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

The microbial community of river sediments and their relationship to enviro nmental factors is largely unknown. In this study the abundance of bacteria , flagellates, ciliates, and Micrometazoa was investigated for eight differ ent sediment types. The sediment types were classified by discharge (stable versus flood period), location (upper versus lower reach), and depth (supe rficial versus deep sediment layer). Abundances in the lower reach were mor e than two times higher than in the upper reach but decreased markedly at b oth sites after flooding. Organism densities were similar between the two s ediment layers, although deeper habitats served as potential refugia, as in dicated by reduced transport of coarse particles into the deep sediment lay er. The organism abundances correlated with concentration of fine organic p articles. A habitat templet model was used to classify favourableness and d isturbance of the sediment types. For an empirical placement of sediment ty pes in the model, results on abundances, fine organic particles, nutrient c oncentrations, particle transport, and flood frequency were integrated. Loc al processes, mainly related to sediment transport, decreased the predictic ability of the habitat templets.