Sammendrag
There are great challenges to developing improved water quality in the Halden river course and local counties in the region have worked for years to address pollution problems in a coordinated manner. The Haldenvassdraget river basin district determined that compilation of long term monitoring data from selected lakes in the river course might provide a better understanding of the developmental processes of water quality. Included in this study are the lakes Bjørkelangen, Rødenessjøen, Femsjøen and Hemnessjøen (Øgderen).
In addition, paleolimnological studies were conducted using sediment from two lakes in the Halden river course, Bjørkelangen and Hemnessjøen. Accumulation of sediments in a lake acts as an archive with various depths in the sediment corresponding to different historical times. Paleolimnological methods can be used to reconstruct aquatic ecosystems that could include information before human influence.
The aim of compiling this long time series was to study trends in the development of the water quality in the selected lakes and, if possible, to detect changes in the Halden river course system based on the data collected. Furthermore, paleolimnological studies in Bjørkelangen and Hemnessjøen allowed us to compare and evaluate the historical findings with the long time series data. The aim of this study was to assess the reference conditions in the two lakes and to study the development in water quality. Another goal was to evaluate the environmental objective given in the classification system of the Water Framework Directive.
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