Why is it important?
Good water quality is the basis of a healthy ecosystem with rich biodiversity. Aquatic ecosystems also provide essential services for drinking water, irrigation, recreation, aquaculture and fisheries. The EU Water Framework Directive recognizes this and requires member states to monitor and, if necessary, improve water quality. Although the spatial component is key to gaining insight into water processes, regular sample-based monitoring only provides point data.
What does CoastObs offer?
WFD relevant products can be based for example on satellite-based chlorophyll-a maps (feeding into WFD phytoplankton abundance), on satellite-based turbidity maps (feeding into WFD transparency) or on seagrass percentual coverage maps. CoastObs offers several products for the WFD status based on EO data:
- Pixel extracts at specific locations: time series at certain points. These can be treated as data points in the same way as time series from in situ measurements. Calculating e.g. the P90 over time provides a temporally aggregated result, which can be classified according to the WFD thresholds. This option will probably increase the frequency of the data availability in comparison to (only) manual sampling.
- Applying the WFD thresholds on each satellite image. This will generate a series of maps with the spatial distribution of the WFD classes and allow users to take advantage of the spatial component of Earth Observation data. This can help to understand the system: where is the status good, or moderate, or bad? Why is that the case, and which measures would therefore be the most effective? It can also help to determine if the in situ sampling stations are located at representative and strategic locations.
- Spatial aggregation over a WFD area. A global average over a region along a series of images can be used to calculate the P90 over time. The result is a spatial-temporal aggregate, which can be classified according to the WFD thresholds. Such aggregates can be presented as histograms, e.g. P90 values over time and space.
How was the data validated?
The accuracy of the WFD products directly relates to the accuracy of the Chl-a, turbidity, seagrass coverage or other product that was used as input (which are illustrated elsewhere in this document). The applicability of earth observation (EO) data for WFD reporting was illustrated in detail by the H2020 EOMORES and CoastObs white paper "Satellite-assisted monitoring of water quality to support the implementation of the Water Framework Directive". Details of the case study can be found in D3.8 higher-level products.
Case study example: Wadden Sea
The Ems estuary is part of the Wadden Sea; it is a highly dynamic area. Although there are several in situ monitoring stations, the spatial variations are still hard to catch. We used this area to illustrate two of the above-mentioned types of products for WFD reporting.
Figure 1. Map of the Sea Surface Tempature in the coast of Galicia, Spain.
Figure 2. Histogram showing the number of satellite pixels in each class. This example is based on one satellite image, for reporting purposes a complete year of imagery could be intergrated.