The shifting sands of the Sand Engine: Using environmental geochemistry to evaluate the Sand Engine’s ecological and toxicological risks

Coastal zones are densely populated areas, but under threat because of global climate change. Due to a global rise in sea level, many sandy coasts are eroding, of which the Dutch coast is an example. Already in 1990 large-scale measures were taken to protect the Dutch hinterland from flooding. Sand was applied on foreshores and beaches to maintain the coastline of 1990. In the future, these sand nourishments are expected to increase in frequency and sand volume. To shift to a more sustainable coastal management practice, the pilot project ‘’the Sand Engine’’ was introduced in 2011. Its design (a large hook-shaped peninsula), volume (21 million m3 of sand) and time-span (20-30 years) are different from regular sand nourishments with an average volume of 5 million m3 and a replenish frequency of 2-5 years. The goal of the Sand Engine is threefold: coastal protection, recreation and nature development. This dissertation focuses on geochemical processes in the nourished sand and on the effects of the bioavailability of nutrients and contaminant mobilization. Three main environmental geochemical hazards were identified: mobilization of trace elements through the transition of nourished sand from anoxic to oxic conditions, dredging of bog iron ore fragments containing high contents of arsenic, exposure of mobilized arsenic to biota at areas where mud settles. These hazards can hamper nature development at the Sand Engine and therefore, not all three goals are being met. To conclude, it is crucial to investigate geochemical processes for a coastal management approach to be sustainable