The lowermost part (below 2.1 m) of core COST-6 (Figure 6) represents muddy sands of ice-marginal lake origin. The radiocarbon dates of the Cerastoderma sp. shells found on the floor buy EPZ5676 of

the marine sediments, within and beneath the sand/gravel layer, at depths of 2.8 m (core COST-3) and 2.15 m (core COST-6) below the seafloor, are 3275–3145 (GdA-2039) and 4775–4590 (GdA-2040) cal. y. BP respectively (95.4% probability). The thickness of the contemporarily mobile layer of sediments, transported by currents and waves during storms, was determined by measuring the content of 137Cs in the cores. Caesium 137 is an artificial radionuclide, which entered the environment after 1945 as a result of nuclear weapons testing and accidents in nuclear power plants. Therefore the presence of caesium in sandy deposits allows the determination of the thickness of the layer undergoing redeposition during the last

few decades. In the cores examined, the thickness of the sand layer containing 137Cs is between about 0.40 m in core COST-8 and about 0.8 m in core COST-3 (Figure 7). The bathymetric map and sonar mosaic, recorded directly after the sand extraction ended, show significant changes in the bottom relief and distribution of sediments resulting from the extraction. As we had planned for the experiment, four pits were formed with diameters of about 80–120 m and depths of 3 to 4.5 m in the northern part of the area designated for stationary suction mining (Figures 8a,b). The maximum gradient of their slopes was 55° (Figure 8c). The surface of the bottom of the selleck kinase inhibitor pits was uneven with 0.5 to 2.0 m irregularities. The total volume of the pits left by stationary extraction was about 58 500 m3. In the part designated

for extraction by trailer suction dredging, a 1 m thick layer of sand was to be taken off in a regular pattern of straight, neighbouring selleck chemical furrows. However, sand exploitation in this part was not carried out according to plan. In effect, several irregularly shaped double furrows of different lengths were formed, and several pits were left by unplanned stationary dredging (Figures 8a,b,c). The lengths of the furrows varied from 30 to 150 m, their width from 5 to 10 m and their depth from 0.3 to 1.9 m. The gradients of the furrow slopes were between 5 and 15° (Figure 8c). The distance between the furrows of 25–30 m was rather stable – it was dependent on the suction dredger’s parameters. Although the furrows should have been the predominant trace of operations in this part of the test field, much more often there appeared small, irregularly distributed, traces of stationary dredging or dredging with the dredger moving very slowly. Such traces were also found in the south of the reference part of the test field, where extraction had not been planned. The diameters of these pits were about 20 to 70 m, their depths from 2.5 to 4 m, and their slopes had gradients as steep as 50°.