Intermittent Rivers: A Wake-Up Call for Biodiversity

What makes intermittent rivers unique?

Thibault Datry: Intermittent rivers are watercourses that periodically stop flowing or even dry out completely. They host species adapted to these alternating wet and dry phases — such as larvae and eggs capable of surviving in dormancy during dry spells and reactivating when water returns. Other species evolve into terrestrial adults just before drying occurs, reproduce outside the water in summer, and lay eggs in autumn when flow resumes.

These rivers play an essential role in food webs, as the invertebrates they shelter serve as food for fish and sustain trophic chains downstream. They also contribute to the carbon cycle, transporting and decomposing organic matter along river networks. Additionally, they help reduce flood risks, recharge groundwater, and can limit the spread of invasive species.

Reference maps show that a large proportion of rivers are naturally intermittent — 60% of the ~7.5 million km of rivers mapped by IGN (BD Topo), including the Albarine (Ain), the Gardons (Gard), and the Drôme (Drôme department).

How does biodiversity evolve in these ecosystems?

Thibault Datry: By comparing biodiversity data from the United States, New Zealand, Australia, and Europe, we found a striking pattern: the rate of species loss increases consistently with the duration of drying, regardless of location. Even in the Bolivian Amazon floodplain, we found identical species responses and patterns — proving the global significance of intermittence and the underlying evolutionary processes common to river ecosystems.

However, climate change amplifies both drying and flooding, disrupting biodiversity. Permanent rivers are becoming intermittent, while others dry out less often. Transitions between aquatic and terrestrial phases are particularly interesting — they can trigger CO₂ emission peaks within hours when water returns, or mobilize accumulated pollutants, endangering connected surface and groundwater bodies. These transitions are also moments of intense interaction between aquatic and terrestrial biodiversity, which we are actively studying to better understand their ecological impacts.

What is original about your research approach?

Thibault Datry: My research has evolved from the local to the global scale through valuable collaborations.

The DRYvER project models the impact of climate change on intermittent rivers and the ecosystem services they provide. Through citizen science, people can report river drying events via the DryRivers app, helping to map intermittent rivers across Europe and improve ecohydrological models for better management.

The “1000 Intermittent Rivers” network now brings together 250 scientists from 28 countries. At INRAE’s EcoFlowS team in Lyon, we are currently comparing 150 environmental DNA samples from water and dried sediments collected in both perennial and non-perennial rivers worldwide.

What impact do you hope to achieve?

Thibault Datry: My goal is to raise awareness among water managers and citizens about the importance of protecting freshwater ecosystems — especially intermittent rivers. Too often considered useless, used as dumping grounds, sites for water storage, or even excluded from legislation because they are seen as “atypical” or “not real rivers,” they urgently need adapted management tools — and above all, a shift in perception.I have contributed recommendations that are now included in France’s national water management plans, and I co-authored a manual for water managers (SMIRES project). As France’s expert within the European ECOSTAT group, I advocate for recognizing the connectivity — even temporary — between permanent and intermittent rivers among EU member states. A Make Our Planet Great Again grant in 2020 supported the development of a new assessment framework for the ecological status of intermittent rivers. Today, 90% of my datasets and publications are open access, including the IRBAS biodiversity database on intermittent rivers.

And what about the future?

Thibault Datry: The EU Water Framework Directive requires the assessment of the ecological status of water bodies — which raises the challenge of defining specific indicators for intermittent rivers to help managers preserve and restore freshwater biodiversity. New tools such as satellite imagery and environmental DNA are enhancing our understanding of ecohydrological responses in these systems. But it is equally urgent to work with society — citizens, managers, and policymakers — to change perceptions. Finally, understanding how the patterns of river intermittence evolve under global change is a question that deeply motivates my ongoing research.

Portrait of Thibault Datry

The excellence of Thibault Datry’s research was recognized with the 2024 INRAE Scientific Challenge Laureate Award.

Discover his portrait.