SPECTRUM OF THE LAKES: UNVEILING WATER COLOR OF MINNESOTA'S SENTINEL LAKES WITH SATELLITE REMOTE SENSING FOR WATER QUALITY MONITORING

Surface waters are precious natural resources requiring costly time and labor for effective water quality monitoring. New applications of water color analysis by satellite remote sensing are a promising approach to water quality monitoring for scientific, industrial, recreational, and cultural benefit. This research expands previous applications of lake water color analysis and pioneers water color chromaticity analysis for midcontinent lakes in Minnesota, USA. The results of this project are the first accounts of Minnesota’s Sentinel Lake water color, variability of water color by ecoregion, and temporal consistency of water color within major ecoregions. Minnesota state research initiative, Sustaining Lakes In a Changing Environment (SLICE), ordains “Sentinel Lakes” as representative of lake populations within major ecoregions of Minnesota. Following launch in 2013, NASA’s Landsat 8 OLI satellite services a growing public record of Earth’s surface reflectance in the visible spectrum. Generational improvements of the Landsat 8 OLI sensor introduced capabilities for remote sensing of smaller terrestrial surface waters. Chromaticity analysis interprets dominant visible wavelength from tristimulus values of surface reflectance, quantifying unbiased water color. Visible light reflectance from the deepest area within each Sentinel Lakes was gathered during the late summer of 2013 – 2022. The late summer months represent peak insolation and bolstered trophic activity. In 2022, distinguishable colors occur between ecoregions include the Canadian Shield ecoregion lakes that reflected red color near 580nm, and the North Central Hardwood Forests ecoregion contained the bluest colored lakes (555-560nm). Lakes within an ecoregion shared dominant visible wavelengths, evident of similar water color. Preliminary results support hypotheses of distinguishable water colors between neighboring ecoregions, consistent water color within the same ecoregion, and incremental color changes over time in individual lakes. Cost reduction, backlogs, and improving technology are some of the major incentives for further developing satellite remote sensing water color methodology for water resource management.