Denitrification in sediments as a major nitrogen sink in the Baltic Sea: an extrapolation using sediment characteristics

[摘要] Rates of denitrification in sediments were measured with the isotope pairingtechnique at different sites in the southern and central Baltic Sea. Therates varied between 0.5 μmol N m⁻² h⁻¹ in sands and28.7 μmol N m⁻² h⁻¹ in muddy sediments and showed a good correlation to theorganic carbon contents of the surface sediments. N-removal rates viasedimentary denitrification were estimated for the entire Baltic Seacalculating sediment specific denitrification rates and interpolating themto the whole Baltic Sea area. Another approach was carried out by using therelationship between the organic carbon content and the rate ofdenitrification. The N-removal by denitrification in sediments variedbetween 426–652 kt N a⁻¹, which is around 48–73% of the externalN inputs delivered via rivers, coastal point sources, and atmosphericdeposition. Moreover, an expansion of the anoxic bottom areas was consideredunder the assumption of a rising oxycline from 100 to 80 m water depth. Thisleads to an increase of the area with anoxic conditions and an overalldecrease in sedimentary denitrification by 14%. Overall, we show herethat this type of data extrapolation is a powerful tool to estimate thenitrogen losses for a whole coastal sea and may be applicable to othercoastal regions and enclosed seas.

[学科分类] 地球化学与岩石