Patterns of Vegetation Dynamics across Mild Disturbance Gradient in a Freshwater Wetland System in Southern India

P. V. Jyothi & S. Sureshkumar

Wetlands Official Scholarly Journal of the Society of Wetland Scientists

ISSN 0277-5212 Volume 38 Number 4

Wetlands (2018) 38:807-817 DOI 10.1007/s13157-018-1031-8

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Wetlands (2018) 38:807–817 https://doi.org/10.1007/s13157-018-1031-8

ORIGINAL RESEARCH

Patterns of Vegetation Dynamics across Mild Disturbance Gradient in a Freshwater Wetland System in Southern India

P. V. Jyothi1 & S. Sureshkumar2

Received: 13 January 2017 /Accepted: 11 April 2018 /Published online: 2 May 2018 # Society of Wetland Scientists 2018

Abstract Ponnani Kole wetlands, the northward extension of Vembanad Kole Ramsar site in Kerala, Southern India, is facing environ- mental pressures due to increases in human population, changes in land use pattern, improper watershed management and urban developments. The current study describes the community assemblage pattern of macrophytes and their variations within and among areas affected by environmental disturbances in Ponnani Kole wetland system. The macrophyte community structures in the study site were characterized with reference to areas of saline intrusion, intense agricultural activities and sewage disposal. Sphaeranthus africanus and Colocasia esculenta were specific to sewage; Rotala indica, Hedyotis corymbosa, Limnophila heterophylla and Eriocaulon setaceum were specific to agriculture; while, Acanthus ilicifolius, and Mariscus dubius were specific to areas of saline intrusion in the study site. Mean diversity did not vary significantly among the different zones of disturbance with the exception of saline intruded areas. Taxonomically, similar species flourished well in all regions of the study except in the saline intrusion area. In undisturbed areas, considered as control, the occurrence of all macrophytes was observed in equal proportions with the exception of mangroves and suspended hydrophytes. However, in sewage disposal areas, the occur- rence of 45 species was observed with unequal predominance of all taxa, viz. class, order and family of macrophytes. The implementation of decision supporting tools to aid strategy and policy makers explore land-use options and disturbance scenarios along with ecological tools assessing multiple ecosystem services will see Ponnani Kole wetland become established as a macrophyte dominated ecological regime which can be further developed as a conservation and educational site for tropical aquatic macrophytes.

Keywords Intensive agriculture . Saline intrusion . Sewage disposal . community structure . Tropical wetlands . Species diversity

Introduction algal flora, macrophytic flora, avifauna and ichthyofauna. Benefits of wetlands are categorized into provisioning (food, Kole wetlands are vital ecosystems which provide agricultural fiber, fodder, fuel, water, and other materials), regulating (reg- produce, fish, fuel, fiber, fodder, and a host of other day-to- ulation of biogeochemical cycles and micro-climatic condi- day necessities for thousands of inhabitants in its vicinity and tions), supporting (soil formation, supporting biodiversity) are important repositories of aquatic biodiversity in particular and cultural (aesthetics, recreational and spiritual activities) services (MEA 2005). These services ensue from the ecosys- Electronic supplementary material The online version of this article tem functions and depend largely upon the biodiversity of the (https://doi.org/10.1007/s13157-018-1031-8) contains supplementary ecosystem. Macrophyte dominated wetlands are highly val- material, which is available to authorized users. ued for recreation including bird watching, boating and other leisurely activities (Weller and Spatcher 1965). The fabulous * S. Sureshkumar potential of this wetland ecosystem for securing aquatic bio- [email protected] diversity, improving moisture regimes, replenishing aquifers 1 Department of Botany, MES Ponnani College, Ponnani, and emergent eco-tourism sites has remained abhorrently un- Malappuram–Dist., Kerala 679 586, India der-tapped, and demands immediate attention. Usually desig- 2 School of Ocean Science and Technology, Kerala University of nated as wastelands, these fragile ecosystems are being Fisheries and Ocean Studies, Panangad (P.O), Kochi, India reclaimed for various developmental activities bringing Author's personal copy

