The Oder Estuary - IOW

50
µmol/l
µmol/l
350
300
250
200
150
100
50
0
175
150
125
100
75
50
25
0
Jahresgang SiO4-Si im Kleinen Haff
Jahre 1990 - 1999
J F M A M J J A S O N D
Jahresgang SiO4-Si in der Pommerschen Bucht
Jahre 1990 - 1999
J F M A M J J A S O N D
95%
5%
75%
25%
Median
95%
5%
75%
25%
Median
µmol/l
350
300
250
200
150
100
50
0
Jahresgang SiO4-Si im Großen Haff
Jahre 1991 - 1999
J F M A M J J A S O N D
Figure 7.2: Annual course of silicate-Si concentrations (µmol/l) in the Kleines Haff (top, left),
the Pomeranian Bay (bottom, left) 1990 – 1999 and the Wielki Zalew (top, right)
1991 – 1999. Data source: State Agency of Environment, Protection of Nature and
Geology Mecklenburg-Vorpommern (LUNG) and West Pomeranian Voivodeship
Inspectorate in Szczecin (WIOS).
The long-term development of silicate concentrations is very much dominated by the high
variability of concentrations. The trends in the Kleines Haff and Wielki Zalew are not well in
agreement and we refrain from an interpretation of the data (Fig. 7.1).
Silicate is another element where the annual dynamic of the concentrations reflects the biological
activity. During winter we observe high concentrations and a steady decrease towards May. Similar
to phosphorus, silicate is taken up by the diatom bloom in spring and largely depleted in the water
column (Fig. 7.2). Silicate is incorporated into diatoms shells and these shells are subject to
sedimentation when the algae die. Due to dissolution, a steady increase in silicate concentrations is
observed during the rest of the year. This process can be interrupted by diatom developments later
in the year, when silicate is consumed again and partly removed from the water column.
In spring, the spatial pattern of silicate concentrations is controlled by regional differences in
uptake during algae blooms. During summer, regional differences in silicate dissolution create the
spatial pattern in the lagoon. In the winter semi-annual gradients maintained by high Oder river
discharge are prevailing (7.3). The data shows that the lagoon acts as an efficient sink for silicate.
95%
5%
75%
25%
Median