Spatial and seasonal distribution of trace metals in floodplain soils. A case study with the Middle Elbe River, Germany

Field monitoring stations were used to assess selected soil parameters and trace metal concentrations in soil solution (As, Cd, Cu, Cr, Ni, Zn) to assess their behaviour under spatial as well as seasonal variations. We investigated three different plots within a floodplain research area varying in terms of their soil characteristics as well as their trace metal contents. Redox potential was found to be an important factor controlling the release of trace metals under field conditions on all plots coupled with a strong seasonal influence in almost all cases. However, by using generalised additive models it was possible to identify the specific courses of redox potentials related to the several trace metals depending on seasonal changes across the three plots. Whereas Cu and Cr concentrations increased with increasing redox potentials, Cd, Ni and Zn concentrations decreased. No clear pattern could be identified for As, although the data clearly reveal a seasonal dependency on flood events over the year and show increasing As concentrations even during smaller inundation events. The results of the generalised additive mixed models identified hot spots and hot moments of dissolved trace metal concentrations specific to soil horizons within the three plots. Thus we can provide data for further management implications that should be taken into account in an ecosystem that provides a whole host of ecosystem functions and services.