808 Wetlands (2018) 38:807–817 several taxa of immense ecosystem service worth (e.g. Eclipta areas of environmental disturbance in a typical wetland prostrata, Centella asiatica, Lindernia hyssopioides and system in the tropics. It is anticipated that the research natans) to the verge of extirpation. Strict conser- findings will provide an insight for the development of vation and management actions should be implemented to conservation policy for the aquatic macrophytes of this control human-led activities in this Ponnani Kole wetland en- delicate ecosystem and also for the creation of an ideal suring sustainable development and utilisation. in situ conservation and educational location for tropical Ponnani Kole wetland is facing environmental pressures aquatic macrophytes. due to increases in human population, changes in land use pattern, improper use of watersheds, and urban development all leading to increased nutrients and sediment loads, and al- Materials and Methods tered hydrology. To secure long term conservation objectives, the initial step is to assess the baseline diversity of natural Site Description resources in the study area and to identify potential factors which could cause a decline in habitat quality and species Ponnani Kole is situated in the south-western region of population. Aquatic macrophytes play an important role in Malappuram district, in Kerala State, India and is the northern freshwaters by promoting a clear water state through reduced most extension of the Vembanad Kole Ramsar site (Fig. 1). nutrient availability thus reducing competition with algae, This wetland comes under the ‘Central Asian-Indian Flyway’ stabilisation of bottom sediments, and enhancing biodiversity (Anonymous 1996) and serves as a ‘stepping stone’ for trans- by offering shelter and substrate, and providing food for her- continental migratory birds (Srinivasan 2010). According to bivorous waterfowl (Engehardt and Ritchie 2002). The term Srinivasan (2010) Vembanad Kole system supports the third macrophyte used in this research includes all hydrophytic or largest population of waterfowl in India during the winter semi hydrophytic vascular that grow submerged or part- months. Many birds often come here from different regions ly submerged or free floating together with vascular crypto- for nesting and feeding. Kole supports bird species, viz. Spot- gams, and macroscopic algae. Aquatic macrophytes, in tropi- billed pelican (Pelecanthus philippensis), Oriental darter cal regions, constitute the largest single form of biomass on (Anhinga melanogaster), Black headed ibis (Threskiornis freshwater ecosystems (Chandra and Kulshreshtha 2004). melanocephalus), Painted stork (Mycteria leucocephala)and Despite this, when growing in suitable habitats several species Cinereous vulture (Aegypius monachus), under near threat- such as Ipomoea carnea, Salvinia molesta and Eichhornia ened category, Black-bellied tern (Sterna acuticauda), an crassipes are considered aquatic weeds due to their rapid col- endegered species and Greater spotted eagle (Clanga clanga), onization and negative effects upon aquatic diversity and eco- avulnerablespecies,in varying frequencies (Nameer 2002; system functioning (Camargo et al. 2003). Aquatic macro- Praveen 2015). Within the Vembanad-Kole wetland ecosys- phytes are known to be highly productive (Wetzel 2001), tem, the Kole lands cover an area of about 136 sq. km spread and also provide an important structuring role in aquatic en- over Thrissur and Malappuram districts. The study area re- vironments (Jeppesen et al. 1998). Macrophytes serve as a ceives an average annual rainfall of 2047 mm (Table S1) base of aquatic food-chains and contribute to the promotion andtemperaturevariesbetween22.0°Cto34.0°C of food webs and services in freshwater ecosystems (Scheffer (Table S2) during the study period. Geologically, Ponnani and Jeppesen 2007; Smith 2011). The function of macro- Kole is a low lying area with alluvium deposits brought down phytes in these ecosystems is related to their structural attri- by the Bharathapuzha river. It is a saucer shaped basin flanked butes like species composition, distribution, abundance and by laterite hills in the western and eastern margins. Some diversity which, in turn, depend on substrate composition, portions of Kole area exhibit lacustrine environments and con- disturbance, competitive interactions and quality of water tain black clay with many plant parts and in some places and sediment nutrients (Cronk and Fennessy 2001; Wetzel withered tree trunks (Johnkutty and Venugopal 1993). 2001;Capers2003; Pankhurst 2005; Feldmann 2012; Subsurface of Kole land has fine sandy deposits and mining Tamire and Mengistou 2012). This is extremely relevant since has become an important activity in certain parts of this Kole aquatic biodiversity has been related to spatial heterogeneity land. (Grenouillet et al. 2002). The role of certain macrophytes like Nine stations were selected with different disturbances re- Eichhornia crassipes and Alternanthera philoxeroides has al- gimes: two saline intrusion sites (Porangue and Cheerppu), so been demonstrated to be vital in the removal of heavy three stations in the areas of agricultural activity (Kalachal, metals such as Copper (Cu2+), Cadmium (Cd2+), Nickel Uppungalkadav, Muchikadav) and two stations (Ni2+), Lead (Pb2+)andZinc(Zn2+)withinwetlandsys- (Kummipalam, Thuyyam) in sewage disposal regions tems (Southichak et al. 2006). The current research ob- representing anthropogenic disturbance and two undisturbed jective is to describe the baseline community assemblage sites (Naranipuzha, Mukolamtazhah) selected as control pattern of macrophytes and their variation within and among stations (Fig. 1 and Table 1). Author's personal copy

