Development of water quality in Lake Brønnerødtjern : studied by paleolimnological methods, with special focus on heavy metals

Abstract

Lake Brønnerødtjern is a freshwater lake located in Våler municipality in Viken county, city of Moss. It belongs to the Mossevassdraget water courses which is a part of the Vansjø watershed. This thesis aims to reconstruct the long-term development of heavy metals in Lake Brønnerødtjern, based on paleolimnological methods by evaluating natural and anthropogenic sources of heavy metals, the level of heavy metals in the lake sediment and impact of climate change and land use changes on the transport of heavy metals. In the first part of the thesis the general information about the lake Brønnerødtjern is represented with natural and anthropogenic effect in the watershed. The two sediment cores collected from the lake are analysed to obtain concentration of different chemical constituents (P, Cr, Mn, Co, Cu, Zn, C, S, Fe, Hg, Cd, Pb and N). The period with high sedimentation rate and concentration of the elements mentioned above was detected. Then, the results obtained were interpreted with respect to the available information from the lake. The research covers the development study of Lake Brønnerødtjern for last 164 years. The most probable primary sources of the inorganic pollution since 1853 until present are considered as the long-distance atmospheric deposition and industrial emission. Moreover, geochemical processes and the bedrock composition of the catchment area also influenced concentration of some metals. The small tunnels made in the surrounding of the catchment during peat extraction in the past have impacted the sedimentation rate. This study is anticipated to curtail the research gap in the lake Brønnerødtjern, with a special focus on the presence of the heavy metals using different methods.