Denitrification Rates in the Low-Oxygen Waters of the Stratified Baltic Proper

Denitrification activity was shown in the deep, low-oxygen waters of the Baltic proper by both in vitro and in situ methods. The vertical distribution of NO₃⁻ in the water column showed nitrate consumption and NO₂⁻ and N₂O maxima in the deep waters when O₂ was below 0.2 ml liter⁻¹, which is suggestive evidence for denitrification. Direct in situ evidence for denitrification was obtained by finding an N₂ saturation of up to 108% in the deep waters. When these waters were incubated with ¹⁵NO₃⁻, ¹⁵N₂ was produced. Quantification of the denitrification rate done by the addition of C₂H₂ to water samples from the active depths showed a rate of about 0.10 μmol liter⁻¹ day⁻¹.