Freshwater - State and impacts (France)

Rainfall

In metropolitan France, average annual rainfall for the past 60 years has been estimated at 487 billion m³. Of this volume, on average only 175 billion m³ of effective rainfall actually replenish continental water resources; 75 billion m³ run off at the surface and 100 billion m³ infiltrate into the groundwater. Taking into account exchanges with neighbouring countries, the total average annual balance for water resources amounts to 168 billion m³ for metropolitan France. The quantities of effective rainfall vary greatly from one year to the next and are not spread uniformly throughout the territory. 2005 was marked by a substantial deficit for most of the territory. In 2008 the situation in four regions, including the Paris basin, was a cause for concern.

Total effective rainfall in 2008

Source: Météo-France, 2008-2009; processing: SOeS.

Surface waters in France

Watercourses exceeding 1 km in length in metropolitan France, three quarters of which are small or very small, represent a total length of 525 000 km. Apart from the wetlands, standing water is made up of ponds and natural lakes as well as lake reservoirs. There are also brackish ponds which may or may not be directly linked with the sea. There are nearly 34 000 stretches of freshwater of which 535 have an area in excess of 50 ha. Five hundred and forty stretches are reservoirs created by large dams – those more than 20 m high and where the volume of the reservoir exceeds 15 million m³.

Quality of the watercourses

Quality is evaluated by measuring several physico-chemical parameters, in particular by looking for and quantifying substances that, above a concentration threshold, are toxic to humans or ecosystems.

In the watercourses biochemical oxygen demand (BOD), an indicator of the quantity of biodegradable organic substances in the water, has been falling by 30 % since 1998, the result of increased performance of wastewater treatment plants. Ammonium, another characteristic indicator of the efficiency of treatment, also shows a downward trend, but is influenced by the low rainfall of 2003 and 2005 which resulted in poor dilution. Similarly, orthophosphates fell by almost 40 % over that period.

The trend is less pronounced for nitrates, where the index is, for the most part, stable or even a slight upward trend, with fluctuations as a result of climatic conditions. The trend for nitrates, which is very closely linked to weather conditions, shows a greater contrast geographically. The highest concentrations are observed in the north-east quarter of the country. The use of nitrogenous fertilisers has fallen since 2001 but nevertheless the drought years created leached nitrogenous surpluses in the following years.

In 2007, pesticides were detected and quantified at least once at 91 % of the measurement points. The concentrations measured were sometimes very low and in these cases had little effect on the quality of the water. This nevertheless reflects a considerable spread of pesticides and their generalised presence in aquatic environments.

Eighty-two percent of the stations selected showed, on average, a total pesticides concentration of less than 0.5 μg/l in 2007, and at 164 of these, 9 %, no quantity at all was recorded during the year. These stations are located mainly in the mountain regions of Auvergne, Alps, and Pyrenees which are little affected by agricultural pressures. The stations with an average of more than 0.5 μg/l are in the regions noted for intensive agricultural: Midi-Pyrénées, the Paris basin, the Rhône valley and northern.

The pesticides most often found are herbicides of the triazine family – atrazine and its metabolites, urea substitutes – diuron, isoproturon, or others such as glyphosate and its derivative AMPA. In spite of having been banned since 2004, metolachlor was still found in high amounts at three stations in Lot-et-Garonne and the Gers in 2007.

Annual average total concentration of pesticides in watercourses in 2007

Groundwater

Groundwater is generally stored in aquifers in geological formations such as sandstone and limestone. France has about 200 major aquifers of which 175 are unconfined and 25 confined. There are numerous small aquifers spread throughout the rest of the country (approximately 6 300).

Quality of groundwater

Source: Agences de l’Eau (Water Agencies) - Ministère chargé de la Santé (Ministry of Health) – BRGM (French geosciences institution), Ades database (of groundwater resources) combined networks. Processing: SOeS, 2009.

A slow deterioration of groundwater in relation to nitrates seems to have been continuing at the national level since the 1960s. While some improvements have been observed locally, the general deterioration has continued over the past ten years,  although the drought years from 2003 to 2005 recorded levels that were markedly better in selected areas mainly as a result of a shortage of rainfall generating less runoff and therefore less infiltration to the groundwater. In the past ten years, there have been fewer water-points with levels below 10 mg/l and an increase in water-points with nitrate concentrations exceeding 50 mg/l.

In 2007, 666 groundwater stations – bores, wells, etc. – 43 of a total of 1 534, were free of pesticides. These were in deep groundwater layers, well protected from surface pollution, or located in mountain ranges which have no major aquifers, such as Brittany, the Massif Central, the Alps and the Pyrenees, and which tend to be given over to livestock farming.

The stations recording the highest levels of pesticides are located in the large sedimentary basins – chalky, limestone, sandstone aquifers  – of the Paris basin and the surrounding region, the Aquitaine basin and the Rhône valley. Only 4 % of the stations show levels higher than the threshold value of 0.5 µg/l, compared with 17 % in the watercourses. Three stations – just 0.2 % of the total – exceed the threshold of 5 µg/l, above which purification of the water is no longer possible.

Compared with watercourses, groundwater layers are characterised by two phenomena linked with their slower rate of renewal: the greater persistence of banned compounds, and the predominance of their metabolites.