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Fig. 1 Location of the nine stations in the Ponnani Kole wetland

Area of Saline Intrusion Area of Agricultural Activities

The stations in the area of saline intrusion are located where Rice cultivation is practiced in this area whereby earthen coir retting was practiced (Coir is extracted from coconut husk bunds and dams are constructed to improve agricultural crop after a decaying process called Bretting^. The process is car- yields. Reclamation activities via unauthorized encroachment ried out by immersing coconut husks in lakes, rivers and of wetland areas for constructing housing and buildings have ponds for a period ranging from 6 months to 1 year started on one side of the paddy fields. During periods of for loosening the fibres. Areas for retting are almost devoid flooding typical suspended, submerged and anchored floating of higher aquatic life because of anoxic condition). The area hydrophytes were present but during pre-monsoon wetland was dominated by salt tolerant plants (Avicennia officinalis, plants alone were noticed. Cattle grazing and duck farming Clerodendron inerme, Acanthus ilicifolius, Ipomoea pes- were also taking place at these stations. Infrastructure devel- caprae and Mariscus dubius). During the monsoon, floating opment in the form of roads and other lines of communication macrophytes like Eichhornia, Pistia and Salvinia are flushed fragmented the contiguity of the wetland. This kole land is to this area by water currents. also an attractive sight for many wetland birds as it supports

Table 1 Geographic positions of the stations, in the Ponnani Kole No. Stations Longitude Latitude Zones Average depth (mm) wetland, selected for the study 1 Naranipuzha 75.9897 10.7185 Control 590.8 2 Mukolamtazhah 75.9668 10.7843 Control 851.3 3 Kummipalam 75.9755 10.7266 Sewage 320.8 4 Thuyyam 75.9692 10.7859 Sewage 663.3 5 Kalachal 76.0094 10.7611 Agriculture 442.1 6 Uppungalkadav 75.9972 10.6850 Agriculture 485.8 7 Muchikadav 75.9971 10.7348 Agriculture 697.5 8 Porangue 75.9493 10.7612 Saline 266.7 9 Cheerppu 75.9447 10.7512 Saline 340.4 Author's personal copy

810 Wetlands (2018) 38:807–817 good nesting habitats with aquatic and marginal flora. Sivadasan 2009). Author citation and binomial of collected Migratory birds visit the stations in post-monsoon times and species was verified using the International Plant Names use this aquatic ecosystem as a stop-over or transit area be- Index (IPNI 2009). Identified specimens from each quadrate cause of easy food availability. Three stations were selected in were dried separately in a hot air oven at 105 °C to constant agricultural areas in order to cover the larger extent of agricul- weight for dry weight biomass determination (Wetzel and ture fields in the study site. Likens 2000). Sum of the biomass of each species from var- ious samples with respect to control and different disturbance Area of Sewage Disposal Activities zones were worked out to determine relative abundance (as dry mass per square meter (gm. M−2)) and diversity An area with domestic sewage disposal and water contaminat- indices. Furthermore, all the identified macrophytes ed with oil discharge from vehicles were noticed. Eichhornia, were categorized into seven groups namely: Free float- Pistia and Salvinia were the characteristic plants of this re- ing, Suspended hydrophytes, Submerged hydrophytes, gion. This may be due to the leaching of nutrients from the Anchored floating, Emergent hydrophytes, Wetland disposed sewage, which is diluted