first and second axes explaining 38.8% and 16.1%, respectively) and 76.3% of the species- environment variation (with first and second axes describing 53.8% and 22.5%, respectively). This variation was, however, not significant (P = 0.3340). The macroinvertebrates showed a significant response to the environmental variable stones-in- current (P = 0.0420).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 77 Macroinvertebrates
Figure 4.4: RDA tri-plot of the IHAS scores in relation to macroinvertebrate community structures for sites on the Harts- and Vaal Rivers during the low (L) flow period. SIC= stones-in-current; SC= stream condition; Veg= vegetation; OH= other habitat.
100 HR 1L HR 2L HR 3L HR 4L 80 HR 5L VR 1L
VR 2L
%
e
c n
a 60
n
i
m
o
D
e
v
i
t a
l 40
u
m
u C
20
0 1 10 100 Species rank Figure 4.5: Ranked species K-dominance plot for macroinvertebrate communities at low (L) flow for sites on the Harts- and Vaal Rivers, using abundances to indicate cumulative dominance.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 78 Macroinvertebrates
The RDA tri-plot (Figure 4.6) describes 69.5% of the variation in species, as well as species- environment data, with the first axis describing 42.1% and the second axis 27.4% of the variation amongst the study sites. The macroinvertebrate community structures did not show a significant linear correlation with the explanatory variables in Figure 4.6 (P = 1.000).
Figure 4.6: RDA tri-plot showing the relationship between selected environmental variables and macroinvertebrate community structures during the high (H) flow season for sites on the Harts- and Vaal Rivers.
The Harts River sites (HR 1, HR 2 and HR 3) showed an average similarity of 71.74% in their macroinvertebrate community structure during the high flow season. The taxa that contributed the most to this similarity were: Chironomidae, Oligochaeta, Ancylidae, Ceratopogonidae, Simuliidae, Caenidae, Baetidae and Hydroptilidae. The study sites HR 4, HR 5 and VR 1 showed a similar community structure (64.61%). The taxa that contributed the most to their community structure were: Hydropsychidae, Simuliidae, Chironomidae, Baetidae, Hydroptilidae, Corbiculidae, Atyidae and Coenagrionidae.
Figure 4.6 shows a spatial trend, with the Harts River sites separated from the Vaal River sites on the left hand side of the RDA plot. The RDA tri-plot (Figure 4.6) shows that the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 79 Macroinvertebrates
environmental variable Total IHAS was strongly correlated with the relative references sites (HR 1 and VR 1), as well as the agriculturally impacted sites HR 3 and HR 4. The ASPT variable showed a strong correlation with VR 1. Nutrients ordinated towards the lower left hand side of the RDA tri-plot (agricultural sites) and turbidity, pH and dissolved oxygen towards the Vaal River sites.
Figure 4.7: RDA tri-plot of the IHAS scores in relation to macroinvertebrate community structures for sites on the Harts- and Vaal Rivers during the high (H) flow period. SIC= stones-in-current; SC= stream condition; Veg= vegetation; OH= other habitat.
The RDA tri-plot in Figure 4.7 explains 60.6% of the variation in species data (first and second axes explaining 33.9% and 26.7%, respectively) and 83.7% in the species- environment variation (first and second axes describing 46.9% and 36.8%, respectively). The macroinvertebrates showed a strong correlation with the environmental variables, with the first and second axes explaining 0.934 and 0.986 of the species-environment correlations, respectively. These correlations were, however, not significant (P = 0.3100).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 80 Macroinvertebrates
100 HR 1H HR 2H HR 3H HR 4H 80 HR 5H
% VR 1H
e c
n VR 2H
a n
i 60
m
o
D
e
v
i t
a 40
l
u
m
u C 20
0 1 10 100 Species rank Figure 4.8: Ranked species K-dominance plot for macroinvertebrate communities at high (H) flow for sites on the Harts- and Vaal Rivers, using abundances to indicate cumulative dominance.
The K-dominance plots (Figures 4.5 and 4.8) for macroinvertebrates at low- and high flow periods showed that the Vaal River site VR 2 had a dominance of a particular taxon (i.e. Atyidae) during both seasons.
The Relative Reference Sites The relative reference site HR 1 was dominated by the following macroinvertebrate orders: Ephemeroptera (i.e. Baetidae and Caenidae), Trichoptera (i.e. Hydropsychidae) (Figures 4.3 and 4.6), Diptera (i.e. Chironomidae and Simuliidae) and Mollusca (i.e. Corbiculidae). This reference site had the highest abundances of Baetidae (also VR 1L, VR1H and HR 4H), Caenidae and Hydropsychidae compared to the other study sites (Appendix C – Tables C1 and C2).
The Vaal River reference site VR 1 was dominated by Ephemeroptera (i.e. Baetidae) and Trichoptera (i.e. Hydropsychidae). Dipteran taxa known to be more tolerant to perturbations were also dominant at this relative reference site such as Chironomidae and Simuliidae. This reference site (VR 1) was the only study site that was inhabited by the sensitive taxa Heptageniidae, Leptophlebiidae and Tricorythidae, therefore showing a unique community structure compared to the rest of the study sites. Pyralidae, which is a taxon considered to be very sensitive, also occurred in higher abundance at this site (Figure 4.3). Compared to the Harts reference site, VR 1 had lower abundances of the tolerant taxa Chironomidae, Simuliidae and Corbiculidae. Therefore, VR 1 appears to be in a better ecological condition
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 81 Macroinvertebrates
than HR 1. Elmidae were also found to be a taxon that occurred in high abundance at VR 1 compared to the other study sites (Figures 4.3 and 4.6).
According to Figures 4.4 and 4.7, stream condition and stones-in-current scores were strongly correlated with the relative reference sites during both seasons. During both seasons, these relative reference sites were associated with macroinvertebrate families such as Baetidae, Hydropsychidae and Caenidae, which seemed to be good indicators of stream condition. The macroinvertebrate families Heptageniidae, Leptophlebiidae, Tricorythidae, Pyralidae, Elmidae, Baetidae, Caenidae and Hydroptilidae are relatively sensitive taxa and therefore good indicators of stream condition. Heptageniidae, Leptophlebiidae, Tricorythidae, Hydropsychidae, Elmidae and Simuliidae are taxa that prefer cobble habitat and were therefore correlated with the stones-in-current biotope.
The Agricultural Sites A pollution gradient was evident in Figures 4.3 and 4.6 from HR 1 to HR 5 and from VR 1 to VR 2. The agricultural sites (HR 2 to HR 5) were mostly dominated by Ephemeroptera (i.e. Baetidae), Trichoptera (i.e. Hydropsychidae) and Diptera (i.e. Chironomidae and Simuliidae). The dipteran taxa Chironomidae and Simuliidae showed marked increases at the agricultural site HR 3 compared to the other study sites. Annelida (i.e. Oligochaeta and Hirudinea) dominated at the agricultural sites compared to the relative reference sites (especially at HR 3 and HR 5). Mollusca showed higher abundances at the agricultural sites with taxa such as Physidae (especially at HR 3 and HR 5), Ancylidae (HR 3 and HR 5), Corbiculidae (HR 4) and Planorbidae (HR 5) (Figures 4.3 and 4.6). Increased abundances of Coenagrionidae, Ceratopogonidae and Atyidae occurred at the agricultural sites during the high flow period compared to the low flow period (Appendix C – Tables C1 and C2).
During the low flow period, vegetation was more correlated with the agricultural sites HR 3 and HR 4 (Figure 4.4). Taxa such as Coenagrionidae, Belostomatidae, Helodidae, Planorbidae and Physidae, which were associated with these agricultural sites, prefer to inhabit vegetation and therefore dominated at these sites that consisted of lush aquatic and marginal vegetation (especially HR 3). Habitats other than stones and vegetation such as the gravel, sand and mud biotope (GSM) were more correlated with the agricultural sites HR 2 and VR 2. The macroinvertebrate family Tipulidae, which prefer GSM habitats were associated with HR 2. Atyidae, Hydrophilidae and Dytiscidae showed a correlation with VR 2, which consisted of lush aquatic and marginal vegetation.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 82 Macroinvertebrates
Figure 4.7 shows that other habitat (which includes sand, mud, and gravel biotope; stones- out-of-current; bedrock) and stones-in-current were the most significant habitat integrity variables. The mollusc families Ancylidae, Thiaridae and Planorbidae showed a strong, positive correlation towards the other habitat variable, whereas Simuliidae, Hydroptilidae, Hydropsychidae and Ecnomidae showed a strong correlation towards the stones-in-current biotope. During the high flow season, other habitat (especially HR 3) and vegetation (especially HR 3 and VR 2) were more correlated with the agricultural sites HR 2, HR 3, HR 5 and VR 2 (Figure 4.7). The macroinvertebrate families Atyidae, Coenagrionidae, Belostomatidae, Lymnaeidae and Physidae were more strongly correlated with the vegetation biotope, which is their preferred habitat. A greater dominance of Culicidae, Muscidae, Corixidae and Veliidae were noted at these sites, which are taxa that inhabit the actual surface water of the river. Ceratopogonidae, Turbellaria, Hirudinea and Ancylidae were also present, which are taxa that mostly inhabit stones.
4.3.5. Functional Feeding Groups 4.3.5.1. Temporal Variation The RDA tri-plot as shown in Figure 4.9 indicates the relationship between the macroinvertebrate FFGs and the selected environmental variables during both seasons. The RDA tri-plot describes 59.4% of the variation in species data, with 45.1% described by axis one and 14.3% described by axis two. Species-environment correlations were 0.937 and 0.905 for axis one and two, respectively, and explained 58.6% and 18.6% of the species-environment variation amongst the study sites. The macroinvertebrate FFGs showed a significant relationship with the explanatory variables (Figure 4.9, P = 0.006).
From Figure 4.9 it is evident that there was no clear seasonal trend regarding the macroinvertebrate FFGs for all of the study sites, except HR 4. Predator-piercers, detritivores, shredder-omnivores and shredder-detritivores seemed to dominate the study sites located on the upper half of the RDA tri-plot (HR 3H, HR 3L, HR 2L, HR 2H, HR 4L, VR 2L, VR 2H) (Figure 4.9). Predators, piercer-herbivores, scavengers, shredders, shredder- herbivores, collector-gatherers and collector-filterers seemed to dominate the study sites located on the lower half of the RDA tri-plot (HR 1H, HR 1L, VR 1H, VR 1L, HR 5H, HR 5L, HR 4H) (Figure 4.9). Nutrients showed a strong correlation towards the agricultural site HR 3 for both seasons. The ASPT showed a stronger correlation towards the Vaal River reference site VR 1 (Figure 4.9).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 83 Macroinvertebrates
Figure 4.9: RDA tri-plot showing the relationship between selected environmental variables and macroinvertebrate FFGs during both seasons for sites on the Harts- and Vaal Rivers.
4.3.5.2. Spatial Variation Redundancy Analysis was used to illustrate how the macroinvertebrate FFGs changed in relation to the selected environmental variables for both seasons (Figures 4.10 and 4.11). The RDA tri-plot (Figure 4.10) describes 78.3% of the species, as well as species- environment data variation, with 59.1% and 19.2% of the variation explained by axis one and two, respectively. Figure 4.11 describes 83.4% of the species, as well as species- environment data, with the first axis explaining 59.6% of the variation and the second axis 23.8%. A strong relationship between the macroinvertebrate FFGs and the selected environmental variables therefore, exists. This relationship was, however, not significant (P = 1.000).
The study sites (HR 1 to HR 5; VR 1) showed an average similarity of 83.95% regarding their FFGs during the low flow period. Collector-filterers, predators, collector-gatherers, scavengers, predator-piercers and detritivores contributed the most to their FFG structure.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 84 Macroinvertebrates
Figure 4.10: RDA tri-plot showing relationship between selected environmental variables and macroinvertebrate FFGs for sites on the Harts- and Vaal Rivers during the low (L) flow season.
From Figure 4.10 a spatial trend can be depicted. The ASPT ordinated towards VR 1 and nutrients showed a strong correlation with the agricultural site HR 3. The reference site HR 1 showed the highest abundances of predators, collector-gatherers, collector-filterers and shredder-omnivores compared to the other study sites during the low flow period. Detritivores occurred in the highest abundances at the agricultural sites HR 3 and HR 5. Shredder-herbivores, shredders and surface-film scavengers showed a strong correlation with VR 1 and shredder-detritivores with the agricultural site HR 2 (Figure 4.10).
The study sites (HR 1 to HR 5; VR 1) showed an average similarity of 83.14% regarding their macroinvertebrate FFGs during the high flow period. Collector-filterers, predators, collector-gatherers, scavengers, predator-piercers, piercer-herbivores and detritivores contributed to this similarity between the above mentioned sites.
Figure 4.11 shows a spatial trend between the study sites. The environmental variables turbidity, pH and dissolved oxygen showed a strong correlation with the Vaal River sites. The nutrients tended to ordinate towards the Harts River sites HR 1 and HR 3. The ASPT showed a strong correlation with VR 1, indicating better water quality at this relative reference site. The Total IHAS scores showed a strong correlation with the Harts River sites
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 85 Macroinvertebrates
HR 1, HR 3 and HR 4, as well as VR 1. These environmental variables contributed to the respective FFGs found at each site.
Figure 4.11: RDA tri-plot showing the relationship between selected environmental variables and macroinvertebrate FFGs during the high (H) flow season for sites on the Harts- and Vaal Rivers.
The agricultural site HR 3 had the highest abundances of predators (also HR 1), detritivores (also HR 2), collector-filterers, scavengers, predator-piercers, piercer-herbivores (also HR 1) and surface-film scavengers during the high flow period. The reference site HR 1 had the highest abundances of collector-gatherers and shredder-omnivores (also HR 2). Shredders showed a stronger correlation with the agricultural site HR 4 and shredder-herbivores with VR 1 (Figure 4.11).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 86 Macroinvertebrates
4.4. Discussion 4.4.1. Macroinvertebrate Community Structure in Relation to Land Use In this section of the chapter, the response of the macroinvertebrate communities to habitat and water quality will be discussed. The community structures found at the relative reference sites will be compared to the communities found at the agriculturally impacted sites during both seasons, in order to elucidate whether spatial and temporal trends do exist and; if community structures did show changes in their composition, can these changes be attributed to agricultural pollution?
Invertebrate Habitat Assessment System (IHAS) The relative reference sites were mostly associated with stream condition and stones-in- current habitats (Figures 4.4 and 4.7). The Vaal River reference site VR 1 showed a unique assemblage in having the only abundances of the following sensitive taxa: Tricorythidae, Leptophlebiidae and Heptageniidae (Gerber and Gabriel, 2002). These taxa have preferences for stones (cobble) habitat and moderate to high water quality (Thirion, 2007). These taxa are also more specifically associated with riffle habitat, which was the dominant stone habitat at VR 1. Heptageniidae and Leptophlebiidae were also found to be indicators of good stones habitat at the relative reference site on the Magalies River in the study by Walsh (2008). According to Roy et al. (2003) invertebrates that show a preference for riffle habitat, are more sensitive to changes resulting from land cover change and are therefore important indicators of such changes. These taxa, however, are not good indicators of such changes at VR 1, because their presence at VR 1 is mainly due to a modified Vaal River site, in which these riffle habitats were created by construction. The absence of these taxa at the Harts River reference site HR 1 (which showed the presence of Leptophlebiidae in the RHP data for the year 2003; Appendix C – Table C10) and the agricultural sites may indicate that these sites are impacted upon by land cover changes.
Walsh (2008) found that agricultural sites were mostly affected by modified stream conditions and general habitat metrics (e.g. GSM, stones-out-of-current and algal presence) in the assessment of the macroinvertebrate community structures of the Crocodile- and Magalies Rivers. It was found that the agricultural sites had higher amounts of finer sediments, which contributed to their sediment makeup and that these sites also suffered from stream disturbance and the clearance of riparian zones. The agricultural sites HR 2 and HR 5 were associated with poor riparian zones. Walsh (2008) also noted that one of the agricultural sites showed lowered flows in addition to sedimentation, due to the placement of
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 87 Macroinvertebrates
an illegal farm weir upstream of the agricultural site. All of the agricultural sites were impacted upon by reduced flows due to the presence of weirs (sandy roads, cement weirs, canalisation) in the present study. The agricultural site HR 5 was also impacted upon by the presence of Spitskop Dam, and it is thought that the presence of this dam may also have caused irregular flows and sediment loads to HR 5. These alterations therefore, changed the flow and riffle availability and resulted in increased silty substrates at HR 5. According to Poff (1997) this kind of habitat would be limited to biota that are silt tolerant and not migratory.
According to Amis et al. (2007) natural vegetation is the most important predictor of both riparian and instream integrity. This is because natural vegetation may regulate stream processes like erosion and sediment transport (Osborne and Kovacic, 1993) and thus channel morphology (Naiman et al., 1993). Agricultural development can substantially increase the loading of fine sediments to river courses due to increased erosion, which is exacerbated by overgrazing (Harrison 1995; Pandit, 1999 cited in Malmqvist and Rundle, 2002). Cattle and other domestic animals were present at most of the agricultural sites in this study, which contributed to increased sedimentation and the destruction of marginal vegetation at these sites. Deposition of sediment may change the character of the substrate (Luedtke and Brusven, 1976 cited in Ryan, 1991), block interstices and reduce interstitial volume (Ryder, 1989 cited in Ryan, 1991), which may cause macroinvertebrate drift.
The South African Scoring System (SASS5) It was initially assumed that the ecological categories calculated for the different sites (Table 4.5), as well as the ASPT scores, which is an indicator of general water quality, would fall into groups based on the type of adjacent land use (relative reference sites and agricultural related). This type of trend was only noted during the low flow period, where the agricultural sites on the Harts River did show that deteriorating conditions existed compared to the relative reference site HR 1. A recovery was noted after HR 4, where the agricultural site HR 5 showed to be in a good ecological state. This is thought to be the result of slightly better water quality (higher ASPT score) compared to the other agricultural sites, since habitat has shown to be impaired at this site compared to the agricultural sites HR 3 and HR 4. It is then also thought that during low flow, Spitskop Dam serve as a sink for nutrients and other agricultural inputs, which is the cause for the better water quality found at HR 5 compared to the other agricultural sites. A decrease in the SASS5 score and ASPT occurred at HR 5 during the high flow season, which would then be related to increased nutrient and sediment inputs from rainfall (runoff), as well as inputs from Spitskop Dam.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 88 Macroinvertebrates
There seems to be a trend regarding the SASS5 scores, number of taxa and ASPT scores calculated for the Harts reference site HR 1 and agricultural site HR 3, when data from the RHP (DWAF, 2007) are compared at these sites (Appendix C). According to the RHP data (DWAF, 2007) the SASS5 scores, number of taxa and ASPT showed reduced scores in January and February. In April there seems to be an increase in these scores, which indicate a recovery in the macroinvertebrate communities found at these sites. In July, HR 1 and HR 3 show another decrease in these scores, indicating a decrease in water quality and therefore a decrease in sensitive species. This trend is also evident in this study. The SASS5 scores, number of taxa and ASPT were lower during the dry season (July) and higher during the wet season (January) in the RHP data (DWAF, 2007). The latter is also evident in this study for the sites HR 1 and HR 3, as well as the other study sites.
A change from RHP historical data (DWAF, 2007) is therefore present, with the loss of expected sensitive macroinvertebrate taxa at HR 3. Chlorolestidae, Lestidae and Pisuliidae were absent at HR 3 during July and January in the RHP data (DWAF, 2007), as well as in this study (Appendix C – Tables C12 and C13). These taxa are present in April according to the RHP data (Appendix C – Table C14). These families are indicators of good water quality (Gerber and Gabriel, 2002) and their absence from HR 3 during July and January indicates a decline in water quality. The SASS5 index did not show definite cause-effect relationships between macroinvertebrate communities and their ambient environment. In the study by Walsh (2008) it was found that habitat-based factors, in particular flow, explained the variation of macroinvertebrate taxa from natural conditions. Substrate instability caused by changes in flow resulted in a decrease in viable habitat for macroinvertebrate taxa. Pesticides and high turbidity levels contributed to the decline in water quality at a downstream site in the study by Thiere and Schulz (2004), which were impacted upon by agricultural activities in the surrounding orchard areas.
