Initial ecological recovery post‐weir removal amidst catchment‐wide improvements, in a groundwater‐dominated chalk stream

Abstract

Physical habitat modification is one of the main pressures affecting river environments, impacting their ecosystem health and compromising their ability to adapt to the effects of climate change. Addressing the impacts of physical modification through reinvigorating natural processes has become a globally established river restoration technique. Here, we appraised such an approach by assessing ecological responses to a weir removal project on an English groundwater‐dominated ‘chalk’ stream. Using a Before‐After‐Control‐Impact (BACI) approach, we found that 3 years post‐restoration the macroinvertebrate communities are moving towards those of the target community both in terms of structural complexity (e.g., taxonomic composition) and functional integrity (e.g., trait composition). The progress is ongoing and has occurred alongside wider catchment improvements. Our results indicate that ecological responses to passive restoration undertaken on low energy streams, such as chalk streams, may be gradual, and thus longer‐term assessment is needed to fully appraise ecological recovery. We highlight the importance of a BACI approach to understand the local responses to restoration in a catchment context. Our findings also provide further evidence highlighting complementary ecological information provided by assessing taxonomic and functional properties concurrently in post‐project appraisals. A better understanding of ecological recovery times should be incorporated into future restoration planning. Such evidence would help develop robust assessments over appropriate timescales, increasing the likelihood of accurately and effectively appraising restoration project success, and helping to build support to increase the scale and pace of restoration actions needed to address biodiversity loss.