The Oder Estuary - IOW

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development of algae in the Pomeranian Bay started earlier, already in March during the 1980’s.
The concentrations during spring became more pronounced during the 90’s (Fig. 8.3).
µg/l
30
20
10
0
-10
-20
-30
-40
J F M A M J J A S O N D
Kl. Haff
Gr. Haff
Bucht
Figure 8.3: Differences in median chlorophyll-a concentrations (µg/l) between the 1990’s
compared to the 1980’s in the Kleines Haff, the Wielki Zalew (Grosses Haff) and the
Pomeranian Bay (Bucht). Data source: State Agency of Environment, Protection of
Nature and Geology Mecklenburg-Vorpommern (LUNG) and West Pomeranian
Voivodeship Inspectorate in Szczecin (WIOS).
The spatial chlorophyll pattern in the lagoon is influenced by the Oder river during several months.
It is well known that phytoplankton forms patches, which are driven by wind and currents, and
show strong vertical concentration gradients. These effects create an intensive patchiness, which
cannot be represented by the existing few sampling locations.
The nitrogen as well as the phosphorus concentrations in the lagoon are very high and nutrients are
abundant most of the time. Like in other temperate zone estuaries (NIXON & PILSON 1983) nitrogen
becomes a scarce resource during late summer. Phosphorus can play a role as a limiting element for
algae biomass in spring, indicated by low PO4 values between April and June. The same is true for
silicate. However, especially in the eastern part of the lagoon even intensive phytoplankton blooms
during summer usually do not deplete nutrients. One reason is the constant nutrient supply by the
Oder river and another reason is the mineralization of organic material, which is an important
source for nutrients. Due to self-shading effects and high water turbidity as a result of sediment
resuspension, light is the most important resource in the lagoon. In winter low temperatures play a
role, too. With decreasing nutrient loads with the Oder river during the 1990’s, the importance of
nutrients in the lagoon slightly increased.
In the Pomeranian Bay nutrients, especially nitrogen plays a more important role as limiting
resources for algae biomass.