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| Titel |
Estimation of the denitrification in Baltic Sea deep water from gas tension measurements |
| VerfasserIn |
Annekatrin Loeffler, Martin Schmidt, Bernd Schneider |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033764
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| Zusammenfassung |
| Denitrification is considered to be the most important process removing nitrogen in oceanic
waters. 50-70% of marine denitrification occurs in organic rich sediments and oxygen
depleted water bodies of continental shelf regions or marginal seas like the Baltic Sea, where
a high percentage of riverine discharge of nitrogen is denitrified before entering the open
ocean.
Measurements of the gas tension (= sum of the partial pressures of all dissolved gases in
the water) provide a new experimental way for the quantification of denitrification by directly
measuring the reaction product of this process. Continuous pumping of water from a defined
depth trough the gas tension device with a pump-CTD allows getting integrated
results.
Changes in N2 concentrations were calculated from gas tension by subtracting the partial
pressures of the most important other dissolved gases (O2, Ar, CO2, H2S, water vapor). The
pO2, pCO2 and H2S-concentrations were measured; other parameters (pAr, pH2O, solubility
coefficients) were obtained from temperature and salinity. The method allows the estimation
of N2-concentrations with a maximum error of 0.5%, corresponding to a standard error of 1.5
μmol L-1.
Results of gas tension measurements and calculation of N2 concentrations in the Gotland
Basin deep water, central Baltic Sea, from 2008 and 2009 are presented. In the deep water
below the permanent halocline the estimated N2 partial pressure is continuously rising
towards the oxygen depleted water layers. The calculated N2 excess compared to
equilibrium concentration reached values up to 20 μmol N2 L-1 in the stagnant anoxic
water layer, indicating a mean N release of 10 μmol N L-1 y-1 after 4 years of
stagnation.
The increase of total dissolved inorganic nitrogen (due to the N2 excess and formation of
ammonium in the deep water) in relation to nitrogen background values was compared with
the increase of total inorganic carbon due to mineralization processes. The resulting C:N
ratios were close to the Redfield value. |
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