Monitoring the Bio-optical State of the Baltic Sea Ecosystem with Remote Sensing and Autonomous In Situ Techniques - The Baltic Sea Basin - page 425

Fig. 20.10 Diffuse attenuation has been shown to be the most accurate product for the Baltic Sea.
The image presented here shows that it is possible to monitor water quality in coastal areas of
the northwestern Baltic Sea (from Kratzer et al. 2008 ) . H2, H3, H4, and H5 are standard stations
of the Swedish national monitoring program. H5 is situated about 0.7 km south of the outlet of
Himmerfjärden sewage treatment plant
20.3.2 Optical Gradients of Inorganic Suspended Matter
in Coastal Waters
Using bio-optical data, Kratzer and Tett ( 2009 ) have developed an attenuation model
for the northwestern Baltic Sea that explains the contribution of each optical com-
ponent to the diffuse attenuation of light. Figure 20.11 illustrates the changes in
attenuation from source (coast) to sink (open sea, in this case Landsort Deep).
CDOM is the dominant optical component in both the open sea and the coastal
areas, with a steady increase towards the head of the fjord. Organic suspended par-
ticulate matter (organic SPM) did not show a spatial trend when comparing open sea
to coastal data. However, inorganic suspended particulate matter (inorganic SPM)
showed a clear spatial trend. The optical influence of inorganic SPM can be detected
to approximately 15-20 km off the coast, which means that the coastal influence
reaches much beyond the one nautical mile line (i.e. 1.85 km) from the coastal
baseline as defined by the EU Water Framework Directive (WFD). This means that
strictly speaking the breadth of the coastal zone should be in the range of tens of
kilometres, which is also in the same dimension as the influence of coastal upwelling
(5-20 km off the coast), which may bring up nutrient-rich bottom waters into the