An investigation to determine the impact drying pans for silt are having on a formerly agricultural region in the alluvial floodplain of the Elbe Estuary revealed that some of the water bodies and upper layers of sediment had already been moderately to strongly contaminated by Cd, Cu, Ni, Pb, Zn, As, and halogenated hydrocarbons, which arrive through the air as fallout and accumulate in the wetlands. The only toxic heavy metal traced exclusively to the drying pans is Hg, which is only detectable in water bodies directly contaminated with the Elbe silt and has not yet reached appreciable concentrations. Some local sources of ground water contain unusually high concentrations of ferrous or chloride ions. The most serious impact of the water drained from the drying pans on the biota can be attributed to very high concentrations of ammonium. A decimation of the species in one unmodified ditch receiving ammonium-rich outflow from the drying pans was actually observed during the year of the study. More damaging than the chemical contamination has been to the extensive habitat destruction during the construction of the drying pans, which has fully eliminated several water bodies together with their entire stocks of plants and animals. The region has long been reputed to support a rich and diverse flora and fauna, but the investigation revealed that an impoverishment has probably already occurred. The loss of still more natural wetland areas will have a serious local impact. The shallow ditches draining the region of the drying pans act as sinks for the toxic heavy metals and persistent halogenated hydrocarbons, and the substances already deposited therein will present a constant danger both to man and to the local wildlife for a long time to come. The deeper layers of sediment beneath the water bodies are generally free of these substances, attesting to the relatively recent input of these contaminants. The continual outflow of ammonium and other inorganic nutrients from the drying pans will greatly promote the eutrophication of the adjacent water bodies. The biota in the region is responding to the contamination in accord with the principles outlined by THIENEMANN, by which stresses on the ecosystem manifest themselves by a reduction of species diversity and the formation of massive populations by individual resistant species. Large discrepancies between the numbers of species present at the individual sites were actually observed, and these cannot be attributed to the morphology of the water bodies, which is similar. Disregarding bacteria, the numbers of aquatic and marsh species found at the individual sites range from 41 to 165. Specific effects attributed to toxic substances at individual sites include the absence or extreme scarcity of algae and molluscs from water bodies heavily contaminated with copper; the elimination of fishes and most water plants from ditches in which the ammonium concentration was increased; the development of massive populations of dipterans, cladocerans, and other resistant organisms after serious disturbances to the water body; the development of many kinds of toxic microhabitat within relatively small areas; and the development of a system of food webs through which large vertebrates, including man, could become contaminated by the environmental pollutants.
Several of the wetland species identified during the study are rare enough to warrant protection, and conservation measures are recommended.