Bioaccumulation and long-term monitoring in freshwater ecosystems — knowledge gained from 20 years of zebra mussel analysis by the German environmental specimen bank

Abstract

With due regard to high standards, the zebra mussel (Dreissena polymorpha) has been utilized as an indicator of bioaccumulative substances in the German Environmental Specimen Bank for over 20 years. On an exemplary basis, the acquired time series of mercury and p, p′-DDE-concentrations underline their high value for freshwater ecosystem monitoring as well as their specific information content. The trends of mercury serve as a mirror of the industrial changes in Eastern Germany. A comparison with other sample specimens further emphasizes its usefulness in biomagnification studies. The p, p′-DDE concentrations demonstrate the diverse application history of the insecticide pp′-DDT, as well as the high persistency of this transformation product. Furthermore the mussel’s biometric parameters highlight various water body specific developments, which in turn illustrate the different developments of its living conditions in the large German river systems. In the meantime, the severely lacking sample availability at many sampling sites partially underscores these changes. Reduced nutrient availability, predatory pressure, and competition by the invasive quagga mussel, D. rostriformis, are being discussed as possible causes. Overall, the sample availability is susceptible to considerable temporal discontinuities due to the complex dynamics of flowing water systems, which renders the latter crucial to the success of long-term monitoring studies.