Long-Term Water Quality Trends in Lake Vomb, Sweden

Lake Vomb is a 12 km² large lake located in southern Sweden which has served as a vital drinking water source for approximately 500,000 inhabitants since the 40s. The lake is highly productive due to its location in a highly dense agricultural region and, therefore, has high phosphorous concentrations that periodically cause extensive and occasionally toxic algal blooms. This poses challenges not only for the drinking water production but also for the local communities in the area. Various measures, such as artificial wetlands and natural flooding areas, have been implemented in the catchment to decrease nutrient loading. However, these measures have shown limited effects on improving water quality in the lake.

Monitoring data has been collected since the 50s, but much of this historical data has remained unused due to a lack of digitalisation. In this study these archived records was recovered and digitalised to create a comprehensive long-term dataset with the aim of analysing trends in nutrient fluxes, the effectiveness of mitigation measures, changes in land-use and agricultural activities and the impact of climate change. Preliminary results show a decrease in nutrient concentrations in the inflowing waterbodies which is not seen in the lake itself, posing the question of in-lake processes continuing driving the eutrophication of the lake, such as internal phosphorus loading. By evaluating these long-term trends insight in lake dynamics could be gained as well as help to identify relevant and cost-effective measures for improving the lake water quality.