Discussion

The analysis of diatom distribution is not restricted to water quality monitoring studies but also done for characterization of micro habitats and ecological significance in a defined section of ecosystems (Weilhoefer and Pan, 2007).  This study reveals  macrophytes as one of the necessary habitats for benthic diatom assemblages. Habitat specific diatoms and its accumulation on different macrophytes were well noticed through species richness, which is probably the widely used diversity indices (Maguran, 2004). Typha sp., the commonly spread macrophyte at Ramasandra lake is known to reduce biological oxygen demand and thereby increase dissolved oxygen in water body. Thus, Ramasandra showed a moderate BOD/COD range. But, the burgeoning growth of Eichornia covered the entire water surface at Yelahanka lake, hindering light penetration and hence low species richness.

Earlier reports indicate that diatom assemblage is significantly different under varying nutrient, ionic concentrations and host macrophytes (Soininen et al., 2004; Cejudo-Figueiras et al., 2010). In the current study, we documented more species assemblage from macrophytes compared to stone habitat. In earlier studies, subsequent lower species richness and diatom diversity has been observed on hard substrata (rocks and wood) than on soft substrata (Kitner and Poulίcková, 2003). Further, application of epiphytic diatoms might be useful for computing water quality indices as it is likely to reveal more precise information about water quality in south Indian lakes than epilithic samples. Besse-Lototskaya et al. (2006) and Yallop et al., 2009 observed that the Trophic diatom index (TDI) and other diatom indices are influenced by choice of substrate and are accurate on using macrophytes attached diatom assemblages.

Pollution tolerant species Staurosirella pinnata (Ehrenberg) Williams & Round and Cyclotella meneghiniana Kützing were dominant diatom community of Yelahanka lake while Achnanthidium exiguum (Grunow) Czarnecki was abundant at Ramsandra lake. Ulsoor a restored lake with no macrophytes showed high conductivity values with low species richness and dominance of Ulnaria ulna var. acus. Kommaghatta lake showed high species diversity (27 species) on epiphytic habitat macrophytes before restoration and low species diversity (14 species) in post-restoration samples due to lack of suitable habitats. This also has decreased aquatic insects and molluscan diversity, leading to imbalance in the food chain and microbial activity (Masseret et al., 1998). Most conservation studies particularly anurans and fish diversity reported epiphytic diatoms as important tool in understanding interrelationship within trophic food chain of complex aquatic ecosystems (de Sousa Filho et al., 2007). This conform that benthic diatom species, its preference and patterning are important to study and are determined by macrophyte availability and consequent water quality.

Due to improper management strategies, most restoration practices disregard the importance of shoreline aquatic plants which has led to the decline in aquatic biodiversity particularly in degraded urban region (Ramachandra and Kumar, 2008). Urban lakes need robust water monitoring regulations, taking into account microhabitat availability and prominent pollution load. Excessive growth of invasive weeds such as Eichornia sp. hinder navigation, choking in irrigation channels and lakes, impede drainage and increase silt deposition. Thus, restoration and pollution prevention measurement needs to implement macrophytes management, removal of excessive weed growth and retain nominal aquatic plants for colonization of macro invertebrates, tadpoles and microbial activities. Wetland region is a vital component of the lake ecosystem, to be maintained at inflow region for substantial microbial community, in particular to diatom distribution and macro habitat that function in lake purification, colonization and for sustained ecosystem health.