Changes in sediment characteristics after a sand nourishment at the German Baltic Sea coast

Sand nourishments are a common nature-based coastal protection measure at the German Baltic Sea coast to prevent dune breaches. These nourishments cover parts of the dune, the beach and extend into the shallow water. During a two-year campaign, changes in sediment properties before and after a sand nourishment at Ahrenshoop, located at the microtidal Baltic Sea, were followed by taking sediment samples in the nourished ecosystems. The nourishment led to a temporary increase in water content and a reduction in organic and carbonate content. After two years, the water content returned to pre-nourishment conditions, but the organic and carbonate content were still lower than before the nourishment. Although the nourished sediment was selected to have a similar mean grain size to the existing beach and dune, there were changes in the degree of sorting. During the two-year campaign, the sorting degree returned to conditions prior to the nourishment. Therefore, the changes in sediment conditions caused by the sand nourishments are only short-term and similar to changes appearing after nourishments at the coasts of tidal oceans. However, nourishments could have long-term consequences for coastal ecosystems due to the repetition of the nourishment every few years.