Distribution, Development and Total Amounts of Nutrients in the Gulf of Finland

Hydrographical parameters and nutrient concentrations have been measured from the year 1964 onwards in the Gulf of Finland. The development during 1964–92, and the recent distribution are discussed. Over the whole period, both for the dissolved inorganic nitrogen and the total nitrogen, an average upward trend of approximately 0.3 μmol l−1was observed, corresponding to an increase of roughly 5500 tons of nitrogen annually in the water mass. However, both nitrate and total nitrogen concentrations trends have shown stabilized or even decreasing values for the last 4–5 years. According to the present budget evaluations, the nitrogen sinks and sources in the Gulf of Finland are roughly in balance, in agreement with the observations of the recent years. This is probably due to the weakening of the halocline, resulting in improved oxygen concentrations in the Gulf of Finland, which affect the removal processes of both nitrate and phosphate. For the Gulf of Finland, the Baltic Proper functions as a sink for nitrogen and as a source for phosphorus.