What has happened to river macroinvertebrate biodiversity in England and Wales over the past 30 years?

Freshwater systems have experienced 200 years of escalating pressure from growing human populations, industrialisation and agricultural intensification leading to pollution and degraded biodiversity. In Europe and North America, the last 30 years have seen large-scale efforts to reduce river pollution via legislation such as the EU Urban Wastewater Treatment Directive and the US Clean Water Act. Concern over water quality in rivers has received increasing public interest over the past five years, and there are questions about the true impacts of pollution on wildlife. Recent evidence suggests that the richness and abundance of freshwater macroinvertebrates (a group commonly used as indicators of water quality) has improved, especially in formerly polluted urban rivers in developed Western countries, although more recently this recovery has slowed or plateaued. Here, we examine available evidence on changing macroinvertebrate biodiversity in UK rivers, focusing on trends in England and Wales over the past 30 years. By summarising current research on the status and trends of freshwater invertebrates using multiple sources of evidence, we confirm an aggregate increase in several measures of biodiversity, including family richness, species occupancy and the abundance of pollution-sensitive groups, although this stops short of the diversity expected in completely unpolluted locations. There are also local or regional departures from this aggregate trend, in some cases linked to nutrient pollution and climate change. We highlight a significant decline in government agency monitoring effort over the last 15 years. The continuation of monitoring across England and Wales is critical to detecting and diagnosing changes in invertebrate diversity and identifying solutions. Furthermore, we argue that current approaches for assessing the ecological status of rivers should more prominently report measures of biodiversity to aid our understanding of, and to better communicate to the public, the impacts of pollution and other related pressures at the national scale.