Macroinvertebrate Diversity In a review conducted by Vinson and Hawkins (1998) it was shown that different types of substrates supported different numbers of taxa. Physically complex substrate types such as leaves, gravel, cobble, macrophytes, moss and wood, generally supported more taxa than structurally simple substrates such as sand and bedrock (Vinson and Hawkins, 1998). This can also be seen in the present study where the relative reference sites HR 1 and VR 1, together with the agricultural site HR 3 were more taxa rich (had wider variety of substrates) than the agricultural site HR 4 and HR 2, which were mostly embedded with sand and bedrock (Figure 4.1a).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 89 Macroinvertebrates
According to Lenat (1984) taxa richness is an excellent measure of water quality. As the level of pollution increases, the more intolerant species will be eliminated, and therefore, lower taxa richness relative to the control is indicative of reduced water quality. The agricultural sites showed decreased water quality (lower ASPT scores) compared to the relative reference sites, but taxa richness was still maintained at the agricultural sites compared to the relative reference sites (Figure 4.1a). Addition of low levels of sediment into a stream may create a new type of habitat, and the probability of collected sand- associated species will increase (Lenat, 1984). If agricultural runoff did not adversely affect the normal stream fauna, this could account for the increase in taxa richness (Lenat, 1984) at the agricultural sites HR 2, HR 4 and HR 5.
Average number of organisms per sample (average density) can be either increased or decreased by agricultural runoff. Inputs of organic particulates and nutrients will tend to increase average density (as can be seen for the agricultural site HR 3; Figure 4.1b), while toxics and sediment addition generally cause a reduction (Lenat, 1984). Macroinvertebrate abundances were higher during the low flow period compared to the high flow period (Figure 4.1b). Rainfall may have produced this decline in abundances during the high flow season due to macroinvertebrate flush out, but most species can still be represented by few individuals which resisted disturbance. This is an indication that these species are well adapted to this kind of hydraulic stresses and according to Jacobsen and Encalada (1998 cited in Buss et al., 2004) this reduction in invertebrate density is a stochastic process. Insects utilize mechanisms to resist floods, which include refuge-seeking behaviour (Davies and Day, 1998) and high colonization rates. The decreased abundances of invertebrate taxa during the wet season may also be as a result of the emergence of large numbers of adult aquatic insects (Flint, 1991; Oliveira, 1996 cited in Buss et al., 2004), using this strategy for dispersal of eggs with the stream discharge. Sub-lethal doses of applied agricultural pesticides may reduce nymph density by reduced survivorship, as well as by increased emergence because of stress (Alexander et al., 2008). The decrease in the density of the macroinvertebrate taxa may also be as a result of reduced reproductive success caused by pesticide runoff (Alexander et al., 2008) during the wet season.
Macroinvertebrate Community Composition The agricultural sites HR 3 and HR 5 were impacted upon by nutrients and increased pH levels (Figure 4.3). The agricultural site HR 3 (both seasons) showed an overwhelming abundance in Simuliidae compared to the other study sites. Simuliidae also showed a correlation towards nitrate (Figure 4.3). The diatom community assemblages (sections
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 90 Macroinvertebrates
3.3.2.2 and 3.3.3) indicated that this site was impacted upon by organic pollution. Simuliidae (blackfly larvae) are characteristic of particulate organic matter inputs (Lenat, 1984). The highest abundance of Oligochaeta was also found at HR 3 (both seasons) and HR 5 (low flow), respectively. Oligochaeta has been identified as a tolerant taxon and has been associated with hypoxic conditions, organic pollution and nutrient enrichment in other studies (Lenat and Crawford, 1994; Kucuk, 2008). A study by Cosser (1988 cited in Kucuk, 2008) found high tolerance of the gastropods Planorbidae and Physidae, as well as Chironomidae, in response to organic pollution. Physidae was also found in high abundance (Appendix C – Tables C1 and C2) compared to the other study sites at HR 3 (both seasons) and HR 5 (low flow). Thus, according to these biological indicators, it can be assumed that HR 3 is impacted upon by organic pollution, and as mentioned in Chapter 3, sewage spills and faecal matter from cattle, seem to be the sources for this type of pollution. Tolerant taxa such as Chironomidae and Simuliidae dipterans have also been shown to increase in richness and abundance in streams receiving agricultural pesticides (e.g. Heckman, 1981; Thiere and Schulz, 2004). Thus, although pesticides weren’t measured in this study, pesticides may have also contributed to this type of community structure at the agricultural sites.
A marked decrease in the abundance of Hydropsychidae (Appendix C – Tables C1 and C2) occurred at the agriculturally impacted sites (HR 2 to HR 5) during both seasons, which may be the result of changes in the hydrological regime, leading to a decrease in the current velocity, lower oxygen concentrations and sedimentation (fine silt clogs up the fine meshes of the nets constructed by the larvae) of fine mud particles. A decline in the oxygen concentration occurs particularly concomitant with pollution, forming indirectly a side cause. The dissolved oxygen levels measured at HR 2 and especially at HR 3 (5.2mg/l) were lower compared to the reference site HR 1 during the low flow period (Table 3.3). Pollution with toxic substances and canalisation lead directly to the disappearance of Hydropsyche species in the study of Higler and Tolkamp (1983). Dickens et al. (2008) found that Hydropsychidae (in particular Cheumatopsyche afra) and Simuliidae dominated at a site immediately downstream of the Albert Falls Dam. These taxa were noted to increase on the uMngeni in response to the regulated flow regime below Albert Falls Dam. The reference site HR 1 is situated below Taung Dam, therefore it is thought that because this site showed high abundances of Hydropsychidae (showed the highest abundance) and Simuliidae, especially during the low flow period (Appendix C – Table C1), that this site is impacted upon by regulated flow from Taung Dam. The Caenidae also showed the highest abundances at the relative reference site HR 1. This taxon was also associated with the Albert Falls sites in the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 91 Macroinvertebrates
study of Dickens et al. (2008). Skoroszewski and De Moor (1999) found this mayfly to become more abundant after the completion of Katse Dam and were thought to reflect a more stable substrate that is not influenced so frequently by flash floods. Thus, this taxon is therefore also an indicator of regulated discharge in this study.
A change in macroinvertebrate composition was observed by Buss et al. (2004), with the replacement of Ephemeroptera, Plecoptera, Trichoptera (EPT) species, often reported as sensitive species, by molluscs and Odonata species, which are more tolerant to environmental impacts. The sensitivity of EPT taxa to siltation is often reported (Rosenberg and Resh, 1993), particularly because of the accumulation of fine sand and inorganic silt on gills (Lemly, 1982). The dominance of Simuliidae and other filter-feeders at most of the agricultural sites corroborates the idea of high downstream transportation of fine particulate organic matter (FPOM). The elimination of sensitive EPT taxa in the present study suggests high inorganic matter transportation and is indicative of the high siltation observed at the agricultural sites (Buss et al., 2004).
Turbidity, dissolved oxygen and pH were more strongly correlated with the Vaal River sites (Figures 4.3 and 4.6). The relative reference site VR 1 had a high abundance of the family Elmidae, which was mostly absent at the agricultural sites (Appendix C – Table C2). According to Castillo et al. (2006) species of Elmidae, Caenidae and Hydropsychidae were more prevalent in reference sites than in the banana farm waters. The authors suggest that these taxa could prove to be more sensitive to chemical stress and might be good candidates for toxicity testing. However, Lenat (1984) found Elmidae to be abundant in agricultural streams in piedmont and mountain streams in his study. It was found that this taxon was the only group whose abundance was unaffected by agricultural runoff. In contrast to the findings of this study, with regard to the decrease in abundance of Hydropsychidae at agricultural sites, Lenat (1984) and Kyriakeas and Watzin (2006) found the relative percentage compositions of Hydropsychidae to be greater at agriculturally impacted sites compared to the reference site. Although Hydropsychidae occurred in lower abundances in the present study, their presence may also be indicative of organic pollution at the agricultural sites, since caddisflies prefer streams with high concentrations of suspended organic matter (DeShon, 1995 cited in Kyriakeas and Watzin, 2006). Thus, it is then also thought that the relative reference site HR 1 may also be impacted upon by increased nutrients (most likely from faecal matter of domestic animals, as well as pulse loadings from Taung Dam). The macroinvertebrate taxon Atyidae was associated with VR 2 (Figures 4.5 and 4.8), as well as the agricultural sites HR 2, HR 4 and HR 5 (Figure 4.6)
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 92 Macroinvertebrates
during the high flow season. Coenagrionidae showed a marked increase at the agricultural sites HR 2, HR 3, HR 4 and HR 5 (Appendix C – Table C2) compared to the reference site HR 1 (high flow). Atyidae were shown to be very tolerant organisms under acute laboratory exposure to salinity in the study of Horrigan et al. (2007). Kefford et al. (2003b cited in Horrigan et al., 2007) also found that decapods were more tolerant than most insects and all non-arthropods tested, yet decapods were not found in streams having conductivity levels exceeding 12mS/cm. Horrigan et al. (2007) suggested that a possible reason why decapods might have a more limited salinity range than what the laboratory experiments suggested, is that decapods may have life-stages that are more salinity sensitive than the adult stage and that these more sensitive stages may limit their distributions. Kefford et al. (2004) found that the acute lethal salinity tolerance in hatchlings and adults in three species of decapods increased as the young aged. Decapods may therefore be able to survive at high salinity, but may be indirectly affected via ecological interactions such as the salinity impacts on their prey, habitat, competitors and predators (Horrigan et al., 2007). Horrigan et al. (2007) also observed salt tolerances of some molluscs. Molluscs are soft-bodied and therefore may have limited defence against increasing osmotic pressure (Hart et al., 1991; Kefford et al., 2003b cited in Horrigan et al., 2007). Horrigan et al. (2007) found that several gastropod families were moderately salinity tolerant, with Hydrobiidae and Thiaridae (present in low abundance at the agricultural sites HR 2, HR 3 and HR 5) withstanding conductivity levels as high as 30.6mS/cm. In addition to being tolerant of a variety of other water quality factors often associated with elevated conductivity (e.g. nutrients), molluscs can actually increase in abundance as conductivity increases, until levels exceed their physiological tolerance. The authors considered Hydrophilidae (present in low abundance at the agricultural site VR 2) as very tolerant, the molluscs Physidae and Planorbidae as generally tolerant (because gastropods can benefit from slightly elevated salinity – need a certain amount of dissolved salts to build their shells) (Berezina, 2003; Kefford and Nugegoda, 2005). However, in cases with relatively high conductivities (approaching or exceeding LC50), gastropods should be considered as sensitive (Horrigan et al., 2007). Dunlop et al. (2008) found Ephemeroptera (10.9mS/cm) and Gastropoda (19.2mS/cm) to be amongst the most sensitive taxa tested, and Coleoptera (35mS/cm), Decapoda (41.9mS/cm) and Isopoda (>55mS/cm) to be the most salinity tolerant. Conductivity levels did not exceed the tolerance ranges of these taxa in the present study, but did show an increase at the agricultural sites, which are reflected by the increased abundances of molluscs and Atyidae at the agricultural sites.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 93 Macroinvertebrates
4.4.2. Functional Feeding Groups in Relation to Land Use Agricultural runoff can affect macroinvertebrate food supplies, either by the addition of particulate organic matter (POM), or by the addition of nutrients which promote algal growth. This type of perturbation can be examined by studying the feeding types of organisms found in agriculturally impacted streams. According to Lenat (1984) it is important to remember that the response of any single species can be highly variable, sometimes increasing in one study area, but declining in another. This may also explain the variation in the macroinvertebrate diversity indices (Figure 4.1). This is because runoff from each agricultural area can have unique characteristics, which are dependant on soil type, crop and the application of chemicals (Lenat, 1984).
The slight temporal differences (Figure 4.9) amongst the study sites were mostly attributed to changes in the abundances of the dominant FFGs found at the study sites from low- to high flow, due to increased impacts from land use practices, rather than changes in FFG structure. Spatial differences can also be attributed to the latter.
According to Lenat (1984) the following feeding groups are characteristic of agricultural streams: scrapers, collector-gatherers and filter-feeders. In the study by Compin and Céréghino (2007) it was found that predators and scrapers dominated in agricultural landscapes and to a lesser degree shredders. There was a high proportion of collector- gatherers and a low proportion of shredders in the study by Aguiar et al. (2002). Filterers were abundant at agricultural sites in the study by Bacey and Spurlock (2007). Collector- filterers, predators, collector-gatherers and scrapers were found in high abundances at all of the study sites on the Harts River, including the Vaal River reference site VR 1.
According to Shepard and Minshall (1981) and Lenat (1984) the high proportion of collector- filterers can be related to abundant suspended particulate organic matter present at the study sites during both seasons. The relative reference site HR 1 was associated with the highest abundances of collector-filterers compared to the agricultural sites. As mentioned in the previous section (4.4.1), HR 1 is situated below Taung Dam and therefore exposed to regular discharge (e.g. Dickens et al., 2008). The high proportion of collector-gatherers is also related to the abundant organic matter, which may be supplemented by fine particulate allochtonous inputs of agricultural origin that usually offer considerable nutritional value (Shepard and Minshall, 1981). Herbaceous/algal growth is also known to be an abundant food supply that is readily accessible through either grazing (therefore increase in scrapers) or the detrital pathway (Lenat, 1984; Ferreira and Moreira, 1999). Bacey and Spurlock
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 94 Macroinvertebrates
(2007) also found that fine sediments were the dominant substrates at the agricultural sites, which explained the high numbers of gatherers and filterers. Therefore, sedimentation has also contributed to the increase in gatherers and filterers in this study.
Shredding macroinvertebrates represent an important component of the biological processing of coarse particulate organic matter. Shredders are typically most abundant where there is a strong interaction between the riparian zone and the stream (Vannote et al., 1980). Shredders, although present at most of the sites, occurred in very low abundance in this study, with shredder-herbivores occurring in higher abundances at the Vaal River reference site VR 1 (Figures 4.10 and 4.11). Dance and Hynes (1980) also observed the pattern in which grazers and gatherers were abundant and shredders were rare in an impacted stream. According to these authors many grazers, particularly among the Ephemeroptera and Coleoptera can also utilize detritus. It is therefore likely that during the low flow season and other occasions when algal growth may have been low, grazing macroinvertebrates were feeding on detritus, therefore making use of alternative food sources. A decrease in scraper abundance during the low flow period was found at all sites in this study. Limited litterfall throughout the length of the Harts River has diminished the role and density of shredders.
According to Bacey and Spurlock (2007) scrapers are specialized feeders. Increases in algal growth and nutrients, or a reduction in oxygen levels (HR 1 and HR 3; Figures 4.10 and 4.11) provide suitable habitat for scrapers. These conditions tend to occur when waters are stagnant or have reduced flows. Therefore the study sites may also be impacted upon by these factors in this study. In contrast, filterers, although very tolerant, require constant flowing waters in order to filter fine organic matter (Bacey and Spurlock, 2007). Their abundance was greatest at HR 1, HR 2, HR 3 and HR 4 during the dry season, with the dry season also having greater abundances of filterers compared to the wet season (Appendix C – Tables C15 and C16). Other dominant taxa found in the study by Bacey and Spurlock (2007) were predators, which can increase in response to gatherer numbers if habitat conditions are suitable, which was the case in this study (especially at HR 1 and HR 3; Figures 4.10 and 4.11).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 95 Macroinvertebrates
4.5. Summary and Conclusion The overall habitat integrity didn’t change very much temporally and the study sites’ habitat showed to be impaired by human activities. Therefore no clear trend between differing land uses could be depicted. The SASS5 (high flow) and macroinvertebrate diversity indices also didn’t indicate differing land use practices.
The macroinvertebrate index, as well as the macroinvertebrate community structures indicated that during the low flow period the agricultural sites were impacted upon by deteriorating instream habitat conditions and water quality compared to the relative reference sites. The agricultural sites showed increased sediment loads, changes in flow regime, increased nutrient inputs and salinization, all of which were reflected by the macroinvertebrate taxa residing at these sites. During the high flow period these changes were exacerbated. Indicator taxa included Simuliidae, which showed to be an indicator of both organic pollution and regulated flows; Chironomidae, Oligochaeta and molluscs (e.g. Planorbidae and Physidae) indicated increased nutrient inputs; the reduction of Hydropsychidae at the agricultural sites indicated increased sediment loads and Atyidae showed the presence of higher concentrations of salt at the agricultural sites. The changes in flow and increased sediment changed the instream habitat of the agricultural sites. These changes resulted in increased abundances of taxa tolerant to these changes and therefore the macroinvertebrate diversity indices showed no significant relation to land use, because the diversity were still high, if not higher, at the agricultural sites compared to the relative reference sites. The macroinvertebrate FFGs indicated that the presence of FPOM was the main food resource at all of the study sites with collector-filterers, collector-gatherers, predators and scrapers being the dominant FFGs.
The results of this study therefore suggest that land use caused changes in the macroinvertebrate community structures of the Harts- and Vaal Rivers, but that these changes could not be significantly differentiated between the different sites according to the macroinvertebrate indices, and therefore not be attributed to land use (i.e. agriculture). This study therefore shows that no single group of organisms is always best suited for detecting the diversity of environmental perturbations associated with human activities and that a multi-faceted approach may be a useful tool to the assessment of specific land use effects on the ecological condition of a river system.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 96
Chapter 5: Riparian Vegetation Integrity and Macroinvertebrates
5.1. Introduction 5.1.1. Riparian Vegetation and Macroinvertebrate Integrity Riparian habitats have significant effects on material fluxes between terrestrial and riverine ecosystems (Naiman and Decamps, 1997). Riparian areas are powerful indicators of catchment quality, since they are at the boundary of terrestrial and aquatic systems (Rapport et al., 1998). Human habitation and development have resulted in the degradation of riparian zones and consequently their ecological integrity. Direct degradation includes the clearance of vegetation for agriculture (Bellows, 2003), grazing and trampling by livestock (Jansen and Robertson, 2001), pollution from the surrounding land use (Bellows, 2003) and the invasion of alien species (Nel et al., 2004; Holmes et al., 2005). The construction of dams has greatly altered the hydrological regime of many rivers, which indirectly impacts on the functioning of aquatic and riparian ecosystems (Jansson et al., 2000; Shafroth et al., 2002).
Research in invasion ecology is needed to understand the consequences, including the influence on delivery of ecosystem goods and services, of invasive alien plants on terrestrial and freshwater ecosystems in South Africa. South African research has made a large contribution to invasion ecology (Rejmánek and Richardson, 1996; Van Wilgen et al., 1996; Higgins et al., 2001; Nel et al., 2004; Richardson and Van Wilgen, 2004), for example the Scientific Committee on Problems for Ecosystem Research (SCOPE) programme on biological invasions, the Invasive Plant Ecology Programme, South African Plant Invaders Atlas, and the establishment of the Working for Water programme. The Riparian Vegetation Response Assessment Index (VEGRAI, Kleynhans et al., 2006) is a tool used to assess the riparian vegetation condition of rivers in South Africa. The VEGRAI model was used in the environmental impact assessment of the Dube TradePort development and possible impacts of this proposed development on the existing riparian habitats of the uMdloti and Tongati Rivers (Dickens et al., 2007).
Many catchment studies have made use of geographical information systems and/or multivariate statistics to quantify landscape structure and revealed the longitudinal and lateral influences of the terrestrial ecosystems on water quality and stream biota (Richards et
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 97 Riparian Vegetation Integrity and Macroinvertebrates
al., 1996; Johnson et al., 1997; Johnson and Gage, 1997; Townsend et al., 1997; Amis et al., 2007). Bis et al. (2000) studied the relation between landscape patchiness and land- water ecotone structure and their influence on benthic fauna composition, biomass and functional organization. The authors found that the use of macroinvertebrate community structure, as well as the assessment of water quality, directly revealed human-induced alterations (e.g. land use, lack of riparian vegetation, channelization). Riparian canopy cover, stream hydraulic processes and nutrient inflow were the most important variables affecting the structure and trophic organization of stream communities (Bis et al., 2000). Deforestation and channelization resulted in an increase of incident radiation and enhanced algal productivity and significantly affected the occurrence of scrapers (Gastropoda, Elmidae). Fine particulate organic matter was an important energy and nutrient source in the Grabia River and resulted in a significantly higher density and biomass of gathering collectors such as Oligochaeta and Chironomidae (Bis et al., 2000). Aguiar et al. (2002) found that riparian features had greater influence (which explained 18% of the macroinvertebrate variation) than other environmental characteristics, such as conductivity and distance from source, on the macroinvertebrate community composition in the Sado basin, with the reason being that riparian vegetation is closely related to food types.
5.1.2. Aims The aims of this chapter are as follows: To determine if the riparian zones are impacted upon by agricultural practices. To determine whether the riparian vegetation interacts with agricultural inputs that may cause changes in the macroinvertebrate community structures and FFGs.
