Response of macroinvertebrates to fine sediment accumulations within the hyporheic zone of a calcareous sandstone stream (Weidlingbach, Austria)

Abstract

The role of the hyporheic zone as a habitat for macrozoobenthos was investigated within the clogged sediments of a calcareous sandstone stream near Vienna. From September 1997 to October 1998 sediments were sampled for vertical distribution of grain size, organic matter and invertebrates to a depth of 60 cm every second month using the freeze-coring-technique with electropositioning. The amount of fine particles within the hyporheic zone was strongly influenced by channel morphology. Sediments at the deep and narrow run section accumulated significantly less fine particles down to 60 cm depth than at the riffle section. The degree of clogging strongly affected hyporheic colonization by stream biota. Invertebrate densities were significantly higher in sediments of the run than in those of the riffle section. Generally, hyporheic abundances of the mainly epigean fauna decreased with depth, although the decline was more distinct within the riffle section. Densities were strongly influenced by sediment depth and morphological subunit and significantly and negatively correlated with the percentage of fine particles, fine particulate organic matter and particulate nitrogen within the hyporheic zone.