to a level of low impact. plants, Mangrove and associates depending on their habit The bank of the water body is contaminated with solid wastes (Sunil and Sivadasan 2009). such as disposed utensils and containers, rags and domestic refuse. Free Floating Hydrophytes Plants live on the water surface in contact with air. They mainly occur in sheltered habitat and Control Site stagnant water (eg Eichhornia crassipes, Salvinia molesta and Pistia stratiotes). A typical wetland ecosystem having different species of macrophytes is selected as control sites. Suspended hy- Suspended Hydrophytes Plants live below the surface water, drophytes like Utricularia and Hydrilla, similarly an- but not anchored. Usually found in stagnant water bodies (eg chored floating like Nymphoides were very common in Hydrilla verticillata, Ceratophyllum demersum and this area. The area is devoid of any Anthropogenic ac- Utricularia aurea). tivities and saline intrusion. Water in this area is clear and having good number of fishes and other organisms. Submerged Hydrophytes Plants live well below the surface The area is a spot for fishing and collection of fresh- water and are usually anchored (eg. Najas graminea and water mussels. People were commonly using this area Vallisneria natans). for drawing water for domestic purpose. Anchored Hydrophytes Plants inhabit shallow stagnant waters Vegetation Surveys and are anchored to substrate. They produce branches which trail or creep on the water surface with rooting nodes (eg. Vegetation surveys were conducted for 2 years between 2014 Nymphaea nouchali, Nymphoides crystatum and Bacopa and 2016, and covered all three seasons namely pre-monsoon, monnieri). monsoon and post monsoon for four different disturbance zones. From each zone of study, one 100 m transect was laid Emergent Hydrophytes Plants reside most of their life in water and macrophyte composition were recorded from four ran- by producing aerial representative organs. Majority of the domly placed sites and from which samples were collected members are showing heterophylly (eg. Sacciolepis interupta, for further identification in the laboratory. Vegetation from Schoenoplectus supinus and Monochoria hastata). random 1M2 quadrates, along the fixed transect, were also collected in quadruplicates for biomass determination Wetland Plants Coastal low lands, margins of pond, lakes, (Westlake 1965). All the macrophytes collected from each canals and paddy fields provide ideal habitat for wetland spe- quadrate were placed in separate labelled polythene bags cies. They require saturated soil for their survival (eg. Leersia and transported to the laboratory, washed thoroughly, hexandra, Cynodon dactylon and Polygonum glabrum). completely drained, sorted and weighted to the nearest mg for biomass determination. Herbarium sheets were prepared Mangrove and Associates Mangroves are salt-tolerant hal- and specimens preserved in the MES Ponnani College muse- ophytes and are adapted to live in saline environment. um for identification and further reference. Taxonomic identi- They have complex salt filtration system and root sys- fication of the preserved plants was carried out using Flora of tem to cope with salt water immersion and wave action. British India (Hooker 1897), Flora of the Presidency of They also adapted to anoxic conditions of waterlogged Madras (Gamble 1915), Flora of Calicut (Manilal and mud (eg. Mariscus javanicus, Avicennia officinalis and Sivarajan 1982)andFlora of Alappuzha District (Sunil and Acanthus ilicifolius). Author's personal copy