5.1.3. Objectives To achieve the aims listed above, the following objectives were set: To determine the riparian vegetation composition and riparian integrity of the seven study sites. To determine whether a relationship exists between riparian vegetation and the integrity of the macroinvertebrate community structures and FFGs.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 98 Riparian Vegetation Integrity and Macroinvertebrates
5.2. Materials and Methods 5.2.1. Study Sites The study sites described in Chapter 2 were used in the riparian vegetation assessment.
5.2.2. Field Survey The VEGRAI model (Kleynhans et al., 2006) is a tool used to assess riparian zone health and functionality in relation to stream integrity. Theoretical site reconstruction was undertaken to determine the reference condition. Impacts at each site were evaluated and the sites were assessed according to the reference condition (what the site would have looked like in the absence of those impacts). Vegetation samples were taken from each site, as well as photographs for identification. The vegetation was identified with the aid of literature (Van Wyk and Van Wyk, 1997; Gerber et al., 2004; Van Wyk and Van Oudtshoorn, 2006; Pers. Comm.1 Andrew Hankey). In the case of herbaceous shrubs identification to the lowest taxonomical group was not always possible and therefore the data represented in this chapter is of low confidence.
5.2.3. Riparian Index The VEGRAI model (part of the EcoStatus suite of models) has a spreadsheet component that is composed of a series of metrics and metric groups. The metrics in the VEGRAI model compare differences between the riparian vegetation’s current and reference states as a measure of vegetation response to an impact regime. The VEGRAI level 3 model was used to assess the riparian vegetation EC of each study site. For VEGRAI level 3, the marginal and non-marginal vegetation metric groups were assessed in terms of their ‘woody’ and ‘non-woody’ components. These vegetation components were assessed by rating cover, abundance and species composition metrics in response to their change from the reference condition. The marginal and non-marginal metric groups were rated and weighted as separate components, followed by another rating and weighting of each zone relative to its importance in the particular study. An EC (A-F) was determined for the riparian vegetation state, which is an overall percentage change from the natural riparian condition. Table 5.1 gives the EC description, class and integrity scores.
1 Mr. Andrew Hankey, South African National Biodiversity Institute, Walter Sisulu National Botanical Garden, Gauteng, Wilro Park, September 2008.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 99 Riparian Vegetation Integrity and Macroinvertebrates
Table 5.1: Generic ecological categories for EcoStatus components (modified from Kleynhans et al., 2006). Ecological Description Score (% of Category total) (EC) A Unmodified, natural. 90-100
B Largely natural with few modifications. A small change in 80-89 natural habitats and biota may have taken place but the ecosystem functions are essentially unchanged. C Moderately modified. Loss and change of natural habitat and 60-79 biota have occurred, but the basic ecosystem functions are still predominantly unchanged. D Largely modified. A large loss of natural habitat, biota and 40-59 basic ecosystem functions has occurred. E Seriously modified. The loss of natural habitat, biota and 20-39 basic ecosystem functions is extensive. F Critically modified. Modifications have reached a critical level 0-19 and the lotic system has been modified completely with an almost complete loss of natural habitat and biota. In the worst instances the basic ecosystem functions have been destroyed and the changes are irreversible.
5.2.4. Statistical Analysis Redundancy Analysis was used to illustrate how the macroinvertebrate communities and their associated FFGs changed according to changes in riparian vegetation along a longitudinal gradient of agricultural practices. The statistical analysis was carried out using the computer package CANOCO version 4.5 (Ter Braak and Šmilauer, 2002). Data were log-transformed and significance tests were carried out using Monte Carlo permutation tests (499 permutations; P ≤ 0.05).
5.3. Results 5.3.1. Riparian Vegetation Community Composition The riparian vegetation showed no clear relationship with land use (i.e. agriculture) (Table 5.2), with the study sites ranging from a moderately to a largely modified or impacted condition (Tables 5.1 and 5.2). For most of the study sites (HR 1, HR 2, HR 4, HR 5 and VR 2) the non-marginal zone showed greater intactness than the marginal zone ranging from 53.2% to 71.8%. The agricultural site HR 3 showed the highest overall riparian vegetation intactness with a similarity of 69.7% to the extrapolated reference conditions, followed by the Vaal River site VR 2 with a similarity of 69.2%.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 100 Riparian Vegetation Integrity and Macroinvertebrates
Table 5.2: Integrity scores (VEGRAI) for marginal, non-marginal, total intactness (%) and ECs for riparian vegetation at sites on the Harts- and Vaal Rivers during the high (H) flow period. VEGRAI HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H Marginal Zone Intactness (%) 57.3 57.9 72.2 56.9 51.6 66.8 66.7 Non-Marginal Zone Intactness (%) 66.7 60.2 67.2 72 53.2 64.9 71.8 Total (%) 63.5 59.4 69.7 64.8 52.3 65.9 69.2 Ecological Category (EC) C C/D C C D C C
Table 5.3: The dominant plant species found at sites on the Harts- and Vaal Rivers during the high (H) flow period. Species Status HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H
Acacia karoo R X X X X X Acacia tortilis subsp. R X X heteracantha Acanthaceae sp. indet. R X X X 001 Argemone mexicana W X X Asteraceae sp. indet. 001 R X Asteraceae sp. indet. 002 R X Asteraceae sp. indet. 003 R X X Asteraceae sp. indet. 004 R X Bidens bipinnata R X Brachiaria brizantha G X X X X Cirsium vulgare W/I X X X Cyperus eragrostis A X X X Cyperus marginatus A X X X X X X Diospyros lycioides R X Eucalyptus sp. indet. 001 E X Fabaceae sp. indet. 001 R X X Fabaceae sp. indet. 002 R X Flaveria bidentis R X X Gomphocarpus fruticosus W X X X X Lactuca serriola R X Nicotiana glauca W/I X X X X Persicaria decipiens A X X Phragmites australis A X X X X Populus X canescens E/I X Prosopis sp. indet. 001 R X
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 101 Riparian Vegetation Integrity and Macroinvertebrates
Table 5.3 (cont.): The dominant plant species found at sites on the Harts- and Vaal Rivers during the high (H) flow period. Species Status HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H
Rhus lancea R X X Salix mucronata R X Schkuhria pinnata R X Schoenoplectus A X X X brachyceras Setaria pallide-fusca G X Sida sp. indet. 001 R X Solanum cf. nigrum R X Tribulus terrestris R X Typha capensis A X Verbena cf. bonariensis E X Xanthium spinosum W X Ziziphus mucronata R X X Status: R= Riparian; W= Weed; I= Invader; A= Aquatic; G= Grass. Indet= unidentified.
The dominant plant species found at sites on the Harts- and Vaal Rivers are indicated in Table 5.3. Exotics such as Eucalyptus (HR 3), Populus X canescens (HR 2) and Verbena cf. bonariensis (VR 1) were present at some of the study sites, as well as weeds, which indicated disturbed conditions. The study sites showed to have some vegetation species in common, but were mostly separated from each other regarding the composition of the riparian communities.
5.3.2. Riparian Vegetation and Macroinvertebrate Community Composition The RDA tri-plot in Figure 5.1 shows the relationship between macroinvertebrate communities and riparian vegetation integrity at the study sites. Figure 5.1 describes 24.5% of the variation in species data, with the first axis explaining 16.7% and the second axis 7.8%. Species-environment correlations for the first and second axes were 0.758 and 0.834, respectively, and explained 60.1% and 28.1% of the species-environment variation, thus indicating a moderate relationship between the macroinvertebrate communities and riparian vegetation integrity. The variation amongst the study sites was not significant (P = 0.1960).
Macroinvertebrate families that prefer vegetation as habitat were correlated with VEGRAI and marginal vegetation. These taxa included Belostomatidae, Atyidae, Pyralidae, Planorbidae, Coenagrionidae and Hydrophilidae. These taxa (except for Pyralidae) are not
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 102 Riparian Vegetation Integrity and Macroinvertebrates
very sensitive to water quality changes based on SASS5 data and were mostly present at the agricultural sites.
Figure 5.1: RDA tri-plot of the relationship between riparian vegetation and macroinvertebrate community structures for sites on the Harts- and Vaal Rivers.
5.3.3. Riparian Vegetation and FFGs The FFGs (Figure 5.2) showed the same type of ordination as the relationship between the macroinvertebrate communities and riparian vegetation integrity (Figure 5.1). The RDA tri- plot shown in Figure 5.2 describes 23.4% of the variation in species data, with the first and second axes explaining 18.1% and 5.3%, respectively. Species-environment correlations were 0.641 and 0.626 for the first and second axes, respectively, which is an indication that the relationship between the macroinvertebrate FFGs and riparian vegetation were not that strong (with P = 0.3900). The first axis explained 76.0% of the variation in the species- environment data and the second axis 19.2%.
There was a strong correlation between marginal (Figure 5.2) and to a lesser degree, overall VEGRAI scores and shredder and detritivore FFGs (SH, SHD, SHH and DT). It is clear from Figures 5.1 and 5.2 that non-marginal vegetation was negatively correlated with the macroinvertebrate community structures and FFGs and that marginal vegetation seemed to be the most important component affecting macroinvertebrate integrity.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 103 Riparian Vegetation Integrity and Macroinvertebrates
Figure 5.2: RDA tri-plot of the riparian vegetation integrity in relation to macroinvertebrate FFGs for sites on the Harts- and Vaal Rivers.
5.4. Discussion 5.4.1. Riparian Vegetation Integrity The study sites were moderately to largely modified by anthropogenic disturbance (Table 5.2). Human-induced disturbance (e.g. stream-flow regulation, corridor fragmentation, land use) affects the longitudinal patterns of species richness not only through loss of habitat, but through species introductions as well (Planty-Tabacchi, 1993 cited in Tabacchi et al., 1998). The relative reference sites HR 1 and VR 1 did not show the highest overall riparian intactness. The relative reference site HR 1 was mostly impacted upon by flood regulation, since this site is situated downstream of Taung Dam. Clear signs of decreased flow were noticed at this site, because the present marginal zone used to be part of the river channel. After construction of dams, a period of geomorphic adjustment to the changed flow is expected, followed by an adjustment in riparian vegetation (Johnson, 1998 cited in Webb and Leake, 2006). Flow diversions, whether partial or total, strongly affect riverine riparian ecosystems (Webb and Leake, 2006). Water use for agriculture can also lower river flows and thereby stress riparian plants in the season when they need water the most. Dams reduce peak discharges and the amount of water available to riparian systems, as well as changes in the seasonality of flooding. Species dependent on flooding for germination and establishment can only rarely reproduce (Webb and Leake, 2006). Thus, long-term flood control may cause reduced flooding, coupled with lowered variability in daily discharge, which may benefit established riparian species on the streamward side of floodplains, because formerly scoured channel margins become stable habitat for new plant
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 104 Riparian Vegetation Integrity and Macroinvertebrates
establishment. In this study, the establishment of invasive weeds. Construction practices along the relative reference site VR 1 impacted this site through clearance of vegetation, particularly woody species in the non-marginal zone (Table 5.2).
The riparian integrity of the agricultural sites was mostly impacted upon by livestock trampling, which significantly modified the riparian vegetation. Animals may affect vegetation by providing organic matter (e.g. carcasses, faeces), deplete and/or destroy seed banks (Naiman and Rodgers, 1997) and cause bank instability. The agricultural sites showed signs of disturbance as indicated by the composition of the riparian vegetation, which consisted of weeds. Weeds were also present at the Harts reference site. Disturbances in plant communities provide opportunities for weed germination, propagation, spread and invasion (Florentine et al., 2006). Cirsium vulgare is an herbaceous weed that invades disturbed areas, and was found at most of the agricultural sites, mostly in the marginal zone (Table 5.3). The spiny nature of the plant renders it unpalatable to wildlife and livestock and therefore reduces the forage potential of this plant occurring in riparian zones (Klinkhamer and De Jong, 1993). Another weed noticed at most of the study sites was Nicotiana glauca (Table 5.3). Cunningham et al. (1981 cited in Florentine et al., 2006) reported extensive stands of N. glauca on stream floodplains and drainage channels in Australian arid and semi-arid landscapes. This species was notably evident in the marginal zone or otherwise flooded areas (e.g. HR 1) in the present study. Thus, the presence of N. glauca in flooded areas may inhibit the germination of seeds belonging to other species (Florentine et al., 2006). This was found to be the case in a study by Florentine and Westbrooke (2005) who demonstrated that leachates obtained from dry leaves and twigs of N. glauca had negative impacts on the germination of Lactuca sativa seeds. Nicotiana glauca can therefore, be linked to regulated flow regimes at HR 1, since this species is known to have an invasive character and to be resilient during floods and drought (Florentine et al., 2006).
According to Henderson (1998 cited in Holmes et al., 2005) are N. glauca and Prosopis glandulosa the most frequently recorded invaders in the arid areas of Southern Africa, as well as the trees Acacia species and P. X canescens. According to Tabacchi (1998) trees represent the most stable component of the riparian community, although some (e.g. poplars and willows) are pioneer species and adapted to disturbance. According to Forsyth et al. (2004) can Eucalyptus species (especially E. camaldulensis) transform riparian vegetation, altering riparian ecosystem functioning. An unidentified Prosopis specie was found at the relative reference site VR 1, P. X canescens at HR 2 and an unidentified Eucalyptus specie
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 105 Riparian Vegetation Integrity and Macroinvertebrates
(which is thought to be E. camaldulensis) at HR 3. The effects of alien species in riparian zones usually lead to the suppression and replacement of indigenous vegetation (Richardson et al., 1997 cited in Holmes et al., 2005), increased transpiration and reduction in flows (Le Maitre et al., 2000; Dye and Jermain, 2004; Richardson and Van Wilgen, 2004), quality of nutrient resources in biogeochemical cycles, and the modification of physical resources such as habitat, sediment, light and water (Vitousek, 1990 cited in Richardson and Van Wilgen, 2004) .
5.4.2. Riparian Vegetation, Macroinvertebrate Composition and FFGs Healthy riparian zones have a dense growth of vegetation that prevents eroded sediment from entering streams, as well as a diversity of plants that facilitate the removal of nutrients carried into riparian zones by runoff and groundwater. Riparian areas also facilitate the degradation of many soil contaminants (Bellows, 2003). When upland conditions are degraded, heavy runoff can flow over or through riparian plants and flow directly into the river system. Riparian areas can become buried under sediments if severe erosion is present in upland areas. As indicated in Chapter 4, erosion can degrade stream habitat by filling in stream pools, altering the shape of stream channels and covering rocky stream bottoms and thereby eliminating important food producing and shelter areas (Wohl and Caline, 1996). Runoff and erosion also transport seeds of non-native or non-riparian plant species, as seen in section 5.3.2. Thus, as runoff and erosion (also exacerbated by livestock trampling) from upland areas continue to degrade the integrity of riparian zones, streamside areas loose their ability to buffer and protect streams, resulting in the damage of aquatic habitat (Bellows, 2003) and consequently destuction of the macroinvertebrate community integrity.
An increase in fine sediments was noted at the agricultural sites, especially at HR 2. Stone et al. (2005) found that the agricultural sites with the lowest riparian forest cover and highest percentage of adjacent crops had significantly higher percent silt substrates. The agricultural site HR 2 was situated adjacent to agricultural fields and was characterized by the presence of large willows (Salix mucronata), which were situated along the riverbanks, as well as in the river channel. In a study by Read and Barmuta (1999) willow roots had invaded the river bed and caused a reduction in flow, as well as a decrease in oxygen levels especially in isolated pools. The macroinvertebrate family Baetidae, which respires with gills and thus very susceptible to reduced dissolved oxygen (Dallas and Day, 1993), was found in reduced numbers during the winter season at the agricultural site HR 2 compared to the other study sites (Appendix C; Figure 5.1). By decreasing flow speeds, the willow roots
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 106 Riparian Vegetation Integrity and Macroinvertebrates
probably enhanced the deposition of fine sediments during the low flow period, which resulted in the increased abundance of filtering taxa reliant on suspended FPOM (e.g. Simuliidae). Read and Barmuta (1999) also found higher standing stocks of FPOM in autumn and that the willow-lined reaches were more turbid in both summer and autumn. Turbidity levels were found to be high at the agricultural site HR 2 (Table 3.3) during the dry season, which may have resulted in reduced light penetration and primary productivity and hence, the disappearance of higher consumers due to reduced food availability (Dallas and Day, 1993). The abundances of scrapers and predators declined considerably at HR 2 compared to the reference site HR 1 (Appendix C; Figure 5.2). Shredder-detritivores were present in the highest abundances at HR 2 (Figure 5.2), which is in accordance with increased willow litter deposits in this stretch of the river. There was little ground cover at HR 2 which could have lead to the increased sediment loads at HR 2.
Instream habitat integrity seems to play a primary role in structuring the macroinvertebrate communities, and riparian vegetation a secondary role in this study. The largely modified riparian vegetation resulted in increased sediment loads and absorbed pollutants at the agricultural sites, and also played a role in the regulation of flow and therefore contributed to the changes in instream habitat conditions to which the macroinvertebrates showed a stronger response (Figures 5.1 and 5.2 – marginal vegetation). In the study by Walsh (2008) it was found that the macroinvertebrate community intactness increased with increased riparian integrity and that macroinvertebrate FFGs showed a stronger correlation with riparian integrity (indicating impacts due to organic matter inputs) compared to the actual community structure. In the study by Stone et al. (2005) collector-filterers decreased with increasing riparian forest and instream habitat was the primary factor influencing biotic integrity. In the study by Dudgeon (1994) the community functional organization of six streams was related to riparian shading (from savanna grassland to primary rainforest). It was found that this relationship was rather conservative, and streams were co-dominated by collector-gatherers and grazers, followed by filter-feeders and predators. Shredders did not exceed 2% of benthic populations in any of the Sepik River tributary streams (Dudgeon, 1994). Collector-filterers and collector-gatherers dominated at all of the study sites in the present study, indicating decreased riparian forest. Shredders (present in low abundance) were more correlated with the marginal zone than the non-marginal zone (Figure 5.2) and are therefore an indication that allochtonous inputs were not the primary food source for these river systems, but rather autochtonous sources that were stimulated by nutrient runoff from upland areas. Since most of the study sites were mostly open and not shaded by large trees (except HR 2), primary algal production was high in these systems. In the study by
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 107 Riparian Vegetation Integrity and Macroinvertebrates
Dudgeon (1994) algae and detritus was an important predictor of the relative abundance of collector-gatherers (dominated), grazers (dominated) and had a significant effect on the population densities of shredders (low abundance). Increased nutrient loads at HR 3, HR 4 and HR 5 increased the presence of aquatic weeds and also lead to the increase in filter feeders and collector-gatherers at these sites. Although the agricultural sites HR 3 and HR 4 showed better riparian integrity than the reference site HR 1, as well as the agricultural sites HR 2 and HR 5 (Table 5.2), phosphorus levels were found in the greatest amounts at HR 3 and HR 4 (Table 3.3). Over-application of fertilizer and manure can overload the soil with phosphorus. Iron, aluminium and calcium in the soil can bind excess phosphorus. In agricultural areas phosphorus is mainly exported with sediments to which it is chemically bound and may be trapped by riparian vegetation only to be transported into streams at a later stage, for example, through floods (Naiman and Decamps, 1997). According to Fabre et al. (1996) riparian soil can either be considered as a source or a sink of phosphorus, depending on the soil texture and the form of phosphorus. Simuliidae, Chironomidae and molluscs such as Physidae are good indicators of increased nutrient loads and were found in high abundance at the agricultural sites, especially at HR 3, in this study (Section 4.4.1). Increased nutrient loads at HR 3 resulted in the lush growth of marginal vegetation such as reeds and grasses and showed high abundances of vegetation inhabiting macroinvertebrate tolerant families such as Physidae, Coenagrionidae and Belostomatidae (Figure 5.1). A review conducted by Haycock et al. (1993) showed that nitrogen buffering in the riparian zone was due to the combined effect of plant uptake and microbial denitrification. According to Tabacchi (1998) ‘the efficiency of a given riparian zone in regulating subsurface nitrogen fluxes is not a simple function of the surface area covered by riparian vegetation, rather, nitrogen and the attenuation of other pollutants is a function of the length of the hydrological contact zone as the pollutant plume moves through the riparian zone from upland drainage areas toward the stream channel’. The increased nutrient loads observed at HR 3 (Table 3.3) and HR 4, which were found to be above normal ranges, is thought to be a combined effect of sewage spills, livestock faecal matter and inorganic nitrogen from irrigation return- flows. It is therefore thought that the increase of nitrogen fluxes at these agricultural sites might be due to a decrease in the filtering potential of the riparian zone at these agricultural sites.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 108 Riparian Vegetation Integrity and Macroinvertebrates
5.5. Summary and Conclusion The riparian vegetation integrity (VEGRAI) showed a spatial trend, but did not show a trend in relation to land use. The riparian vegetation integrity was impaired at all of the study sites due to human-induced activities such as riparian removal at VR 1, construction of dams, regulated flow, livestock trampling, and the introduction of invasive weeds and alien vegetation. It is thought that riparian vegetation integrity only played a secondary role in the structuring of the macroinvertebrate community structures, which responded directly to instream habitat (marginal vegetation) changes due to the largely modified riparian vegetation. This in turn resulted in increased sedimentation and possibly associated absorbed pollutants (e.g. nutrients and pesticides) and impaired flow regimes. The riparian vegetation integrity indicated disturbance due to anthropogenic activities and therefore indirectly impacted the macroinvertebrate communities and macroinvertebrate FFGs of the lower Harts/Vaal River systems. It is therefore important to preserve and maintain riparian ecosystems in order to conserve aquatic invertebrate communities.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 109
Chapter 6: Conclusions and Recommendations
6.1. Introduction Water resources in South Africa are scarce, and due to this semi-arid nature, water management and conservation are an integral component to protect our country’s water resources for future generations. There is an increased demand on use of South Africa’s water resources, together with the return of effluent water from diffuse sources, which significantly alter the natural state of receiving water bodies (Taylor et al., 2007b). In an attempt to overcome water shortage and quality, a number of legislation, strategies, policies, programmes and initiatives have been formulated and implemented such as the NWA of 1998 (RSA, 1998) and NWRS (DWAF, 2004a), which gives direction for the implementation of the NWA. The NWA also deals with the Ecological Reserve, which relates to the amount of water required to sustain aquatic ecosystems and also refers to the quantity and quality of the water in the resource (Van Wyk et al., 2006). The important role that biotic components play in natural ecosystem functioning contributed to the development of biological monitoring programmes to assess ecosystem health and integrity. A biological programme was developed for South Africa, which is carried out by the national initiative known as the RHP to assess the status of rivers around the country and make use of aquatic invertebrate fauna, fish, riparian vegetation and river habitats. The following section presents a summary of the relationship between the environmental variables measured in the lower Harts/Vaal River systems and the aquatic biota community structures and indices to elucidate whether the agricultural activities at Vaalharts, impacted the ecological integrity of these river systems.
