Ecological Characteristics of Benthic Diatom Communities in Assessment of Lake Trophic Status
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Lake 2010: Wetlands, Biodiversity and Climate Change Ecological Characteristics of Benthic Diatom Communities in Assessment of Lake Trophic Status Alakananda, B1,2. Supriya Guruprasad1. Mahesh M.K2 and Ramachandra T.V1 1 Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore, India 2 Department of Botany, Yuvaraja’s College, Mysore, India The ecology of benthic diatoms was investigated in 15 lakes which are in the fringe of urbanization impacts. The aim of this study was to examine the community composition and diversity of benthic diatoms in different microhabitats viz. epilithic, episammic and epiphytic. This study also contributed to the understanding of whether environmental factors control the species composition? Water and benthic diatom samples were collected from different habitats and sampling sites during February – May 2009. Results showed that physical and chemical variables of water varied spatially. The water quality of lakes which were contaminated with sewage and/or industrial discharge was influenced by pH, electric conductivity, chemical oxygen demand, and biological oxygen demand and nutrient concentrations. This was also evident by principal component analysis (PCA). The cluster analysis groups the lake sampling sites which are categorized into different water quality classes. Total diatom data consisted of 122 taxa and varied with change in habitat. The dominance of Gomphonema parvulum, Nitzshia umbonata, N. linearis, N. palea conveyed the eutrophic to hypertrophic lake trophic condition. The genus Achnanthidium had a wide range for water quality parameters and was found abundance across all the sites. The high nutrient filled inflow was confirmed by the ecological preferences and tolerance of benthic diatoms to sustain in such pollution. The diatom indices (TDI, GDI, and SPI) are used to classify mesotrophic from eutrophic lakes and thus monitoring strategies including benthic diatoms can also aid in conservation of urban diversity. INTRODUCTION Aquatic ecosystem and its ecology have been the major concern during last century owing to rapid urbanization, intensification of agriculture and anthropogenic changes with impacts on the physical, chemical and biological shifts. These changes in any aquatic ecosystem will affect the species uniqueness and ecological characteristics of biotic community composition with loss of biotic integrity. The environment and its habitat are considered as a niche, when it is apt for biotic community composition with precise ecological preferences to inhabit. Thus, the requisite understanding of the biotic ecological 22nd-24th December 2010 Page 1 Lake 2010: Wetlands, Biodiversity and Climate Change characteristics portrays varying environmental conditions, emphasizing for measure of the extent of degradation and restoration of the environment in these habitats. Amongst all the biotic community, benthic diatoms provide a representative group of indicative species, thus the community composition as a whole changes in response to changes in environmental conditions. Benthic diatoms are ubiquitous and diverse components of aquatic biodiversity in ponds, lakes (Flower 2005), rivers, streams (Taylor et al., 2007b) and so on. Benthic diatoms in particular are patchily distributed and hence extremely vary in community composition at different spatial scales (Pan et al., 1999, Soinien, 2004). Such Heterogeneity in diatom composition at various scales could be due to multiple factors such as light, grazing, chemical variables and habitat availability (Sommer 2000). Thus benthic diatoms are being increasingly established as bioindicators because of their strong response to environmental change and biotic integrity of the ecosystem (Whitton et al., 1991; Potapova and Charles, 2002; Yellop and Kelly, 2006). Several pollution assessment methods developed using benthic diatom community composition and autecological indices aided in evaluating the changes in the diatom assemblages due to sensitivity and tolerance of the species to environmental variables (Sgro et al., 2006). Juttner et al., 2003; Taylor et al., 2007; Soininen & Weckström 2009 studied diatom community and diatom indices in relationships with environmental conditions, biodiversity and to monitor pollution in streams. Many of these indices have been developed and applied in European countries, especially in France, Belgium and Luxemburg (Prygiel & Coste, 1995). The diatom index IBD (Indice Biologique Diatomees; Prygiel & Coste, 1998) has recently been tested in France for routine monitoring. The tropical diatom indices- TDI in South Africa (Taylor et a., 2007b), Pollution sensitivity indices- IPS, Generic diatom