Zbigniew Witek, Aleksander Drgas, Anetta Ameryk and STANISŁAW Ochocki
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: primary production, bacterial production, respiration, eutrophication, carbon budget, Baltic Sea, estuary

Abstract.
The aim of this work was to estimate the influence of the Oder River on the biological production of the Pomeranian Bay and to identify the role of the local community in organic matter mineralization. The first problem was examined through the comparison of local nutrient resources and local primary production with nutrient loads and organic matter loads reaching the Pomeranian Bay from outside. The latter problem, concerning organic matter decomposition in the bay, was examined on the basis of measurements of oxygen consumption conducted in various seasons (March 1996, July 1996, May 1997 and October 1997).
It was calculated that 67% of nitrogen in the Pomeranian Bay came from the Oder River, 12% from the atmosphere and 21% was of marine origin. In the case of phosphorus, the marine and land-based shares were approximately even. As opposed to the open parts of the Baltic Proper, where nitrogen is the nutrient limiting primary production, phosphorus is a potentially limiting factor in the Pomeranian Bay. The annual organic matter load from the Oder River and atmosphere exceeded the annual "new" primary production by a factor of 2-3, but the amount of the biologically decomposable organic matter from these sources was close to the value of "new" primary production. Full decomposition of the degradable allochthonous organic material depends, however, on adequately high temperature and requires a longer period of time. The utilization of this material for bacterial production, and, thus, its inclusion into the trophic cycle was rather small and was concentrated around the river mouth area. Despite this the total community (dark) respiration appears to exceed  (¹⁴C) primary production by 30-50% throughout most of the vegetation period, thus suggesting an important contribution of the allochthonous organic material in the community energy budget. However, methodological uncertainties involved in primary production and community respiration measurements make this conclusion only hypothetical.