6.2. Relationship between Agricultural Land Use Practices and Aquatic Communities.
The first aim was to elucidate whether the diatom- and macroinvertebrate community structures found at sites adjacent to, and below agricultural activities differed taxonomically from communities found upstream of agricultural practices. The water quality data changed in relation to land use (Figure 6.1), indicating that agricultural practices contributed to the change in physico-chemical water quality properties from reference conditions. The diatom community structures changed in relation to changes in water quality conditions (Figure 6.1) and consequently to agricultural land use. Sedimentation and salinization were the key contributors to these changes in the diatom community structures and seemed to mask the
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 110 Conclusions and Recommendations
effects of nutrients on the particular communities found at the agricultural sites. Macroinvertebrate communities were affected by changes in instream habitat conditions, as well as water quality, specifically nutrients, and changed in relation to agricultural land use.
Land Use
Relative Agricultural Reference Land Use Condition
Water Turb; Cond; Quality Sulphate; Turb; Ca Nitrate; Ca
Diatom General water quality indices (BDI, SPI, GDI) indices showed decreased values at agricultural sites compared to relative reference sites. EPI and %PTV indicated organic pollution at HR 3 and HR 4.
HR 2 – HR 5 HR 1, VR 1
Diatom e.g. Navicula spp. e.g. A. minutissimum indicators Nitzschia spp. E. microcephala N. frustulum P. salinarum A. pediculus C. pediculus T. fasciculata
VR 2
e.g. Achnanthidium sp. P. brevistriata M. smithii
Figure 6.1: Summary of the results for water quality and indicator diatoms in relation to land use.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 111 Conclusions and Recommendations
Land Use
Relative Agricultural Reference Land Use Condition
Low flow – clear separation SASS5 between land use. High flow – no clear separation.
IHAS No clear separation between land use. Moderately to largely modified. Sedimentation & irregular flow changed habitat availability.
HR 2 – HR 5, VR 2 HR 1, VR 1
Macroinvertebrate e.g. e.g. indicators Simuliidae Baetidae Chironomidae Caenidae Physidae Hydropsychidae Oligochaeta Leptophlebiidae Atyidae Heptageniidae Tricorythidae
No clear separation between land FFGs use. Influenced by FPOM, with COF, COG, PR, SC dominating the study sites.
Figure 6.2: Summary of the results for habitat, macroinvertebrate index, community structures and FFGs.
The second aim of this study was to determine whether macroinvertebrate FFGs changed according to changing land use. The macroinvertebrate FFGs didn’t show changes according to agricultural land use, but did indicate that the presence of FPOM was the main food source available at the study sites. Collector-filterers, collector-gatherers, predators
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 112 Conclusions and Recommendations
and scrapers were the dominant FFGs (Figure 6.2). The presence of these feeding groups indicated that all the study sites were impacted upon by nutrients and sedimentation.
The third aim was to elucidate if indicator taxa exist that can be used as indicators of changing land use. The agricultural sites showed an increase in tolerant taxa and a decline in sensitive taxa compared to the relative reference sites. Diatom indicators included the motile genera Navicula and Nitzschia species (indicators of sedimentation and organic pollution), N. frustulum and A. granulata (high phosphates), C. pediculus and T. fasciculata (turbidity and conductivity) was found at the agricultural sites (Figure 6.1). Macroinvertebrate indicators included Simuliidae (regulated flow and nutrients), Chironomidae, Oligochaeta, molluscs (nutrient loads); Hydropsychidae (sedimentation) and Atyidae (salinization) (Figure 6.2). The diatom indices and ecological descriptors were also able to separate the relative reference sites from the agricultural sites and reflected the findings of the diatom community structures very well. The SASS5, IHAS (Figure 6.2) and VEGRAI (Figure 6.3) indices weren’t able to clearly differentiate between the relative reference sites and the agricultural sites, but indicated that the study sites were impacted or modified by anthropogenic activities. Disturbances such as riparian removal, construction of dams, regulated flow and livestock trampling were indicated by the presence of invasive weeds and alien vegetation. Nicotiana glauca and C. vulgare showed to be good indicators of riparian disturbance (Figure 6.3). The moderate to largely impacted riparian vegetation played a secondary role in the structuring of the macroinvertebrate community structures and FFGs, which responded directly to instream habitat changes. Changes in instream habitat integrity were caused by increased sedimentation and possibly associated absorbed pollutants (Figure 6.2), decreased litterfall, and impaired flow regimes as a result of the modified riparian vegetation (Figure 6.3) and presence of dams. The use of indices is particularly useful if one wants to indicate deteriorating conditions due to human impacts, but taxonomic data were able to separate land use and were more appropriate in the present study than indices to show this separation.
It can be concluded that the study sites could be separated according to land use based on the diatom- and macroinvertebrate community structures. However, it must be noted that the diatoms showed a better response to land use practices compared to the macroinvertebrates. Biological trait analysis of FFGs wasn’t able to separate between different land uses in this study. Diatom communities and indices showed to be reliable indicators of both specific water quality problems such as organic pollution and salinity, as well as general water quality. The macroinvertebrate indices couldn’t be fully explained by
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 113 Conclusions and Recommendations
the water quality variables used in this study and the macroinvertebrate community structures indicated that other factors such as habitat diversity or unmeasured water quality variables (such as pesticides) may also affect the macroinvertebrate indices. The importance of preserving and maintaining riparian ecosystems to conserve aquatic biota was also demonstrated. The results of this study support the original study hypothesis and it is therefore accepted.
Land Use
Relative Agricultural Reference Land Use Condition
No clear separation between land Riparian uses. Riparian integrity moderately to integrity largely modified. Impacted through (VEGRAI) riparian removal, flow regulations, livestock trampling, and introduction of alien and invasive plants (e.g. Eucalyptus, N. glauca, C. vulgare).
Riparian Riparian degradation played a degradation & secondary role in the structuring of the macroinvertebrates particular macroinvertebrates and FFGs. Changed instream habitat conditions through irregular flow, sedimentation, changes in litterfall, and water quality (increased salts, sediment and nutrients).
Figure 6.3: Summary of the results for riparian integrity and macroinvertebrate community structures and FFGs.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 114 Conclusions and Recommendations
6.3. Recommendations
The present study revealed several recommendations for further studies and management practices within the Vaalharts area. Firstly, the macroinvertebrate, habitat and riparian vegetation index scores failed to discriminate between different land use activities. Although these indices did indicate that the study sites were impacted and indicated spatial variation, it wasn’t clear if agriculture was the main contributor to these alterations from the norm. The macroinvertebrate community structures could differentiate between different land uses, and it is therefore recommended that future studies include a higher taxonomic level of identification to at least genus level, which will result in higher confidence levels and clearer separation between land use practices. Data are also available on the tolerances and optima for a number of species. Macroinvertebrate FFGs showed to be a biological trait which couldn’t differentiate between land uses in this study. However, the use of other biological traits that indicate resilience or resistance such as body size, body form (e.g. flexible body, streamlining or flattening), mobility, presence of relatively invulnerable life stages, number of descendants per reproductive cycle, attachment mechanisms, reproductive period and respiration showed to be reliable traits in other studies (Pianka, 1970; Townsend and Hildrew, 1994 cited in Charvet et al., 1998; Charvet et al., 1998) and are therefore recommended for use in further studies. It is also recommended that biological traits be used in biomonitoring to discover the behaviour of biological traits versus different types of human disturbance compared to undisturbed or favourable conditions (Charvet et al., 1998). By studying how macroinvertebrates behave under more specific land use disturbances such as agriculture, biological trait indices can be developed that point towards a specific disturbance or pollution impact, as is the case with the diatom indices, which can point out specific impacts such as pollution by nutrients, metals and acidification. It is recommended that the riffle and pool parts of macroinvertebrate samples also be assessed separately to provide additional information useful when combined effects of organic pollution and morphological degradation (e.g. sedimentation due to erosion) are to be considered (Brabec et al., 2004). It can therefore be estimated more accurately whether the effects of particulate solids, for example, were greater on the pool fauna than the riffle fauna. Epilithic diatoms were sampled in the Harts River and epiphytic diatoms in the lower Vaal River, which complicated comparisons between these river systems. It is
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 115 Conclusions and Recommendations
therefore recommended that epipelon samples also be collected together with epilithic and epiphytic diatom samples to indicate how the study sites would have changed in regard to its motile genera and if agricultural inputs would have increased the diversity and taxa richness of motile genera tolerant to agricultural pollutants adsorbed to sediment particles. Diatom sampling also has fewer restrictions in terms of habitat requirements compared to macroinvertebrates, and it is therefore recommended that diatoms be used in the monitoring of the water quality of the irrigation water in the drainage canals of the Vaalharts irrigation scheme. According to Round (2001) river diatoms can colonize large rivers but also ‘rivers’ millimetres deep and centimetres wide. Diatoms proved to be reliable indicators of water quality and should therefore be included in the routine biomonitoring of river ecosystems. Since the measured water quality variables and instream habitat and riparian vegetation integrity didn’t explain all of the variation in the diatom- and macroinvertebrate data, and organic pollution was found at some of the agricultural sites, organic inputs from pesticides could explain some of this unmeasured variation in the data. It is therefore recommended that pesticide analysis, as well as other toxicants such as heavy metals (impurities from fertilizers and pesticides) are undertaken, which will allow for the explanation of some of the unmeasured variation and taxonomic response of the aquatic biota, which may result in a higher significance value. It is recommended that a detailed study on the riparian vegetation integrity of the lower Harts- and Vaal Rivers be undertaken to increase the confidence levels of the results found in this study, which were of low confidence. This includes studies on the ecological characteristics of weeds in order to take appropriate management action at an early stage of invasion. Studies on the clearance of alien vegetation (different methodologies for alien control) on native vegetation species and instream biota should also be undertaken for management purposes. The removal of livestock from the riparian zones will also aid in its restoration. It is therefore recommended that farmers and rural settlements make provision for alternative watering points in order to reduce the impacts of grazing and trampling on riparian habitats (Godwin and Miner, 1996). Rest rotation is also recommended, where cattle are excluded from the riparian zone during spring, to enhance successful germination and regeneration of streamside vegetation (Askey-Doran, 1999). The planning and management of discharge are also important in structuring the riparian vegetation and it is recommended that studies be undertaken to investigate the suitable discharge flow required by riparian zones in order to conserve the mosaic structure of
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 116 Conclusions and Recommendations
the riparian zones in the lower Harts/Vaal River systems. Maintenance of a good riparian zone will aid in the buffering capacity of the riparian zone and ultimately lead to the minimization of pollutant runoff from agricultural fields.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 117
Chapter 7: References
Aguiar, F.C., Ferreira, M.T., and Pinto, P. (2002). Relative influence of environmental variables on macroinvertebrate assemblages from an Iberian Basin. Journal of the North American Benthological Society 21: 43-53.
Alexander, A.C., Heard, K.S., and Culp, J.M. (2008). Emergent body size of mayfly survivors. Freshwater Biology 53: 171-180.
Allan, J.D., Erickson, D.L., and Fay, J. (1997). The influence of catchment land use on stream integrity across multiple spatial scales. Freshwater Biology 37: 149-161.
Allen, A.P., Whittier, T.R., Larsen, D.P., Kaufmann, P.R., O’Connor, R.J., Hughes, R.M., Stemberger, R.S., Dixit, S.S., Brinkhurst, R.O., Herlihy, A.T., and Paulsen, S.G. (1999). Concordance of taxonomic composition patterns across multiple lake assemblages: Effects of scale, body size, and land use. Canadian Journal of Fisheries and Aquatic Sciences 56: 2029-2040.
Almeida, S.F.P. (2001). Use of diatoms for freshwater quality evaluation in Portugal. Limnetica 20: 205-213.
Amis, M.A., Rouget, M., Balmford, A., Thuiller, W., Kleynhans, C.J., Day, J., and Nel, J. (2007). Predicting freshwater habitat integrity using land use surrogates. Water SA 33: 215-221.
Anderson, N.J. (2000). Diatoms, temperature and climatic change. European Journal of Phycology 35: 307-314.
Anderson, B.S., Hunt, J.W., Phillips, B.M., Nicely, P.A., De Vlaming, V., Connor, V., Richard, N., and Tieerdema, R.S. (2003). Integrated assessment of the impacts of agricultural drainwater in the Salinas River (California, USA). Environmental Pollution 124: 523- 532.
Askey-Doran, M. (1999). Managing stock in the riparian zone. In: Lovet, S., and P. Price (Editors) Riparian management technical guidelines. Land and Water Australia, Canberra.
Bacey, J., and Spurlock, F. (2007). Biological assessment of urban and agricultural streams in the California Central Valley. Environmental Monitoring and Assessment 130: 483- 493.
Barbour, M.T., Gerritsen, J., Griffith, G.E., Frydenborg, R., McCarron, E., White, J.S., and Bastian, M.L. (1996). A framework for biological criteria for Florida streams using benthic macroinvertebrates. Journal of the North American Benthological Society 15: 185-211.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 118 References
Barbour, M.T., Gerritsen, J., Snyder, B.D., and Stribling, J.B. (1999). Regional tolerance values, functional feeding groups and habit/behavior assignments for benthic macroinvertebrates. Appendix B. In: Rapid bioassessment protocols for use in streams and wadeable rivers: Periphyton, benthic macroinvertebrates, and fish, Second Edition. EPA 841-B-99-002. U.S. Environmental Protection Agency: Office of Water, Washington, DC.
Baron, J.S., Poff, N.L., Angermeier, P.L., Dahm, C.N., Gleick, P.H., Hairston, N.G., Jackson, R.B. (Jr.), Johnston, C.A., Richter, B.D., and Steinman, A.D. (2003). Sustaining healthy freshwater ecosystems. Issues in Ecology 10: 1-16.
Baskin, C.C., and Baskin, J.M. (1998). Seeds: Ecology, biogeography and evolution of dormancy and germination. Academic Press, CA.
Basu, B.K., and Pick, F.R. (1996). Factors regulating phytoplankton and zooplankton biomass in temperate rivers. Limnology and Oceanography 41: 1572-1577.
Bate, G.C., Adams, J.B., and Van der Molen, J.S. (2002). Diatoms as indicators of water quality in South African river systems. WRC Report No. 814/1/02. Water Research Commission, Pretoria, South Africa.
Beaton, J.D., Roberts, T.L., Halstead, E.H., and Cowell, L.E. (1995). Global transfers of P in fertilizer materials and agricultural commodities. In: Tiessen (Editor) Phosphorus in the global environment: Transfers, cycles and management. John Wiley, New York, USA.
Bellinger, B.J., Cocquyt, C., and O’Reilly, C.M. (2006). Benthic diatoms as indicators of eutrophication in tropical streams. Hydrobiologia 573: 75-87.
Bellows, C. (2003). Protecting riparian areas: Farmland management strategies, soil systems guide. Appropriate Technology Transfer for Rural Areas (ATTRA). 1-800-346- 9140. http://www.attra.ncat.org/attra-pub/PDF/riparian.pdf. (Accessed September, 2008).
Berezina, N.A. (2003). Tolerance of freshwater invertebrates to changes in water salinity. Russian Journal of Ecology 34: 261-266.
Biggs, B.J.F. (1995). The contribution of flood disturbance, catchment geology and land use to the habitat template of periphyton in stream ecosystems. Freshwater Biology 33: 419-438.
Biggs, B.J.F. (1996). Patterns in benthic algae of streams. In: Stevenson, R.J., M.L. Bothwell, and R.L. Lowe (Editors) Algal ecology: Freshwater benthic ecosystems. Academic Press, San Diego, CA.
Bis, B., Zdanowicz, A., and Zalewski, M. (2000). Effects of catchment properties on hydrochemistry, habitat complexity and invertebrate community structure in a lowland river. Hydrobiologia 422/423: 369-387.
Blinn, D.W. (1993). Diatom community structure along physicochemical gradients in saline lakes. Ecology 74: 1246-1263.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 119 References
Blinn, D.W., and Bailey, P.C.E. (2001). Land-use influence on stream water quality and diatom communities in Victoria, Australia: A response to secondary salinization. Hydrobiologia 466: 231-244.
Bott, T.L. (1996). Algae in microscopic food webs. In: Stevenson, R.J., M.L. Bothwell, and R.L. Lowe (Editors) Algal ecology: Freshwater benthic ecosystems. Academic Press, San Diego, CA.
Boucher, C. (1999). Consulting services for the establishment and monitoring of the instream flow requirements for river courses downstream of LHWP dams. Specialist Report, Riparian Vegetation, Report No. LHDA 648-F-16 (Volume 1).
Brabec, K., Zahrádková, S., Němejcová, D., Pařil, P., Kokeš, J., and Jarkovský, J. (2004). Assessment of organic pollution effect considering differences between lotic and lentic stream habitats. Hydrobiologia 516: 331-346.
Burkholder, J.M., and Cuker, B.E. (1991). Response of periphyton communities to clay and phosphate loading in a shollow reservoir. Journal of Phycology 27: 373-384.
Buss, D.F., Baptista, D.F., Nessimian, J.L., and Egler, M. (2004). Substrate specificity, environmental degradation and disturbance structuring macroinvertebrate assemblages in neotropical streams. Hydrobiologia 518: 179-188.
Cairns, J. (Jr). (2003). Biotic community response to stress. In: Simon, T.P. (Editor) Biological response signatures, indicator patterns using aquatic communities. CRC Press, USA.
Cao, Y., Williams, D.D., and Williams, N.E. (1998). How important are rare species in aquatic community ecology and bioassessment? Limnology and Oceanography 43: 1403-1409.
Capítulo, A.R., Tangorra, M., and Ocón, C. (2001). Use of benthic macroinvertebrates to assess the biological status of Pampean streams in Argentina. Aquatic Ecology 35: 109-119.
Carpenter, S.R., Caraco, N.F., Correll, D.L., Howarth, R.W., Sharpley, A.N., Smith, V.H. (1998). Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecological Applications 8: 559-568.
