This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The EU Nature Restoration Regulation adopted in 2024 establishes the restoration of ecosystem functions as an objective of stream restoration. But can conventional measures that focus primarily on restoring the physical structure of rivers and streams fulfill this task?
A meta-analysis by an international research team coordinated by the Helmholtz Centre for Environmental Research (UFZ) shows that this is not necessarily the case. Although restoration measures can improve stream structure and biodiversity, important ecological processes such as nutrient uptake and organic matter decomposition do not necessarily recover. In their study published in Global Change Biology, the researchers therefore recommend incorporating functional indicators more systematically into monitoring and assessments of restoration success and targeting restoration measures more specifically at the functions they are intended to restore.
Many rivers and streams in Europe have been extensively modified through the construction of barriers, the reinforcement of banks and streambeds, and the straightening and channeling of streams. According to the Federal Environment Agency, fewer than 10% of rivers and streams in Germany have at least good ecological status. Structural modifications and pollutant inputs reduce biodiversity and weaken the natural self-purification capacity and resilience of rivers and streams.
Restoration measures are intended to mitigate these impacts and improve the ecological status of water bodies. Typical measures include channel reconfiguration, the removal of barriers, the reconnection of floodplains, the restoration of riparian vegetation and the addition of large wood to streams. Such measures can improve the diversity and composition of aquatic communities.
An international team of river ecologists from 13 research institutions coordinated by the UFZ analyzed 66 scientific studies to assess how ecosystem functions respond to restoration and whether they recover alongside biodiversity. They analyzed data from 281 stream sites in Europe, North America, Asia and Oceania and identified 27 functional parameters, nine of which had sufficient comparable data for the meta-analysis. These included gross primary production, nutrient uptake, denitrification and decomposition of organic matter.
These parameters reflect key processes in freshwater ecosystems and indicate how environmental pressures or restoration affect ecosystem functioning. Gross primary production involves the formation of organic biomass by algae and aquatic plants using sunlight and nutrients. Denitrification involves the conversion of nitrate into gaseous nitrogen compounds by microorganisms, including nitrous oxide, a potent greenhouse gas.
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