Characteristics of Sediments in a Changing Environmental Conditions in Vistula Lagoon (Poland)

Abstract

The Vistula Lagoon has been evolving since its formation in the late Atlantic period. At the beginning, the changes were mainly driven by the stabilization of the Baltic Sea level, and the development of hydrographic network. Later on, anthropogenic activities have become an important factor. Hydrotechnical works conducted at the turn of the 20th century, aimed at regulating the outflow of the Vistula River waters, have significantly limited the riverine input into the lagoon. In the past, the Vistula Lagoon contained freshwater and was constantly filing with sediments that made the basin shallow. With time, the lagoon has filled with brackish water, while its area became subjected to strong interactions between the driving forces of marine and terrestrial origin. As a result, the regime of sedimentation processes in the lagoon have been changed. The interpretation of sedimentation conditions for clastic sediments was based on the analysis of grain-size parameters that had been determined on the samples of bottom sediments and suspension collected in November 2016. The obtained results were compared to the pertinent data on bottom sediments collected by the Polish Geological Institute National Research Institute in 1994. Significant contrasts in particle size distributions were found. Also, the conducted study allowed the determination of underlying causes of these changes. Due to the shallow depth of the Vistula Lagoon, the sedimentation processes in this basin are significantly influenced by resuspension phenomenon. Resuspension is responsible for the differentiation and redistribution of sediment that originates from various sources, on the bottom of the basin. The process takes place in shallower areas, but this study indicates that its effectiveness increases in the deeper areas of the lagoon, which manifests itself in the replacement of clayey silt with silt. In connection with the plans of the Polish side of the cross-cutting of the Vistula Spit, the sedimentation conditions of Vistula Lagoon will be changed.