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Estimation of nitrogen and phosphorus loads in small Mediterranean coastal rivers

Congress: 2008
Author(s): Yin Chu, Christian Salles, Marie-George Tournoud, Claire Rodier
Université Montpellier 2(UM2), HydroSciences Montpellier (UMR CNRS-IRD-UM1-UM2), F-34095 Montpellier Cedex 5, France

Keyword(s): nitrogen, phosphorus, flood loads, Mediterranean rivers, statistical models
AbstractLevels and loads of nutrient exported from 3 small Mediterranean rivers in the south of France are studied. The results show that they were under the influence of both anthropogenic pressures and hydrological factors. Nitrogen and phosphorus levels were at similar scales during and out of the floods for each river. To find best explanatory factors and to predict loads during floods, stepwise forward regression analysis is realized on Event Mean Concentrations (EMC) and Total Flood Loads (TFL) of Total Nitrogen (TN), Dissolve Inorganic Nitrogen (DIN), Total Phosphorus (TP) and Soluble Reactive Phosphorus (SRP), versus hydrological variables and catchment descriptors. For the concentrations it highlighted the significant impacts of human pollution sources, together with an antecedent hydrological condition factor, with the exception of the concentration of TP, which was under the influence of the magnitude of flood and rain; for the loads, the magnitude of the flood and an antecedent hydrological condition factor appeared to be the best explanatory variables for all the determinants. The best 1-factor and 2-factor linear regression models, regarding validation results, related TFLs to flood mean discharge and an antecedent hydrological condition factor, for both N and P. Model application showed that a small Mediterranean river brings about 5~60 tonnes-N and 1~11 tonnnes-P annually, with great variation from catchment to catchment and from year to year, to its outlet during flood periods, which represent from less than 10% to about 20% of the whole time. The ratio of annual flood load to annual total load of TN and TP varied from about 30% to 99%, depending on catchment and hydrological year.
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