indices (Kelly et al., 1998, Brabecz and Szoszkiewicz, 2006), Trophic diatom indices for lakes- TDIL (Stenger-Kovács et al., 2007) and so on have been discussed for water quality in rivers and streams. However, investigations of diatom based monitoring specific to an eco-region and specific for urban lakes are very scare or do not yet exist for Indian lakes. The urban lake represents altered ecosystems and hence research studies are particularly needed for both ecosystem restoration and management. Bangalore lakes were investigated for the better perceptive of urban lakes and pollution impacts on ecological characteristics of benthic diatoms. Advancement of urbanization in Bangalore has led to decline in the number of lakes due to immense agriculture, encroachment, nutrient inflow (sewage and industrial waste) and so on. In the past study physical and chemical analysis of several lakes such as Varthur, Bellandur, Rachenahalli, Amruthalli, Madiwala and were monitored and documented while it lack the ecological characteristic investigation of key indicator organisms primarily benthic diatoms. The objective of the current study was to investigate the relationship between diatom composition and the 22nd-24th December 2010 Page 2 Lake 2010: Wetlands, Biodiversity and Climate Change impacts of environmental variables on its ecological characteristics at 15 lakes of Bangalore to comparatively assess the lake trophic status. STUDY AREA BANGALORE Figure 1: Map of Bangalore presenting lakes selected for study 22nd-24th December 2010 Page 3 Lake 2010: Wetlands, Biodiversity and Climate Change Bangalore lies at 77°37’19.54’’ E longitude and 12°59’09.76’’ N latitude with an area of 751 sq. km. Bangalore is located at an altitude of 920 metres above mean sea level, delineating four watersheds: Hebbal, Koramangala, Challaghatta and Vrishabhavathi watersheds (Sudhira et al., 2007). The city harbors many man-made lakes facilitating the domestic and agricultural needs. Bangalore has grown spatially more than ten times since 1949 (69 square kilometres) and is a part of both the Bangalore urban and rural districts. Lakes of Bangalore occupy about 4.8% of the total geographic area covering both urban and non-urban regions. Among several lakes of Bangalore 15 were selected covering a range of environmental conditions and across sampling sites. The lake names and code are mentioned in Annexure 1. METHOD Water quality analysis Water samples were collected from all possible sampling sites (at least more than 2 sampling sites at each lake) covering the inlets and outlets and also depending on the lake size during February 2009 and February 2010. Samples were stored in polythene bottles and were carried to laboratory for further analysis. Dissolved oxygen was analyzed on site using 125ml BOD bottles. On site parameters viz., pH, water temperature (°C); total dissolved solids (mgL-1); salinity (mgL-1) and electric conductivity (µScm-1) were measured using EXTECH EC500 Probe immediately after collection. Other water chemistry variables like chloride, hardness, magnesium, calcium, sodium, potassium and phosphates were analyzed in laboratory and analyses were carried out as per standard methods for the examination of water quality as mentioned in Trivedy and Goel (1986) and American Public Health Association (APHA, 1998). Diatom sampling Diatom sampling along with water sampling was carried out and collected in polythene bottles from all available habitats such as plants (epiphytic), stones or boulders (epilithic) and sediments (episammic) following Taylor et al., 2007a and Karthick et al., 2010. Epiphytic diatoms were collected from crushing the submerged stems and leaves in a polythene cover. Epilithic diatoms from stones were brushed slightly with a toothbrush in a tray. The fine 5 mm upper layer of the soil containing diatoms was carefully collected excluding soil particles. All the samples were transferred to 125 sampling bottles separately with labels on it. Live samples were observed immediately after collection and then ethanol was added to preserve it. The diatom samples were processed for cleaning following KMnO4 and Conc HCl method. The cleaned samples were then centrifuged at 2500 rpm and slides were prepared using Pleurax mountant. The cleaning, processing and slide preparation was followed as per Taylor et al., 2007a. At least 400 valves 22nd-24th December 2010 Page 4 Lake 2010: Wetlands, Biodiversity and Climate Change were counted in each slide and species were recorded along with its abundance. The individuals were identified using identification guides and literatures of Krammer and lange- Bertalot 1986; 1988, Taylor et al., 2007b and Karthick et al., 2009. Statistical analysis Statistical analyses comprising Principal Component Analysis (PCA) was performed using PAST 2.04