Denitrification in the Baltic proper deep water

Abstract

The mean total denitrification rate and its vertical distribution in the Baltic proper deep water are calculated by the natural coordinate conservation method. After a sensitivity analysis for a range of ‘reasonable’ choices of input functions to the method (mean inflow, mean vertical concentration distributions, relative composition of organic matter, all expressed as functions of salinity), the mean denitrification rate was 4.7 ± 1.0 × 10 11 g N y −1. Also the results suggest that 80 to 90% of the total takes place in the sediment, where mean rates of up to 2.5 × 10 −2 g N(m 2d) −1 are indicated. Mean rates for the remaining 10 to 20%, which takes place in the oxygen-deficient zone of the water column with O 2 values around 10 μmol 1 −1 were estimated to be about 5 × 10 −7 g N(l d) −1. Due to denitrification, only about 15 to 20% of the inorganic nitrogen released in or transported into the Baltic proper deep water reaches the surface layer. This explains the observed low N:P ratios of about 6 to 7:1 in the late winter surface layer.