Contaminant Mass Balances in Soil Monitoring

Abstract

The assessment and balancing of mass fluxes is a promising method for predicting and detecting the accumulation of contaminants such as heavy metals in soils before it can be actually observed by direct soil surveys. Previous studies have demonstrated that this approach works well on a regional or larger scale, e.g. for monitoring farm land pollution by heavy metals such as lead, copper, zinc, and cadmium. However, the applicability of the mass balance approach to much smaller areas, such as the sites of a permanent soil monitoring network, is still an open question. With decreasing size of the mass balance compartment, the required degree of spatial and temporal resolution increases, rendering small scale variability increasingly important. This paper introduces the principles and problems of applying the mass balance approach in soil pollution monitoring and discusses in particular the conceptual difficulties of determining mass fluxes in the underground as well as their dependence on the choice of the system boundaries and the scale of spatial resolution. It is concluded that the mass balance approach is most problematic where fluxes across the highly structured soil-vegetation interface and fluxes between soil and groundwater have to be assessed.