Su kolonunun oksijenli-oksijensiz arayüzey tabakasındaki fosfat ve nitrat döngülerinin modellemesi

Data collected extensively in the water of the central Baltic Sea show the development of nitrate deficits, likely caused by denitrification and anammox. Observations of temperature and salinity, oxygen, hydrogen sulfide and nutrient concentrations in the central Gotland Sea reveal the rate of formation of nitrate deficits to be largest in the oxic waters above and in the halocline. The reason that large accumulated deficits are observed in stagnant deeper waters is simply that there they can build up over years to decades of stagnation. The magnitude of the nitrate deficit formation varies between years, mainly depending on the annual maximum depth of the mixed layer and related late-winter nitrate concentration in surface water. The bulk of nitrogen losses is by denitrification (anamox maximum 12%?) in the oxic part of the Baltic where it is only possible in sediments. Deep waters turning anoxic can have very high rates of denitrification, but for short periods only. Therefore, and with the small water volume involved, this is of no importance for the Baltic N-balance. The results show that denitrification is not high in the Baltic Sea because it is prone to anoxia at depth. Especially, an often invoked negative feedback removing nitrogen (high nitrate - high production – high sedimentation – high oxygen consumption – anoxia – high denitrification, hence lowered nitrate delivery to the surface) is not at work here. On the contrary, oxic conditions of the water favour nitrogen removal. The stagnation period in the seventies had lower denitrification than the more oxic period of the nineties. Other processes than denitrification and burial in sediments contribute to bound-nitrogen removal in the Baltic Sea, since nitrate deficits are smaller than observed N2 supersaturation.