An integration of water physicochemistry, algal bioassays, phytoplankton, and zooplankton for ecotoxicological assessment in a highly polluted lowland river

Results of different approaches potentially useful for the evaluation of water ambient quality were analysed and compared in a small temperate lowland river with mixed diffuse and multiple-point source pollution. The Reconquista River ( Buenos Aires Province, Argentina), one of the most polluted watercourses of Latin America, receives agrochemicals as well as domestic and industrial ( mostly untreated) effluents. Physical and chemical water variables were determined; unispecies algal bioassays ( with Chlorella pyrenoidosa and Scenedesmus acutus) were carried out in laboratory; and density and structure of phyto- and zooplankton were analysed at three sites in four dates ( representing a range of likely conditions in the river). A general scheme of association among plankton, bioassays and physical/chemical variables was elaborated, that helped to infer possible control factors in this multi-stressed system. Some empirical methods, but mainly mathematical ones including multivariate techniques ( as PCA, cluster analysis), were applied for evaluation of samples. A preliminary selection of indices and attributes as potential indicators of the water river quality was made, and then applied for assay a tentative integrative ordination of samples. The relative best water quality was recorded when-where dissolved oxygen concentration, algal diversity and planktonic crustacean density were higher. The worst water quality corresponded to the lack of cladocerans and lowest crustacean density, and higher: organic and industrial pollution, major nutrients ( ammonium and orthophosphates), BOD, hardness, conductivity, algal biomass in bioassays, phytoplankton density (> 10 000 ind. mL(-1)), dominance of a single algal species (> 90%), and rotifer proportion in zooplankton (> 85%).