Relationships of macrobenthos with dissolved oxygen and organic matter at the sediment-water interface in ten French lakes

Previous papers have underlined the major role played by dissolved oxygen and organic matter in macrobenthos distribution in lakes, especially in the bathymetric decrease in faunal richness. The present study deals with relationships between these two factors and a biotic index based on endobenthos taxon richness and density. Biological and environmental data refer to 40 sites plotted at 4 different relative depths in 10 lakes of the French Jura (9 lakes) and Pre-Alps (Lake Annecy). From 735 samples of soft sediment and 640 values of dissolved oxygen, the observed relationships of total organic carbon (TOC % dw) and dissolved oxygen (DO % sat) with a biodiversity gradient are presented in three figures. Despite the complexity in determining any biodiversity, the limiting effect of minimum DO values and maximum TOC values on the biotic potential are underlined. DO proved to be limiting below 90 % saturation and very limiting below 65 %. For TOC, a preferendum appeared around 3 % dw. From samples selected in non-limiting conditions of oxygen or organic carbon contents, each of these two factors was connected with the biodiversity index by a regression. In lake typology a 10 % sediment organic matter content indicates the onset of dysbiotic features for macroconsumers. The proposed results might be used as guidelines for lake monitoring and functional studies.