Evaluation of biotic responses to urban stream restoration: a comparison of the sampling methods of chironomid pupal exuviae vs. benthic invertebrates
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Abstract
Stream restoration in the Mid-Atlantic USA is intended to reduce delivery of nutrients and sediment to Chesapeake Bay. However, the macroinvertebrate communities of urban streams have shown little improvement following restoration. To detect biological responses to restoration of Cloisters Branch, two sampling methods and two analytical approaches were compared. The restoration minimized disturbance of the existing forest buffer and wetlands to the extent possible during construction. Concurrent sampling using benthic D-net and collection of floating chironomid pupal exuviae (CPEX) occurred once pre- (2013) and twice post-restoration (2023 and 2024) at five stations on Cloisters Branch. Additional CPEX sampling of Cloisters Branch and three non-restored control streams, for two years pre- and post-restoration, in a Before-After-Control-Impact design allowed us to distinguish a restoration response from other sources of interannual variation. Multimetric analysis of D-net samples indicated declines of biotic integrity post-restoration. In contrast, multivariate analyses of D-net and CPEX samples showed significant taxonomic responses to restoration. Lower conductivity in Cloisters Branch facilitated a strong increase in CPEX diversity and abundance of Chironominae. Post-restoration increase in stability and abundance of epilithic algae suggests that restoration improved physical habitat stability. Temporal and spatial variation in conductivity showed that road salt deicers were a greater biotic stressor than nutrients.
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