A procedure for incorporating spatial variability in ecological risk assessment of Dutch River floodplains

Floodplain soils along the river Rhine in the Netherlands show a large spat ial variability in pollutant concentrations. For an accurate ecological ris k characterization of the river floodplains, this heterogeneity has to be i ncluded into the ecological risk assessment. In this paper a procedure is p resented that incorporates spatial components of exposure into the risk ass essment by linking geographical information systems (GIS) with models that estimate exposure for the most sensitive species of a floodplain. The, proc edure uses readily available site-specific data and is applicable to a wide range of locations and floodplain management scenarios. The procedure is a pplied to estimate exposure risks to metals for a typical foodweb in the Af ferdensche and Deestsche Waarden floodplain along the river Waal, the main branch of the Rhine in the Netherlands. Spatial variability of pollutants i s quantified by overlaying appropriate topographic and soil maps resulting in the definition of homogeneous pollution units. Next to that, GIS is used to include foraging behavior of the exposed terrestrial organisms. Risk es timates from a probabilistic exposure model were used to construct site-spe cific risk maps for the floodplain. Based on these maps, recommendations fo r future management of the floodplain can be made that aim at both ecologic al rehabilitation and an optimal flood defense.