Carpenter, K.D., and Waite, I.R. (2000). Relations of habitat-specific algal assemblages to land use and water chemistry in the Willamette Basin, Oregon. Environmental Monitoring and Assessment 64: 247-257.
Castillo, L.E., Martínez, E., Ruepert, C., Savage, C., Gilek, M., Pinnock, M., and Solis, E. (2006). Water quality and macroinvertebrate community response following pesticide applications in a banana plantation, Limon, Costa Rica. Science of the Total Environment 367: 418-432.
CEMAGREF (1982). Etude des methods biologiques d’appréciation quantitative de la qualité des eaux. Rapport Q.E. Lyon, Agence de l’eau Rhône-Méditerranée-Corse-Cemagref, Lyon, France.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 120 References
CEN (2004). Water quality – Guidance standard for the identification and enumeration of benthic diatom samples from rivers, and their interpretation. European Standard. EN 14407:2004.
Chapman, D., and Kimstach, V. (1996). Selection of water quality variables. In: Chapman, D. (Editor) Water quality assessments – A guide to use of biota, sediments and water in environmental monitoring, Second Edition. UNESCO/WHO/UNEP. E&FN Spon, University Press, Great Brittain, Cambridge.
Charvet, S., Kosmala, A., and Statzner, B. (1998). Biomonitoring through biological traits of benthic macroinvertebrates: Perspectives for a general tool in stream management. Archiv für Hydrobiologie 142: 415-432.
Chessman, B.C. (1986). Diatom flora of an Australian river system: Spatial patterns and environmental relationships. Freshwater Biology 16: 805-819.
Chessman, B., Growns, I., Currey, J., and Plunkett-Cole, N. (1999). Predicting diatom communities at the genus level for the rapid biological assessment of rivers. Freshwater Biology 41: 317-331.
Cholnoky, B.J. (1953). Diatomeenassoziationen aus dem Hennops-rivier bei Pretoria. Verhandlungen der Zoologisch-Botanischen Gesellschaft in Wien 93: 135-149.
Cholnoky, B.J. (1968). Die Ӧ kologie der Diatomeen in Binnengewӓ ssern. J Cramer, Lehre.
Chutter, F.M. (1998). Research on the rapid biological assessment of water quality, Impacts in streams and rivers. WRC Report No. 422/1/98. Water Research Commission, Pretoria, South Africa.
Clarke, K.R., and Gorley, R.N. (2006). Primer v6: User Manual or Tutorial. PRIMER-E, Plymouth.
Compin, A., and Céréghino, R. (2007). Spatial patterns of macroinvertebrate functional feeding groups in streams in relation to physical variables and land-cover in southwestern France. Landscape Ecology 22: 1215-1225.
Cooper, C.M. (1993). Biological effects of agriculturally derived surface water pollutants on aquatic systems – A review. Journal of Environmental Quality 22: 402-408.
Cosser, P.R. (1988). Macroinvertebrate community structure and chemistry of an organically polluted Creek in south-east Queensland. Marine and Freshwater Research 39: 671- 683.
Coste, M., and Ayphassorho, H. (1991). Étude de la qualité des eaux du Bassin Artois- Picardie à l’aide des communautés de diatomées benthiques (application des indices diatomiques). Rapport Cemagref. Bordeaux – Agence de l’Eau Artois-Picardie, Douai.
Cumming, B.F., and Smol, J.P. (1993). Diatoms and their relationship to salinity and other limnological characteristics from 65 Cariboo/Chilcotin region (British Columbia, Canada) lakes. Hydrobiologia 269/270: 179-196.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L., and Leigh, J.H. (1981). Plants of western New South Wales. N.S.W. Government Printing Office. Sydney.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 121 References
Dallas, H.F., and Day, J.A. (1993). The effect of water quality variables on riverine ecosystems: A review. Water Research Commission, Report No. TT61/93, Pretoria, South Africa.
Dallas, H.F. (2007). River Health Programme: South African Scoring System (SASS) data interpretation guidelines. A report by the Freshwater Consulting Group/Freshwater Research Unit, prepared for the Institute of Natural Resources and Department of Water Affairs and Forestry. University of Cape Town, Cape Town, South Africa.
Dallas, H.F., and Day, J.A. (2007). Natural variation in macroinvertebrate assemblages and the development of a biological banding system for interpreting bioassessment data – A preliminary evaluation using data from upland sites in the south-western Cape, South Africa. Hydrobiologia 575: 231-244.
Dance, K.W., and Hynes, H.B.N. (1980). Some effects of agricultural land use on stream insect communities. Environmental Pollution (Series A) 22: 19-28.
Davies, B., and Day, J. (1998). Vanishing waters. UCT Press, Cape Town, South Africa.
Deksissa, T., Ashton, P.J., and Vanrolleghem, P.A. (2003). Control options for river water quality improvement: A case study of TDS and inorganic nitrogen in the Crocodile River (South Africa). Water SA 29: 209-217.
De la Rey, P.A., Taylor, J.C., Laas, A., Van Rensburg, L., and Vosloo, A. (2004). Determining the possible application value of diatoms as indicators of general water quality: A comparison with SASS 5. Water SA 30: 325-332.
De la Rey, P.A., Van Rensburg, L., and Vosloo, A. (2008). On the use of diatom-based biological monitoring Part 1: A comparison of the response of diversity and aut- ecological diatom indices to water quality variables in the Marico-Molopo River catchment. Water SA 34: 53-60.
Dell’Uomo, A. (1996). Assessment of water quality of an Apennine river as a pilot study. In: Whitton, B.A., and E. Rott (Editors) Use of algae for monitoring rivers II. Institut für Botanik, Universitӓ t Innsbruck.
Delong, M.D., and Brusven, M.A. (1998). Macroinvertebrate community structure along the longitudinal gradient of an agriculturally impacted stream. Environmental Management 22: 445-457.
Dennis, H.J., and Nell, W.T. (2002). Precision irrigation in South Africa. Paper prepared for presentation at the 13th international farm management congress, Wageningen, The Netherlands, July 7-12, 2002. Centre for Agricultural Management, Faculty of Natural and Agricultural Sciences, University of the Free State, Bloemfontein, South Africa.
DeShon, J.E. (1995). Development and application of the Invertebrate Community Index (ICI). In: Davis, W.S., and T.P. Simon (Editors) Biological assessment and criteria: Tools for water resources planning and decision making. Lewis Publishers, Boca Raton, Florida.
Detenbeck, N.E., Batterman, S.L., Brady, V.J., Brazner, J.C., Snarski, V.M., Taylor, D.L., Thompson, J.A., and Arthur, J.W. (2000). A test of watershed classification systems for ecological risk assessment. Environmental Toxicology and Chemistry 19: 1174-1181.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 122 References
Dickens, C.W.S., and Graham, P.M. (2002). The South African Scoring System (SASS) Version 5, Rapid bioassessment method for rivers. African Journal of Aquatic Science 27: 1-10.
Dickens, C., Sekwele, R., Govender, V., Simpson, D., Coke, M., King, D., and Wadeson, R. (2007). Specialist study for the environmental impact assessment, Dube TradePort development proposal. Institute of Natural Resources, South Africa.
Dickens, C., Graham, M., De Winnaar, G., Hodgson, K., Tiba, F., Sekwele, R., Sikhakhane, S., De Moor, F., Barber-James, H., and Van Niekerk, K. (2008). The impacts of high winter flow releases from an impoundment on in-stream ecological processes. WRC Report No. 1307/1/08. Water Research Commission, Pretoria, South Africa.
Dixit, S.S., Dixit, A.S., and Smol, J.P. (1991). Multivariate environmental inferences based on diatom assemblages from Sudbury (Canada) lakes. Freshwater Biology 26: 251- 265.
Dixit, S.S., Smol, J.P., Kingston, J.C., and Charles, D.F. (1992). Diatoms: Powerful indicators of environmental change. Environmental Science and Technology 26: 22-33.
Dixit, S.S., and Smol, J.P. (1994). Diatoms as indicators in the Environmental Monitoring and Assessment Program-Surface Waters (EMAP-SW). Environmental Monitoring and Assessment 31: 275-306.
Dostine, P.L. (2002). Assessment of the ecological condition of freshwater streams in the Darwing region: Evidence from a survey of macroinvertebrate communities and water quality in the early dry season 2001. Natural Resource Management Division Conservation and Natural Resources Group. Department of Infrastructure, Planning and Environment. Northern Territory Government, Report No. 43/2002.
Dovciak, A.I., and Perry, J.A. (2002). In search of effective scales for stream management: Does agroecoregion, watershed, or their intersection best explain the variance in stream macroinvertebrate communities? Environmental Management 30: 365-377.
Dudgeon, D. (1994). The influence of riparian vegetation on macroinvertebrate community structure and functional organization in six new Guinea streams. Hydrobiologia 294: 65- 85.
Dunlop, J.E., Horrigan, N., McGregor, G., Kefford, B.J., Choy, S., and Prasad, R. (2008). Effect of spatial variation on salinity tolerance of macroinvertebrates in eastern Australia and implications for ecosystem protection trigger values. Environmental Pollution 151: 621-630.
DWAF (1996). South African water quality guidelines, Second Edition, Volume 7: Aquatic ecosystems. Pretoria, South Africa.
DWAF (1997). White paper on a national water policy for South Africa. Department of Water Affairs and Forestry, Pretoria, South Africa.
DWAF (2003). Assorted groundwater data and management spreadsheets. Geohydrology. Northern Cape, South Africa.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 123 References
DWAF (2004a). National water resources strategy, First Edition. Department of Water Affairs and Forestry, Pretoria, South Africa.
DWAF (2004b). Lower Vaal water management area: Internal Strategic Perspective (ISP). Prepared by PDNA, WRP Consulting Engineers (Pty) Ltd, WMB and Kwezi-V3 on behalf of the Directorate: National Water Resource Planning. DWAF Report No. P WMA 10/000/00/0304.
DWAF (2007). Rivers Database: Data Owners: Marie Watson (2003-07-17; 2003-02-13; 2005-01-25; Torangstad Road; Pampierstad); and Hermien Roux (2007-04-17; 2007- 04-16; Torangstad Road; Pampierstad).
DWAF (2008a). National water resource strategy, South Africa’s water situation and strategies to balance supply and demand. Lower Vaal WMA 10. www.dwaf.gov.za/Documents/Other/WMA/010_Lower%20Vaal.ppt. (Accessed August, 2008).
DWAF (2008b). Resource quality services, Water quality data for Lower Vaal water management area. Available from www.dwaf.gov.za/wqs/wms/data/WMA10_reg_WMS_nobor.htm (Accessed June, 2008).
Dye, P., and Jermain, C. (2004). Water use by black wattle (Acacia mearnsii): Implications for the link between removal of invading trees and catchment streamflow. South African Journal of Science 100: 40-44.
Eekhout, S., Brown, C.A., and King, J.M. (1996). National biomonitoring programme for riverine ecosystems: Technical considerations and protocol for the selection of reference and monitoring sites. NBP Report Series No.3. Institute for Water Quality Studies, Department of Water Affairs and Forestry, Pretoria, South Africa.
Ellington, R.G. (2003). Quantification of the impact of irrigation on the aquifer underlying the Vaalharts irrigation scheme. Submitted in fulfilment of the degree Magister Scientiae in the Faculty of Natural and Agricultural Sciences, Institute for Groundwater Studies, University of the Free State, South Africa.
Eloranta, P., and Soininen, J. (2002). Ecological status of Finnish rivers evaluated using benthic diatom communities. Journal of Applied Phycology 14: 1-7.
Elwood, J.W., Newbold, J.D., Trimble, A.F., and Stark, R.W. (1981). The limiting role of phosphorus in a woodland stream ecosystem: Effects of P enrichment on leaf decomposition and primary producers. Ecology 62: 146-158.
Fabre, A., Pinay, C., and Ruffinoni, C. (1996). Seasonal changes in inorganic and organic phosphorus in the soil of a riparian forest. Biogeochemistry 35: 419-432.
Ferreira, M.T., and Moreira, I. (1999). River plants from an Iberian basin and environmental factors influencing their distribution. Hydrobiologia 415: 101-107.
Flint, O.S. (Jr). (1991). Studies of neotropical caddisflies, XLV: The taxonomy, phenology and faunistics of the Trichoptera of Antioquia, Columbia. Smithsonian Contributions to Zoology 52: 1-113.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 124 References
Florentine, S.K., and Westbrooke, M.E. (2005). Invasion of the noxious weed Nicotiana glauca R. Graham after an episodic flooding event in the arid zone of Australia. Journal of Arid Environments 60: 531-545.
Florentine, S.K., Westbrooke, M.E., Gosney, K., Ambrose, G., and O’Keefe, M. (2006). The arid land invasive weed Nicotiana glauca R. Graham (Solanaceae): Population and soil seed bank dynamics, seed germination patterns and seedling response to flood and drought. Journal of Arid Environments 66: 218-230.
Fore, L.S., and Grafe, C. (2002). Using diatoms to assess the biological condition of large rivers in Idaho (U.S.A.). Freshwater Biology 47: 2015-2037.
Forsyth, G.G., Richardson, D.M., Brown, P.J., and Van Wilgen, B.W. (2004). A rapid assessment of the invasive status of Eucalyptus species in two South African provinces. South African Journal of Science 100: 75-77.
Fritz, S.C., Juggins, S., and Battarbee, R.W. (1993). Diatom assemblages and ionic characterization of lakes of the northern Great Plains, NA: A tool for reconstructing past salinity and climate fluctuations. Canadian Journal of Fisheries and Aquatic Science 50: 1844-1856.
Gerber, A., and Gabriel, M.J.M. (2002). Aquatic invertebrates of South African rivers, Version 1. Department of Water Affairs and Forestry, Pretoria, South Africa.
Gerber, A., Cilliers, C.J., Van Ginkel, C., and Glen, R. (2004). Easy identification of aquatic plants, A guide for the identification of water plants in and around South African impoundments. Department of Water Affairs and Forestry. Directorate: Resource Quality Services, Pretoria, South Africa.
Gilliam, J.W. (1994). Riparian wetlands and water quality. Journal of Environmental Quality 23: 896-900.
Godwin, D.C., and Miner, J.R. (1996). The potential of off-stream livestock watering to reduce water quality impacts. Bioresource Technology 58: 285-290.
Gombar, O., and Erasmus, C.J.H. (1976). Vaalharts Ontwateringsprojek, Technical Report GH2897. Department of Water Affairs.
Gregory, S.V., Swanson, F.J., McKee, W.A., and Cummins, K.W. (1991). An ecosystem perspective of riparian zones. BioScience 41: 540-551.
Growns, J.E., Chessman, B.C., Jackson, J.E., and Ross, D.G. (1997). Rapid assessment of Australian rivers using macroinvertebrates: Cost and efficiency of 6 methods of sample processing. Journal of the North American Benthological Society 16: 682-693.
Gruessner, B., and Watzin, M.C. (1995). Patterns of herbicide contamination in selected Vermont streams detected by enzyme immunoassay and gas chromatography/mass spectrometry. Environmental Science and Technology 29: 2806-2813.
Haase, R., and Nolte, U. (2008). The Invertebrate Species Index (ISI) for streams in southeast Queensland, Australia. Ecological Indicators 8: 599-613.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 125 References
Hall, R.L., and Smol, J.P. (1992). A weighted-averaging regression and calibration model for inferring total phosphorus concentration from diatoms in British Columbia (Canada) lakes. Freshwater Biology 27: 417-434.
Hancock, F.D. (1973). The ecology of the diatoms of the Klip River, southern Transvaal. Hydrobiologia 42: 243-284.
Harding, J.S., Young, R.G., Hayes, J.W., Shearer, K.A., and Stark, J.D. (1999). Changes in agricultural intensity and river health along a river continuum. Freshwater Biology 42: 345-357.
Harding, W.R., Archibald, C.G.M., and Taylor, J.C. (2005). The relevance of diatoms for water quality assessment in South Africa: A position paper. Water SA 31: 41-46.
Harrison, A.D. (1995). Northeastern Africa rivers and streams. In: Cushing, C.E., K.W. Cummins, and G.W. Minshall (Editors) Ecosystems of the world 22. River and stream ecosystems. Elsevier, Amsterdam, The Netherlands.
Hart, B.T., Bailey, P., Edwards, R., Hortle, K., James, K., McMahon, A., Meredith, C., and Swadling, K. (1991). A review of the salt sensitivity of the Australian freshwater biota. Hydrobiologia 210: 105-144.
Haycock, N.E., Pinay, G., and Walker, C. (1993). Nitrogen retention in river corridors: European perspectives. Ambio 22: 340-346.
Heckman, C.W. (1981). Long-term effects of intensive pesticide applications on the aquatic community in orchard drainage ditches near Hamburg, Germany. Archives of Environmental Contamination and Toxicology 10: 393-426.
Henderson, L. (1998). Invasive woody alien plants of the southern and south-western Cape region. Bothalia 28: 91-112.
Higgins, S.I., Richardson, D.M., and Cowling, R.M. (2001). Using a dynamic landscape model for planning the management of alien plant invasions. Ecological Applications 10: 1833-1848.
Higler, L.W., and Tolkamp, H.H. (1983). Hydropsychidae as bio-indicators. Environmental Monitoring and Assessment 3: 331-341.
Hill, B.H., Herlihy, A.T., Kaufmann, P.R., Stevenson, R.J., McCormick, F.H., and Johnson, C.B. (2000). The use of periphyton assemblage data as an index of biotic integrity. Journal of the North American Benthological Society 19: 50-67.
Hirst, H., Chaud, F., Delabie, C., Jüttner, I., and Ormerod, S.J. (2004). Assessing the short- term response of stream diatoms to acidity using inter-basin transplantations and chemical diffusing substrates. Freshwater Biology 49: 1072-1088.
Hodgkiss, I.J., and Law, C.Y (1985). Relating diatom community structure and stream water quality using species diversity indices. Water Pollution Control 84: 134-139.
Holmes, P.M., Richardson, D.M., Esler, K.J., Witkowski, E.T.F., and Fourie, S. (2005). A decision-making framework for restoring riparian zones degraded by invasive alien plants in South Africa. South African Journal of Science 101: 553-564.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 126 References
Horner, R.R., Welch, E.B., Seeley, M.R., and Jacoby, J.M. (1990). Responses of periphyton to changes in current velocity, suspended sediment and phosphorus concentration. Freshwater Biology 24: 215-232.
Horrigan, N., Dunlop, J.E., Kefford, B.J., and Zavahir, F. (2007). Acute toxicity largely reflects the salinity sensitivity of stream macroinvertebrates derived using field distributions. Marine and Freshwater Research 58: 178-186.
Jacobsen, D., and Encalada, A. (1998). The macroinvertebrate fauna of Ecuadorian high- land streams in the wet and dry season. Archiv für Hydrobiologie 142: 53-70.
James, K.R., and Hart, B.T. (1993). Effect of salinity on four freshwater macrophytes. Australian Journal of Marine and Freshwater Research 44: 769-777.
Jansen, A., and Robertson, A.I. (2001). Relationships between livestock management and the ecological condition of riparian habitats along an Australian floodplain river. The Journal of Applied Ecology 38: 63-75.
Janse van Vuuren, S. (2001). Environmental variables and the development of phytoplankton assemblages in the Vaal River between the Rand Water Barrage and Balkfontein. Unpublished PhD Thesis, PU for CHE, Potchefstroom, South Africa.
Janse van Vuuren, S., and Pieterse, A.J.H. (2005). The use of multivariate analysis as a tool to illustrate the influence of environmental variables on phytoplankton composition in the Vaal River, South Africa. African Journal of Aquatic Science 30: 17-28.
Jansson, R., Nilsson, C., Dynesius, M., and Anderson, E. (2000). Effects of river regulation on river-margin vegetation: A comparison of eight boreal rivers. Ecological Applications 10: 203-224.
Johnson, L.B., and Gage, S.H. (1997). Landscape approaches to the analyses of aquatic ecosystems. Freshwater Biology 37: 113-132.
Johnson, L.B., Richards, C., Host, G.H., and Arthur, J.W. (1997). Landscape influences on water chemistry in Midwestern stream ecosystems. Freshwater Biology 37: 193-208.
Johnson, W.C. (1998). Adjustment of riparian vegetation to river regulation in the Great Plains, USA. Wetlands 18: 608-618.
Jongman, R.H.G., Ter Braak, C.J.F., and Van Tongeren, O.F.R. (1995). Data analysis in community and landscape ecology. Cambridge University Press, Cambridge.
