Influence of Fluvial Structure on Benthic Macroinvertebrates in a Restored Meandering River, Geul Basin, Netherlands

Benthic macroinvertebrates are indicators of water quality and riparian ecosystem health. Their abundance and distribution in streams are associated with river basin environmental factors, including stream biotic and abiotic fluvial processes. We examined benthic macroinvertebrate diversity and abundance in relation to large wood (LW) and pool‐riffle morphology along the Geul River (NL), a small meandering river typical of European landscapes. Restoration since 1998 that includes remeandering and beaver ( Castor fiber ) reintroduction (2002 to 2004) has enhanced the riparian ecosystem. Field sampling was designed to determine abundance and taxa composition of benthic macroinvertebrates, differentiating between sites with LW and without (control) and between pools and riffles. Additional variables included velocity, depth, bed material and canopy cover. Macroinvertebrate diversity to measured environmental factors was evaluated with alpha and beta diversity indices and diversity t ‐tests. Relationships between LW and environmental variables on community composition were assessed using nonmetric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM). Thirty‐one macroinvertebrate taxa were identified, most at the Genus and Family level. Gammaridae (freshwater shrimp) was dominant across all sites. Macroinvertebrate diversity was significantly higher in riffles than pools, while taxa richness was higher for LW in comparison to control sites. Invertebrate community composition was not significantly affected by LW or measured environmental variables. Despite stream restoration, the index of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa amounted to 33%, indicating degraded water quality. At a basin scale management authorities should strive to reduce agricultural runoff, especially silt inputs. At the channel‐reach scale the pool‐riffle morphology and design of effective LW structures should be a guiding management goal for attaining riparian health consistent with targets of the EU Water Framework Directive.