Investigating The Role of Dominant Drivers in Limiting the Ocean Primary Productivity in Swedish Large Lakes Vättern and Vänern Using Remotely Sensed Observations

Understanding the dynamics of algal blooms in freshwater ecosystems is crucial for sustainable water resource management. This study investigates the long-term variability of Chlorophyll-a (Chl-a) concentrations, a proxy for primary productivity, in Sweden’s two largest lakes, Vänern and Vättern, from 2004 to 2023. Utilizing MODIS Aqua satellite data and meteorological datasets, we analyzed the spatial and temporal trends of Chl-a and its controlling factors, including turbidity, sea surface temperature (SST), and aerosol optical depth (AOD).Lake Vänern exhibited an increasing Chl-a trend (+0.2 $\mathrm{mg} / \mathrm{m}^{3}$), primarily influenced by rising turbidity and SST. In contrast, Lake Vättern displayed a declining Chl-a trend (< $0.2 \mathrm{mg} / \mathrm{m}^{3}$), associated with reduced turbidity despite increasing SST. AOD was found to have minimal impact on primary productivity in both lakes. These results emphasize the role of turbidity and SST in shaping algal bloom dynamics and offer insights into mitigating harmful algal blooms. This study contributes to the development of region-specific water quality management strategies and supports the establishment of sustainable ecological practices for freshwater systems.