Schwermetall-Status und Schwermetallmobilität in Auenböden und Stauseesedimenten unter besonderer Berücksichtigung von Durchfeuchtungs- und Wasserstandsänderungen

Depending on their river catchment, heavy metals and arsenic are often accumulated in floodplain soils or reservoirs. Big parts of these trace elements are bound in minerals or adsorbed on the surface of soil particles, so that only their (easily) dissolved fraction can reach the food chain. As redox processes influence the soluble concentrations, dissolved heavy metal amounts can underlie variations within fluctuating water levels or changing moisture conditions. Extent and consequences of redox changes depend on their continuity, frequency and intensity, as well as the specific properties of the affected substrate. Changing levels of ground and river water can occur during different seasons and episodic flood- or low water events. Therefore it also seems plausible that upcoming flow- and moisture-changes as consequence of the climate change can influence the resulting risk of heavy metal accumulations. Additionally variations of water levels, moisture conditions and dissolved metal amounts can be triggered by human intervention during the emptying of water basins. To analyze the pollution state and the mobilization behavior of dissolved heavy metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) during seasonal and periodic fluctuations of water tables and soil moisture, floodplain soils of the Lahn valley (Germany) have been observed in field investigation for 2 years. Therefore soil profiles were chosen, that are situated in different distances to the riverbed as well as up- and downwards of watergates, where different frequencies and amplitudes of river- and groundwater changes are present. Out of the given moisture differences, variations of the mobile heavy metal phases and their key factors were recorded. The soils downward the water gates showed bigger influences by changing groundwater and a higher amplitude of redox variations, especially in deeper profile parts. The upward situated profile showed instead a more regular ground water level that caused only little changes in deeper soil parts, and a bigger influence of capillary waters in medium depths. A soil in bigger distance to the river showed a weaker response to the coupling of river- and groundwater changes in the dissolved heavy metal fraction. An impact of changing climate conditions on the heavy metal mobility is, at least for upper soils of the investigation area, expected to be very low. Anthropogenically induced changes of water tables and their impact on dissolved heavy metal conditions in interstitial- and river waters were analyzed in three reservoirs. The analyses were conducted during and shortly after the complete emptying of two reservoirs (Aartalsperre, TS Driedorf), whereas the third basin (TS Klingenberg) was prospected after a 1,5 year lasting exposure. After the emptying the interstitial waters of the lake sediments were marked, because of good water-holding capacities, by mostly small and slowly beginning variations of dissolved trace metals. The water of the draining creeks showed simultaneously, affected by draining interstitial waters, significantly rising concentrations of several heavy metals. The longer exposed lake sediments showed instead a vertical differentiation of soil horizons with clear contrasts of dissolved metal amounts. The sediment passing creek underlay, with the exception of dissolved Mn, no continuous enrichment of the regarded elements.