Présentations Colloques

Oral Presentation
5.05
Session 5.05: Groundwater and Ecosystems – Hydrological role of forests and wetlands
Léger Marie
Mill dam owners, farmers, fishermen and the ecological continuum- how to decide between them? The answer of infiltration, river-aquifer flow and denitrification in a natural wetland.
The EU framework directive on water advocates the dismantling of artificial limits on secondary waterways to restore ecological continuity on these watersheds where land use and quality of groundwater is marked by agriculture. One wonders about the disturbance that could cause dam leveling to the functioning of wetlands in the accompanying aquifer. These natural environments, valuable aids for the maintenance of the ecological status of the basin, are expected very sensitive to a metric variation in the level of the river. To test this hypothesis, instrumentation has been introduced within the Hauterive mill site, upstream of the Sarthe, a stream of low energy in rural area.**On this site laid long ago by a dam supplying a mill, where the Sarthe is lined with a diversion channel, piezometers, limnimeters and a meteorological device were implanted. Continuous monitoring of water levels and weather parameters has enabled a water balance and a hydrodynamic model of the site. Measures infiltration and hydromorphic soil textural analysis were conducted. Contamination is characterized by chemical analysis of the water of the river and piezometers. The purifying power of natural wetland accompanying the stream and feed by the regional water table is characterized and discussed in light of nitrate and glyphosate and drug residues.**The results show that the main process responsible for temporal variations in short time (less than monthly) of the groundwater level within the wetland is the couple infiltration - evapotranspiration. The water flow between the river and the aquifer and reciprocally is very slow and such is the seasonal evolution of the piezometric level in accordance with the river. A conclusion will be drawn as to the relevance of dam dismantling on such waterways that may be favourable to some fauna species but result in wetland loss and degradation of the overall quality of the river and groundwater.
France