Functional and structural characteristics of the epipelic biofilms in a lowland Pampean stream (Argentina) exposed to the increase of the urbanization

Abstract

The purpose of the present study was to analyze the structural (organisms density, total biomass, autotrophic biomass and autotrophic index) and functional (net primary production, respiration, gross primary production and assimilation rate) responses of the epipelic biofilm at three sites of a Pampean stream presenting different proportions of land use exposed to urbanization. The results showed that the increase in the percentage of land use destined to urbanization was evidenced by the changes in the water quality and by the functional and structural descriptors of the epipelic biofilm. In this regard, the quality of water diminished at the most urbanized sites mainly as a consequence of the nutrient increase. This affected the net primary production, the assimilation rate and the gross primary production/respiration ratio, reflecting that the biofilm was markedly autotrophic and more efficient photosynthetically. These changes in the metabolic descriptors are coincident with the pattern followed by the chlorophyll which reflected a change in the trophic state from mesotrophic to eutrophic. Likewise, the specific composition in those sites showed changes favoring the increase of organisms tolerant to pollution.