The influence of natural and anthropogenic factors on grain size distribution along the southeastern Baltic spits

The influence of natural and anthropogenic factors on the distribution of sand grain size along sandy beaches is assessed, based on study of three spits of the southeastern Baltic Sea: the Curonian, Vistula and the Hel. 330 sand samples were collected from the beach and foredune at 1 km intervals. Our findings show that although the three spits have some characteristics in common, e.g. a predominance of fine- and medium-grained marine sand on their beaches and foredunes, the grain size distribution patterns of the recent sediments along these spits differ significantly. The key factors determining the grain size distribution include the dominant hydrometeorological regime, anthropogenic activity and geological framework. Trends in the mean grain size differentiation along the Vistula and Curonian spits directly correlate with the direction of the longshore sediment transport: as the distance from sources of the longshore sediment transport increases, the size of sand particles, both on the beach and the foredune, decreases. By contrast, on the Hel Spit, this pattern is disturbed in areas of hydrotechnical construction and artificial beach nourishment. Sand differentiation along the beach can also be predetermined by the geological framework, particularly in lithologically anomalous sections, such as the Juodkrantè settlement on the Curonian Spit.