Introduction

Lakes are fragile ecosystems which while contributing to suitable climatic conditions for life on the earth also meet vital needs of humans in many ways.  These fragile ecosystems function as kidneys of the landscape through the uptake of nutrients from their surroundings. They are sources of water for agriculture, drinking, domestic use and livestock rearing (Ramachandra, 2009a). Close to human habitations the lakes make the air cooler in hot summer months. Their very presence renders aesthetic beauty to the landscape and promotes tourism and recreation.  While supporting inland fisheries, the lakes especially their edges, overgrown with marsh grasses and other herbage furnish fodder for livestock. Large lakes support water transport energy, help in stabilizing local climate. They recharge ground water and channalise water flow to prevent water logging and flooding. They act as important crucibles for aquatic biodiversity of which the macroinvertebrates play a critical role in ecosystem balance by facilitating flow of energy and matter through food web and constitute an important trophic level in the aquatic ecosystem. (Verneaux et al., 2004; Ramachandra 2009b)

Macroinvertebrate composition, abundance and distribution are influenced by water quality. Most of urban lakes of India have been polluted due to unplanned urbanisation by organic matter from both point source (industries and domestic), non-point source pollution (agri and storm water runoff) and autochthonous sources (mainly planktons) directly influencing the light penetration and affecting the production efficiencies in lakes (Zutchi et al., 2008; Ramachandra, 2009). Anthropogenic stresses are disturbing complex fragile interactions and self-cleansing or treatment capability of aquatic ecosystems. These influence aquatic macroinvertebrates as reflected in their assemblages and species compositions.  If the inflows of pollutants are below the lake’s self cleaning capacity, then impacts get attenuated in the lakes as evidenced by improved water quality at outlets compared to inlets. However, in most urban lakes, levels of pollution have crossed the threshold resulting in eutrophic status.

The distribution and diversity of macroinvertebrates are interrelated to water quality, evident from the rising richness of macroinvertebrates in tune with levels of organic pollution. Their relative abundance has been used to make inferences about pollution loads (Azrina et al., 2006). Presence and absence of dominant species and the degree of community assemblages reflect pollution levels making macro-invertebrates good bioindicators. Bhattacharya (2000), Khan and Ghosh (2001), Saha et al. (2007) and Jana et al. (2009), documented the diversity and ecology of lake ecosystems in north and north-east regions of India. Benjamin et al., (1996) reported the causal factors for fish mortality in Bangalore lakes. Earlier studies focusing on wetland restoration and conservation (Ramachandra and Ahalya, 2001, Ramachandra, 2009a, b), physico-chemical analysis and role of phytoplankton (Roselene and Paneerselvam, 2008) and macroinvertebrate diversity and water quality of nine lakes of Bangalore (Balachandran and Ramachandra, 2010), reveal diversity, health of lake ecosystem and conservation related issues. The assemblage and abundance of aquatic macroinvertebrates varies in inlet and outlets depending upon the nutrient availability in urban stressed lakes (Richardson and Mackay 1991) and there are very few studies supporting this model. In this context, the present study examines the macro invertebrate diversity and abundance in inlet and outlets along with environmental parameters of selected lakes in and around the Bangalore city to explore the possibility of using macro invertebrates as as surrogates for environmental conditions.