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Diversity Measurements & Statistical Analyses Limnophila heterophylla, L. indica, L. repens, Aponogeton natans, Najas graminea, N.indica, Eriocaulon setaceum and Diversity indices such as Shannon-Wiener Diversity Index Oryza rufipogon were specific to the intensive agriculture (SDI - H′) and Simpson’s Evenness Index (SEI - 1- ) were areas; while Ipomoea pes-caprae, Acanthus ilicifolius, calculated from the biomass of each species collected from Avicennia officinalis, Clerodendron inerme and Mariscus stations and Average Taxonomic Distinctness (AvTD - Δ+) dubius were specific to saline areas at the study site. and Variation in Taxonomic Distinctness (VarTD - Λ+) from Nymphoides indica, Merremia tridentata, Utricularia the presence or absence data using Primer 6.0 software reticulata, Alternanthera philoxeroides, Schenoplectus (Clarke and Warwick 1998). Preliminary analysis of the bio- articulatus, Schenoplectus supinus, Cynodon dactylon, mass of macrophytes data showed no significant variation in Monochoria hastata and Leersia hexandra showed wider eco- the macrophyte community composition within the different logical tolerances and were observed in all the study zones. disturbance zones hence the data was pooled per disturbance The biomass of each species recorded from the four differ- zone. Differences between the mean diversity indices record- ent study zones are provided in Table S3. Of the 77 species ed from the three disturbed and control areas were compared recorded, 26 species were common in all the stations while using ANOVA’swithDuncan’s multiple range post-hoc anal- others were more specific to the zones of environmental dis- ysis in the statistical package SPSS 17.0. The k-dominance turbances (Table S3). The highest dry weight biomass of mac- plot was constructed to explain the percentage cumulative rophytes was recorded in the area of saline intrusion with a abundance against log species rank (Lambshead et al. 1983). mean value of 627.98 g/m2 and the lowest for the same was To measure the deviation of the taxonomic distinctness (both observed in the area of intensive agriculture (269.57 g/m2). Δ +andΛ+) of the assemblage of macrophytes, observed from Mean biomass of aquatic macrophytes in the area of sewage different zones, from the global mean, a funnel plot was disposal was 472.21 g/m2 and 405.96 g/m2 in the control area. constructed (Clarke and Warwick 1998). The null hy- This is due to the overgrowth, by size, of certain species like pothesis assumes that each sample carries the species Salvinia molesta, Pistia stratiotes, Eichhornia crassipes, randomly selected from the global list and that it should Vallisneria natans, Polygonum barbatum, Ipomoea carnea fall within the 95% confidence intervals. To examine and I. aquatica in the area of sewage disposal. spatial patterns in macrophyte assemblages in four dif- The K-dominance plot clearly shows the diversity pattern ferent zones the Bray-Curtis dissimilarity metrics of biomass in the four different zones where percentage cumulative dom- was evaluated using non-metric multidimensional scaling inance values are plotted against log species rank (Platt et al. (NMDS) for representing their similarity/dissimilarity in 1984). The curve for saline zone rises rapidly and lies above assemblage pattern (Clarke 1993). the curves of sewage, control and agriculture zones because only a few species were recorded from this zone (Fig. 2). The upper most curve representing the macrophytes of saline zone Results corresponds to least diversity and dominated by only few spe- cies. However, the curves representing agriculture fields, sew- Distribution Pattern of Macrophytes in Different age and control zones lie on the lower side, extending further ZonesofDisturbance and rising slowly because of the occurrence of a large numbers of species with dominance of many species (Fig. 2). Vegetation surveys were conducted at nine study stations over two years, covering three different seasons pre-monsoon, Variation in Diversity Indices of Macrophytes monsoon and post monsoon. Random samples, in quadrupli- Composition in Different Disturbances cate, were taken using 1m2 quadrat along the 100 m fixed transect in each station. A total of 216 samples were collected Various diversity indices, Species Richness (S), Biomass (M), in which 48 samples each from areas of control, saline intru- Shannon Diversity Index (SDI, H′), Simpsons Evenness Index sion and sewage disposal and 72 samples from agriculture (SEI, 1- ), Average Taxonomic Distinctiveness (AvTD, Δ+) activity area. and Variation in Taxonomic Distinctiveness (VarTD, Δ), Community structure of aquatic macrophytes in different worked from the basic data collected from different zones regions of mild disturbances in Ponnani Kole wetlands are presented in the Table 2 and Table S4. No significant showed significant variation. (Table 2). 77 species of aquatic variation (p = 0.068) was observed in the macrophyte species macrophytes from 53 genera and 31 families was recorded richness between the control (4.27), sewage disposal (4.13) from the study area. Sphaeranthus africanus and Colocasia and intensive agricultural areas (4.90). However, a significant esculenta were specific to the sewage zones; Aeschynomene variation (F = 25.35 p < 0.001) in macrophyte species richness indica, Myriophyllum oliganthum, Rotala indica, R. was observed between the area of saline intrusion (1.67) and malampuzhensis, Centella asiatica, Hedyotis corymbosa, the other three study zones. In Ponnani Kole wetlands, the Author's personal copy