Jüttner, I., Sharma, S., Dahal, B.M., Ormerod, S.J., Chimonides, P.J., and Cox, E.J. (2003). Diatoms as indicators of stream quality in the Kathmandu Valley and Middle Hills of Nepal and India. Freshwater Biology 48: 2065-2084.
Karr, J.R. (1991). Biological integrity: A long-neglected aspect of water resource management. Ecological Applications 1: 66-84.
Karr, J.R. (1993). Defining and assessing ecological integrity: Beyond water quality. Environmental Toxicology and Chemistry 12: 1521-1531.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 127 References
Kay, W.R., Halse, S.A., Scanlon, M.D., and Smith, M.J. (2001). Distribution and environmental tolerances of aquatic macroinvertebrate families in the agricultural zone of southwestern Australia. Journal of the North American Benthological Society 20: 182-199.
Kefford, B.J., Paradise, T., Papas, P.J., Fields, E., and Nugegoda, D. (2003a). Assessment of a system to predict the loss of aquatic biodiversity from changes in salinity. Draft final report to Land and Water Australia. Project No. VCE 17. Department of Sustainability and Environment and RMIT University, Melbourne.
Kefford, B.J., Papas, P.J., and Nugegoda, D. (2003b). Relative salinity tolerance of macroinvertebrates from the Barwon River, Victoria, Australia. Marine and Freshwater Research 54: 755-765.
Kefford, B.J., Dalton, A., Palmer, C.G., and Nugegoda, D. (2004). The salinity tolerance of eggs and hatchlings of selected aquatic macroinvertebrates in south-east Australia and South Africa. Hydrobiologia 517: 179-192.
Kefford, B.J., and Nugegoda, D. (2005). Lack of critical salinity thresholds: Effects of salinity on growth and reproduction of the freshwater snail Physa acuta. Environmental Pollution 54: 755-765.
Kelly, M.G., and Whitton, B.A. (1995). The trophic diatom index: A new index for monitoring eutrophication in rivers. Journal of Applied Phycology 7: 433-444.
Kelly, M.G. (1998). Use of community-based indices to monitor eutrophication in European rivers. Environmental Conservation 25: 22-29.
Kelly, M.G., Cazaubon, A., Coring, E., Dell’Uomo, A., Ector, L., Goldsmith, B., Guasch, H., Hürlimann, J., Jarlman, A., Kawecka, B., Kwandrans, J., Laugaste, R., Lindstrom, E.A., Leitao, M., Marvan, P., Padisák, J., Pipp, E., Prygiel, J., Rott, E., Sabater, S., Van Dam, H., and Vizinet, J. (1998). Recommendations for the routine sampling of diatoms for water quality assessments in Europe. Journal of Applied Phycology 10: 215-224.
Kelly, M.G. (2003). Short term dynamics of diatoms in an upland stream and implications for monitoring eutrophication. Environmental Pollution 125: 117-122.
Kleynhans, C.J., Mackenzie, J., and Louw, D. (2006). River ecoclassification – Manual for ecostatus determination, Version 2, Module F: Riparian Vegetation Response Assessment Index (VEGRAI). Joint Water Research Commission and Department of Water Affairs and Forestry report, Pretoria, South Africa.
Klinkhamer, P.G.L., and De Jong, T.J. (1993). Cirsium Vulgare (Savi) Ten. The Journal of Ecology 81: 177-191.
Krammer, K., and Lange-Bertalot, H. (1986). Susswasserflora von Mitteleuropa, Bacillariophyceae. Teil I. Gustav Fischer Verlag, Jena.
Krammer, K., and Lange-Bertalot, H. (1988). Susswasserflora von Mitteleuropa, Bacillariophyceae. Teil II. Gustav Fischer Verlag, Jena.
Krammer, K., and Lange-Bertalot, H. (1991a). Susswasserflora von Mitteleuropa, Bacillariophyceae. Teil III. Gustav Fischer Verlag, Jena.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 128 References
Krammer, K., and Lange-Bertalot, H. (1991b). Susswasserflora von Mitteleuropa, Bacillariophyceae. Teil IV. Gustav Fischer Verlag, Jena.
Kremser, U., and Schnug, E. (2002). Impact of fertilizers on aquatic ecosystems and protection of water bodies from mineral nutrients. Landbauforschung Völkenrode 2: 81- 90.
Kriel, G.P. (2008). Urban water quality monitored, waste and pollution management. Urban Green File (UGF) 13: 30-33.
Kucuk, S. (2008). The effect of organic pollution on benthic macroinvertebrate fauna in the Kirmir Creek in the Sakarya Basin. ADÜ Ziraat Fakültesi Dergisi 5: 5-12.
Kutka, F.J., and Richards, C. (1996). Relating diatom assemblage structure to stream habitat quality. Journal of the North American Benthological Society 15: 469-480.
Kwandrans, J., Eloranta, P., Kawecka, B., and Wkryzsysztof, W. (1998). Use of benthic diatom communities to evaluate water quality in rivers of southern Poland. Journal of Applied Phycology 10: 193-201.
Kyriakeas, S.A., and Watzin, M.C. (2006). Effects of adjacent agricultural activities and watershed characteristics on stream macroinvertebrate communities. Journal of the American Water Resources Association (JAWRA) 42: 425-441.
Lavoie, I., Vincent, W.F., Pienitz, R., and Painchaud, J. (2004). Benthic algae as bioindicators of agricultural pollution in the streams and rivers of southern Québec (Canada). Aquatic Ecosystem Health and Management 7: 43-58.
Lecointe, C., Coste, M., and Prygiel, J. (1993). ‘OMNIDIA’: Sotfware for taxonomy, calculation of diatom indices and inventories management. Hydrobiologia 269/270: 509-513.
Leira, M., and Sabater, S. (2005). Diatom assemblages distribution in catalan rivers, NE Spain, in relation to chemical and physiographical factors. Water Research 39: 73-82.
Leland, H.V. (1995). Distribution of phytobenthos in the Yakima River basin, Washington, in relation to geology, land use, and other environmental factors. Canadian Journal of Fisheries and Aquatic Sciences 52: 1108-1129.
Leland, H.V., and Porter, S.D. (2000). Distribution of benthic algae in the upper Illinois River basin in relation to geology and land use. Freshwater Biology 44: 279-301.
Leland, H.V., Brown, L.R., and Mueller, D.K. (2001). Distribution of algae in the San Joaquin River, California, in relation to nutrient supply, salinity and other environmental factors. Freshwater Biology 46: 1139-1167.
Le Maitre, D.C., Versfeld, D.B., and Chapman, R.A. (2000). The impact of invading alien plants on surface water resources in South Africa: A preliminary assessment. Water SA 26: 397-408.
Lemly, A.D. (1982). Modification of benthic insect communities in polluted streams: Combined effects of sedimentation and nutrient enrichment. Hydrobiologia 87: 229-245.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 129 References
Lenat, D.R., Penrose, D.L., and Eagleson, K.W. (1981). Variable effects of sediment addition on stream benthos. Hydrobiologia 79: 187-194.
Lenat, D.R. (1984). Agriculture and stream water quality: A biological evaluation of erosion control practices. Environmental Management 8: 333-344.
Lenat, D.R. (1993). A biotic index for the southeastern United States: Derivation and list of tolerance values, with criteria for assigning water-quality ratings. Journal of the North American Benthological Society 12: 279-290.
Lenat, D.R., and Crawford, K. (1994). Effects of land use on water quality and aquatic biota of three north Carolina piedmont streams. Hydrobiologia 294: 185-199.
Lenoir, A., and Coste, M. (1996). Development of a practical diatom index of overall water quality applicable to the French National Water Board network. In: Whitton, B.A., and E. Rott (Editors) Use of algae for monitoring rivers II. Institut für Botanik. Universitӓ t Innsbruck.
Lobo, E.A., Bes, D., Tudesque, L., Ector, L. (2004). Water quality assessment of the Pardinho River, RS, Brazil, using epilithic diatom assemblages and faecal coliforms as biological indicators. Vie Milieu 54: 115-125.
Lohman, K., Jones, J.R., Baysinger-Daniel, C. (1991). Experimental evidence for nitrogen limitation in a northern Ozark stream. Journal of the North American Benthological Society 10: 14-23.
Luedtke, R.J., and Brusven, M.A. (1976). Effects of sand sedimentation on colonization of stream insects. Journal of the Fisheries Research Board of Canada 33: 1881-1886.
Malmqvist, B., and Rundle, S. (2002). Threats to the running water ecosystems of the world. Environmental Conservation 29: 134-153.
Margalef, R. (1951). Diversidad de especies en las comunidades naturales. Publicaciones del Instituto de Biologia Aplicada de., Barcelona 6: 59-72.
Martin, T.L., Kaushik, N.K., Trevors, J.T., and Whiteley, H.R. (1999). Review: Denitrification in temperate climate riparian zones. Water, Air, and Soil Pollution 111: 171-186.
McCormick, P.V., and Cairns, J. (Jr.). (1994). Algae as indicators of environmental change. Journal of Applied Phycology 6: 509-526.
McGarrigle, M.L. (1993). Aspects of river eutrophication in Ireland. Annals of Limnology 29: 355-364.
McMillan, P.H. (1998). An Integrated Habitat Assessment System (IHAS v2) for the rapid biological assessment of rivers and streams. A CSIR research project No. ENV-P-I 98132 for the water resources management programme, CSIR.
Merritt, R.W., Cummins, K.W., and Berg, M.E. (Editors). (1996). An introduction to the aquatic insects of North America, Third Edition. Kendall/Hunt Publishing Company, Dubuque, Iowa.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 130 References
Moore, J.W. (1977a). Seasonal succession of algae in a eutrophic stream in southern England. Hydrobiologia 53: 181-192.
Moore, J.W. (1977b). Seasonal succession of algae in rivers II. Examples from Highland Water, a small woodland stream. Hydrobiologia 80: 160-171.
Munn, M.D., Black, R.W., and Gruber, S.J. (2002). Response of benthic algae to environmental gradients in an agriculturally dominated landscape. Journal of the North American Benthological Society 21: 221-237.
Naiman, R.J., Decamps, H., and Pollock, M. (1993). The role of riparian corridors in maintaining regional biodiversity. Ecological Applications 3: 209-212.
Naiman, R.J., and Decamps, H. (1997). The ecology of interfaces: Riparian zones. Annual Review of Ecology and Systematics 28: 621-658.
Naiman, R.J., and Rodgers, K.H. (1997). Large animals and system-level characteristics in river corridors. BioScience 47: 521-529.
Nel, J.L., Richardson, D.M., Rouget, M., Mgidi, T.N., Mdzeke, N., Le Maitre, D.C., Van Wilgen, B.W., Schonegevel, L., Henderson, L., and Neser, S. (2004). A proposed classification of invasive alien plant species in South Africa: Towards prioritizing species and areas for management action. South African Journal of Science 100: 53- 64.
Nielsen, D.L., Brock, M.A., Rees, G.N., and Baldwin, D.S. (2003). Effects of increasing salinity on freshwater ecosystems in Australia. Australian Journal of Botany 51: 655- 665.
Oliveira, L.G. (1996). Aspectos da biologia de comunidades de insetos aquáticos da ordem Trichoptera Kirby, 1813, em córregos de cerrado do município de Pirenópolis, Estado de Goiás. Dissertação de doutorado Instituto de Biologia da Universidade de São Paulo, São Paulo.
Ongley, E.D. (1996). Control of water pollution from agriculture – FAO irrigation and drainage paper 55. Food and Agriculture Organization of the United Nations, Rome.
Osborne, L.L., and Kovacic, D.A. (1993). Riparian vegetated buffer strips in water quality restoration and stream management. Freshwater Biology 29: 243-258.
Oschwald, W.R. (1972). Sediment-water interactions. Journal of Environmental Quality 1: 360-366.
Palmer, C.G., Maart, B., Palmer, A.R., and O’Keeffe, J.H. (1996). An assessment of macroinvertebrate functional feeding groups as water quality indicators in the Buffalo River, eastern Cape Province, South Africa. Hydrobiologia 318: 153-164.
Pan, Y., Stevenson, R., Hill, B., Herlihy, A., and Collins, G. (1996). Using diatoms as indicators of ecological conditions in lotic systems: A regional assessment. Journal of the North American Benthological Society 15: 481-495.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 131 References
Pan, Y., Stevenson, R.J., Hill, B.H., Kaufmann, P.R., and Herlihy, A.T. (1999). Spatial patterns and ecological determinants of benthic algal assemblages in Mid-Atlantic streams, U.S.A. Journal of Phycology 35: 460-468.
Pandit, A.K. (1999). Freshwater ecosystems of the Himalaya. The Panthenon Publishing Group, New York, USA.
Pederson, C.L., and Vaultonburg, D.L. (1996). Metals concentrations in periphyton and sediments of the Embarras River and Brushy Fork, Douglas County, Illinois. Transactions of the Illinois State Academy of Science 89: 41-52.
Philibert, A., Gell, P., Newall, P., Chessman, B., and Bate, N. (2006). Development of diatom-based tools for assessing stream water quality in south-eastern Australia: Assessment of environmental transfer functions. Hydrobiologia 572: 103-114.
Pianka, E.R. (1970). On r- and K-selection. The American Naturalist 104: 592-597.
Pielou, E.C. (1966). Shannon’s formula as a measure of specific diversity: Its use and misuse. The American Naturalist 100: 463-466.
Pienitz, R., Smol, J., and Birks, H. (1995). Assessment of freshwater diatoms as quantitative indicators of past climate change in the Yukon and Northwest Territories, Canada. Journal of Paleolimnology 13: 21-49.
Pimentel, D., and Levitan, L. (1986). Pesticides: Amounts applied and amounts reaching pests. BioScience 36: 86-91.
Plafkin, J.L., Barbour, M.T., Porter, K.D., Gross, S.K., and Hughes, R.M. (1989). Rapid bioassessment protocols for use in streams and rivers: Benthic macroinvertebrates and fish. U.S. Environmental Protection Agency, Washington, DC. EPA/440/4-89-001.
Planty-Tabacchi, A.M. (1993). Invasions des corridors river-ains fluviaux par des espèces végétales d’origine étrangère. PhD Thesis, University of Paul Sabatier, Toulouse III, France.
Poff, N.L. (1997). Landscape filters and species traits: Towards mechanistic understanding and prediction in stream ecology. New concepts in stream ecology: Proceedings of a Symposium of the Journal of the North American Benthological Society 16: 391-409.
Potapova, M.G., and Charles, D.F. (2002). Benthic diatoms in USA rivers: Distributions along spatial and environmental gradients. Journal of Biogeography 29: 167-187.
Potapova, M., and Charles, D.F. (2003). Distribution of benthic diatoms in U.S. rivers in relation to conductivity and ionic composition. Freshwater Biology 48: 1311-1328.
Rapport, D.J., Gaudet, C., Karr, J.R., Baron, J.S., Bohlem, C., Jackson, W., Jones, B., Naiman, R.J., Norton, B., and Pollock, M.M. (1998). Evaluating landscape health: Integrating societal goals and biophysical process. Journal of Environmental Management 53: 1-15.
Raschke, A.M., and Burger, A.E.C. (1997). Risk assessment as a management tool used to assess the effect of pesticide use in an irrigation system, situated in a semi-desert region. Archives of Environmental Contamination and Toxicology 32: 42-49.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 132 References
Read, M.G., and Barmuta, L.A. (1999). Comparisons of benthic communities adjacent to riparian native eucalypt and introduced willow vegetation. Freshwater Biology 42: 359- 374.
Reavie, E.D., Hall, R.I., and Smol, J.P. (1995). An expanded weighted-averaging model for inferring past total phosphorus concentrations from diatom assemblages in eutrophic British Columbia (Canada) lakes. Journal of Paleolimnology 14: 49-67.
Reid, M.A., Tibby, J.C., Penny, D., and Gell, P.A. (1995). The use of diatoms to assess past and present water quality. Australian Journal of Ecology 20: 57-64.
Rejmánek, M., and Richardson, D.M. (1996). What attributes make some plant species more invasive? Ecology 77: 1655-1661.
RHP (2005). State-of-Rivers Report: Monitoring and managing the ecological state of rivers in the Crocodile (West) Marico water management area. Department of Environmental Affairs and Tourism, Pretoria, South Africa.
Richards, C., Johnson, L.B., and Host, G.E. (1996). Assessing the influence of landscape- scale catchment features on physical habitat and stream biota. Canadian Journal of Fisheries and Aquatic Science 53: 295-311.
Richardson, D.M., Macdonald, I.A.W., Hoffmann, J.H., and Henderson, L. (1997). Alien plant invasion. In: Cowling, R.M., D.M. Richardson, and S.M. Pierce (Editors) Vegetation of Southern Africa. Cambridge University Press, Cambridge.
Richardson, D.M., and Van Wilgen, B.W. (2004). Invasive alien plants in South Africa: How well do we understand the ecological impacts? South African Journal of Science 100: 45-52.
Robertson, P. (2006). The influence of agricultural land use and the mediating effect of riparian vegetation on water quality in Jones Creek, Alberta, Canada. Enquiries Journal of Interdisciplinary Studies for High School Students 2: 13-24.
Rosén, P., Hall, R., Korsman, T., and Renberg, I. (2000). Diatom transfer-functions for quantifying past air temperature, pH and total organic carbon concentration from lakes in northern Sweden. Journal of Paleolimnology 24: 109-123.
Rosenberg, D.M., and Resh, V.H. (1993). Introduction to freshwater biomonitoring and benthic macroinvertebrates. In: Rosenberg, D.M., and V.H. Resh (Editors) Freshwater biomonitoring and benthic macroinvertebrates. Chapman and Hall, USA.
Rott, E., Duthie, H.C., and Pipp, E. (1998). Monitoring organic pollution and eutrophication in the Grand River, Ontario, by means of diatoms. Canadian Journal of Fisheries and Aquatic Sciences 55: 1443-1453.
Round, F.E., Crawford, R.M., and Mann, D.G. (1990). The diatoms: Biology and morphology of the genera. Cambridge University Press, Cambridge.
Round, F.E. (1991). Diatoms in river water-monitoring studies. Journal of Applied Phycology 3: 129-145.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 133 References
Round, F.E. (1993). A review and methods for the use of epilithic diatoms for detecting and monitoring changes in river water quality. HMSO, London.
Round, F.E. (2001). How large is a river? The view from a diatom. Diatom Research 16: 105-108.
Roy, A.H., Rosemond, A.D., Leigh, D.S., Paul, M.J., and Wallace, J.B. (2003). Habitat- specific responses of stream insects to land cover disturbance: Biological consequences and monitoring implications. Journal of the North American Benthological Society 22: 292-307.
RSA (Republic of South Africa) (1997). The Water Services Act (Act No. 108 of 1997). Government Gazette, Cape Town, South Africa.
RSA (1998a). The National Water Act (Act No. 36 of 1998). Government Gazette, Cape Town, South Africa.
RSA (1998b). The National Environmental Management Act (Act No. 107 of 1998). Government Gazette, Cape Town, South Africa.
Ryan, P.A. (1991). Environmental effects of sediment on New Zealand streams: A review. New Zealand Journal of Marine and Freshwater Research 25: 207-221.
Ryder, G.I. (1989). Experimental studies on the effects of fine sediment on lotic invertebrates. Unpublished PhD thesis. Department of Zoology, University of Otago, Dunedin, New Zealand.
Sabater, S., and Roca, J.R. (1992). Ecological and biogeographical aspects of diatom distribution in Pyrenean springs. British Phycological Journal 27: 203-213.
Sandin, L., and Johnson, R.K. (2000). The statistical power of selected indicator metrics using macroinvertebrates for assessing acidification and eutrophication of running waters. Hydrobiologia 422/423: 233-243.
Shafroth, P.B., Stromberg, J.C., and Patten, D.T. (2002). Riparian vegetation response to altered disturbance and stress regimes. Ecological Applications 12: 107-123.
Shepard, R.B., and Minshall, G.W. (1981). Nutritional value of lotic species compared with allochtonous materials. Archiv für Hydrobiologie 90: 467-488.
Shieh, S-H., and Yang, P-S. (2000). Community structure and functional organization of aquatic insects in an agricultural mountain stream of Taiwan: 1985-1986 and 1995- 1996. Zoological Studies 39: 191-202.
Skoroszewski, R., and De Moor, F. (1999). Consulting services for the establishment and monitoring of the instream flow requirements for river courses downstream of LHWP dams. Specialist Report – Macroinvertebrates. Report No. LHDA 648-F-17.
