Denitrification in the central Baltic: evidence for H2 S-oxidation as motor of denitrification at the oxic-anoxic interface

Abstract

Denitrification was investigated in August 1986 and July 1987 in the water column of the Gotland Deep, an anoxic basin in the Baltic Proper. Denitrification was restricted to a layer of c10 m at the oxic-anoxic interface (130 m depth), where NO3- and H2S coexisted. Rates in 1986 and 1987 were 110 and 44 nmol N l-1 d-1 respectively. Samples from above the interface never showed denitrification, even after incubation periods of up to 12 d, obviously due to the combined effect of too high oxygen and too low carbon concentrations. Denitrification in the oxic-anoxic interface could be efficiently driven by oxidation of reduced sulfur compounds provided by the anoxic deep water. Conceivable ecological implications of these findings are uncoupling of denitrification from carbon flux derived from phytoplankton primary production and strong dependence on mixing processes at the oxic-anoxic interface. -from Authors