Temporal variations in an estuarine biofilm: with emphasis on nitrate reduction

Biofilm formed on plexiglass panels in an Indian estuary was studied by monitoring its physical, chemical, biochemical and biological parameters. Time series investigation showed both temporal and spatial variations of various parameters assayed. Biofilm thickness and biomass showed similar trends in distribution. During an exposure period of 7 days, the biofilm thickness ranged from 65 to 270 lm. Nutrient levels in the biofilm were 3 to 4 orders of magnitude higher when compared to ambient water. Significant correlations were observed between biofilm thickness and biomass (r ¼ 0:95 and p ¼ 0:0001), diatom counts and hexose sugar levels (r ¼ 0:95 and p ¼ 0:0001) and nitrate reducers and ammonia production (r ¼ 0:97 and p ¼ 0:0001). The various bacterial types assayed showed a population range of 102 to 106 cfu cm 2. Facultative anaerobic bacteria such as nitrate reducers (NRB) were observed after 24 h of biofilm growth. Although, nitrate reduction was observed in the biofilm up to 96 h, by the end of 168 h the estuarine biofilm showed significant levels of nitrate. Ammonia oxidising bacteria (AOB) were noticed after 96 h of biofilm growth. The biofilm was initially dominated by bacteria, and then followed by diatoms. Infestation by bacteriovores altered the biofilm community and architecture after 72 h of biofilm growth. The final community after 168 h was composed of heterotrophic bacteria, NRB, AOB, diatoms, barnacle cyprids and oyster larvae.