Paimionjoen pohjasedimentti Someron alueen maankäytön historiallisten muutosten kuvaajana

The study area of this study was the upper part of the catchment of River Paimionjoki in Somero, which is located in the Varsinais-Suomi region in southwest Finland. The water system of River Paimionjoki is one of the biggest water systems of southwest Finland, and with it's flow and catchment area, the biggest river flowing to Saaristonmeri. The river flows through a clay ground stratified in an old ocean floor, so cultivation and farming have been practiced around the area already since the 14th century. Agricultural practices have had a significant impact on the area's changing landscape and the water quality of river Paimionjoki for hundred's of years. The water system has also been strained by the catchment area's scattered settlements and urban areas. The water quality of the river and it's catchment's lakes' have been researched a couple of times during the last two decades, and the water quality has been found to be below average. The purpose of this study was to bring a historical perspective to the environmental research of the river Paimionjoki area with palaeoecological methods. The aim of the study was with the stratigraphy of the bottom sediment of the river and with concentration of different elements, to find out how the river catchment's historical changes in landscape and the developments in agricultural practices and other human activities are visible in the physical and chemical composition of the sediment. Furthermore the aim was to solve the changes in the rate of sedimentation. The research material was two 200 cm long sediment cores from the bottom of Lake Åvik and Lake Pitkäjärvi. The samples were collected in March of the year 2009. Loss on ignition, water content and magnetic susceptibility as well as several concentrations of elements (Na, Mg, Al, Si, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Sn, Sb, Ba, Pb, C,N,S) were measured from the samples. Pollen analysis, C-14 radiocarbon dating and Cesium-137 dating were used to date the sediment samples. The results showed that the reforming of landscape to more open environment in the 14th century, and the beginning of the earliest agricultural activities can be seen in both cores in the depth of approximately 100 cm, where the magnetic susceptibility and loss on ignition show a remarkable change with mineral matter increasing distinctly. The intensification of human activities as well as agricultural and industrial activities is shown in both sample cores as a gradual steady rise in element concentrations. However, sudden anthropological events affecting the environment locally are not recorded in the sediment very clearly. The concentrations of heavy metals show a clear rise in the depth of 40 cm. This reflects the time after World War II when industry started growing and living standards rising. Led in addition to pollen analysis and Cs-137 dating proved to be a crucial factor in dating of the sediment especially with the top layers of the sediment where the maximum and decrease of led use has been recorded clearly. The sedimentation rate has distinctly increased as a result of agricultural and other human activities. However after the 1970s the rate has slowed down again. All in all of the region's historical changes in the environment only the main characteristics have been deposited in the river Paimionjoki sediment.