Karakterisering av fysisk-kjemiske parametere langs en blågrønn bekk

Summary

Climate change leads to more frequent and more intense extreme weather, which increases the risk of flooding, particularly in urban areas. Blue-green infrastructures are seen as an effective measure to deal with increased surface runoff, and at the same time contribute to increased biodiversity. The prevalence of blue-green streams is therefore likely to increase in the years to come. Urban streams are often characterised by challenges with poor water quality due to large inputs of pollutants from impervious surfaces in the catchment area, which affects the aquatic ecosystem. When designing blue-green streams, knowledge about the water's physical and chemical conditions is needed, as well as how the water quality is affected by precipitation. This thesis investigates physical and chemical conditions along Campusbekken, a blue-green stream in the university park at Norwegian University of Life Sciences (NMBU) in Ås, Norway. Campusbekken is compared with the conditions in the natural and agriculturally affected stream, Vollebekken, in the same area. Water samples were taken at five different locations along Campusbekken, as well as upstream in Vollebekken, approximately once a month from June to October 2022. The water samples were taken both before rainfall and during subsequent rainstorms to investigate any changes in water quality. The water samples were analysed for turbidity, nutrients (total phosphorus, phosphate-P, total nitrogen, ammonium-N and nitrate-N) and road-related metal pollution (copper, zinc, nickel and lead). Additionally, metal samples were taken weekly, regardless of weather conditions. Water temperature was logged every 15 minutes in the streams, throughout the field work season. High water temperatures (up to 32,9℃) and large daily temperature variations (up to 15℃) were measured in Campusbekken, unlike in Vollebekken, which is affected by groundwater. The turbidity in Campusbekken was generally low, but with some exceptions (up to 300 NTU). Very high concentrations of phosphorus (up to 0,91 mg/l TP and 262 µg/l PO4-P) were found upstream in Campusbekken. However, in Campusbekken, nutrient concentrations decreased downstream, which indicates that the stream can remove phosphorus and nitrogen from the water. The metal concentrations in Campusbekken were generally low (good status), but in one station the zinc concentrations exceeded the Water Framework Directive’s limit values for AA-EQS and MAC-EQS, which indicates chronic and acute toxic effects on organisms. There was no clear change in water quality after rainfall in Campusbekken, while in Vollebekken the concentrations increased after rainfall events. No difference in turbidity and phosphorus was found between Campusbekken and Vollebekken. The concentration of nitrogen and metals were higher in Vollebekken, because of runoff from agriculture and roads, respectively.