Brownification in Lake Bolmen, Sweden, and its relationship to natural and human-induced changes

Abstract

Study region: This study focuses on the twelfth largest lake in Sweden, Lake Bolmen and its catchment. Study focus: During the last decades the process of brownification has resulted in water with browner color, affecting water quality and ecosystems. The occurrence of brownification and its governing factors, especially with regard to the interaction with the environment, is not yet fully understood. This study therefore performed different statistical analysis to detect spatial and temporal patterns in brown color and associated forcing factors. In addition, models were developed to describe the water flows in the lake and their influence on the water color. New hydrological insights for the region: Seasonal variations in color are dominated by meteorological parameters such as precipitation and temperature, whereas long-term (decadal) variations are functions of trends in these parameters as well as changes in land use, primarily related to forestry. Modeling the water flows yielded the residence time for different sub-basins in the lake, indicating the effects of travel time on the color. Calculated wind-generated surface waves and their effects on resuspension showed that such events may occur on a limited event and time scale.

Keywords

• Brownification
• Lake hydrology
• Climate and land use change
• Catchment properties
• Drinking water production