Modeling mercury pollution in the Lom River basin (East 2 Cameroon) to assess small-scale gold mining pressures over 3 surface water

In this study, the PEGASE model is used to assess the pressure-impact relationships of artisanal and small-scale gold mining activities over the Lom basin water resource and to model mercury transport and pollution. The study uses a spatial analysis for mining site representation, a pragmatic approach for estimating mercury concentrations from soil leaching, and a ratio-based method for estimating mercury releases from semi-mechanized mining. Including mining surfaces in land use classes improved the calibration and validation of mercury concentration simulations. Mining surfaces (~259.34 km²) account for 45.6 % and 86.6 % of the entire mercury inputs to the river, respectively in dry and rainy seasons. 89 kg and 291 kg of mercury reach the basin outlet during dry and rainy seasons, respectively. Among mercury transport processes, adsorption onto suspended matter and evaporation are more significant during the dry season (51 % and 48 % respectively). Industrial discharges significantly influence mercury concentrations, particularly near mining sites, where levels can exceed Environmental Quality Standards by up to ten times, leading to localized pollution. Thanks to the model, we have enhanced the understanding of mercury transport pro-cesses, and we have identified mining surfaces as the main contributor to mercury pollution in the Lom River.