Fish and macroinvertebrate assemblages reveal extensive degradation of the world's rivers

Abstract

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate‐ and fish‐based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3‐class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen‐Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico‐chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity.

Perspectives from the Global South inform and affirm the contemporary river conservation paradigm: A commentary on Feio et al.

“…The research paper by Feio et al (2022) COMMENTARY less than that when considering fishes. Furthermore, nearly one in three river systems were found to be severely impaired.…”

Landscape Reading for Alpine Rivers: A Case Study from the river Biya

“…Following centuries of anthropogenic interferences, rivers are affected by a multitude of stressors (Lemm et al 2020). Rivers are among the most heavily degraded ecosystems in the world (Tickner et al 2020, Malmqvist and Rundle 2002, Sala et al 2000, putting freshwater megafauna at severe threat (He et al 2019, He et al 2018) and reducing the capacity to further fulfil ecosystem services that human societies rely on (Feio et al 2022, Abily et al 2021. The natural regimes of most of the world's larger river systems were altered, and it is assumed that 48% of rivers worldwide are moderately to severely impacted by flow regulation, fragmentation, or both (Grill et al 2015).…”

“…Next to these direct anthropogenic impacts, less obvious, indirect changes, like climate or land use change, are continuously transforming hydrological boundary conditions, as well as the sediment cycle, leading to significant alterations in water temperatures and other abiotic habitat factors and consequently destabilising many riverine ecosystems (Liu et al 2020, Sala et al 2000. Ecologically intact, or free flowing rivers have become increasingly rare and are largely restricted to remote areas with lower degrees of human development, usually found in snow climates (Feio et al 2022, Grill et al 2019.…”

Biotic homogenization of stream macroinvertebrates in an Afrotropical Anthropocene: Land use and ecological correlates

“…The most significant signature of the Anthropocene world is the anthropogenic modification of the ecosystem (McGill et al, 2015;Petsch et al, 2021a), leading to negative impacts such as biodiversity loss (Watson et al, 2016) and biotic homogenization (Dornelas et al, 2015;Magurran et al, 2015), especially in developing parts of the world (Newbold et al, 2015). These have resulted in a global biodiversity condition that is equivalent to earlier worldwide mass extinction incidents (Barnosky et al, 2011, Ceballos et al, 2015, indicating that we are already in a critical state of biodiversity globally (Feio et al, 2022). In particular, freshwater ecosystems (for example, rivers and streams) are among the mainly affected systems by anthropogenic pressures (Keke et al, 2017;Brittain et al, 2020;Keke et al, 2021a).…”

“…The Afrotropical streams, despite being hugely diverse ecological systems and biodiversity hotspots (Boyero et al, 2011;Collen et al, 2014;Tonkin et al, 2016;Keke et al, 2020a;, have remained understudied. The Afrotropical region is currently affected by massive forest conversion into anthropogenic uses (Feio et al, 2022), and the expected rapid growth of this region will further deteriorate the current state (Laurance et al, 2014;Keke et al, 2021a). In the light of this, the region has an urgent need to evaluate the effects of forest conversion in the bid to conserve the biodiversity of the tropical ecosystem.…”