Modeling Phosphorous Dynamics in an important Swedish Drinking Water Source

The population growth and the resulting increased food demand resulted in more intense agricultural practices. This resulted in significant changes in land use and a substantial rise in phosphorus inputs to aquatic systems over the past few decades, primarily through fertilizer application and runoff. Lakes, particularly those situated within agricultural landscapes, now face an increased risk of eutrophication due to elevated nutrient inputs. This poses serious threats to water quality, ecosystem health, and the services these freshwater systems provide. Degraded water quality, algae blooms, which deplete oxygen and threaten aquatic life, are serious ecological consequences. Beyond these impacts, decreased recreational value and complications for drinking water production are effects to the human usage of such water sources. Even though the main drivers of eutrophication are fairly well understood, the dynamics within the lake, especially the mobilization and the release of phosphorus, are poorly known.  

Lake Vomb, located in southern Sweden, is an important drinking water resource for 5% of the Swedish population. Mitigation measures have been implemented within the lake's catchment, with limited effect on the lake's P concentration. The lake regularly experiences harmful algal blooms affecting the lake’s ecosystem as well as drinking water production, which increases the necessity for further management measures. Previous studies have indicated that internal P loading continues to sustain the lake's high P concentration, particularly during the summer. Furthermore, this appears to be coupled to physical forcing, such as wind direction. To implement successful measures is only possible when the internal dynamics of the phosphorus in the lake are fully understood.  

To analyze the pathways, patterns, and future development of phosphorus levels in the lake together with the effluent water quality, a multidimensional model of Lake Vomb has been developed. The model combines long-term monitoring data of hydrology, in-situ measurements of total phosphorous, determining water quality parameters, and publicly available meteorological data. Modeling was performed using a combination of the open TELEMAC-MASCARET model with the WAQTEL module. Possibilities to extend the model through the application of the AED2 library are explored and analyzed. 

The results of the model analysis will be used to optimize lake management strategies, including the placement of nature-based mitigation measures. In addition, current drinking water treatment methods and strategies will benefit from increased understanding of phosphorous transport. Finally, the concept of this specific model and results may be applied to other regions facing similar problems.