= 1194 —
2: a transition zone, where the blue greens are rather evenly distributed
in the watercolumn along the shore, and
3: an accumulation zone, where the blue green algae are accumulating
on the surface off the shore. In this latter zone we believe the blue
greens to be in a rather bad shape physiologically, partially dead or
decaying.
Enlargement of fig. 5 shows an interesting source of turbidity near the mouth
of the Oder, something probably evolving there from below.the surface (fig. 6).
The MSS 6 range shows a direct prolongation of a channel (Kaiserdurchfahrt),
extending from the north/west to the south/east. The fact that the straight
prolongation can be seen in the water, suggests the "cloud" to be in the
(surface) water. There is hardly an indication of this "prolongation" in the
MSS 4 or MSS 5 region, so in the O,5 - O,7 ,um band the "cloud" seems to cover
up any reflection of the channel, as pollution or blue green algae would.
Another LANDSAT scene, processed by DIBIAS!?), shows a presentation of the
blue greens east of the Danish island of Moen on August 9, 1975 (fig. 7).
(Using the MSS 4, 5, and 6 spectral bands for false colour presentation serves
to distinguish between algae and sandbanks near shore).
Also on August 9, 1975, large amounts of algae were detected on another LANDSAT
Scene, showing the Qresund between the Danish island of Seeland in the west '
(with Kopenhagen), and the Swedish mainland Schonen in the east (fig. 8).
Structures seem to indicate surface currents and turbulences. Little can be
said about their origine without further studies. Eddies;20 - 4O km in dia-
meter, shown on satellite images, seem to indicate Rossby waves (fig. 9) ^).
Blue green algae, being drifted by the Baltic stream, are thought to trans-
port phosphate from the shore to the central Baltic sea. Both nitrogen and
phosphate are considered limiting factors for the growth of phytoplancton.
The euphotic, light penetrated surface layer of the Baltic during early summer
is mainly depleted of nitrogen. If additional phosphate is supplied by sources
from land (pollution), then nitrogen will be the limiting factor. So the ability
of the blue green algae, to fix nitrogen from air dissolved in water, favours
and "pushes" their development compared to other algae that need dissolved
nitrogen and may be an explanation for their sudden mass growth. We consider
this to be an explanation for the growth of blue green algae in the Baltic.
The influence of nutrients on the growth of phytoplancton as well as nitrogen
fixation_and development of heterocysts has been investigated by Horstmann
(fig.10) 7).
The calculation via satellite measurements of the amount of nitrogen fixed
in the Baltic by the cyanophyceae per year, for several reasons up to now
won't be accurate enough:
1: the nitrogen fixing mechanisms of blue green algae are different, i.e.,
equal masses of algae don't have equal nitrogen fixing ability,
2: the areas covered by algae appear differently in size, depending on the
use of multispectral LANDSAT channels MSS 4, 5, or 6, so the volume of algal
masses, calculated therefrom for the estimation of the amount of nitrogen
fixed, varies accordingly, i.e., an average formula, taking into account
different spectral appearance as well as different depth of algal masses,
has to be found ‚and
