Managing and restoring fragmented Anthropocene rivers
Rivers are hotspots for global biodiversity, and bring a host of benefits to both humans and the catchments through which they flow. However, river systems across the world are increasingly fragmented by dam and hydroelectric construction, and by droughts exacerbated by climate change.
Healthy river systems depend on environmental processes taking place across entire landscapes: from wetlands, springs and sources through tributaries and channels as waters flow towards an estuary. Scientists increasingly recognise that the health of river system depends on these catchment processes being connected and free-flowing.
“Flows of water, nutrients, sediment, fish and insects through catchments all require well-connected river courses,” says Dr. Thibault Datry, a freshwater scientist at INRAE. “To adequately consider this connectivity in management, monitoring or restoration plans for rivers requires a broad, so-called river-network, approach. However, the majority of practices and policies for freshwater ecosystem management are based on local scale processes.”
Dr. Datry and a team of colleagues led by Dr. Núria Cid Puey, have published a new study seeking to address this issue. Writing in Frontiers in Ecology and the Environment, the research team argue that sustainable management of rivers in the Anthropocene – the present global epoch in which humans cause wide-scale changes to Earth environments – requires approaches which span entire catchments.
“The scientific understanding of how biodiversity and ecosystems are organised in dynamic river environments has progressed substantially in the past decade,” says Dr. Datry. “In particular, meta-system theory tells us how local populations, communities and ecosystems are connected by gene flows, the dispersal of individuals, and flows of resources across a landscape.
“Our paper proposes that this metasystem approach can, and should, be better integrated into conservation, restoration and biomonitoring of rivers,” says Dr. Datry. “We recommend a series of measurements and indicators that could be integrated into European and national biodiversity and water governance to make management of river networks fit for the Anthropocene.”
The research team, supported by the ALTER-Net High Impact Action initiative, outline that river fragmentation – for example, through dam construction – doesn’t only affect local biodiversity and water flows, but can have cascading impacts on wider catchment ecosystems. For example, fragmentation can isolate populations of species which live across a river system, meaning that gene flows and biological interactions are reduced.
This fragmentation of a river system can have significant effects on how its ecosystems function, and the benefits they can bring to people. For example, the decomposition of leaf litter – a key source of nutrients to river ecosystems – is particularly impaired by fragmentation, so altering nutrient cycling across catchments.
The research team propose three recommendations for river policy and management in the Anthropocene. First, they suggest that conservation management needs to identify how ‘metapopulations’ of species are spread across river catchments, and design protected areas which ensure their ongoing health.
Second, they identify the need to develop methods for monitoring the connectivity and fragmentation of river systems in order to understand how species move across catchments. This work could allow the identification of key sites for species to recolonise river systems through restoration initiatives.
Third, the team advocate for adaptive ecosystem-based management which is based on an understanding of the flows of water, sediment, nutrients and species through a river system. They outline the need for management which addresses biodiversity and ecosystem processes, and the benefits they provide, across entire catchments.
In so doing, the team suggest that fragmented Anthropocene rivers might be better protected and restored, so contributing to the implementation of major environmental policies such as the European Biodiversity Strategy, the US Endangered Species Act and the Aichi Biodiversity Targets.
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