Cadmium in the Lot-Garonne River system: Fluxes, predictive model and mass balance

Abstract
The evolution of the Cd pollution in the Lot-Garonne-Gironde fluvio-estuarine system was evaluated by a ten-years-observation (1990-2000) based on high frequency sampling and measurements. Data of water discharge and Suspended Particular Matter content (SPM), combined with monthly analyses of dissolved and particulate Cd concentrations permitted determining annual dissolved and particulate Cd fluxes. Based on the dataset for 1990-1998, an empiric predictive model of Cd fluxes and Cd mass balance is proposed for the Lot-Garonne fluvial system. The model permits predicting 90% of the annual gross dissolved and particulate Cd fluxes entering the Gironde Estuary, only using hydrological data. The empiric model reliably reproduces annual dissolved and particulate Cd fluxes estimated from field data in 1999 and for dissolved Cd fluxes in 2000 with discrepancies lower than 25% and 30% for dissolved and particulate fluxes, respectively. Cadmium mass balances and model-predicted particulate Cd fluxes in 2000, suggest that human activities, as river-bed dredging, create new point sources modifying the budget of the fluvial system. Mass balances show that the anthropogenic Cd point source in the upper Lot River watershed accounts for ~43% of the gross Cd inputs into the Gironde Estuary via the Garonne River.