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Table 2 Diversity indices of aquatic macrophytes and results of ANOVAand post-hoc analysis for different study zones within Ponnani Kole wetlands

Diversity indices Saline Agriculture Sewage Control F P

Species richness (S) 1.67a 4.90b 4.13b 4.27b 25.35 <0.001 Biomass (M) 627.98c 269.57a 472.21b 405.96b 10.08 <0.001 a b b b Shannon diversity index (H′(log2)) 0.38 1.30 1.11 1.21 17.61 <0.001 Simpson’s evenness index (1- ) 0.16a 0.46b 0.41b 0.44b 15.36 <0.001 Average taxonomic distinctness (AvTD; Δ+) 30.77a 76.51b 73.74b 74.51b 33.36 <0.001 Variation in taxonomic distinctness (VarTD, Λ+)40.24a 246.04b 379.40c 193.43b 19.83 <0.001

Values with same superscript in a row does not vary significantly (P <0.05) agricultural area (1.30) showed the highest SDI whereas lower study, 25 species were observed in saline area under 21 genera SDI was observed in saline areas (0.38) (Table 2). In the con- and 10 families; 64 species were found in area of agricultural trol area (1.21) and sewage disposal (1.11) area, higher SDI activities which belong to 39 genera and 27 families; 45 spe- was observed which infer the occurrence of optimal environ- cies under 34 genera and 21 families were established in sew- mental conditions supporting the growth of many macrophyte age area and 39 species were observed in control area under species. Mean SDI showed no significant variation (p =0.228) 31genera and 18 families. Intensive agricultural area had the between the intensive agriculture, sewage disposal and control highest mean value of AvTD (76.51) and smallest number of areas indicating a uniform macrophyte assemblage. However, families when compared to sewage disposal and control areas. mean SDI was lower in the saline intrusion areas when com- In the area of saline intrusion, which had the lowest mean pared to the other three study areas and showed a significant value of AvTD (30.77), all the species observed were belong difference (F = 17.60; p < 0.001) when considering all sites to 10 closer families. Significantly, lower AvTD was also ob- (Table 2). served in saline (30.77) areas when compared to the other Simpson’s evenness index (SEI, 1- ) was high in the control three regions of study (F = 33.35; p < 0.001) and did not vary (0.44), intensive agricultural (0.46) and sewage disposal zones significantly (p = 0.627) between intensive agriculture (0.41) compared to the areas of saline intrusion (0.16) (76.51), sewage disposal (73.74) and control sites (74.51) (Table 2). The results showed an even distribution of macro- (Table 2). phytes in undisturbed, intensive agricultural and sewage dis- Variation in taxonomic distinctness (VarTD, Λ+)was posal areas and dominance of specific saline tolerant species lower in areas of saline intrusion (40.238) (Table 2) due in saline intrusion zones. Similar to SDI no significant varia- to the occurrence of closely related species belonging to tion was observed in SEI between the control, sewage disposal closely related families like Menyanthaceae, Convolvulaceae, and intensive agriculture areas (p = 0.353). However, mean Lentibulariaceae, Verbenaceae, Avicenniaceae, Amaranthaceae, SEI was significantly lower in the saline (0.16) intrusion areas Pontederiaceae, Cyperaceae and Poaceae. Simulation tests to when compared to the other three study areas (F = 15.36; check the deviation of AvTD recorded from the global mean p <0.001)(Table2). using funnel plots showed that the AvTD in saline intrusion areas Higher average taxonomic distinctness (AvTD) indicates a was well below the 95% confidence level of global mean widespread distribution of species within species rich zones (Fig. 3). Mean AvTD values in the area of intensive agricultural and is sensitive to the taxonomic relatedness of species. In this activities and the control area were very close to the expected

Fig. 2 Dominance plot of the macrophytes recorded from different disturbance zones of Ponnani Kole wetland Author's personal copy

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Fig. 3 Average taxonomic distinctness (Δ+) for the four different study areas within Ponnani Kole wetlands

range simulated from the global assemblage, while AvTD in associates, like Ipomoea pes-caprae, Acanthus ilicifolius, sewage disposal area (73.74) fell below the 95% confidence Clerodendron inerme, Avicennia officinalis and Mariscus level (Fig. 3). javanicus, which constituted about 58% of the total bio- VarTD values for intensive agriculture (246.04), sewage mass (Table 3). In the areas of intensive agricultural disposal (379.40) and control (193.43) were observed within activity, anchored floating macrophytes like Nymphaea the 95% confidence limit of the global mean for all the nouchali, N. pubescence, Nymphoides crystatum, sites with values for saline intrusion (40.24) shown Marsilea quadrifolia, (30.37%) and wetland plants like above the global mean limits (Fig. 4). The result shows Aeschynomene indica, Hygrophila schulli, Alternanthera an equal dominance of all macrophyte species belonging sessilis and Eragrostis gangetica (23.54%) were domi- to various higher taxa in all zones of study except that of the nated. In the sewage disposal area, anchored floating saline intrusion areas. (30.83%) and free floating plants (30.36%) were the Macrophytes assemblages within the four different zones dominant group with free floating plants like Salvinia showed 60% similarity (Fig. 5). However, between the sew- molesta, Eichhornia crassipes, Pistia stratiotes, Lemna age, agriculture and control zones macrophyte assemblages perpusilla and Salvinia molesta very recurrent. In undis- showed 40% similarity. Only 20% similarity was observed turbed area, wetland plants (28.06%) and anchored floating between the macrophyte assemblages of saline zones with (28.61%) were the dominant group. Rotala macrandra, all other studied areas (Fig. 5). Ludwigia perennis, Hedyotis brachypoda Merremia tridentata, Alternanthera sessilis, Polygonum barbatum, P. Habit Wise Distribution of Macrophytes in Different glabrum, Cyperus difformis, Eragrostis gangetica, Disturbance Zones Hymenachne acutigluma, Leersia hexandra and Cynodon dactylon were the wetland plants observed in the undisturbed Macrophytes recorded from the different zones of Ponnani area whereas Nymphaea nouchali, N. pubescence, Kole wetland were categorised based on their habits and the Nymphoides indica, Ipomoea aquatica, Bacopa monnieri results are presented in Table 3. In the area of saline intrusion, and Marsilea quadrifolia were the anchored freshwater spe- the dominant macrophytes include mangroves and its cies observed for the control sites.

