Biomonotoring of the Great Kei River System
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BIOMONOTORING OF THE GREAT KEI RIVER SYSTEM FEBRUARY 2009 REPORT PREPARED BY: Lungile Gaulana Resource Protection, Department of Water Affairs & Forestry (ELS) Mlondolozi Mbikwana Resource Protection, Department of Water Affairs & Forestry (ELS) Weni Elliot. Resource Protection, Department of Water Affairs & Forestry (ELS) DATA COLLECTION: M.N. Mbikwana, E. Weni, M. Rubuxa (excused for sick leave) and L. Gaulana EXECUTIVE SUMMARY The main objective of the South African National Aquatic Environmental Health Monitoring Programme (NAEHMP) makes use of the instream and riparian biological communities like vegetation, invertebrates and fish to assess the ecological ‘health’ of rivers as well as physical attributes or drivers of the ecosystem like hydrology, geomorphology and water quality. These biological communities are always found in rivers and they are often affected by any disturbance that occurs in the river ecosystem. This report provides the results of the biomonitoring survey that was undertaken in in the Great Kei River Basin in February 2009 (Summer survey). Field indices used for data collection included the Geomorphology, Water Quality, South African Scoring System version 5.0 (SASS5) for macro invertebrates, and the Fish Assemblage Integrity Index (FAII) for fish. The Department: Water Affairs and Forestry (DWAF): Eastern Cape National Aquatic Environmental Health Monitoring Programme (former RHP) involves the use of Biomonitoring as a tool to determine the health of the aquatic ecosystems. The programme aims to promote standardized and continuous monitoring and reporting on the Eastern Cape rivers ecosystem health. The Great Kei River is one of the systems monitored by the Eastern Cape DWAF, hence monitoring survey was conducted. This report provides information on the Present Ecological State of the Great Kei River Basin. 2 INTRODUCTION AND BACKGROUND The Great Kei River starts from an altitude of approximately 2 100 meters above sea level (masl) and meanders its way towards the Indian Ocean. Using the ArcView GIS software with 1: 50 000 image data, it can be estimated that the Great Kei Basin occupies the area of approximately 20 480 square kilometers. The mainstem of the drainage basin originates as two branches; the Black Kei in the West and a White Kei in the East and it becomes the Great Kei River at the confluence until it opens in the Indian Ocean. Major tributaries of the Great Kei River are the Tsomo, Kubusi, Gcuwa and Tyityaba rivers; the latter being inaccessible due to its location in a gorge area and a rough, steep terrain (see 1:50 000 toposheets and Google Earth images). The Great Kei River and its tributaries flow through confined valleys with gentle slopes hence meandering. The figure below shows the terrain of the Kei River Basin from source to mouth. 3 Figure 1: Topography of the Kei River drainage basin. Climate The Kei River catchment receives its rainfall mainly in summer. Due to its location in the driest part of the country, numerous dams and weirs had been built to extend water supply potential and to meet water requirement demands. Major reservoirs include the following: o Lubisi Dam with the capacity of 158 million cubic meters. o The Ncora Dam with about 150 million cubic meters o The Xonxa of about 97.5 million cubic meters and o Wriggleswage Dam of about 91.5 million cubic meters (www.ewisa.co.za). Other numerous dams include the Bongolo, Bushmanskrantz, Doringrivierdam, Gubu, Limietskloof, Macubeni, Mitford, Oxkraal, Sam Meyer, Shiloh, Tentergate, Thrift, Toleni, Waterdown and Tsajana. These dams increase evaporation potential on the catchment. 4 In addition, a lot of windmills for harvesting groundwater could be observed, especially on the upper part of the catchment. This suggests that the catchment is facing water resource deterioration crisis, including the groundwater, surface water and rainwater. Geology and Soils The Great Kei catchment is dominated by rocks of the Karoo Supergroup (mainly shale, mudstones and sandstones) the Molteno along the Tsomo, the Tarkastad along the entire Great Kei and some patches of Adelaide and Suurberg Supergroups (Figure 2). Both the Adelaide and the Tarkastad consist of sandstones and mudstones; the Molteno, Clarens, Elliot formation contains sandstones, mudstones, shales and siltstones. Soils in the Great Kei Basin comprise mainly of moderate to deep clayey loams along the Thomas River sub-catchment and very shallow and rocky soils in the Tsomo River subctchment (see also www.waterinformation.co.za). According, soils on the area are poorly developed, being shallow and rocky and mostly not suitable for crop production with alluvial soils mainly obtained on the valleys. 