Key Points:
-Introduction of a Google Earth Engine app that allows a globally consistent assessment of eutrophication in a way never done before
-The app identifies eutrophication trends worldwide solely based on satellite-derived chlorophyll-a
-The app can detect areas with severe symptoms of eutrophication and those with improving water quality
An international research team led by Dr. Eligio Maúre of Northwest Pacific Region Environmental Cooperation Centre (NPEC) has successfully developed a technique for mapping coastal eutrophication on a global scale using satellite remote sensing.
Eutrophication is an emerging global issue associated with the increasing anthropogenic nutrient loading. The impacts and extent of the eutrophication phenomena are often limited to the regions with dedicated monitoring programmes in place. This article introduces the Global Eutrophication Watch, the first global and Google Earth Engine-based interactive assessment tool of coastal eutrophication potential (CEP) (Figure 1).
NPEC developed this tool as a cost-effective means for a coastal eutrophication assessment. The methodology applied in the Global Eutrophication Watch is a part of the Common Procedure for the eutrophication assessment of the NOWPAP (Northwest Pacific Action Plan) CEARAC (Special Monitoring and Coastal Environmental Assessment Regional Activity Centre).
Figure 1. Global eutrophication watch app interface. The left panel shows the control panel of the app. The map of CEP in the NOWPAP region based on the MODIS Aqua global dataset is shown in the middle. The right panel shows the CHL max time series of a select point on the map. The CEP classes are also shown.
The tool opens a new era of eutrophication assessment for the global coastal waters. By evaluating trends in the satellite-derived chlorophyll-a (CHL) time-series, it devises a global map of CEP innovatively in terms of speed for data computation and its spatial and temporal coverage. The tool effectively identifies areas of known eutrophication with severe symptoms, like dead zones (areas with very low dissolved oxygen) and those with limited to no information of the eutrophication. For example, the app can highlight an improving water quality in the Bohai Sea, as shown in the two comparative assessments in the image below (Figure 2).
Figure 2. Map of coastal eutrophication potential (CEP) in the Bohai Sea. LD, LN, and LI depict the status as low CHL (α < 5 mg m–3) with decreasing, no, and increasing trends, respectively. HD, HN and HI indicate high CHL (α ≥ 5 mg m–3) with the three trends mentioned above, respectively. a Preliminary assessment of CEP for the period 1998-2015. b Same as (a) but for the period 1998-2019. The rectangle in magenta (b) shows the location of the Bohai Sea.
Therefore, the Global Eutrophication Watch introduces the prospect for consistent global assessments of eutrophication trends with major implications for monitoring Sustainable Development Goals (SDGs) and the application of Earth Observations in support of SDGs.
The obtained map of CEP from the Global Eutrophication Watch is relevant in providing eutrophication extent and context and providing information of water quality to coastal water managers for required management interventions.
The results of this research were published online in Nature Communications on October 22, 2021 (Friday), DOI: 10.1038/s41467-021-26391-9
GEE app: https://eutrophicationwatch.users.earthengine.app/view/global-eutrophication-watch
