Dynamics of Metal Concentration and Mass Transport in an Old Mining Area

Several different approaches were used to analyse the metal pollution in the mining area at Bersbo. Using extensive water flow and metal concentration data, the mean annual transport of copper, cadmium and zinc at a weir downstream from one of the tailings deposits was estimated to be 330, 5.9 and 1700 kg/yr, respectively. Furthermore, it was found that differences in water balance between the deposit itself and the surrounding area could explain a considerable fraction of the temporal variation in metal concentrations in the draining creek. Assuming that sulphate concentrations could be used to estimate the dilution in this creek, it was also shown that there was a pH-dependent sorption of metals to the bottom sediments of the creek. The use of the PULSE model for the simulation of water flow made it feasible to describe and compare the dynamics of metal transport at different sites in the study area. While the weathering rate was an important factor for the dynamics close to the deposit, the dynamics further downstream were almost exclusively determined by the water flow and, thus far unidentified, mechanisms maintaining fairly constant metalconcentrations in the stream water. Furthermore, the estimates of metal transport at different sites showed that the transport was considerably larger further downstream than close to the deposit. At a general level, the application of the PULSE model to the Bersho problem illustrated the power of this type of model to contribute to redefinitions of pollution problems. The concept of a single point-source was replaced by a multi-source concept, and the crucial role of the factors maintaining a fairly constant metal concentration further downstream was demonstrated.