Wassmann, P. Norwegian College of Fishery Science, paulw@nfh.uit.no
Tamminen, T. Finnish Environment Institute, tamminen@vyh.fi

 
RIVER RUN-OFF, PELAGIC EUTROPHICATION AND SEDIMENTATION IN THE GULF OF RIGA, BALTIC SEA
 
The impact of the rivers on the Gulf of Riga is substantial, but area-specific load from the catchment is comparatively low. This was unexpected in light of the generally inefficient sewage treatment and the previous intensive agriculture. The more than 50-fold N:P ratio on an average annual basis indicates that rivers and the inner recipient are phosphorus-limited. However, N limitation predominates over the entire gulf. Basin-wide the distribution of phytoplankton correlates clearly with the patterns of nutrient-rich freshwater. The nutrient load from the rivers generates a south-north, while the east-west gradient is more variable, depending on predominating winds. Thus the spatial variability of the suspended biomass and sedimentation rates are less than the time variation. The only significant sedimentation of fresh phytoplankton biomass takes place in spring before the pelagic system develops sufficient complexity to greatly reduce vertical losses. C and N is lost vertically in excess while P is strongly recycled in the pelagic system. The trophic complexity of the planktonic community and the variable, but continuous supply of nutrients by rivers give rise to a high "buffering capacity" of the pelagial throughout major parts of the productive season.
 
Day: Friday, Feb. 5
Time: 04:30 - 04:45pm
Location: Eldorado Hotel
 
Code: SS48FR0445E