Monitoring Eutrophic Conditions in Lanalhue Lake (Chile): Insights into Pollution Sources with Landsat-8 OLI Data

This study examines the trophic state of Lake Lanalhue, in the south-central region of Chile, and its relation with the anthropogenic pressure. To assess the impacts on water quality, Landsat-8 OLI satellite imagery was integrated with in-situ data collected between 2014 and 2022. The analysis focused on estimating Chlorophyll-a (Chl-a) and Total Suspended Solids (TSS), by developing retrieval models based on spectral relationships and direct measurements obtained from the lake. For Chl-a estimation, an exponential relationship derived from green band showed strong correlation with in-situ data. Estimation of TSS was based on the spectral red/blue ratio, optimized to capture the optical scattering characteristics associated with suspended sediments in the water column. These models enabled the generation of spatial distribution maps highlighting differences in water quality, with the southern sector of the lake being the most impacted by eutrophication process. This area consistently recorded the highest concentrations of Chl-a and TSS, confirming an advanced trophic state associated with significant nutrient and sediment inputs from agricultural, livestock, and urban activities in the watershed. A comparison of 2014 and 2022 data revealed an intensification of the eutrophication process. The study underscores the utility of remote sensors as an efficient tool for long-term environmental monitoring of water bodies. This information is essential for guiding environmental management and informing the implementation of effective management strategies.

Keywords: Water Quality; Eutrophication; Landsat-8 OLI; Retrospective Analysis; Chilean Lakes