Heavy metal contents and mobility of artificially inundated grasslands along River Weser, Germany

At the beginning of the 20th century municipal wastewater was used to fertilize grassland in the freshwater marsh of the river Weser. In 1987, 150 ha of the marsh became part of a mitigation area with artificial inundation during winter and spring. Heavy metal input may be expected from former wastewater treatment and artificial flooding nowadays. In addition, inundation may increase the availability of heavy metals that were accumulated during municipal wastewater treatment. In order to get an idea of heavy metal content and availability, the content of Cd, Cr, Cu, Ni, Pb, and Zn of the soil, the vegetation, and the input due to inundation were determined. Metal enrichment in the epipedon is evident for Cr, Cu, Pb, and Zn. Total content of Pb and Zn exceed the precaution limit. Soils treated with wastewater seems to contain more heavy metals than the ones without. Inundation causes an input of metals, but it is very low and varies in a broad range. Metal input is higher by atmospheric deposition than the one due to inundation. Degree of enrichment can be arranged in the order: atmospheric deposition > municipal wastewater >> inundation. In shallow ditch soils heavy metals are becoming more available.