5 Figure 2. Geology and soils of the Kei River Basin The Natural Vegetation. The plateau area is mainly covered by grasslands (Moist upland and South-Eastern Mountain Grasses) with unreliable degrees of Acacia Karoo thornveld as well as some patches of Afromontane forest and huge proportion of Sub-arid thorn bushveld. Valley thicket is located in the lower reaches of the Black Kei River valley, lower reaches of the White Kei River valley, middle and lower reaches of the Thorn River, upper reaches of Kubusi River and the rest of Great Kei River. Alien invasive vegetation includes the black wattle (Acacia meansii) that can be observed throughout the river system. This was more invasive especially at Tsomo at Komkhulu site. The figure below shows the vegetation types on the Great Kei River Basin. 6 Figure 3: Vegetation of the Great Kei River Basin (After Louw and Rebelo 1996). Ecoregions. The large portion of the Great Kei River Basin consists of the Drought Corridor Level I Ecoregion around Queenstown and the South Eastern Uplands Level I Ecoregions around areas of Cala, Komga and Butterworth. Small percentage of the catchment has the Eastern Escarpment Mountains and the Eastern Coastal Belt Level I Ecoregions on the upper reaches and coastal areas respectively. The figure below shows the Levels I and II ecoregions of the Great Kei River Basin. 7 Figure 4: Levels I and II Ecoregions of the Great Kei River Basin. Quaternary Catchments By dividing the catchments into smaller units can increase the efficiency of the management of any ecosystem. Therefore each Catchment Management Agency can be allocated to manage a particular Quaternary catchment effectively. The figure below shows the Quaternary catchments of the Great Kei River Basin. 8 Figure 5: Quaternary catchments of the Great Kei River Basin. Major Land Use Activities Observed on the study area are markedly different units of landuse activities which include the following: • Live stock farming (Beef, dairy, sheep, poultry and goats) • Subsistence farming (maize and vegetables) • Game farming (Builder beast, antelope, bushpig or warthog and kudu) • Rural and Urban settlements. • Commercial farming lands occur mostly on the western side of the catchment (mainly Lucerne). This is where extensive irrigation occurs. It could be noticed that most of the land in the catchment is unimproved and degraded grassland. The figure below demonstrates the landuse map of the Kei River Basin. 9 Figure 6 Landuse of the Kei River Basin. METHODOLOGY The Great Kei River survey was conducted in summer (2nd February 2009 until 6th of February 2009). Site selection for the survey was previously done during the ground truthing survey conducted in 10th to 19th November 2008 and some additional sites on the lower reaches of the Great Kei before the estuary, and other sites on the Gcuwa and the Klass Smith tributaries with the aim of finding reference sites for the South-Eastern Uplands and Drought Corridor Level I Ecoregions respectively. Ecosystem components assessed were two drivers of the ecosystem; geomorphology and water quality as well two responses of the ecosystem, mainly macro invertebrates and fish. 10 This was a transect survey that was conducted on the Mzimvubu to Keiskamma Water Management Area. The survey was done by collecting data on predetermined accessible sites. These sites were selected in three sections of the catchment viz: 1. The upper reaches, where the survey took place right upstream of all the selected major tributaries. 2. The middle reaches, where the preference was on the confluences and impoundments. 3. The lower reaches, where the survey will be done to assess the overall impact on the Great Kei River Basin. The following implements were utilized during the survey: a) The Geomorphological Assessment Index (GAI), which was used to assess the Present Geomorphological State of a river at a particular reach. b) A measuring tape: to measure sediment categories on transect selected on each accessible site. The idea being to assess sediment distribution so as to predict environmental flows that would be required to meet the requirements of a recommended Environmental Management Class (EMC). c) The Water Quality meter to measure the water quality parameters (pH, Oxygen absorbed, Water temperature and Conductivity, as well as bottles to collect samples for chemical analyses) d) SASS trays and nets: for macroinvertebrate evaluation. e) Fish shocker and net: for fish assessment. f) 1: 50 000 topographic maps, 1: 250 000 toposhets and Google images. These were used to find and locate the predetermined survey sites, as well as to act as a desktop estimate at a catchment scale. g) The Global Positioning System (GPS), to locate the sites of assessment and to navigate the directions to the site. h) ArcView 3.2: a GIS software tool that was vital for data storage, analyses, manipulation and interpretation of data. The maps with ecoregions, sites, geology and soils, vegetation, landuse were created using the Geographical Information System (Arcview 3.2), the GPS (Global Positioning System) readings for each site and the spreadsheet (Microsoft Excel 2003) for graphics and changing GPS co-ordinates to decimal degrees (GIS format). 11 AIMS The main aim of the survey was to review the overall Present Ecological State of Great Kei River Basin.