Unexpected experiment of sediment transport and its effect on the benthic habitat on the Baltic Sea nearshore area of Lithuania

During the works of beach nourishment in spring of 2011 an accidental leak of sand occurred through the pipe within 9-10 m depth. It was unexpected opportunity to study sediment transport in the deeper area, where very few observations had been obtained yet. We assessed the general patterns of spilled sediment transport and its impact on the benthic habitats. We found that the spilled sand covered till within 9.300 m² area, while after 7 months it spread more than four times. Most of the sediments migrated northward on average 91±17 m, eastward 83±12 m and southward 74±15 m, whereas the western limit of spilled sand area had moved only 48±29 m. The spread of spilled sediments correlated with wind speed >;6 m s^-1 (r= 0.72, n= 16, p<; 0.01) and bottom velocity >;40 cm s^-1 (r= 0.56, n= 16, p= 0.02) according to 16 compass points, indicating that the sediment transport was mainly dependent on relatively strong bottom currents. The spilled sand destroyed the habitat, the till overgrown by red alga (Furcellaria lumbricalis), which is included in the I annex list of EU Habitat Directive. However, the habitat with densest cover of species was not affected by spilled sand and the destroyed area of habitat was about 0.1% compared to the intact area of habitat, therefore the effect of spilled sand could be classified as relatively small. Nevertheless, the sediment transport can have impact in a wider scale, thus continuing monitoring of spilled sediment spread is needed.