Spruce Forests and Peat Wetlands in Lake Bolmen’s Catchment Both Leak and Degrade Coloured Dissolved Organic Carbon
Lake browning in the northern hemisphere is endangering crucial ecosystem services. Darker water decreases fish and primary production as well as touristic and recreational values. It furthermore requires intensive treatment to receive safe drinking water. Brownification is connected to iron and coloured dissolved organic carbon (DOC). In Sweden, spruce plantations leak DOC, possibly depending in their DOC rate on tree age. Whereas wetlands are known to purify water and might contribute to the degradation of DOC. This thesis aims to investigate how different land use types and other parameters affect water colour. Ditches flowing through old spruce forests, young spruce forests, and peat wetlands in the Lake Bolmen catchment, southwestern Sweden, were sampled at in- and outlet. Highly significantly positive relationships between DOC, iron and absorbance were found. The relationship was strongest between DOC and absorbance (R² = 0.88; p < 0.001) and weakest between DOC and iron (R² = 0.54; p < 0.001). High variability led to no significant differences in the release of DOC and iron between the three land use types. However, older forests tended to increase DOC and iron loading compared to younger forests. This study suggests that not only spruce forests in general are affecting the brownification, but that several different factors like age and underlying soil type might play a critical role.