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River fauna benefits from warmer, better quality water

Trichoptera larva © Irstea / J-P Balmain


A team from Irstea’s Lyon-Villeurbanne Center has carried out a study on changes in the status of rivers in mainland France over the last 25 years by examining aquatic macroinvertebrate communities. The results are encouraging! This study highlights the considerable work carried out in collecting and processing data from 150 monitoring stations, underlining the long-term importance of these monitoring networks as recommended by the European Water Framework Directive.

Will the abundance of aquatic life suffer following global changes, thus canceling out progress made in the fight against water pollution? In a summary published in the international scientific journal Science of Total Environment [1], a team of researchers from Irstea’s Lyon-Villeurbanne center has revealed an increase of 42% in the abundance of benthic macroinvertebrates [2] in French mainland rivers between 1987 and 2012!

These insect larvae, molluscs, worms and crustaceans are an important link in the aquatic food chain (trophic network), providing food for fish, amphibians and birds. Their life cycles (evolution, reproduction, etc.) are closely dependent on the quality of their environment and water temperature in particular. They are therefore used as bioindicators of ecological status as well as chemical status under the European Water Framework Directive (EWFD).

Good to know

When the European Water Framework Directive (EWFD) was set up in 2000, it set a target of good status for bodies of water by 2015. This meant that Member States had to analyze the status of bodies of water regularly (every 6 years) and at the same time, study the risk of not achieving environmental targets due to several types of degradation. Each Member State has implemented monitoring programs using networks of stations distributed across their lands (mainland and overseas departments), covering all types of bodies of water (rivers, lakes, and coastal and underground waters). The aim is the long-term monitoring of the aquatic environment using biological, physicochemical, chemical and hydromorphological data.

In 2007, over 2,700 monitoring stations were surveyed (source: Onema/OIEau, 2010).

Improving water quality

This growth can be explained by the overall improvement of water quality (decreasing levels of phosphorus, nitrites, ammonium, etc.) and by an increase in water temperature (+1-2°C on average). These parameters seem to have played a positive role in activating the primary production used by these benthic organisms and, by extension, the whole food chain affected by global changes.

The results were based on around 150 monitoring stations in order to compare the levels of anthropogenic and climate pressures.

Since 2010, the team has focused on collecting data: a considerable task that took two years, as most of the older data was not digitized. "There is no national database. We therefore had to sort and harmonize this historical data," points out Yves Souchon, research director in hydroecology at Irstea. Why start the study using data from 1987 on the quality of rivers? "Simply because there were fewer observation stations in the past, and the monitoring frequency was much more spaced out, resulting in less usable data. These aquatic environment monitoring networks date back for the most part to the 1970s. Over time, they were reorganized as part of the EWFD implementation in 2000. Monitoring protocols were then stabilized, standardized and became comparable."

Global interest trends

Armed with field data and physicochemical analyses completed either by civil servants responsible for managing rivers or consultants, the researchers carried out statistical analyses in order to uncover development trends over the 25-year period: period of homogeneity, division, etc. These are definitely global trends rather than individual studies for specific monitoring stations.

Samples of aquatic invertebrates in a river © Irstea / D. Palanque

A clear change was discovered between 1997 and 2003, with an initial level of significant community development linked to climate change (increased temperatures). "We experienced exceptional heat (duration, degree) in 2003. It is important to have ongoing monitoring in place when this type of event occurs to ensure the data is interpreted correctly.”

Creating sustainable monitoring station networks

Beyond the encouraging results, the study makes the case for the long-term sustainability of monitoring station networks in order to understand future developments in a context of global climate change and uncertain predictions.

Data is precious; without it, debates can quickly become alarmist and devoid of any scientific basis. "We should be measuring, interpreting and adapting debate in a manner that is consistent with our observations. This is difficult as all the factors are changeable (climate, anthropogenic)." Finally, having access to this data makes it possible to show the results of any improvement policies in place well before the EWFD in 2000. "Operating these networks is expensive, particularly in terms of human resources. Moreover, this is a long-term project, which sometimes means acceptability issues faced with new monitoring standards." As the 2nd cycle of the EWFD starts, Souchon reminds us that things take time...

The publication.

For further information


[1] A-grade scientific journals specialized in chemistry and ecotoxicology and more generally in ecology. Publication: Kris Van Looy, Mathieur Floury, Martial Ferréol, Marta Prieto-Montes, Yves Soucon, "Long-term changes in temperate stream invertebrate communities reveal a synchronous trophic amplification at the turn of the millennium." Science of Total Environment, September 2016.

[2] The term "macroinvertebrate" is used to refer to any animal visible to the naked eye (bigger than 0.5 mm) that doesn't have a skeleton made of bones or cartilage. Benthic macroinvertebrates such as insect larvae, molluscs, crustaceans, etc. live in wet environments.