Land Use Impact Assessment on the Nutrient Transport in the lake Mälaren.

Abstract: Stockholm and its surroundings are facing strong urban changes and it is forecasted that the increase of population will be the principal driver for the urban regions surrounding the lake Mälaren in the next decades. A thorough regional and urban planning is needed in order to build a sustainable society and protect the environment. In this sense Coupled Human and Natural Systems (CHANS) are useful tools for the creation of future scenarios of how urbanization and landuse changes will impact the ecosystems and the water resources. This master thesis is focused on how population growth and landuse changes impact both the surface water discharges and the nutrient transport in the Norrström Drainage Basin. In this regard the different comprehensive plans of 26 municipalities in the Stockholm-Mälardalen region were studied in order to create a landuse evolution model until 2040. The impacts of the changes of urbanization on the surface waters and the nutrient transport were obtained using the PCRaster environmental modelling tool following the guidelines of the PolFlow model. The results show an increase of the built-up urban areas of a 25% by 2040. Regarding the increase of flow in the surface waters, the results show a very small increase in the flow, due to the large scale of the study area. Finally the results for the nutrient transport show an increase of the nutrient loads at the outlet of the lake Mälaren of 20% in the case of nitrogen and 15% for phosphorus.