Carlos Garcia de Leaniz’s research pioneers river restoration and river connectivity, vital for biodiversity and ecosystem services. Barriers fragment rivers, threatening aquatic life and economies. Despite efforts, Europe’s rivers struggle due to uncertainties hindering restoration. Leaniz’s work addresses epistemic, ontological, and operational uncertainties, guiding effective connectivity restoration. The AMBER project shifts focus to low-head barriers, highlighting dam removal’s potential. Methods and tools inform policies, aiding Europe’s 25,000 km free-flowing target. Fragmented rivers lose biodiversity, fisheries, and flood control. Garcia de Leaniz’s research aims to efficiently reconnect rivers, fostering thriving ecosystems.

Which wall does your research break?

My research is helping to break walls (both epistemological and physical) that fragment rivers, thereby helping to reconnect them. Rivers provide 12 million tonnes of fish/year, the only source of drinking water for 2 billion people and the sediments that sustain the livelihoods of 500 million humans. However, rivers also rank among the most threatened ecosystems in the world and can only deliver the full range of ecosystem services if they are connected (healthy rivers are flowing rivers). River fragmentation caused by barriers has also increased the impact of flooding by disconnecting rivers from their floodplains, costing the global economy over US $104 billion/year.

Despite two decades of concerted efforts since the Water Framework Directive (WFD) was implemented, Europe still has some of the most heavily modified rivers in the world, and also the aquatic fauna that has suffered some of the steepest declines. Only 40% of surface waters in the EU have achieved good ecological status, due in part to the impact of artificial instream structures and other hydro-morphological pressures that interrupt the continuity of natural river processes. As part of its new Biodiversity Strategy (BDS), the EC has set a target of making at least 25,000 km of rivers free-flowing by 2030, and this has now become enshrined in the new EU Nature Restoration Law (NRL). However, restoration of river connectivity across Europe is being hampered by three types of uncertainties: (1) epistemic uncertainty, caused by data deficiencies and imperfect knowledge, (2) ontological uncertainty resulting from the inherent variability and unpredictability of river systems and (3) operational uncertainty motivated by ambiguities in the definition of free-flowing rivers, a plurality of views on dam removal and questions regarding optimal barrier prioritization and implementation across scales. Addressing these uncertainties is critical for river restoration because funds are limited and time left short, and there is a risk that without guidance governments may fail to meet the EU restoration targets. The ultimate aim of my research is to make the restoration of connectivity more effective and help deliver on the EU Free-Flowing target.

Our research in the AMBER project initiated a paradigm shift in the restoration of river continuity that focused on low-head barriers which are collectively the ones that fragment rivers the most (‘death by a thousand cuts’). It also revealed the widespread occurrence of abandoned and obsolete barriers and drew attention to the unprecedented opportunities for river restoration offered by dam removal. The methods and decision support tools developed by AMBER are being used by river basin managers and civil society across Europe and were the subject of many peer-reviewed papers, policy briefs and guidance on best practices (available from that helped to inform the 25,000 km free-flowing target of the EU Biodiversity Strategy.

What inspired or motivated you to work on your current research or project?

My research was motivated by the desire to bridge a knowledge gap (a known unknown) in river restoration. In 2018, the European Environment Agency concluded that river continuity was unknown in the majority of cases in Europe as there was no global inventory of dams and other instream barriers. Our research in the AMBER project addressed this important knowledge gap. AMBER provided the first comprehensive atlas of river barriers in Europe (the AMBER Barrier Atlas) and estimated the extent of river fragmentation. With 629,955 unique barrier records, the AMBER Barrier Atlas is the largest of its kind anywhere in the world and has been viewed by more than 100,000 people. Our 2020 Nature paper (doi: 10.1038/s41586-020-3005-2) demonstrated the existence of over 1.2 million barriers in Europe’s rivers and revealed the huge cumulative impacts caused by hundreds of thousands of small barriers that were largely absent from national inventories.

In what ways does society benefit from your research?

The defining characteristic of rivers is that they flow, healthy rivers are flowing rivers. There is continuity between the headwaters and the sea. When rivers become fragmented by barriers, habitats become isolated, and the continuity of river processes becomes severed. Broken rivers lose biodiversity, and the movements of migratory fish become blocked, resulting in the loss of valuable fisheries, recreational opportunities, and jobs. We also lose our beaches because there is no new sand coming from upriver, we lose fertile lands due to bank incision and we lose water because it warms up and evaporates more easily in reservoirs where there is no current. We lose the natural ability of rivers to purify the water and recycle nutrients. It also costs us money, and lives, because fragmented rivers which are disconnected from their valleys and their aquifers are more likely to flood and cannot dissipate as much energy as there is no buffering from the riparian vegetation and the natural meandering of the river channel. Resources available for river restoration are limited. My research tries to remove uncertainties on barrier prioritization, and bridge knowledge gaps to reconnect rivers more efficiently.

Looking ahead, what are your hopes or aspirations for the future based on your research or project?

My vision is to have more resilient, better-connected rivers – for people and nature. We want to expand the AMBER project to cover lateral barriers, to incentivize free flow with a certification scheme and to promote river restoration through education and training.

Further information

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