Impact of sand extraction from the bottom of the Southern Baltic Sea on the relief and sediments of the seabed

Investigations of the geological structure and seabed dynamics as well as the morphological and sedimentological effects of sand extraction generated by different mining techniques were carried out in Polish waters of the Baltic Sea, NW of the Gulf of Gdańsk, at a water depth of 15–17 m. Three research cruises took place: just before, directly after and 11 months after dredging operations. Seismoacoustic profiling, a multibeam echosounder, a side-scan sonar, a 3 m vibro-corer and a box-corer were used during the research cruises. The grain size distribution and 137Cs content of the sand samples were determined. Marine shells were dated by the AMS14C technique and pollen analyses were carried out on samples of muddy sands lying below the marine sand. A 2 to 4.5 m thick layer of marine sands lies on the boulder till and locally on late Pleistocene ice margin lake deposits. The 137Cs content indicates that the 0.4–0.8 m thick sand layer is mobile during storms. After the dredging operations, four pits with diameters from 80 to 120 m, depths from 3 to 4.5 m and slopes with gradients up to 30–55° were measured. Several smaller irregularly shaped pits and double furrows 30–150 m in length and 0. 3–0.5 m in depth were found. The sonar mosaic also shows a 50–100 m buffer zone of fine sand around the pits which flowed over the dredger’s side with water and settled on the bottom. During one year after the dredging operation the furrows generated by trailer suction hopper dredging as well as the fine sand cover around the pits disappeared completely. The four post-dredging pits left by stationary suction dredging were shallower by 2–2.5 m, their diameters increased by 40–50 m, the gradient of the slopes was reduced by up to 5–10°, and the total volume was only about 3.5% smaller than directly after dredging

Palynological evidence of human activity on the gulf of Gdansk coast during the late holocene

The Gulf of Gdansk is located in the southern part of the Baltic Sea. The shores of the Gulf are dominated by the sandy barriers which have developed in front of the Vistula Lagoon and the Vistula Delta Plain to the south-east and south and in front of the Puck Lagoon in the north-west such as the Hel Peninsula. Cliffs occur on the western coast of the Gulf. Neolithic settlements around the coast of the Gulf of Gdansk are mainly located at the foot of the upland slope and on the Vistula Spit and the Vistula Delta and are closely related to the rise and displacement of the shoreline during the Late Holocene. Pollen analyses of the sediment cores from the Vistula Delta, the Vistula Lagoon and the coast of the Puck Lagoon allow four anthropogenic phases to be distinguished in the area of the Gulf of Gdansk. It has been shown that the first indicators of an early husbandry economy in the vicinity of the Gulf of Gdansk appeared in the Atlantic Period. Pollen grains of plants related to this kind of human activity those of the goosefoot family (Chenopodiaceae), motherwort (Artemisia), sorrel (Rumex) are present and the first pollen grains of the plantain (Plantago lanceolata) also appear. The second anthropogenic phase of Neolithic settlement is one of the best investigated cultures. This is the Rzucewo Culture. Pollen analyses indicate increasing human activity at the beginning of the Subboreal Period. The preserved traces of fauna show that the seal hunting and fishing economy was preferred. Radiocarbon dating of archaeological artifacts indicates the beginning of the settlement at ca. 2 400 B.C. (ca. 4 400 years B.P.) (Król 1997). The altitude of peat and marine mollusks shells and their radiocarbon age shows that during the Early Subboreal Period the water level rose from ca. 2.8 m to 1.1 m below the present-day sea level. The date of the beginning of the seal hunters settlement correlates well with the period when the shores of the Puck Lagoon approached their recent position. The development of the Neolithic settlement on the Puck Bay coast as well as those on the Vistula Delta, where the main activity was related to amber processing, seal hunting and fishing, clearly shows a close relationship to the sea-level rise. The occurrence of the third and fourth settlement phases was related to the high sea-level stands in the Subboreal and Subatlantic Periods (post-Littorina, Late Holocene regressions) but their character was still strongly related to the coastal environments. The settlement was connected with the dry habitats whose areas increased after the development of the barriers. In the area of the Vistula Delta, settlement conditions depended mainly on the stages of the delta's development. On the shores of Puck Bay, however, the intensity of settlement was closely related to the water level changes.<br>O Golfo de Gdansk está localizado na parte sul do Mar Báltico. As praias do Golfo são dominadas por barreiras de areia formadas em frente à Lagoa do Vistula e à planície deltaica do Vistula pelo lado sudeste-sul, e em frente a Lagoa de Puck a noroeste, tal como acontece na Peninsula de Hel. Paredões costeiros ocorrem, por sua vez, na costa oeste do Golfo. Assentamentos neolíticos ao redor da costa do Golfo de Gdansk estão localizados principalmente no sopé do talude e no Delta do Vistula, sendo estritamente relacionados com a elevação do nível do mar e as decorrentes variações da linha de costa ao longo do Holoceno Tardio. Análises do polen do sedimento obtido nos corers do Delta do Vistula, Lagoa do Vistula e Lagoa Puck permitiram distinguir 4 fases antropogênicas para a área do Golfo de Gdansk. Foi visto que os primeiros indicadores da economia baseada em criação de animais domésticos nas vizinhanças do Golfo apareceram no Período Atlântico. Foram encontrados grãos de polen das plantas relacionadas com esse tipo de atividade humana familia Amaranthaceae (Chenopodiacea), "motherwort" (Artemisia), "sorrel" (Rumex) aparecendo também os primeiros grãos de polen de Plantago lanceolata. O assentamento neolítico da cultura Rzucewo, situado na costa oeste da Lagoa de Puck, é um dos que tem sido melhor investigados. As análises de polen indicam um incremento da atividade humana no início do Período Sub-boreal. Os traços preservados da fauna mostram que a caça da foca e a economia pesqueira eram as atividades preferidas. A datação radiocarbônica dos artefatos arqueológicos indicam que o começo do assentamento deve ter ocorrido há c.a. de 2400 AC (KROL, 1997). A altura das turfas e das conchas de moluscos marinhos, além de suas idades determinadas por radiocarbono, mostram que durante o Periodo Sub-boreal Inferior o nível da água aumentou entre 1,0 e 2,5 m em relação ao nível atual. A data do inicio do assentamento dos caçadores de foca correlaciona-se bem com o período em que as praias da Lagoa de Puck se aproximaram de sua condição quase atual. O desenvolvimento do assentamento Neolítico nas costas da Baía de Puck, assim como no Delta do Vistula, onde a caça às focas e pesca ocorreram embora a atividade principal fosse relacionada ao processamento do âmbar, mostram uma clara relação com o aumento do nível do mar. Esses assentamentos podem ser relacionados não só com a migração humana, efetuada no sentidodo do interior para a praia, mas muito provavelmente foi o resultado de uma retração causada pelas mudanças da linha de costa. A ocorrência das terceira e quarta fases do assentamento, durante o período Subatlântico foram relacionadas ao baixo posicionamento do nível do mar. Na área do delta do Vistula as condições de assentamento dependeram principalmente dos estágios de desenvolvimento do Delta. Entretanto, nas praias da Baía de Puck a intensidade do assentamento esteve relacionada às mudanças do nível das águas