Ecotoxicological risk of trace element mobility in coastal semi-artificial depositional areas near the mouth of the River Rhine, the Netherlands

Abstract

Artifical sand replenishments are globally used as innovative coastal protection measures. In these replenishments elevated pore water concentrations of trace elements are found. This study investigated possible ecotoxicological risks at two intertidal depositional sites, the Sand Engine (SE) as a recent innovative Dutch coastal management project, and a semi-artificial tidal flat (TF). Using the Sediment Quality Triad approach, we considered three major lines of evidence (LoE): geochemical characterization, toxicity characterization using bioassays with the estuarine amphipod Corophium volutator and ecological field survey. In both depositional areas C. volutator is at risk: moderate (SE) and low (TF). For TF, the bioavailability of trace elements differs between the field site and the laboratory. Contamination from arsenic and copper is present, but the low survival rate of C. volutator from the bioassay suggests presence of additional contaminations. The highly morphological dynamic environment of SE creates a less favourable habitat for C. volutator, where local spots with stagnant water can temporary create hypoxic conditions and sulphate becomes reduced. The dynamic system mobilises especially arsenic, triggering adverse ecotoxic effects at low original sediment concentrations. To conclude, the Sediment Quality Triad approach shows that a semi-artificial tidal flat is preferred over a highly dynamic coastal management project like the Sand Engine. The Sand Engine concept does not provide suitable conditions for macrobenthos species like C. volutator, therefore limiting the nature development goal set together with the coastal protection goal. Assessing each LoE from the approach together with additional measurements established more precise and realistic conclusions, showing the need that evaluating contributions of this method is necessary to understand the causes of risk in a site-specific manner. This article is protected by copyright. All rights reserved.