Rates and regulation of nitrogen cycling in seasonally hypoxic sediments during winter (Boknis Eck, SW Baltic Sea): Sensitivity to environmental variables
Dale, AW; Sommer, S; Bohlen, L; Treude, T; Bertics, VJ; Bange, HW; Pfannkuche, O; Schorp, T; Mattsdotter, M; Wallmann, K
HERO ID
1679908
Reference Type
Journal Article
Year
2011
Language
English
| HERO ID | 1679908 |
|---|---|
| In Press | No |
| Year | 2011 |
| Title | Rates and regulation of nitrogen cycling in seasonally hypoxic sediments during winter (Boknis Eck, SW Baltic Sea): Sensitivity to environmental variables |
| Authors | Dale, AW; Sommer, S; Bohlen, L; Treude, T; Bertics, VJ; Bange, HW; Pfannkuche, O; Schorp, T; Mattsdotter, M; Wallmann, K |
| Journal | Estuarine, Coastal and Shelf Science |
| Volume | 95 |
| Issue | 1 |
| Page Numbers | 14-28 |
| Abstract | This study investigates the biogeochemical processes that control the benthic fluxes of dissolved nitrogen (N) species in Boknis Eck - a 28 m deep site in the Eckernforde Bay (southwestern Baltic Sea). Bottom water oxygen concentrations (O(2-BW)) fluctuate greatly over the year at Boknis Eck, being well-oxygenated in winter and experiencing severe bottom water hypoxia and even anoxia in late summer. The present communication addresses the winter situation (February 2010). Fluxes of ammonium (NH(4)(+)), nitrate (NO(3)(-)) and nitrite (NO(2)(-)) were simulated using a benthic model that accounted for transport and biogeochemical reactions and constrained with ex situ flux measurements and sediment geochemical analysis. The sediments were a net sink for NO(3)(-) (-0.35 mmol m(-2) d(-1) of NO(3)(-)), of which 75% was ascribed to dissimilatory reduction of nitrate to ammonium (DNRA) by sulfide oxidizing bacteria, and 25% to NO(3)(-) reduction to NO(2)(-) by denitrifying microorganisms. NH(4)(+) fluxes were high (1.74 mmol m(-2) d(-1) of NH(4)(+)), mainly due to the degradation of organic nitrogen, and directed out of the sediment. NO fluxes were negligible. The sediments in Boknis Eck are, therefore, a net source of dissolved inorganic nitrogen (DIN = NO(3)(-) + NO(2)(-) + NH(4)(+)) during winter. This is in large part due to bioirrigation, which accounts for 76% of the benthic efflux of NH(4)(+), thus reducing the capacity for nitrification of NH(4)(+). The combined rate of fixed N loss by denitrification and anammox was estimated at 0.08 mmol m(-2) d(-1) of N(2), which is at the lower end of previously reported values. A systematic sensitivity analysis revealed that denitrification and anammox respond strongly and positively to the concentration of NO(3)(-) in the bottom water (NO(3BW)(-)). Higher O(2-BW) decreases DNRA and denitrification but stimulates both anammox and the contribution of anammox to total N(2) production (%R(amx)). A complete mechanistic explanation of these findings is provided. Our analysis indicates that nitrification is the geochemical driving force behind the observed correlation between %R(amx) and water depth in the seminal study of Dalsgaard et al. (2005). Despite remaining uncertainties, the results provide a general mechanistic framework for interpreting the existing knowledge of N-turnover processes and fluxes in continental margin sediments, as well as predicting the types of environment where these reactions are expected to occur prominently. |
| Doi | 10.1016/j.ecss.2011.05.016 |
| Wosid | WOS:000298266000002 |
| Is Certified Translation | No |
| Dupe Override | No |
| Is Public | Yes |
| Language Text | English |
| Keyword | denitrification; modelling; anammox; Kiel Bight; nitrogen cycle; hypoxia |