The use of a simple sediment budget model to estimate long-term contaminant export from small catchments

A novel approach is presented to estimate the long-term contaminant export from agricultural fields or small catchments due to soil erosion using the spatial pattern of contaminant inventories in soil. This approach uses a simple geographical information system based sediment budget model, which provides a spatially distributed relative index of erosion and deposition. The observed contaminant inventories in the soil profile are related to this relative index of erosion and deposition. The contaminant export from the area is then estimated as the difference between the intercept of this relation, which represents the 'reference contaminant inventory' in the absence of erosion and deposition, and the mean observed soil contaminant inventory. This approach was applied to quantify copper fungicides losses from two vineyard fields in south-eastern France. The relative index of erosion and deposition explained between 32% and 56% of the variation in the soil Cu inventories. The respective average rates of Cu export from the two vineyards studied were estimated to be 0.74 kg ha− 1 year− 1 and 1.02 kg ha− 1 year− 1. The proposed method is especially useful in cases where 'reference sites', where the contaminant input into soil has been equal to the field or catchment under study but where no erosion or deposition has occurred, are lacking. As effective reference sites are often absent in locations where agricultural contaminants have been used, further refinement of this model is warranted.