Evidence of biological recovery from gross pollution in English and Welsh rivers over three decades

• Published in: The Science of the total environment 2023-06, Vol.878, p.163107-163107, Article 163107
• Main Authors: Pharaoh, Emma, Diamond, Mark, Ormerod, Steve J., Rutt, Graham, Vaughan, Ian P.
• Format: Article
• Language: English
• Subjects: Animals; Biodiversity; Ecosystem; Environmental Monitoring; Environmental Pollutants; Freshwater; Invertebrates; Land use; Long-term; Macroinvertebrate; Richness; Rivers; Trends; Water Pollution; Water Quality
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.163107

Uncertainty around the changing ecological status of European rivers reflects an evolving array of anthropogenic stressors, including climate change. Although previous studies have revealed some recovery from historical pollution in the 1990s and early-2000s, there are contrasting trends among pollutants across Europe and recovery may have stalled or been reversed. To provide more contemporary evidence on trends and status, here we investigate changes in English and Welsh river macroinvertebrate communities over almost 30 years (1991–2019) using a network of nearly 4000 survey locations. Analysis comprised: i) trends in taxonomic and functional richness, community composition and ecological traits, ii) gains, losses and turnover of taxa, and the overall homogeneity of macroinvertebrate communities nationally, and iii) an exploration of how temporal trends varied with catchment characteristics. Taxonomic richness increased, primarily in the 1990s, whilst a shift towards pollution-sensitive taxa continued throughout the study period, accompanied by a growing prevalence in traits such as preferences for fast-flowing conditions, coarser substrata, and ‘shredding’ or ‘scraping’ feeding strategies. Changes consistent with improvement occurred in both urbanised and agricultural catchments, but were more pronounced in urban rivers as they gained pollution sensitive taxa that were otherwise more prevalent in rural rivers. Overall, these results indicate continuing biological recovery from organic pollution, consistent with national scale trends in water quality. Results reemphasise the importance of looking at multiple facets of diversity, with periods of near-constant richness disguising changes in taxonomic and functional composition. Whilst this national-scale picture is broadly positive, we highlight the need to investigate more local variations or pollutants that depart from this aggregate picture. [Display omitted] •Public concern about rivers necessitates contemporary evidence on ecological quality.•Routine river macroinvertebrate monitoring provides vital evidence at a national scale.•Macroinvertebrate communities indicated quality improvements over 29 years.•Taxonomic richness increased in the 1990s, with weaker evidence for a post-2015 gain.•Improvements were widespread, but greatest in urban areas.