Abstract

Oxygen uptake rates of undisturbed sediment columns have been used as an integrative 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 reflect the trophic condition of the whole lake. Four small lakes of central Chile, differing strongly in trophic conditions, provided a possibility to compare benthic oxygen uptake rates, under different oxygen conditions (Quinenco, Grande, Chica and Lleulleu). Our objective was to establish the relationship 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: Quinenco 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 Lleulleu 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 community metabolism decreased with oxygen concentrations. The slope of regression lines, relating oxygen uptake rates to oxygen concentrations, differed for the different sites investigated, closely related with the trophic conditions 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 nutrients 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).