Fig. 4 Variation in taxonomic distinctness (Λ+) for the four different study area within Ponnani Kole wetlands Author's personal copy

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for clearing and high nutrient input may be the reason for species rich assemblages in areas of agricultural activity. Sewage disposal areas also seemed to support the luxurious growth of many species of macrophytes. Disturbed sites with very high nutrient loading (70 μg1−1) are characterized by low richness and by the presence of filamentous algae (Thiebaut and Muller 1998). In this study, the sewage disposal may be within the carrying capacity of the wetland system, as the sewage is properly decomposed to release nu- trients slowly. Therefore, this region may be a sink for sewage from nearby areas. However, reclamation and reduction in the extent of the wetland area could seriously hinder the Fig. 5 Non-metric multidimensional scaling plot of macrophyte assemblage in four different zones within Ponnani Kole wetlands ecosystems equilibrium. Reddy and De Busk (1985) sug- gested that some macrophytes grow naturally in water bodies with mild pollution from urban areas and utilize these nutri- ents to produce large amounts of biomass. This is true in the sewage disposal area were higher biomass compared to the Discussion control sites was observed. Though, biodiversity decreases on a global scale as an effect of human activity, mild influxes of Changes in land use patterns within the Ponnani Kole wetland nutrients leads to the enhanced biomass production in tolerant due to anthropogenic interventions like agriculture activities, species. However, at a local scale, as inferred from the present disposal of sewage and saline intrusion results in alterations to study, higher diversity was observed in the area of agricultural the hydrology, as well as, changes in the water chemistry of activities. This is in agreement with studies of aquatic ecosys- the wetlands, which leads to changes in the local plant com- tems in agricultural landscape in West Poland (Goldyn 2010). munity (Owen 1999). The number of individuals of various The high biomass of macrophytes in saline areas was at- species in the assemblage (evenness) is very important for tributed to the large mangrove shrubs with pneumatophores, maintaining significant functions and services such as soil whereas small and herbaceous wetland plants, suspended stability, and nutrient and water availability in wetland eco- hydrophytes and emergent hydrophytes were common in the systems (Valerie and Chapin 2001). Higher species richness in agricultural fields. Nielsen et al. (2003) suggested that rising the zones of agricultural activity and sewage disposal is a salinity in aquatic habitats unfavourably affects many fresh- direct consequence of increased nutrient loading resulting in water macrophytes due to their intolerance of salt. This may the development of species which are not typical of the be the reason for the predominance of specific saline tolerant Ponnani Kole wetland ecosystem. Periodic clearing of wet- macrophytes in saline intrusion areas of the study site. Hart lands and application of higher nutrient load as chemical fer- et al. (2003) suggested that aquatic plants exhibit many sub- tilizers in the area of agricultural activities may provide equal lethal responses to increased salinity including loss of vigour chance for the sprouting of different species and promoting and reduced species diversity. Many of the macrophytes can- their growth (Verhoeven and Setter 2010). Hence, provisions not thrive in the regions of saline intrusion due to narrow salt tolerances and thus, a decrease the macrophyte diversity with- in these areas. Table 3 Percentage occurrence of aquatic macrophytes of different The loss of biodiversity can have important consequences habits in different zones of ecological disturbances in Ponnani Kole wetlands that include reduced ecosystem function and resilience, as well as the loss of genetic diversity (Walker et al. 1999; Folke et al. Habit Disturbance zones Control 2004). Shimoda (2003) revealed high plant diversity in paddy fields compared with vegetation in an abandoned field. This is Saline Agriculture Sewage true with our study area where nutrient rich and herbicide free Free floating 9.00 18.67 30.36 14.27 agricultural fields promote an increase in plant diversity com- Suspended hydrophytes 1.00 9.20 2.15 2.61 pared to other zones. In aquatic vegetation, mono-dominant Submerged hydrophytes Nil 5.07 6.43 5.56 zones are observed frequently (Papastergiadou et al. 2008), Anchored floating Nil 30.37 30.83 28.61 however, periodical clearing of agricultural fields will reduce Emergent hydrophytes 21.00 9.39 14.04 12.29 the chance of mono-species domination. Hence, the similarity Wetland plants 11.00 23.54 15.27 28.06 observed for species richness and Shannon diversity index in Mangrove and its associates 58.00 3.75 0.92 8.59 the current study area can be due to the consistent dominance of several species across the disturbance gradient. Author's personal copy

