In 1990–2025 English river monitoring, smaller gains at equal starting status cause most of the slowdown in invertebrate pollution-sensitivity recovery
Question: The recovery of river invertebrates in England has slowed. Is the cause saturation (fewer degraded sites remain) or a real slowdown (degraded sites now improve less)? Approach: We used 177,162 standard spring and autumn samples from 19,428 Environment Agency river sites, 1990-2025. A validated Python port of the RICT/RIVPACS IV GB model gave the reference expectation at each site. We compared 10-year changes in observed/expected (O/E) WHPT ASPT at sites with the same starting status in an early era (data 1990-2008) and a late era (data 2007-2025). The design is time-symmetric: each site is classified on a centre window and the change is measured from 5 years before to 5 years after that window. This design removes regression to the mean, and a permuted-years placebo gave no class change different from zero. Results: The mean 10-year gain fell from 0.049 to 0.012 O/E. Gains fell in every starting class (moderate status: 0.062 to 0.012; good: 0.045 to 0.015). The shift toward better classes explains 23% (95% CI 19-27%) of the slowdown, and smaller gains at equal status explain about 77%. In the early era, sites with larger deficits improved faster. In the late era this catch-up effect was absent, and all classes gained about 0.01 per decade. The result was similar with the same sites in both eras (19%), with presence-only WHPT (29%), with family richness (13%), and in 6 of 7 regions. A forward design that does not control regression to the mean doubled the apparent saturation share (48%). National raw WHPT ASPT rose 0.35 per decade in the 1990s and 0.07 in the 2010s, with the highest values in 2024-2025. Family richness decreased 0.29 families per decade in 2010-2025. Random-design River Surveillance Network sites had the same 2021-2025 O/E as long-term sites (0.974 vs 0.975). Limitations: The data are observational. The test does not separate less management effort from pressures that are more difficult to remove. Expectations use fixed site variables and unadjusted RICT values.
river macroinvertebrates · biodiversity recovery · WHPT ASPT · RIVPACS · RICT · regression to the mean · England · Environment Agency · water quality · long-term monitoring · saturation · freshwater biodiversity
References
7- challengesdoi:10.1038/s41586-023-06400-1
Reports that European freshwater invertebrate recovery stopped after about 2010. In England we find that gains slowed from about 2005 and that the slowdown is mostly at equal starting status, not a ceiling.
- challengesdoi:10.1016/j.scitotenv.2023.167144
States that pollution-sensitive taxa in English rivers recovered to reference condition, which suggests saturation. We find that saturation explains only about a quarter of the slowdown.
- supportsdoi:10.1016/j.scitotenv.2023.163107
Reports recovery of English and Welsh rivers since 1990 that slowed in later years; we confirm the slowdown with data to 2025.
- supportsdoi:10.1111/j.1365-2486.2012.02662.x
Earlier analysis of long-term trends in British river macroinvertebrates and their link to water quality.
- doi:10.1002/ecog.08573
Site-level trajectory clusters for 803 English EA sites; related work on heterogeneity of trends.
- doi:10.1101/2024.08.13.607735
Reanalysis of the European data set that questions taxonomic resolution and trend estimates; we use family-level WHPT metrics.
- In 261 BioTIME 2.0 studies, start-year dominant species decline equally in time-reversed series, so the pattern is regression to the mean and not a directional loss of dominance sci:sha256:c48d2f550afbef9eab168f407fb4b2e52f819407b0525faf0d8cf8174030b58d
Shows with time reversal that start-state class trends in BioTIME are regression to the mean; our time-symmetric design applies the same principle to classes of river sites.
Cited by
4 publicationsPublic catalog entries on Sciscape.
- usesAt 867 English river sites, fish communities changed by about one third of the amount that the between-site relation to invertebrate ASPT predicts (1990–2004 to 2012–2025)
We use the filtered EA invertebrate sample table that this study retained (SCI dataset sha256-75ce6f8f...), and its result on the 1990-2025 invertebrate recovery is background.
- The fish community temperature index did not increase at 2,006 English river sites in 2000–2025 while air temperature rose 0.29 °C per decade; it followed summer temperature only from year to year
Invertebrate pollution-sensitivity recovery in the same EA river network; background for non-thermal drivers of fish change.
- usesIn 1996–2025 English river samples, native invertebrate richness fell by 2.9 families after the first signal crayfish record at 161 sites, more than after first records of any of 309 native species
We use the unchanged EA Biosys files and the sample filters retained with this publication (shared dataset sha256-75ce6f8f...).
- usesAt English river sites in 1990–2025, brown trout density rose where nearby invertebrate pollution scores improved, but 18 other fish taxa and species richness showed no consistent link
We use the RICT O/E WHPT ASPT site-year tables and EA invertebrate site table that this study retained (SCI shared dataset sha256-75ce6f8f73713c141f2385e31659f3042d74980f55c3f5baffb8bc2678b5dee3).