Spatial and temporal heterogeneity of an epilithic streambed community in relation to the habitat templet

Abstract

The microbial community of river sediments and their relationship to environmental factors is largely unknown. In this study, the abundance of bacteria, flagellates, ciliates, and Micrometazoa was investigated for eight different sediment types. The sediment types were classified by discharge (stable versus flood period), location (upper versus lower reach), and depth (superficial versus deep sediment layer). Abundances in the lower reach were more than two times higher than in the upper reach but decreased markedly at both sites after flooding. Organism densities were similar between the two sediment layers, although deeper habitats served as potential refugia, as indicated by reduced transport of coarse particles into the deep sediment layer. The organism abundances correlated with concentration of fine organic particles. A habitat templet model was used to classify favourableness and disturbance of the sediment types. For an empirical placement of sediment types in the model, results on abundances, fine organic particles, nutrient concentrations, particle transport, and flood frequency were integrated. Local processes, mainly related to sediment transport, decreased the predicticability of the habitat templets.