Environmental context mediates the interaction between fine sediment and hyporheic macroinvertebrate

Abstract

Excessive deposition of fine-sediment filling interstitial spaces in riverbed substrates is widely acknowledged to negatively impact the aquatic ecosystems. Hyporheic invertebrates, sensitive to ecological status, respond to the clogged substratum through more intense bioturbation. To better understand the interaction between hyporheic macroinvertebrates and fine sediment, a continuum of a naturally increasing fine-sediment content in the Weihe River was investigated through field sampling in four seasons. Nonmetric multidimensional scaling (NMDS) and cluster analysis were employed to assess the distribution and the homogeneity in the composition variation of macroinvertebrate assemblages. Canonical correspondence analysis (CCA) was performed to reveal the context-dependent relevance of bioturbation activity with bioturbation potential value. Our results suggest that the impact of finesediment clogging on community composition and bioturbation activity was seasonally dependent due to the variability of environmental factors, such as flood events and water quality. The highest abundance and bioturbation activity occurred at moderately clogged sampling sites, while reductions in richness and bioturbation activity were observed at heavily clogged sampling sites, and the samples collected at some of the heavily clogged sites downstream did not even contain macroinvertebrates.The results indicated that the interaction between organisms and fine sediments is limited due to the complexity of the benthic and hyporheic zone. The study highlights the feasibility of hyporheic macroinvertebrates as indicators for the effects of finesediment loading pressures on lotic ecosystems and the necessity of reach-specific conservation and management strategies, especially in the downstream.