THE EFFECT OF ENVIRONMENTAL PARAMETERS ON ALGAL ASSEMBLAGES IN HUMAN-IMPACTED SUBURBAN BROOKS

The response of the taxonomic structure of algal assemblages, several trophic and saprobic indices and taxa richness to environmental gradients was investigated in small suburban streams with high organic and trophic load. Gradients of nutrient richness, electrical conductivity and substratum (a gradient from muddy to stony substratum) were considered. Although all the gradients explained a significant portion of variance in the taxonomic structure of algal assemblages, the gradient of nutrient richness was the most important. Contrary to our expectations, trophic indices responded well neither to the gradient of nutrient richness nor electrical conductivity; only TI sub(DIA) weakly correlated with nutrient richness, while TI with the substratum gradient, which probably reflected prevailing hydraulic conditions. This was most probably caused by the shortness of the nutrient richness gradient in the heavily polluted studied streams, and by the fact that the indices were primarily set up to distinguish between low and high trophic levels, instead of distinguishing between high and yet higher trophic levels. On the other hand, algal taxa richness reflected quite strongly an additive effect of nutrient richness and electrical conductivity and was identified as a parameter, which might be helpful in identification of streams (sites) of the worst ecological quality which require priority restoration measures. We also suggest that the algal taxa richness should be tested for its performance in extreme parts of other environmental gradients.