Introduction

The inflow of urban runoff (sewage and effluents) into wetland channels enhances nutrient levels resulting in eutrophication with the bloom of invasive species (Craft and Casey, 2000; Conley et al., 2009). Consequences lead to impairment in hydrological components, sediment type, habitat availability and biological components that differ significantly among eutrophic and oligotrophic water bodies, (Galatowitsch and van der Valk, 1996; Gwin et al., 1999). Conventional water treatment systems fail to remove nutrients, which is also expensive unless one opts for algae based treatment systems (Mahapatra et al., 2011a, b). Any physical treatment, for instance, the drastic disturbance in sediments and water levels impair the nutrient and light availability for benthic macroinvertebrates and algae, leading to the imbalance in the higher group of organisms in the food chain (Ellings and Hodgson, 2007). This poses challenges for water resource managers and aquatic ecologists, necessitating effective restoration and conservation practices. Restoration is adapted for recovering the aspects of clean wetland functions that are lost due to physical, chemical and hydrological alterations (US EPA 2005; Kaye et al., 2006). Traditional restoration methods respecting ecological goals have improved the physical functioning of wetlands, with least improvements in biodiversity aspects (Zheng and Stevenson, 2006).

Monitoring of wetlands during prior and post restoration period would help in assessing the effectiveness of restoration and understanding on relation between chemical and biological community. Aquatic biota have been monitored prior to wetland restoration in England (Bennion et al., 1996); Finland (Miettinen, 2003); Denmark (Bradshaw et al., 2005) and other European waters, which provided vital clues on the gaps in the restoration techniques worldwide. Species composition and assemblages of macroinvertebrates, aquatic plants, zooplankton and algae have been investigated to assess metal contamination, nutrient transport, sedimentation and functioning of food chain (Nakano et al., 2007; Bennion et al., 2011). Biota like benthic diatoms is useful potential bioindicator as their species composition corresponds to chemical and habitat impairment (Miettinen, 2003; de la Rey et al., 2004).

Diatoms are a prominent group among photosynthetic algae integrate conditions of their respective habitat types , which  explains better species-environment relationship. Species tolerance level is associated with specific anthropogenic changes (macrophytes, eutrophication and agricultural waste) across globe (Bere and Tundisi, 2011). On the contrary, sensitive species characterize clean or oligotrophic waters, which facilitates as ideal or clean or reference condition to accomplish restoration goals (Bennion et al., 2011). For better understanding of restoration, wetlands located at urban regions are to be investigated along with undisturbed or reference sites. Dong et al., 2008 recorded species assemblage shift to eutrophic conditions over a time period in Taihu lake which aided in the restoration. Bennion et al., 2011 discusses the use of biological proxy like diatoms to identify environmental drivers and derive reference conditions based on sensitive species assemblages. Investigations of diatom distribution prior to restoration would reveal the impact of chemical conditions like nutrients on organisms. Diatom assemblages in lake sediment cores and surface sediments explained nutrient and human influences on present day water conditions (Flower et al., 1997).

In this study, Bangalore, one of the most urbanized regions of peninsular India, was selected because of the rapid urbanization and consequent severe human pressures on wetlands in recent years. Bangalore’s wetlands have been monitored during the last two decades for water’s physical and chemical variables and this has helped in developing appropriate monitoring and restoration strategies in order to achieve good water quality and ecological status (Ramachandra, 2005). However, this aspect has not been implemented in the routine regional wetland management programs. The efficacy of wetland restoration depends on the biological components, socio-economic aspects, apart from the reduction of physical stressors. In this backdrop, diatom based water quality monitoring with the assessment of diatom distribution, ecological significance was undertaken for the first time for the regular monitoring of water bodies in Peninsular India. This study aims to investigate changes in and response of species composition to chemical conditions during prior and post restoration within and among selected wetlands Further, to assess the impact of restoration over a period, previously restored (>10 years) wetlands were compared to a reference (oligotrophic) water body and polluted (eutrophic) water bodies. Wetlands similar to reference (clean) conditions was defined based on Bennion et al., 2011.