Spatial and temporal distribution of macroinvertebrates and trophic variables within the bed sediment of three streams differing by their morphology and riparian vegetation

Abstract

The vertical distribution of invertebrates (>500 μm), trophic variables and sediment structure was studied in three adjacent sites in the French granitic Massif Central. Cores were taken down to a sediment depth of 60 cm with a freezing-core technique. Streams differed mainly in their porosity profiles. Porosity seemed to determine the vertical distribution of UPOM, whereas chlorophyll-a and ATP+ADP were controlled by both depth and porosity. Invertebrate density and taxonomic richness decreased with depth, 70 % to 96 % of the individuals were found in the first 15 cm. Densities were correlated with porosity only in the less porous sites (<2 % in deeper layers). In the site with porous substratum, density profiles differed from porosity profiles, suggesting another limiting factor. Limitation of water penetration and oxygen availability due to surface porosity <5 % was an alternative hypothesis. Low porosity did not affect the dynamics of hypogean organisms. At the stream scale, the sediment characteristics (percentage of fine sediment), the pattern of trophic resources and the proportion of different functional feeding groups seemed to be related to riparian influences. Stream morphology determined availability of trophic resources.