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Taxonomic relatedness indices (AvTD and VarTD) were tend to have more taxonomically distant species suggested to be more sensitive than species richness to intrin- resulting in greater taxonomic distinctness. This is true sic differences among the different study zones and thereby, to with the saline intrusion area where species from related be more amenable to detecting degradation due to anthropo- families like Lentibulariaceae, Acanthaceae, Verbenaceae genic effects (Clarke and Warwick 1998). Since taxonomic and Avicenniaceae, as well as, Poaceae and Cyperaceae spread is more directly related to functional diversity than represented the area. This observation is confirmed by species richness, these novel measures might, in fact, be more the results obtained in the nMDS and dominance plots important when considering the conservation of ecosystem of the species assemblage of aquatic macrophytes re- functioning. Heino et al. (2005) opined that taxonomic dis- corded from the four zones of the study area. It is tinctness also varies along natural gradients and it is unlikely further inferred that the impact of anthropogenic distur- that a site can be determined to be degraded or not degraded bance is not contributing significantly to the biodiversity based only on a measure of taxonomic distinctness. However, variability of aquatic macrophytes in the Ponnani Kole the present findings are of importance to the assessment of wetland region, however the geoclimatic attributes con- anthropogenic effects on biodiversity. The AvTD in intensive tribute significantly to the diversity and assemblage pat- agriculture, sewage disposal and control areas do not show tern of aquatic macrophytes of the region. The similarity much variability when compared to each other but did vary of agriculture and sewage disposal zones to the control when compared to saline intrusion areas. This indicates the and difference in saline intruding area with other zones uniform distribution of species in all study zones except saline obtained in the NMDS plot further confirms the above intrusion areas. When considering the parameters describing inference. the assemblages in relation to disturbance, the taxonomic dis- The analysis of diversity, Simpson ’s evenness and Shannon tinctiveness approach was found to be particularly suitable for diversity index, in the four study areas exhibited the same macrophytes, for which the less-disturbed study zones (inten- pattern. These results are in accordance with the sive agriculture, sewage disposal and control) were character- Intermediate Disturbance Hypothesis (IDH) proposed by ized by species belonging to wide taxonomic groups and Connell (1978) which states that intermediate levels of distur- hence higher taxonomic distinctness. Furthermore, functional bance embrace maximize species diversity because competi- groups of macrophytes were more evenly distributed within tively dominant species exclude minor species at lower distur- these zones. Increased anthropogenic influences could alter bance levels. In the same way, a high limitation level leads to this pattern in the future resulting in biodiversity falling below local disappearance of species. The IDH has important prac- the predicted range. Although AvTD has the ability to discrim- tical implications for the maintenance of biodiversity inate properly between polluted and non-polluted areas, in (Townsend et al. 1997) as it highlights environmental condi- those of low number of species, the results of this study dem- tions that favour the coexistence of numerous species with a onstrated that its power of discrimination decreases when the large set of bio/ecological profiles and consequently may host number of species increases (see confidence limits in the diversified communities. Intensive agricultural areas using the funnel graphic representation, Fig. 1), which leads the authors optimal level of nutrients harbour an appreciable abundance of to think that the index is not able to show correlations within typical aquatic plants and maintain their community structure pollution areas where richness depends on other factors. and distribution. Mangroves were limited in areas with agri- VarTD has the potential to distinguish differences in taxonom- cultural activity which may be due to the absence of saline ic structure resulting in assemblages of some genera becoming intrusion or periodic clearing of agricultural fields before highly species rich whilst other groups are represented by only farming. In aquatic plants, intense competition may be expect- a few species. In the sewage disposal areas, the dominance of ed between species of similar habit occupying a similar area of genera like Ludwigia, Nymphoides, Ipomoea and Utricularia the wetland. The spread of wetland species is typical of which are highly species rich was observed alongside other synanthropization, as observed in other wetland systems higher taxa like Eleocharis, Cynodon, Eragrostis, Leersia, (Faliniski 2000;Jackowiak2003). In spite of evident similar- Paspalum, Sporobolus and Oryza which were represented ities, these species may vary significantly when facing inter- by only one species each. Similarly, in the intensive agricul- ference competition (Gettys et al. 2009). Occurrence of typical tural activities area Rotala, Ludwigia, Limnophila and wetland species indicates that the Ponnani Kole wetland is Utricularia are some genera represented by many species experiencing minimum anthropogenic disturbances. The ob- whereas genera like Eragrostis, Hygroryza, Hymenachne, served disturbances gave an indication that future growth of Leersia and Sporobolus were represented by one species each. agriculture and other human led activities will augment the Clarke and Warwick (2001) hypothesised that under anthro- rate of species loss by typical aquatic plants susceptible to pogenic disturbances perturbed communities have reduced slight disturbances in this wetland system. This phenomenon taxonomic distinctness, being composed on average of more could accordingly alter the functional status and community closely related species than unperturbed communities, which structure of macrophytes in this unique wetland. Author's personal copy

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