Warming and nutrient enrichment: the combined effects on freshwater systems


PRESS RELEASE - In freshwater environments, warming and nutrient enrichment are reducing the diversity of freshwater food-webs, whose richness and complexity are essential to the well-being of ecosystems. This is what researchers from INRAE, Oxford University, the University of Sheffield and Savoie Mont Blanc University have demonstrated by combining large-scale data from lakes and rivers in France. The results, published in the journal Ecology Letters, show that the combined effect of these two stress factors leads to a reduction in the presence of large fish at the top of the food chain.

Warming and nutrient enrichment: the combined effects on freshwater systems © INRAE - NICOLAS Bertrand

Freshwater ecosystems are subject to multiple stressors from human activities. In Europe, only 38% of freshwater ecosystems remain in good chemical condition, and only 40% are in good ecological condition[1].

Populations of migratory freshwater fish—salmon, trout, eels, etc.—have fallen by more than 80% since 1970[2]. Lakes have become major climate traps for fish, making it impossible for them to migrate. Additionally, in France, around 30,000 structures—dams, bridges, etc.—disrupt migration along rivers and streams.

These constraints make freshwater fish particularly vulnerable to stress factors, including eutrophication—an excess of nutrients in aquatic environments—and rising water temperatures linked to climate change.

Until now, little research had been carried out at community levels to study the effects of […]

 

 

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[1] European Commission (2021). The 6th Water Framework Directive and Floods Directive Implementation Report. https://environment.ec.europa.eu/publications/6th-water-framework-directive-and-floods-directive-implementation-report_en

[2] Deinet S., Flint R., Puleston H. et al. (2024) The Living Planet Index (LPI) for migratory freshwater fish 2024 update - Technical Report. World Fish Migration Foundation, The Netherlands.