Nitrogen and phosphorus budgets of the Gulf of Gda sk (Baltic Sea)

A modified LOICZ budget approach was adopted to address the long-term nutrient fluxes in the Gulf of Gdan´ sk using an extended data set covering the period 1993–1998. Water and nutrient exchanges as well as primary production and denitrification rates were estimated from data encompassing several thousands of measurements. Estimated water residence time in the Gulf of Gdan´ sk was about 15 days and corresponded well with 3D model simulations. Between 23 and 34% of the total N and P loads, respectively, were retained in the Gulf. Dissolved inorganic phosphorus was imported from the open Baltic Sea, which moderates the high N/P ratios from land derived and atmospheric sources. Net ecosystem production (NEP) was calculated at 82 gCm 2 yr 1 which, when compared to literature primary productivity data, results in an f-ratio of 0.36. Deviation of the N and P retention from the Redfield ratio is explained by denitrification rates (18 mgNm 2 d 1), which resolves the mismatch between observed burial fluxes (about 4250 t N and 2400 t P yr 1) and calculated retention rates (30 000 tNyr 1 and 3000 t P yr 1).