The boundary of the photic zone in Belgian waters is not relevant for the establishment of a diagnosis of eutrophication. It is therefore not used, in line with the evaluation under the Water Framework Directive and OSPAR. Satellite observations provide a synoptic view of the quantity of matter in suspension and of the turbidity in the Belgian area as a whole. The concentration of matter in suspension and, consequently, the turbidity appears in the Belgian coastal zone. It should be noted that the low depth in the coastal zone is mainly due to sediments placed in suspension by tidal currents. Eutrophication and chlorophyll a concentration play only a marginal role in the luminosity compared to the tidal processes put into suspension, except in the area of the open sea where the matter in suspension is mainly organic.

The dissolved oxygen indicator in Belgian waters is not relevant for the preparation of a diagnosis of eutrophication (not used in OSPAR). The measurements of dissolved oxygen available for the reference period are not below the 6 mg/l threshold and the concentration of dissolved oxygen remains for the greater part of the time close to saturation. Mainly data from sampling close to the surface and in the soil. From the measurements we have and on the basis of the current state of knowledge, we can conclude that there is no known undesirable effect on biotopes which would be linked to a hypoxia phenomenon. The concentration of dissolved oxygen does not pose a problem in Belgian waters, although other eutrophication indicators (nutrients and chlorophyll a) suggest that the good status has not yet been reached in the coastal zone and territorial area.

The mechanism usually referred to to explain the decline of whose nutrient word waters are to be explained by less light as a result of the stimulation of large algae biomass as epiptes and macroalgae in shallow coastal waters or phytoplankton in deeper coastal waters. In the Belgian area, the natural conditions do not allow the development of macrophytes or macroalgae. In particular, light penetration in the water column is, by its nature, low due to sediments put into suspension by the operation of the tides (cf. D5C4). Compared with those astronomical and geological factors, eutrophication and the proliferation of phytoplankton are likely to play only a marginal role in suppressing the development of benthic macrophytes and macroalgae. Consequently, the absence of macrophytes and macroalgae in the Belgian area is by no means an adequate indicator to determine whether eutrophication is increasing or decreasing.

Not relevant (see criterion 6)