Web Release Date: November 13,
Hypoxia in the Baltic Sea and Basin-Scale Changes in Phosphorus Biogeochemistry
Department of Marine Ecology, National Environmental Research Institute, P.O. Box 358, DK-4000 Roskilde, Denmark
Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden
Department of Water and Environmental Studies, Linköping University, SE-581 83 Linköping, Sweden
Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden
Received for review May 3, 2002
Revised manuscript received October 9, 2002
Accepted October 16, 2002
Abstract:
Deep-water oxygen concentrations in the Baltic Sea are influenced by eutrophication, but also by saltwater inflows from the North Sea. In the last two decades, only two major inflows have been recorded and the lack of major inflows is believed to have resulted in a long-term stagnation of the deepest bottom water. Analyzing data from 1970 to 2000 at the basin scale, we show that the estimated volume of water with oxygen, <2 mL L-1, was actually at a minimum at the end of the longest so-called stagnation period on record. We also show that annual changes in dissolved inorganic phosphate water pools were positively correlated to the area of bottom covered by hypoxic water, but not to changes in total phosphorus load, thus addressing the legacy of eutrophication on a basinwide scale. The variations in phosphorus pools that have occurred during the past decades do not reflect any human action to reduce inputs. The long residence time and internally controlled variation of the large P pool in the Baltic Sea has important implications for management of both N and P inputs into this eutrophicated enclosed basin.
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