Monitoring estuarine water quality using satellite imagery. The Mondego river estuary (Portugal) as a case study

Monitoring water bodies is a task not only scientifically relevant but also legally binding in several countries (e.g. Water Framework Directive and the European Marine Strategy Framework Directive). Ecosystem health assessment projects are greatly enhanced by the use of remote sensing technologies. In the present study, a small Portuguese estuary (Mondego river estuary), was used as a case study to assess the feasibility of measuring several key indicators using satellite imagery.The feasibility of using MODIS land/cloud bands to evaluate Secchi Disk Depth (SD) was addressed. The ratio of remote sensing reflectance at 469 and 555 nm was the best predictor for this parameter (R2 = 0.9678; p < 0.05).Landsat-7 ETM+ was, in turn, used to estimate Chlorophyll-a concentration (OC), Turbidity and Salinity. Reflectance values were compared with concurrent in situ data recorded by an automatic sampling buoy. ETM+ data was also used to develop a local water color index, which takes advantage of the relative differences in the reflectance values of the three bands in the visible range of the spectrum.Overall, remote sensing data yielded robust estimates of the selected indicators, favoring its future operational use in the study area.

► We evaluate the use of remote sensing data to monitor water quality in estuaries. ► Strong agreement between satellite and in situ measurements for several parameters. ► Both current and historical data can be retrieved, expanding existing datasets.