Applications

Optimisation of in situ monitoring

Since a few decades eutrophication is a threat to the North Sea. Increased runoff and discharge of nitrogen and phosphate from land cause a higher concentration of these elements in rivers and coastal waters. The high nutrient inflow alters the food balance in the coastal waters, which can have an impact on phytoplankton abundance and species composition and therefore on the rest of the food web.

Environmental managers of the North Sea states have decided to apply a precautionary principle and limit this unnatural change of the coastal ecosystem. In the frame of the OSPAR ( link to www.ospar.org) convention, they established a set of parameters to determine the eutrophication status of different regions in the North Sea . The Belgian authorities are now obliged to perform seaborne monitoring of, inter alia, chlorophyll a concentration and nutrients. These measurements are reported to OSPAR on a 5-yearly basis in the form of a National Assessment of Eutrophication. The introduction of the European Union’s Water Framework Directive (EU-WFD) has expanded greatly the number of parameters for which seaborne monitoring is required. To cope with these increased requirements within the existing resource constraints, a reduced monitoring station network was necessary, ensuring sufficient spatial sampling. BELCOLOUR-2 demonstrated, through an analysis of MERIS imagery, that the essential features of the spatial distribution of chlorophyll a during the high biomass spring bloom could be captured by a reduced monitoring network of about 9 open sea locations. After consideration of other factors (navigation, needs for sampling other parameters, avoidance of areas with usage conflict, etc.) an optimized chlorophyll a monitoring network was designed, allowing a reduction from 17 to 10 sampling locations.

Location of the seaborne measurement stations of the Belgian water quality monitoring network (top) before 2007 and (bottom) after optimisation for EU-WFD and OSPAR requirements [courtesy of the Belgian Marine Data Centre]. Source: Ruddick, K., Y. Park, R. Astoreca, A. Borges, G. Lacroix, and C. Lancelot. 2008. Application of the MERIS algal pigment products in Belgian waters. 2nd MERIS-(A)ATSR workshop. ESA SP-666.