NUTRI-Karst: a project to study the impact of human activities on transfers of water and nutrients in the karst basins of the Jura Mountains

Main results

After six years of work, the results of the NUTRI-Karst project provide a much clearer picture of a concerning environmental issue for the Jura region, against a backdrop of criticisms of Comté cheese production in the media. These results decipher and quantify the multi-factorial origin of the nutrients found in the water, for the various human activities, by highlighting certain risky agricultural practices and wastewater discharges, and the role of climate change.

Agriculture is the main source of the nutrients in the Jura Mountains, accounting for over 90% of inputs, ahead of domestic and industrial waste discharges. Nevertheless, these domestic and industrial discharges are not negligible, depending on the configuration of the basins, since they are usually released near or directly into the aquatic environment.

Most of the nitrogen is taken up by plants through the growth of grass in meadows, used to feed the dairy herds. An analysis of the entire Jura Mountains showed that, depending on the sector, between 10% and 60% (with an average of 20%) of all nitrogen inputs ended up in the main watercourses. This reflects the wide variety of flow patterns within the massif, and the limited ability of certain basins to retain these nutrients. It also shows that permanent grassland with extensive livestock farming (which has occupied 80% of the agricultural land in the Jura Mountains for the last 50 years) helps to significantly limit nitrate leakage into water.

Most of the phosphorus found in the water comes from wastewater discharges, whether from urban areas, cheese dairies or industrial zones.

The cultivation practices posing the greatest risk and with the greatest impact on water are those that involve tillage, the use of mineral fertilisers (temporary grassland and crops) and the spreading of liquid effluents (liquid manure, slurry). A Jura paradox has therefore emerged for this extensive agricultural environment dominated by cattle farming – essentially devoted to milk processing for the production of quality-label Comté, Morbier and Mont d'Or cheeses – because the significant reduction in agricultural inputs over the last few decades has not been sufficient to reverse the trend towards a deterioration in water quality.

This complex situation can be explained firstly by the high vulnerability of karst environments, which are characterised by a very limited water filtration ability (predominantly shallow soil and preferential infiltration) and generally high circulation rates, leading to infiltrated rainwater and leached compounds rapidly returning to the rivers. Secondly, global warming compounds the situation, with droughts intensifying in recent years. These lead to declining water reserves and the mobilisation in autumn of water that was recharged during the spring and summer and is heavily enriched with nitrogen. This comes from the mineralisation of nitrogen in soil when it becomes wet again after a dry period, and the mobilisation of higher nitrogen residues due to lower crop yields.

Three workshops were organised to bring together a wide range of local stakeholders and give them an opportunity to share their knowledge, in order to help build a common understanding of the causes of the deterioration and the associated socio-economic impacts, while collectively identifying certain courses of action.

More than 100 specific actions were proposed at the end of this project, with the aim of improving water quality and supporting local stakeholders in achieving a sustainable reduction in nutrient transfers. These mainly concern adjustments to existing practices rather than more structural and longer-term changes to the agricultural model, with a view to adapting to climate change.