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abstract 708

Impact of the hydrologic behavior on the pollutant dynamics in an intermittent Mediterranean river (Vène, France).

Author(s): Marie-George Tournoud, Jean-Louis Perrin, Christian Salles, Audrey Caro, Bernadette Picot, Claire Rodier, Christine Grillot, Chu Yin
Université Montpellier 2 (UM2), HydroSciences Montpellier (UMR CNRS-IRD-UM1-UM2), F-34095 Montpellier Cedex 5, France. Tel : +33(0)4 67 14 42 72 Fax : +33(0)4 67 14 47 74 Email : marie-george.tournoud@univ- montp2.fr

Keyword(s): intermittent river, hydrological behaviour, pollutant dynamics, pollutant fluxes

Article:

Poster:

Session: OS1n Water quality 2

AbstractIntermittent Mediterranean rivers show long draught periods interrupted by floods of high

intensity and short duration. Their channel network structure is also highly variable in space and time. Water quality

dynamics in these rivers is highly impacted by this specific hydrological behaviour.
During the dry period, the river

channel may dry up completely except in some reaches where anthropogenic point-source inputs (mainly waste

water treatment plant effluents) contribute to maintain some pools. Accumulation of pollutants is observed in these

reaches. During the first floods, flow is rarely continuous throughout the channel network, because of the existence of

transmission losses. At the start of a storm, the advance of flood waves is limited by channel infiltration but also by

localized storage in small pools. Total flood volumes therefore do not increase very much and even decreases

downstream. Some floods observed in the upstream part of the river are not transferred to the outlet. This, in turn,

influences the spatial and temporal dynamics of pollutant fluxes. Along the river course, pollutograph shapes show

significant differences. Intense autumn floods flush away suddenly the pollutants from the soils and the river bed, but

significant quantity of pollutants may remain trapped in the riverbed, if transmission losses are too high.
Although

the hydrological regimes of intermittent Mediterranean rivers are known, more knowledge is needed about the

processes governing pollutant transport as well as the ranking of the origins of the pollutants. Thus, it is necessary to

set up a special observation network in order to determine the temporal and spatial variability of the water and

pollutant contributions to the river.
All these phenomena will be illustrated on the case of the Vène River (67 km²,

South of France) over the observation period : from September 2003 to August 2006, on suspended solids,

nutrients and faecal bacterias. The combination of continuous and event based monitoring coupled with the multi-

scale sampling strategy allows a global understanding of the factors and processes influencing water quality at the

catchment scale: concentration data is used to assess the contamination levels of the river and the bio-disponibility of

pollutants, while by analysing the instantaneous fluxes the various contributions to the river might be established.

Finally the total load is calculated in order to evaluate the exports at the catchment outlet. The multi-disciplinary

approach followed herein improved our knowledge of the integrated catchment response and its impact for

downstream environments.

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Impact of the hydrologic behavior on the pollutant dynamics in an intermittent Mediterranean river (Vène, France).