Global Patterns and Drivers of Lake Color

Abstract:

Lakes are hotspots for biogeochemical processing that provide valuable ecosystem goods and services critical to society. Many of these critical functions depend on the constituents of the lake water, which can be reflected in the color of the water. As such, color as perceived by human eyes is an important metric of the quality of lake water. The idea of using color to inform water quality dates back more than a century with the invention of Forel-Ule color scale, which is still widely used. Today, regular recording of the Earth’s surface by optical satellites allows us to estimate colors of inland water from space, substantially extending our capacity to monitor and manage our lakes. In this study, we calculated the modal color for ~150,000 lakes (>0.1 km²) worldwide using 7 years of images from the Landsat 8’s OLI sensor. Our results place the modal wavelengths of the lake color either in the blue-green region (centered at 493 nm) or in the green-yellow region (centered at 562 nm) of the spectrum. Investigating possible meteorological (temperature, precipitation), morphological (elevation, depth, shoreline complexity), and land cover (percent cover of urban, cropland, bare land in its watershed) drivers, we found that mean lake depth, elevation, and mean annual temperature are the most influential factors of modal lake color, followed by land cover (most notably percent coverage of cropland) and population in lakes’ corresponding drainage basins. With projected increases in air temperature and changes to land use and land cover, many of our studied lakes may experience major changes in their modal color, reflecting shifts in hydrological and ecosystem regimes for these critical systems.