Benthic community metabolism and trophic conditions of four South Americanlakes

Oxygen uptake rates of undisturbed sediment columns have been used as an in tegrative measure of the metabolic activities of benthic communities. Since the intensity of metabolic processes of profundal lake is dependent on the production of organic matter in the pelagic zone, oxygen uptake rates refl ect the trophic condition of the whole lake. Four small lakes of central Ch ile, differing strongly in trophic conditions, provided a possibility to co mpare benthic oxygen uptake rates, under different oxygen conditions (Quine nco, Grande, Chica and Lleulleu). Our objective was to establish the relati onship between the oxygen uptake rates and bottom characteristics of lakes with different trophic conditions. At 8 mg O-2 l(-1) in the overlying water of the cores studied, the oxygen uptake rates of the sediment were: Quinen co 51.2-56.0 mg O-2 m(2) h(-1) (eutrophic), Grande 41.2-46.4 mg O-2 m(2) h( -1) (mesotrophic), Chica 23.2-18.1 mg O-2 m(2) h(-1) (mesotrophic) and Lleu lleu 11.7-16.0 mg O-2 m(2) h(-1) (oligotrophic). By exposing the sediments to different oxygen levels in the laboratory, it was found that benthic com munity metabolism decreased with oxygen concentrations. The slope of regres sion lines, relating oxygen uptake rates to oxygen concentrations, differed for the different sites investigated, closely related with the trophic con ditions of the lakes. It was positively correlated with the organic matter content of the sediment of the cores (r(2)= 0.78, p < 0,05) and the nutrien ts of the bottom waters (total-P: r(2)= 0.73, p < 0,05; total-N: r(2)= 0.73 , p < 0,05), and negatively with the redox potential of the sediments (r(2) = 0.88, p < 0,05).