Globally Consistent Assessment of Coastal Eutrophication

Abstract Eutrophication associated with increasing anthropogenic nutrient loading is an emerging global concern. Often, eutrophication is concomitant with negative impacts on ecosystems and human well-being. Nevertheless, the impacts and the extent of eutrophication are limited to regions with dedicated monitoring programmes. Here we introduce the Global Eutrophication Watch, the first global and interactive assessment map of coastal eutrophication potential (CEP). It is constructed on Google Earth Engine and it evaluates temporal trends in satellite chlorophyll-a (CHL), a proxy for phytoplankton biomass, to devise a global map of CEP. Our analyses suggest that, globally, coastal waters (depth ≤200 m) covering ~1.15 million km2 are eutrophic potential. We found that waters associated with CHL increasing trends—those with potential for further deterioration of water quality—are twofold higher than those showing signs of recovery. The tool effectively identified areas of known eutrophication with severe symptoms, such as dead zones, as well as those with limited to no information of the eutrophication. Our tool introduces the prospect for a consistent global assessment of eutrophication trends with major implications for monitoring Sustainable Development Goals (SDGs). This work contributes to the application of Earth Observations in support of SDGs.