Humans impact terrestrial, marine and freshwater ecosystems, yet many broad-scale studies have found no systematic, negative biodiversity changes (for example, decreasing abundance or taxon richness). Here we show that mixed biodiversity responses may arise because community metrics show variable responses to anthropogenic impacts across broad spatial scales. We first quantified temporal trends in anthropogenic impacts for 1,365 riverine invertebrate communities from 23 European countries, based on similarity to least-impacted reference communities. Reference comparisons provide necessary, but often missing, baselines for evaluating whether communities are negatively impacted or have improved (less or more similar, respectively). We then determined whether changing impacts were consistently reflected in metrics of community abundance, taxon richness, evenness and composition. Invertebrate communities improved, that is, became more similar to reference conditions, from 1992 until the 2010s, after which improvements plateaued. Improvements were generally reflected by higher taxon richness, providing evidence that certain community metrics can broadly indicate anthropogenic impacts. However, richness responses were highly variable among sites, and we found no consistent responses in community abundance, evenness or composition. These findings suggest that, without sufficient data and careful metric selection, many common community metrics cannot reliably reflect anthropogenic impacts, helping explain the prevalence of mixed biodiversity trends.

APEM Ltd Stockport UK

Balaton Limnological Research Institute Tihany Hungary

Centre for Ecological Research Institute of Aquatic Ecology Debrecen Hungary

Chair of Hydrobiology and Fishery Centre for Limnology Estonian University of Life Sciences Elva vald Estonia

Conservation Ecology Center Smithsonian's National Zoo and Conservation Biology Institute Front Royal VA USA

Czech Hydrometeorological Institute Praha Czech Republic

Department Community and Ecosystem Ecology Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin Germany

Department of Animal Sciences and Aquatic Ecology Ghent University Ghent Belgium

Department of Aquatic Ecology Eawag Swiss Federal Institute of Aquatic Science and Technology Dübendorf Switzerland

Department of Aquatic Ecosystems Institute of Biodiversity and Ecosystem Research Bulgarian Academy of Sciences Sofia Bulgaria

Department of Aquatic Sciences and Assessment Swedish University of Agricultural Sciences Uppsala Sweden

Department of Biological Sciences University of Bergen Bergen Norway

Department of Botany and Zoology Faculty of Science Masaryk University Brno Czech Republic

Department of Earth and Environmental Sciences DISAT University of Milano Bicocca Milan Italy

Department of Evolutionary Biology and Environmental Studies University of Zürich Zürich Switzerland

Department of Forest Ecology and Management Swedish University of Agricultural Sciences Umeå Sweden

Department of Hydrobiology University of Pécs Pécs Hungary

Department of Life Sciences University of Coimbra Marine and Environmental Sciences Centre Associated Laboratory ARNET Coimbra Portugal

Department of Plant Biology and Ecology University of the Basque Country Leioa Spain

Department of River Ecology and Conservation Senckenberg Research Institute and Natural History Museum Frankfurt Gelnhausen Germany

Department of Water Atmosphere and Environment Institute of Hydrobiology and Aquatic Ecosystem Management University of Natural Resources and Life Sciences Vienna Vienna Austria

Ecology and Genetics Research Unit University of Oulu Oulu Finland

Environmental Research and Innovation Department Luxembourg Institute of Science and Technology Esch sur Alzette Luxembourg

Eurac Research Institute for Alpine Environment Bolzano Bozen Italy

Faculty of Biology University of Duisburg Essen Essen Germany

FEHM Lab CSIC Barcelona Spain

FEHM Lab University of Barcelona Barcelona Spain

Fisheries Ecosystems Advisory Services Marine Institute Newport Ireland

Flanders Environment Agency Aalst Belgium

Freshwater and Marine Solutions Finnish Environment Institute Oulu Finland

Geography Department Humboldt Universität zu Berlin Berlin Germany

Geography Research Unit University of Oulu Oulu Finland

iES Landau Institute for Environmental Sciences RPTU Kaiserslautern Landau Landau Germany

IHCantabria Instituto de Hidráulica Ambiental de la Universidad de Cantabria Santander Spain

INRAE UR RiverLy centre de Lyon Villeurbanne Villeurbanne France

Institute of Biology University of Latvia Riga Latvia

Institute of Ecology Nature Research Centre Vilnius Lithuania

Institute of Landscape Ecology Chair for Applied Landscape Ecology and Ecological Planning University of Münster Münster Germany

LFI The Laboratory for Freshwater Ecology and Inland Fisheries NORCE Norwegian Research Centre Bergen Norway

NIVA Denmark Copenhagen Denmark

Norwegian Institute for Nature Research Oslo Norway

Norwegian Institute for Water Research Oslo Norway

Oulanka Research Station University of Oulu Infrastructure Platform Kuusamo Finland

School of Science and Technology Nottingham Trent University Nottingham UK

T G Masaryk Water Research Institute p r i Brno Czech Republic

Univ Lyon Université Claude Bernard Lyon 1 CNRS ENTPE UMR 5023 LEHNA Villeurbanne France

Wageningen Environmental Research Wageningen University and Research Wageningen Netherlands

Water Development Department Ministry of Agriculture Rural Development and Environment Nicosia Cyprus

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