Smith, M.J., Kay, W.R., Edward, D.H.D., Papas, P.J., Richardson, K. STJ., Simpson, J.C., Pinder, A.M., Cale, D.J., Horwitz, P.H.J., Davis, J.A., Yung, F.H., Norris, R.H., and Halse, S.A. (1999). AusRivAS: Using macroinvertebrates to assess ecological condition of rivers in western Australia. Freshwater Biology 41: 269-282.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 134 References
Soininen, J. (2004). Benthic diatom community structure in boreal streams, Distribution patterns along environmental and spatial gradients. Academic dissertation in limnology. Department of Biological and Environmental Sciences, University of Helsinki, Finland. ISBN 952-10-1937-9.
Stevenson, R.J. (1984). Epilithic and epipelic diatoms in the Sandusky River, with emphasis on species diversity and water pollution. Hydrobiologia 114: 161-175.
Stevenson, R.J. (1997). Scale-dependent determinants and consequences of benthic algal heterogeneity. Journal of the North American Benthological Society 16: 248-262.
Stewart, J.S., Wang, L., Lyons, J., Horwatich, J.A., and Bannerman, R. (2001). Influences of watershed, riparian-corridor, and reach-scale characteristics on aquatic biota in agricultural watersheds. Journal of the American Water Resources Association 37: 1475-1488.
Stone, M.L., Whiles, M.R., Webber, J.A., Williard, K.W.J., and Reeve, J.D. (2005). Macroinvertebrate communities in agriculturally impacted southern Illinois streams: Patterns with riparian vegetation, water quality, and in-stream habitat quality. Journal of Environmental Quality 34: 907-917.
Strauss, J.S. (1991). ‘n Landbou-ekonomiese evaluasie van alternatiewe besproeiingstelsels in die Vaalhartsbesproeiingsgebied. University of the Free State, Bloemfontein, South Africa.
Tabacchi, E., Correll, D.L., Hauer, R., Pinay, G., Planty-Tabacchi, A.M., and Wissmar, R.C. (1998). Development, maintenance and role of riparian vegetation in the river landscape. Freshwater Biology 40: 497-516.
Taylor, J.C., De la Rey, P.A., and Van Rensburg, L. (2005a). Recommendations for the collection, preparation and enumeration of diatoms from riverine habitats for water quality monitoring in South Africa. African Journal of Aquatic Science 30: 65-75.
Taylor, J.C., Harding, W.R., Archibald, C.G.M., and Van Rensburg, L. (2005b). Diatoms as indicators of water quality in the Jukskei-Crocodile river system in 1956 and 1957, A re- analysis of diatom count data generated by BJ Cholnoky. Water SA 31: 237-246.
Taylor, J.C., Janse van Vuuren, M.S., and Pieterse, A.J.H. (2007a). The application and testing of diatom-based indices in the Vaal and Wilge Rivers, South Africa. Water SA 33: 51-60.
Taylor, J.C., Prygiel, J., Vosloo, A., De la Rey, P.A., and Van Rensburg, L. (2007b). Can diatom-based pollution indices be used for biomonitoring in South Africa? A case study of the Crocodile West and Marico water management area. Hydrobiologia 592: 455- 464.
Taylor, J.C., Harding, W.R., and Archibald, C.G.M. (2007c). A methods manual for the collection, preparation and analysis of diatom samples, Version 1.0. WRC Report No. TT 281/07. Water Research Commission, Pretoria, South Africa.
Taylor, J.C., Harding, W.R., and Archibald, C.G.M. (2007d). An illustrated guide to some common diatom species from South Africa. WRC Report No. TT 282/07. Water Research Commission, Pretoria, South Africa.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 135 References
Ter Braak, C.J.F., and Šmilauer, P. (2002). CANOCO reference manual and Canodraw for Windows user’s guide: Software for canonical community ordination (Version 4.5). Microcomputer Power, New York, USA.
Thiere, G., and Schulz, R. (2004). Runoff-related agricultural impact in relation to macroinvertebrate communities of the Lourens River, South Africa. Water Research 38: 3092-3102.
Thirion, C. (2007). River ecoclassification – Manual for ecostatus determination, Version 2, Module E: Macroinvertebrate Response Assessment Index (MIRAI) in river ecoclassification: Manual for ecostatus determination (Version 2). Joint Research Commission and Department of Water Affairs and Forestry report, Pretoria, South Africa.
Todd, C.P. (2000). Macroinvertebrate functional feeding groups as a method of assessing the ecological integrity of lotic ecosystems. Masters Dissertation. University of the Orange Free State, Free State, South Africa.
Townsend, C.R., and Hildrew, A.G. (1994). Species traits in relation to a habitat templet for river systems. Freshwater Biology 31: 265-275.
Townsend, C.R., Arbuckle, C.J., Crowl, T.A., and Scarsbrook, M.R. (1997). The relationship between land use and physicochemistry, food resources and macroinvertebrate communities in tributaries of the Taieri River, New Zealand: A hierarchically scaled approach. Freshwater Biology 37: 177-191.
Van Dam, H., Mertens, A., and Sinkeldam, J. (1994). A coded checklist and ecological indicator values of freshwater diatoms from the Netherlands. Netherlands Journal of Aquatic Ecology 28: 177-133.
Van Heerden, P.S., Crosby, C.T., and Crosby, C.P. (2001). Using SAPWAT to estimate water requirements of crops in selected irrigation areas managed by the Orange-Vaal and Orange-Riet water user associations. Report No. TT163/01. Water Research Commission, Pretoria.
Vannote, R.L., Minshall, G.W., Cummins, K.W., Sedell, J.R., and Cushing, C.E. (1980). The river continuum concept. Canadian Journal of Fisheries and Aquatic Science 37: 130- 137.
Van Rensburg, L.D., Strydom, M.G., Du Preez, C.C., Bennie, A.T.P., Le Roux, P.A.L., and Pretorius, J.P. (2008). Prediction of salt balances in irrigated soils along the lower Vaal River, South Africa. Water SA 34: 11-17.
Van Tonder, G., and Dennis, I. (2000). Catchment, aquifer and groundwater balance. Course on groundwater and the national water and water services acts. Institute for Groundwater Studies, University of the Free State, Bloemfontein.
Van Wilgen, B.W., Cowling, R.M., and Burgers, C.J. (1996). Valuation of ecosystem services, A case study from South African fynbos ecosystems. BioScience 46: 184-189.
Van Wyk, B., and Van Wyk, P. (1997). Field guide to trees of Southern Africa, featuring more than 1000 species. Struik, Cape Town, South Africa.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 136 References
Van Wyk, E., Breen, C.M., Roux, D.J., Rogers, K.H., Sherwill, T., and Van Wilgen, B.W. (2006). The ecological reserve: Towards a common understanding for river management in South Africa. Water SA 32: 403-409.
Van Wyk, E., and Van Oudtshoorn, F. (2006). Guide to grasses of Southern Africa, Second Edition. BRIZA, Pretoria, South Africa.
Vinson, M.R., and Hawkins, C.P. (1998). Biodiversity of stream insects: Variation at local basin and regional scales. Annual Review of Entomology 43: 271-293.
Vitousek, P.M. (1990). Biological invasions and ecosystem processes: Towards an integration of population biology and ecosystem studies. Oikos 57: 7-13.
Walsh, G. (2008). Diatom, macroinvertebrate and riparian vegetation community structure responses in agriculturally impacted rivers. Unpublished MSc. Dissertation. University of Johannesburg, Johannesburg, South Africa.
Warwick, N.W.M., and Bailey, P.C.E. (1997). The effect of increasing salinity on the growth and ion content of three non-halophytic wetland macrophytes. Aquatic Botany 58: 73- 88.
Warwick, N.W.M., and Bailey, P.C.E. (1998). The effect of time exposure to NaCl on leaf demography and growth of two non halophytic wetland macrophytes, Potamogeton tricarinatus F.Muell. and A.Benn. Ex A.Benn. and Triglochin procera R.Br. Aquatic Botany 62: 19-31.
Watanabe, T., Asai, K., and Houki, A. (1988). Numerical index of water quality using diatom assemblages. In: Yasuno, M., and B.A. Whitton (Editors) Biological monitoring of environmental pollution. Tokai University Press, Tokyo.
Waters, T.F. (1995). Sediment in streams: Sources, biological effects, and control. American Fisheries Society, Monograph 7, Bethesda, Maryland.
Webb, R.H., and Leake, S.A. (2006). Ground-water surface-water interactions and long-term change in riverine riparian vegetation in the southwestern United States. Journal of Hydrology 320: 302-323.
Weigel, B.M., Henne, L.J., and Martinez-Rivera, L.M. (2002). Macroinvertebrate-based index of biotic integrity for protection of streams in west-central Mexico. Journal of the North American Benthological Society 21: 686-700.
Welch, E.B., Quinn, J.M., and Hickey, C.W. (1992). Periphyton biomass related to point- source nutrient enrichment in seven New Zealand streams. Water Research 26: 669- 675.
Wendt-Rasch, L., Friberg-Jensen, U., Woin, P., and Christoffersen, K. (2003). Effects of the pyrethroid insecticide cypermethrin on a freshwater community studied under field conditions II, Direct and indirect effects on the species composition. Aquatic Toxicology 63: 373-389.
Wilhm, T.P., and Dorris, T.C. (1968). Biological parameters for water quality criteria. Biological Science 18: 477-481.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 137 References
Williams, W.D., Taaffe, R.G., and Boulton, A.J. (1991). Longitudinal distribution of macroinvertebrates in two rivers subject to salinization. Hydrobiologia 210: 151-160.
Wilson, S.E., Cumming, B.F., and Smol, J.P. (1994). Diatom-salinity relationships in 111 lakes from the Interior Plateau of British Columbia, Canada: The development of diatom-based models for paleosalinity and paleoclimatic reconstructions. Journal of Paleolimnology 12: 197-221.
Winter, J.G., and Duthie, H.C. (2000). Stream biomonitoring at an agricultural test site using benthic algae. Canadian Journal of Botany 78: 1319-1325.
Wohl, N.E., and Caline, R.F. (1996). Relations among riparian grazing, sediment loads, macroinvertebrates, and fishes in three central Pennsylvania streams. Canadian Journal of Fisheries and Aquatic Sciences 53: 260-266.
Zelinka, M., and Marvan, P. (1961). Zur Präzisierung der biologischen Klassifikation der Reinheit fliessender Gewässer. Archiv für Hydrobiologie 57: 389-407.
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 138
Appendix A: Site Aerial Photos
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 139 Appendix A
HR 1
Figure A1: Aerial photo of the relative reference site HR 1 (Google Earth, 2008).
HR 2
Figure A2: Aerial photo of the agricultural site HR 2 (Google Earth, 2008).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 140 Appendix A
HR 3
Figure A3: Aerial photo of the agricultural site HR 3 (Google Earth, 2008).
HR 4
Figure A4: Aerial photo of the agricultural site HR 4 (Google Earth, 2008).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 141 Appendix A
HR 5
Figure A5: Aerial photo of the agricultural site HR 5 (Google Earth, 2008).
VR 2 VR 1
Figure A6: Aerial photo of the relative reference site VR 1 and the agricultural site VR 2 (Google Earth, 2008).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 142
Appendix B: Water Quality and Diatoms
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 143 Appendix B
Figure B1: Historical water quality graph of available water quality data for the Harts River downstream of Taung Dam, in the vicinity of the relative reference site HR 1 (DWAF, 2008b).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 144 Appendix B
Figure B2: Historical water quality graph of available water quality data for the Harts River at Espagsdrift, in the vicinity of the agricultural site HR 4 (DWAF, 2008b).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 145 Appendix B
Figure B3: Historical water quality graph of available water quality data for the Harts River at the confluence with the Vaal River, in the vicinity of the agricultural site HR 5 (DWAF, 2008b).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 146 Appendix B
Figure B4: Historical water quality graph of water quality data for the Vaal River upstream of the Harts confluence, downstream of the relative reference site VR 1 (DWAF, 2008b).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 147 Appendix B
Table B1: Historical water quality data for the relative reference site HR 1. Physical Water Quality Parameters Monitored Values Conductivity (mS/m) 30.0 Dissolved Oxygen (mg/l) 5.33 (%) 70.4 pH 8.08 Total Dissolved Solids (mg/l) 140.0 Temperature 28.9 Turbidity (NTU) 8.5 DWAF (2007) – Rivers Database: Owner of data – Marie Watson (2005-01-25).
Table B2: Historical water quality data for the agricultural site HR 3. Physical Water Quality Parameters Monitored Values Conductivity (mS/m) 84.0 Dissolved Oxygen (mg/l) 7.01 (%) 88.0 pH 7.5 Total Dissolved Solids (mg/l) 420.0 Temperature 26.9 Turbidity (NTU) 26.0 DWAF (2007) – Rivers Database: Owner of data – Marie Watson (2003-02-13).
Table B3: Historical water quality data for the agricultural site HR 3. Physical Water Quality Parameters Monitored Values Conductivity (mS/m) 102.0 Dissolved Oxygen (mg/l) 4.19 (%) 54.1 pH 7.8 Total Dissolved Solids (mg/l) 510.0 Temperature 27.7 Turbidity (NTU) 25.0 DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2005-01-25).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 148 Appendix B
Table B4: Species list for low (L) flow indicating species abundances, names and acronyms taken from OMNIDIA database. Species Abbreviation HR 1L HR 2L HR 3L HR 4L HR 5L VR 1L VR 2L ACHNANTHIDIUM F.T. Kützing 1844 ACHD 78 88 6 0 1 91 6 Achnanthidium eutrophilum (Lange-Bertalot)Lange-Bertalot ADEU 10 0 0 0 0 0 0 Achnanthidium minutissimum (Kütz.) Czarnecki ADMI 4 35 0 0 0 0 0 Amphora pediculus (Kutzing) Grunow APED 2 3 46 34 2 0 0 Aulacoseira granulata (Ehr.) Simonsen AUGR 0 0 1 2 0 0 0 Amphora veneta Kutzing AVEN 0 0 1 0 0 0 0 Craticula ambigua (Ehrenberg) Mann CAMB 0 1 0 0 0 0 0 Cyclostephanos dubius (Fricke) Round CDUB 1 7 7 2 0 0 0 Cyclostephanos invisitatus(Hohn & Hellerman)Theriot Stoermer & Hakans CINV 0 15 21 3 0 0 0 Cymbella kappii(Cholnoky) Cholnoky CKPP 87 10 0 0 0 11 1 Cyclotella meneghiniana Kutzing CMEN 0 0 1 2 0 0 0 Cocconeis pediculus Ehrenberg CPED 0 0 0 6 332 3 0 Cocconeis placentula Ehrenberg var. placentula CPLA 4 0 5 4 0 26 18 Cocconeis placentula Ehrenberg var.euglypta (Ehr.) Grunow CPLE 0 0 10 9 0 0 0 Craticula cuspidata (Kutzing) Mann CRCU 0 0 1 0 0 0 0 Cymbella tumida (Brebisson)Van Heurck CTUM 0 0 0 0 0 1 7 Diatoma vulgaris Bory 1824 DVUL 0 0 0 27 0 2 0 Epithemia adnata (Kutzing) Brebisson EADN 0 0 0 0 0 1 18 Encyonopsis microcephala (Grunow) Krammer ENCM 198 117 2 2 43 119 281 Eolimna subminuscula (Manguin) Moser Lange-Bertalot & Metzeltin ESBM 0 0 78 9 0 0 0 Epithemia sorex Kutzing ESOR 0 1 0 0 0 0 8 Encyonopsis subminuta Krammer & Reichardt ESUM 0 0 0 0 0 1 11 Fragilaria biceps (Kutzing) Lange-Bertalot FBCP 0 6 2 0 0 0 0 Fragilaria capucina Desmazieres var.vaucheriae(Kutzing)Lange-Bertalot FCVA 0 14 0 0 0 14 0 Fragilaria construens (Ehr.) Grunow f.venter (Ehr.) Hustedt FCVE 0 0 0 0 0 8 1 Fragilaria tenera (W.Smith) Lange-Bertalot FTEN 3 0 0 0 0 0 0 Gomphonema acuminatum Ehrenberg GACU 0 0 0 0 0 0 1 Gomphonema affine Kutzing GAFF 0 0 0 0 0 55 2 Gomphonema gracile Ehrenberg GGRA 2 0 0 0 0 0 5 Gomphonema italicum Kützing GITA 0 1 0 0 0 2 0 Gomphonema laticollum Reichardt GLTC 0 0 0 0 0 2 0 GOMPHONEMA C.G. Ehrenberg GOMP 4 6 0 1 0 31 3 Gomphonema parvulum (Kützing) Kützing var. parvulum f. parvulum GPAR 0 18 4 0 3 15 1
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 149 Appendix B
