Structure and Function of Phytoplanktonic and Microbial Communities in Relation to Industrial Wastewater Discharge: An Ecotoxicological Approach in a Lotic System

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Abstract
Microbial and phytoplanktonic processes of a perturbed river system were evaluated as an ecotoxicological alternative to bioassays in hazard assessment of industrial wastewater discharge. Although phytoplankton species composition was invariable throughout the river gradient, both P/B and ATP/AMP ratios revealed that the community did not acclimate over the spatial scale studied. The adenylate energy charge (ECA) of the microbial community decreased at the station where the wastewater is discharged; however, no significant differences in (ECA) values were observed downstream. Enclosure experiments allowed us to conclude that the microbial community was predominantly affected by the effluent rather than by the lotic physical gradient. In the river gradient, ECAappears to be an insensitive metabolic indicator; however, small changes in ECAare accompanied by much larger changes in the ATP/AMP ratios to which enzymatic activities are responding. The fact that some functional metabolic processes of the microbial community were affected while phytoplankton species composition was invariable suggests that P/B and ATP/AMP ratios would prove useful in the detection of insidiuous effects of industrial effluents at the microbial community level. This approach could also give more insight into the ecological significance of wastewater discharge for monitoring purposes.