MAP Technical Reports Series No. 106 UNEP

- 145 -
- Protection of human health;
- Protection of marine life and its environment;
- Assessment of levels and trends.
9.1 Monitoring of eutrophication
In the pelagic domain, monitoring of eutrophication should be relatively straightforward.
The only difficulty may be in finding the most cost-effective strategy. Two major strategies are
available, namely remote sensing and direct measurements in the field.
a) Remote sensing
Remote sensing may be successfully employed when eutrophication extends over
large areas such as the northern Adriatic Sea or the Aegean Sea. Although the satellite operated
Coastal Zone Colour Scanner (CZCS) has been terminated, the possibility of using LANDSAT's
thematic mapper or SPOT's sensors still exists: their low sensitivity is overcome by the high
chlorophyll content of the upper layers of the eutrophic areas. Another possibility is the use of
airborne spectral scanners or even aerial photographs to monitor the extent of eutrophication
(Zevenboom, 1989; Zevenboom et al., 1989; Zevenboom et al., 1990).
b) Direct measurements made in the field
No single analytical tool is adequate to measure the degree of eutrophication of a given
body of water. Instead, most experts believe the best approach is to measure many different
parameters and to synthesize the results into a general model providing an overall, somewhat
integrated degree of eutrophication for the water. Unless proper selection of the parameters to
be measured is made, the amount of work required to assess the extent and intensity of
eutrophication may be rather costly.
Much in the same way that the information provided by remote sensors on the surface
layer is used to evaluate the entire water column, direct measurement of surface variables may
be used to infer what is happening at deeper layers. However, subsurface and near bottom
waters should also be monitored, particularly in relation to monitoring of the benthic domain.
Direct observations by SCUBA or underwater TV can also be very useful in detecting
changes in benthic populations, especially in the early stages of deterioration.
9.2 Major variables to be sampled
Various parameters such as suspended solids, light penetration, chlorophyll, dissolved
oxygen, nutrients, organic matter, etc. may be determined either at the surface or at various
depths.
If only limited means are available, determination of those parameters that synthesize
the most information should be retained. Chlorophyll determinations for example, although not
very precise representations of the system, are data which provide a great deal of information.
Reliable data on nutrients are extremely useful indicators of potential eutrophication. Turbidity
and water colour may also be a good measure of eutrophication, except near the mouths of
rivers where inert suspended solids may be extremely abundant. Dissolved oxygen is one
parameter that integrates much information on the processes involved in eutrophication,
provided it is measured near the bottom or, at least, below the euphotic zone where an oxycline
usually appears.