Table B4 (cont.): Species list for low (L) flow indicating species abundances, names and acronyms taken from OMNIDIA database. Species Abbreviation HR 1L HR 2L HR 3L HR 4L HR 5L VR 1L VR 2L Gomphonema pumilum (Grunow) Reichardt & Lange-Bertalot GPUM 0 1 0 0 0 0 0 Gyrosigma rautenbachiae Cholnoky GYRO 0 0 0 1 0 0 0 Mastogloia smithii Thwaites MSMI 0 0 0 0 2 1 15 Melosira varians Agardh MVAR 0 0 0 19 0 0 0 Nitzschia amphibia Grunow f.amphibia NAMP 1 0 0 0 0 0 0 NAVICULA J.B.M. Bory de St. Vincent NAVI 0 1 0 42 0 0 0 Navicula capitatoradiata Germain NCPR 7 4 0 0 0 0 0 Navicula cryptotenella Lange-Bertalot NCTE 19 22 16 12 0 0 0 Navicula cryptotenelloides Lange-Bertalot NCTO 0 0 0 0 0 1 0 Nitzschia dissipata(Kutzing)Grunow var.dissipata NDIS 0 24 0 0 0 0 0 Navicula erifuga Lange-Bertalot NERI 0 0 0 7 0 0 0 Nitzschia filiformis (W.M.Smith) Van Heurck var. filiformis NFIL 0 0 0 0 0 0 2 Navicula gregaria Donkin NGRE 0 0 78 13 0 0 0 Nitzschia frustulum(Kutzing)Grunow var.frustulum NIFR 1 3 44 28 0 0 0 NITZSCHIA A.H. Hassall NITZ 3 19 16 0 0 0 0 Nitzschia linearis(Agardh) W.M.Smith var.linearis NLIN 0 0 0 14 0 0 0 Navicula recens (Lange-Bertalot) Lange-Bertalot NRCS 0 0 16 0 0 0 0 Navicula rostellata Kutzing NROS 0 1 5 8 0 0 0 Nitzschia sigma(Kutzing)W.M.Smith NSIG 0 0 1 14 0 0 0 Navicula symmetrica Patrick NSYM 0 1 5 0 0 0 0 Navicula tripunctata (O.F.Müller) Bory NTPT 0 0 0 6 0 0 0 Nitzschia umbonata(Ehrenberg)Lange-Bertalot NUMB 0 0 0 5 0 0 0 Navicula vandamii Schoeman & Archibald var. vandamii NVDA 1 0 0 0 0 0 0 Pleurosigma salinarum (Grunow) Cleve & Grunow PSAL 0 0 0 2 0 0 0 Pseudostaurosira brevistriata (Grun.in Van Heurck) Williams & Round PSBR 0 0 0 0 0 23 19 Rhoicosphenia abbreviata (C.Agardh) Lange-Bertalot RABB 0 0 12 3 1 0 13 Reimeria uniseriata Sala Guerrero & Ferrario RUNI 2 0 0 4 23 0 0 Stephanodiscus agassizensis Hakansson & Kling SAGA 0 0 4 4 1 1 2 Surirella brebissonii Krammer & Lange-Bertalot var.brebissonii SBRE 0 3 12 35 0 0 0 Staurosira elliptica (Schumann) Williams & Round SELI 0 0 0 12 0 0 0 Surirella ovalis Brebisson SOVI 0 0 1 1 0 0 0 Staurosirella pinnata (Ehr.) Williams & Round SPIN 0 0 6 5 0 0 0 Tryblionella apiculata Gregory TAPI 0 1 5 65 0 0 0 Tabularia fasciculata (Agardh)Williams et Round TFAS 0 0 0 0 12 0 6 Tryblionella gracilis w. Smith TGRL 0 0 0 1 0 0 0 Tryblionella hungarica (Grunow) D.G. Mann THUN 0 0 1 0 0 0 0
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 150 Appendix B
Table B5: Species list for high (H) flow indicating species abundances, names and acronyms taken from OMNIDIA database. Species Abbreviation HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H ACHNANTHIDIUM F.T. Kützing 1844 ACHD 111 12 6 0 1 169 44 Amphora pediculus (Kutzing) Grunow APED 67 5 5 58 2 1 0 Aulacoseira granulata (Ehr.) Simonsen var.angustissima (O.M.)Simonsen AUGA 0 0 0 0 1 4 0 Aulacoseira granulata (Ehr.) Simonsen AUGR 0 4 5 0 3 0 0 Amphora veneta Kutzing AVEN 0 0 2 0 0 0 0 CYCLOSTEPHANOS F.E. Round CCST 1 0 0 0 0 0 0 Cyclostephanos dubius (Fricke) Round CDUB 0 0 2 1 0 0 0 Cymbella hustedtii Krasske var.hustedtii CHUS 0 0 0 0 0 2 0 Cyclostephanos invisitatus(Hohn & Hellerman)Theriot Stoermer & Hakans CINV 0 2 0 0 0 0 0 Cymbella kolbei Hustedt var. kolbei CKOL 1 0 0 0 0 3 0 Cymbella kappii(Cholnoky) Cholnoky CKPP 1 0 0 0 0 0 0 Cyclotella meneghiniana Kutzing CMEN 0 2 9 1 14 0 20 Cyclotella ocellata Pantocsek COCE 0 1 0 2 0 0 0 COCCONEIS C.G. Ehrenberg 1837 COCO 0 0 0 0 1 0 0 Cocconeis pediculus Ehrenberg CPED 0 0 15 0 10 5 0 Cocconeis placentula Ehrenberg var. placentula CPLA 1 4 4 11 2 3 5 Cocconeis placentula Ehrenberg var.euglypta (Ehr.) Grunow CPLE 0 1 5 24 2 2 0 Cymbella turgidula Grunow 1875 in A.Schmidt & al. var. turgidula CTGL 2 0 0 0 0 4 0 Cymbella tumida (Brebisson)Van Heurck CTUM 18 1 0 0 0 1 1 DIPLONEIS C.G. Ehrenberg ex P.T. Cleve DIPL 0 0 1 0 0 0 0 Denticula kuetzingii Grunow var.kuetzingii DKUE 0 1 0 0 0 0 0 Diatoma vulgaris Bory 1824 DVUL 0 1 2 0 0 0 0 Epithemia adnata (Kutzing) Brebisson EADN 0 5 0 0 0 0 1 Encyonopsis microcephala (Grunow) Krammer ENCM 21 53 7 2 43 73 21 Eolimna subminuscula (Manguin) Moser Lange-Bertalot & Metzeltin ESBM 1 1 10 9 0 0 0 Epithemia sorex Kutzing ESOR 1 0 0 0 0 1 4 Encyonopsis subminuta Krammer & Reichardt ESUM 0 0 0 0 0 45 5 Fragilaria biceps (Kutzing) Lange-Bertalot FBCP 3 0 0 0 0 0 0 Fragilaria capucina Desmazieres var.vaucheriae(Kutzing)Lange-Bertalot FCVA 3 1 2 0 0 1 0 Fallacia insociabilis (Krasske) D.G. Mann FINS 2 0 0 0 0 0 0 Fragilaria tenera (W.Smith) Lange-Bertalot FTEN 0 0 0 0 0 0 7 Fallacia tenera (Hustedt) Mann in Round FTNR 0 1 0 0 0 0 7 Fragilaria ulna(Nitzsch.)Lange-Bertalot var.acus(Kutz.)Lange-Bertalot FUAC 15 14 5 4 0 0 0 Gomphonema gracile Ehrenberg GGRA 0 0 0 0 3 1 0 GOMPHONEMA C.G. Ehrenberg GOMP 0 1 0 0 0 0 0 Gomphonema parvulum (Kützing) Kützing var. parvulum f. parvulum GPAR 54 5 32 4 1 1 8 Gomphonema pumilum (Grunow) Reichardt & Lange-Bertalot GPUM 1 2 0 0 0 0 0 Gyrosigma rautenbachiae Cholnoky GYRO 3 0 1 2 0 0 0 Mastogloia smithii Thwaites MSMI 1 0 0 0 6 18 241
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 151 Appendix B
Table B5 (cont.): Species list for high (H) flow indicating species abundances, names and acronyms taken from OMNIDIA database. Species Abbreviation HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H Melosira varians Agardh MVAR 0 0 4 1 0 0 0 NAVICULA J.B.M. Bory de St. Vincent NAVI 58 138 126 34 13 0 0 Navicula capitatoradiata Germain NCPR 2 0 0 0 0 0 0 Navicula cryptotenella Lange-Bertalot NCTE 0 0 0 7 9 4 0 Nitzschia desertorum Hustedt NDES 0 1 3 0 0 0 0 Nitzschia dissipata(Kutzing)Grunow var.dissipata NDIS 3 1 0 0 0 0 0 Navicula erifuga Lange-Bertalot NERI 0 0 1 15 5 0 2 Nitzschia filiformis (W.M.Smith) Van Heurck var. filiformis NFIL 10 2 0 0 22 0 11 Navicula gregaria Donkin NGRE 0 0 1 0 0 0 0 Nitzschia frustulum(Kutzing)Grunow var.frustulum NIFR 3 32 21 98 6 0 0 NITZSCHIA A.H. Hassall NITZ 20 34 54 0 16 0 14 Navicula kotschyi Grunow NKOT 1 0 0 0 0 0 0 Nitzschia palea (Kutzing) W.Smith NPAL 0 0 1 0 0 0 0 Navicula recens (Lange-Bertalot) Lange-Bertalot NRCS 0 0 1 21 8 0 0 Navicula rostellata Kutzing NROS 2 11 9 8 0 0 0 Nitzschia sigma(Kutzing)W.M.Smith NSIG 1 0 2 2 0 0 0 Navicula subrhynchocephala Hustedt NSRH 0 0 0 0 0 1 0 Navicula vandamii Schoeman & Archibald var. vandamii NVDA 0 1 0 0 0 0 0 Navicula veneta Kutzing NVEN 0 0 1 1 1 0 0 Navicula zanoni Hustedt NZAN 0 0 0 0 0 1 3 Planothidium frequentissimum(Lange-Bertalot)Lange-Bertalot PLFR 0 2 0 0 0 0 0 Pleurosigma salinarum (Grunow) Cleve & Grunow PSAL 1 50 65 15 33 0 0 Pseudostaurosira brevistriata (Grun.in Van Heurck) Williams & Round PSBR 0 1 0 0 0 46 9 Rhoicosphenia abbreviata (C.Agardh) Lange-Bertalot RABB 0 30 4 0 0 0 0 Rhopalodia gibba (Ehr.) O.Muller var.gibba RGIB 3 0 0 0 0 0 10 Reimeria uniseriata Sala Guerrero & Ferrario RUNI 15 5 7 94 2 0 0 Stephanodiscus agassizensis Hakansson & Kling SAGA 0 1 1 0 0 0 0 Surirella brebissonii Krammer & Lange-Bertalot var.brebissonii SBRE 0 0 8 1 0 0 0 Staurosira elliptica (Schumann) Williams & Round SELI 0 0 2 1 0 37 7 Surirella minima Ross & Abdin SMNM 2 0 0 0 0 0 0 Seminavis strigosa (Hustedt) Danieledis & Economou-Amilli SMST 2 3 1 0 3 0 0 Staurosirella pinnata (Ehr.) Williams & Round SPIN 0 0 0 0 0 1 0 Sellaphora pupula (Kutzing) Mereschkowksy SPUP 3 1 0 0 0 0 0 Tryblionella apiculata Gregory TAPI 0 0 0 0 6 0 0 Tryblionella calida (grunow in Cl. & Grun.) D.G. Mann TCAL 4 0 0 1 2 0 0 Tabularia fasciculata (Agardh)Williams et Round TFAS 1 0 1 0 197 0 0 Tryblionella levidensis Wm. Smith TLEV 1 0 5 0 0 0 0 Tryblionella victoriae Grunow TVIC 0 0 0 1 0 0 0 Thalassiosira weissflogii (Grunow) Fryxell & Hasle TWEI 0 1 2 0 2 0 0
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 152 Appendix B
Table B6: Diatom ecological descriptions (taken from Van Dam et al., 1994).
Classification of Ecological Indicators
i. pH
1. acidobiontic optimal occurrence at pH < 5.5 2. acidophilous mainly occurring at pH < 7 3. circumneutral mainly occurring at pH values about 7 4. alkaliphilous mainly occurring at pH > 7 5. alkalibiontic exclusively occurring at pH > 7 6. indifferent no apparent optimum
ii. Salinity
- Cl (mg/l) Salinity (‰) Cond. (mS/m)
1. Fresh < 100 < 0.2 < 3 2. Fresh-Brackish < 500 < 0.9 < 139 3. Brackish-Fresh 500-1000 0.9-1.8 139-277 4. Brackish 1000-5000 1.8-9.0 277-1385
iii. Nitrogen Uptake Mechanism
1. Nitrogen autotrophic- Tolerating very small concentrations of organically bound nitrogen Sensitive 2. Nitrogen autotrophic- Tolerating elevated concentrations of organically bound nitrogen Tolerant 3. Nitrogen heterotrophic- Needing periodically elevated concentrations of organically bound Facultative nitrogen 4. Nitrogen heterotrophic- Needing continuously elevated concentrations of organically Obligatory bound nitrogen
iv. Oxygen Requirements
1. Continuously High ~ 100% saturation 2. Fairly High > 75% saturation 3. Moderate > 50% saturation 4. Low > 30% saturation 5. Very Low ~ 10% saturation
v. Saprobity
Pollution Oxygen BOD5 (mg/l) Saturation
1. Oligosaprobous Unpolluted to slightly polluted > 85 < 2 2. β-mesosaprobous Moderately polluted 70-85 2-4 3. α-mesosaprobous Strongly polluted 25-70 4-13 4. α-meso-polysaprobous Very heavily polluted 10-25 13-22 5. Polysaprobous Extremely polluted < 10 > 22
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 153
Appendix C: Macroinvertebrates
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 154 Appendix C
Table C1: Macroinvertebrate family abundance data for the low (L) flow period. HR 1L HR 2L HR 3L HR 4L HR 5L VR 1L VR 2L Family TURBELLARIA 0 0 52 0 0 0 0 ANNELIDA Oligochaeta 16 18 111 32 99 1 8 Hirudinea 5 0 4 0 89 1 1 CRUSTACEA Potamonautidae 6 3 1 3 0 0 0 Atyidae 1 1 3 0 1 6 58 EPHEMEROPTERA Baetidae 272 24 75 84 116 307 0 Caenidae 179 8 12 1 9 6 0 Heptageniidae 0 0 0 0 0 20 0 Leptophlebiidae 3 0 0 0 0 22 0 Tricorythidae 0 0 0 0 0 4 0 ODONATA Coenagrionidae 0 1 36 10 17 20 35 Gomphidae 0 0 0 0 0 0 1 LEPIDOPTERA Pyralidae 0 0 2 0 0 10 0 HEMIPTERA Belostomatidae 0 0 1 0 0 0 0 Corixidae 1 4 1 1 8 0 0 TRICHOPTERA Ecnomidae 1 0 6 0 7 7 0 Hydropsychidae 1236 108 275 205 44 233 0 Hydroptilidae 2 0 2 2 2 4 0 COLEOPTERA Dytiscidae 0 0 0 0 0 0 1 Elmidae 4 0 0 1 5 12 0 Gyrinidae 1 1 18 2 7 19 0 Helodidae 0 6 4 0 0 0 0 Hydrophilidae 0 0 0 0 0 0 1 DIPTERA Ceratopogonidae 7 4 0 2 5 0 0 Chironomidae 374 90 726 727 382 85 34 Muscidae 2 5 48 3 22 0 0 Simuliidae 2008 2339 8545 479 123 295 0 Tipulidae 0 3 0 0 0 0 0 GASTROPODA Ancylidae 9 11 47 4 17 7 0 Lymnaeidae 1 0 0 0 0 0 0 Physidae 0 6 69 0 46 7 10 Planorbidae 0 0 0 0 19 4 0 Thiaridae 0 2 1 0 0 0 0 PELECYPODA Corbiculidae 46 4 14 84 16 4 0
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 155 Appendix C
Table C2: Macroinvertebrate family abundance data for the high (H) flow period. Family HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H TURBELLARIA 0 0 3 0 2 0 0 ANNELIDA Oligochaeta 51 130 163 11 44 3 1 Hirudinea 20 10 87 1 22 0 0 CRUSTACEA Potamonautidae 55 29 2 1 1 0 0 Atyidae 0 24 2 85 44 12 52 EPHEMEROPTERA Baetidae 103 24 87 146 15 148 9 Caenidae 156 31 54 9 1 84 2 Heptageniidae 0 0 0 0 0 21 0 Leptophlebiidae 0 0 0 0 0 86 0 Tricorythidae 0 0 0 0 0 18 0 ODONATA Chlorocyphidae 0 0 0 3 0 0 0 Coenagrionidae 5 127 391 67 65 8 10 Gomphidae 0 0 0 0 1 2 0 Libellulidae 1 2 20 0 3 0 0 LEPIDOPTERA Pyralidae 2 0 0 7 4 3 0 HEMIPTERA Belostomatidae 0 27 16 15 3 0 2 Corixidae 1 11 3 0 0 0 0 Naucoridae 5 6 6 0 0 0 0 Veliidae 16 91 35 36 1 1 0 TRICHOPTERA Ecnomidae 1 6 6 0 5 23 0 Hydropsychidae 972 5 539 322 68 291 0 Hydroptilidae 135 12 164 64 20 97 0 COLEOPTERA Dytiscidae 1 0 0 0 0 0 0 Elmidae 2 0 0 1 0 113 0 Gyrinidae 0 0 3 2 2 0 0 Helodidae 8 0 2 0 0 0 0 DIPTERA Ceratopogonidae 303 34 88 8 39 0 18 Chironomidae 185 61 557 392 110 103 27 Culicidae 2 2 5 1 0 0 0 Muscidae 2 1 1 0 0 0 0 Simuliidae 301 16 4549 76 209 550 0 Tabanidae 1 0 0 0 0 1 0 GASTROPODA Ancylidae 116 31 348 36 35 6 0 Lymnaeidae 5 2 0 0 1 0 0 Physidae 0 5 111 2 47 0 24 Planorbidae 0 0 1 4 34 1 0 Thiaridae 2 0 3 0 1 0 0 PELECYPODA Corbiculidae 127 21 29 67 46 21 0
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 156 Appendix C
Table C3: Historical macroinvertebrate SASS5 data for the relative reference site HR 1 during the low flow period. SASS5 Variables Measured Values SASS5 Score 51 No. of Families 11 ASPT 4.64 DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2003-07-17).
Table C4: Historical macroinvertebrate SASS5 data for the relative reference site HR 1 during the high flow period. SASS5 Variables Measured Values SASS5 Score 40 No. of Families 11 ASPT 3.64 DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2005-01-25).
Table C5: Historical macroinvertebrate SASS5 data for the relative reference site HR 1 during the high flow period. SASS5 Variables Measured Values SASS5 Score 99 No. of Families 20 ASPT 4.95 DWAF (2007) – Rivers Database: Owner of Data – Hermien Roux (2007-04-17).
Table C6: Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during the high flow period. SASS5 Variables Measured Values SASS5 Score 67 No. of Families 14 ASPT 4.79 DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2003-02-13).
Table C7: Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during the low flow period. SASS5 Variables Measured Values SASS5 Score 46 No. of Families 10 ASPT 4.60 DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2003-07-17).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 157 Appendix C
Table C8: Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during the high flow period. SASS5 Variables Measured Values SASS5 Score 68 No. of Families 15 ASPT 4.53 DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2005-01-25).
Table C9: Historical macroinvertebrate SASS5 data for the agricultural site HR 3 during high flow. SASS5 Variables Measured Values SASS5 Score 127 No. of Families 25 ASPT 5.08 DWAF (2007) – Rivers Database: Owner of Data – Hermien Roux (2007-04-16).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 158 Appendix C
Table C10: Historical macroinvertebrate family data for the relative reference site HR 1 during the low flow period. Family Abundance PORIFERA A CRUSTACEA Atyidae A EPHEMEROPTERA Baetidae 1sp A Leptophlebiidae A ODONATA Coenagrionidae A HEMIPTERA Veliidae A COLEOPTERA Dytiscidae A Gyrinidae A DIPTERA Chironomidae A Culicidae A GASTROPODA Physidae A DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2003-07-17).
Table C11: Historical macroinvertebrate family data for the relative reference site HR 1 during the high flow period. Family Abundance ANNELIDA Oligochaeta A CRUSTACEA Potamonautidae A EPHEMEROPTERA Baetidae 1sp B Caenidae A ODONATA Coenagrionidae A Libellulidae A HEMIPTERA Corixidae B Pleidae A Veliidae A DIPTERA Culicidae A Simuliidae B DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2005-01-25).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 159 Appendix C
Table C12: Historical macroinvertebrate family data for the agricultural site HR 3 during the low flow period. Family Abundance TURBELLARIA A CRUSTACEA Potamonautidae A EPHEMEROPTERA Baetidae 1sp A ODONATA Coenagrionidae A Platycnemidae A HEMIPTERA Veliidae A COLEOPTERA Gyrinidae A DIPTERA Chironomidae A Simuliidae C GASTROPODA Physidae A DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2003-07-17).
Table C13: Historical macroinvertebrate family data for the agricultural site HR 3 during the high flow period. Family Abundance ANNELIDA Oligochaeta A CRUSTACEA Potamonautidae A Atyidae B EPHEMEROPTERA Baetidae 2sp B Caenidae A ODONATA Coenagrionidae B HEMIPTERA Belostomatidae A Corixidae A Naucoridae A Veliidae A TRICHOPTERA Hydropsychidae 1sp A COLEOPTERA Gyrinidae B DIPTERA Chironomidae A Simuliidae A GASTROPODA Ancylidae A DWAF (2007) – Rivers Database: Owner of Data – Marie Watson (2005-01-25).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 160 Appendix C
Table C14: Historical macroinvertebrate family data for the agricultural site HR 3 during the high flow period. Family Abundance ANNELIDA Oligochaeta B Hirudinea 1 CRUSTACEA Potamonautidae A EPHEMEROPTERA Baetidae 2sp C Caenidae B ODONATA Chlorolestidae 1 Coenagrionidae B Lestidae 1 HEMIPTERA Belostomatidae A Corixidae A Naucoridae B Pleidae B Veliidae B TRICHOPTERA Hydropsychidae >2sp A Pisuliidae B COLEOPTERA Dytiscidae A Gyrinidae B Hydrophilidae A DIPTERA Ceratopogonidae A Chironomidae B Simuliidae B GASTROPODA Ancylidae A Physidae A PELECYPODA Corbiculidae 1 Sphaeriidae A DWAF (2007) – Rivers Database: Owner of Data – Hermien Roux (2007-04-16).
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 161 Appendix C
Table C15: Macroinvertebrate FFG abundance data for the low (L) flow period. FFG HR 1L HR 2L HR 3L HR 4L HR 5L VR 1L VR 2L PR 630 81 421 297 254 168 48 DT 5 6 37 11 33 0.33 3 COG 422 55 273 238 201 217 69 COF 2772 2426 8921 858 304 444 11 SC 159 34 157 47 144 202 10 SH 0 0 2 0 0 10 0 PRP 94 29 230 185 98 21 9 PIH 1 3 2 1 3 1 0 SHH 1 2 1 1 2 4 0 SCS 1 1 9 1 4 10 0 SHD 0 2 0 0 0 0 0 SHO 6 3 1 3 0 0 0
Table C16: Macroinvertebrate FFG abundance data for the high (H) flow period. FFG HR 1H HR 2H HR 3H HR 4H HR 5H VR 1H VR 2H PR 712 190 964 343 177 181 27 DT 17 43 54 4 15 1 1 COG 471 148 350 295 121 338 74 COF 979 105 5050 406 336 766 7 SC 222 57 562 137 132 205 29 SH 2 0 0 7 4 3 0 PRP 71 130 190 142 30 28 8 PIH 47 7 56 21 7 32 0 SHH 3 0 1 1 0 38 0 SCS 0 0 2 1 1 0 0 SHD 0 0 0 0 0 0 0 SHO 55 29 2 1 1 0 0
Determining the Influences of Land Use Patterns on the Diatom, Macroinvertebrate and Riparian Vegetation Integrity of the Lower Harts/Vaal River Systems. 162