Geoscience Reference
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Fig. 18.4 Results of the three-dimensional flow and ecological Baltic Sea model ERGOM for
three stations in the estuary during the period 2000-2001. The data were aggregated to 5-day aver-
ages a) Central lagoon: Chlorophyll-concentrations in the water and organic carbon concentrations
in sediments. b) Central lagoon: Concentrations of iron-phosphate in the sediment, oxygen above
the sediment and phosphate in the water body. The same parameters are shown for the Oder Lagoon
outlet (c) and the Pomeranian Bay (d)
It is well known that oxygen depletion at the sediment surface can cause a large
release of phosphorus from the sediment into the water body, the so-called internal
eutrophication. This is especially true if large amounts of phosphorus are bound to
iron. This is the case in the lagoon, where Fe concentrations between 2 and 6%
were found in surface sediments (Leipe et al. 1998 ) and Fe redox processes can
be expected to play a major role in P dynamics. Dahlke (personal communication)
measured several vertical pore water profiles in the sediments in 1994 and 1995. An
increase in P concentrations, from about 10 mmol P/m 3 below the sediment surface
to 20-40 mmol P/m 3 in a depth of 10 cm, depending on the date, was found. These
concentrations are about 2-3 times higher compared to the concentrations in the
water body.
About 13 t dissolved phosphorus is stored in the pore water of the upper 10-
cm sediment layer of the Kleines Haff and is generally available for a fast release.
The surface sediments (0-6 cm) of the Kleines Haff contain about 0.36% P. This
concentration decreases with increasing sediment depth. According to the data
in Leipe et al. ( 1998 ) , at least 10,000 t P is stored in the upper 10 cm of the
61% muddy sediment surface of the Kleines Haff. The opposite vertical gradi-
ents between pore water and particulate phosphorus suggest that dissolution from
 
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