Atrazine effects on the microbial food web in tidal creek mesocosms

Atrazine effects on the microbial food web were assessed in mesocosms desig ned to simulate a southeastern tidal creek ecosystem. The test chambers sim ulate the major features unique to estuarine systems, such as tidal flow an d salinity changes. Microbial communities were colonized on artificial subs trates and analyzed for productivity, biomass, and community composition. A trazine was found to reduce chlorophyll rr. phototrophic carbon assimilatio n and phototrophic biovolume in the 40 and 160 mu g l(-1) treatments. Signi ficant reductions in phototrophic variables occurred within 24 h of pestici de exposure and no recovery was detected after 9 days. Dissolved oxygen con tent in the mesocosms was not significantly affected by atrazine. Atrazine induced changes in composition of the algal community. Most taxa were reduc ed in abundance by atrazine exposure; however, cyanobacterial taxa generall y became more abundant. Bacterial abundance was significantly elevated in t he highest dose after 24 h, but decreased in a dose-response manner after 4 5 h. There was no significant effect on small ciliates; however, large cili ates and small flagellates increased significantly in number after 48 h and remained elevated after 9 days. Atrazine at 160 mu g l(-1) significantly r educed large flagellate density throughout the experiment. These results su ggest that exposure of the estuarine microbial food web to agricultural pes ticides can lead to both functional and structural changes, which may poten tially impact higher trophic levels. (C) 1999 Elsevier Science B.V. All rig hts reserved.