Unplanned anthropogenic activities have contributed to the shrinkage of wetlands apart from degrading their quality. This necessitates watershed based planning which requires inventorying, mapping and regular monitoring with the cost-effective and reliable assessment protocols. Diatoms, unicellular algae, have been used across continents as bioindicators for reflecting physical, chemical and biological integrity of their own habitats. The current study attempts to understand the role of environmental factors in the formation of diatom community structure in the shallow wetlands of peninsular India. Diatoms from different habitats and water chemical variables were assessed for 43 wetlands of Bangalore, a profoundly urbanized region of Peninsular India. A total of 181 diatom taxa from 45 genera highlights the biodiversity richness of the region. Wetlands located in the densely populated urban regions are dominated by a prolific growth of eutrophilic species such as Gomphonema parvulum Kütz., Nitzschia palea (Kütz.) W.Sm., N. umbonata (Ehrenb.) Lange-Bert., Diadesmis confervacea Kütz., Cyclotella meneghiniana Kütz. and C. atomus Hust.. Wetlands located at the outskirts of the city characterize oligo-mesotrophic conditions where Achnanthidium sp. dominates. Detrended canonical correspondence analysis showed a strong influence of eutrophication and organic/inorganic pollution on diatom assemblages but a relatively weak influence of conductivity. TWINSPAN shows grouping of wetlands based on species composition and highlights that Achnanthidium sp. and Cyclotella meneghiniana are initial indicator taxa for oligo-mesotrophic and eutrophic conditions respectively. These results highlight that the environmental factors consistently act as limiting variables in structuring diatom assemblages at a regional scale in urban ecosystems. The study provided insights to the ecological importance of endemic diatoms found in different environments. Thus, diatom based biomonitoring became a viable surrogate for physical and chemical parameters of water quality. Also, region specific diatom indices would aid in easy and efficient investigation of wetlands.

Key index words: algae, diatom, Bangalore, habitat specificity, Peninsular India, water management