Estuaries denitrification

Eyre, B. D., Rysgaard, S., Dalsgaard, T., and Christensen, P. B. (2004). Reply to comment on Comparison oF isotope pairing and N2 Ar methods For measuring sediment denitrification Estuaries 27, 177—178. 

Estuaries have been shown to be active sites of N2O production. DIN loading to sediments was positively correlated with N2O fluxes, indicating that eutrophication may be linked with increases in global emissions of N2O. In fact, a model of DIN transport by world rivers and estuaries indicates that 90% of the denitrification in rivers and estuaries occurs in the northern hemisphere. 

However, these studies do warn of using stable nitrogen isotopes as indicators of external inputs because of 15N-enrichment nitrification and denitrification processes that occur within the estuary (Cifuentes et al., 1988 Horrigan et al., 1990 Brandes and... 

Figure 10.5 Major processes involved in the biogeochemical cycling of N in estuaries and the coastal ocean (1) biological N2 fixation (2) ammonia assimilation (3) nitrification (4) assimilatory NC>3 reduction (5) ammonification or N remineralization (6) ammonium oxidation (speculative at this time) (7) denitrification and dissimilatory NO3 reduction to NH4+ and (8) assimilation of dissolved organic nitrogen (DON). (Modified from Libes, 1992.)...

Figure 10.6 Global budget of N in the coastal zone (fluxes are in 1012 g N yr 1). = More recent estimates of denitrification in estuaries and continental shelf sediments range from 200 to 300 Tg N y-1 (Seitzinger and Giblin, 1996 Codispoti et al., 2001). (From Wollast, 1993, with permission.)...

Seventeen genera of facultative anaerobic bacteria (e.g., Pseudomonas and Bacillus) can perform denitrification under anaerobic or low-oxygen conditions, where they use NO3- as an electron acceptor during anaerobic respiration (Jaffe, 2000). In fact, in many estuaries, denitrification is limited by the availability of NC>3 (Koike and Sprensen, 1988 Cornwell et al., 1999). Sources of NC>3 and NC>2 for denitrification are from diffusive inputs from the overlying water column and nitrification in the sediments (Jenkins and Kemp, 1984). The activity of other bacterial processes under anoxic conditions has been shown to affect the activity of denitrifying bacteria. For example, SO42- reduction occurs in anoxic sediments whereby SC>42 is reduced to sulfide (Morse et al., 1992)—more... 

Estuary export Atmosphere N fixation wastewater sources inputs column Denitrification Sedimentation landings Other losses Net... 

Micro- and macrophytobenthos act to regulate fluxes of nutrients across the sediment-water interface and also serve to retain N in estuaries, unlike denitrification, which regulates flux and does not retain N. 

An, S., and Gardner, W.S. (2002) Dissimilatory nitrate reduction to ammonium (DNRA) as a nitrogen link, versus denitrification as a sink in a shallow estuary (Laguna Madre/Baffin Bay, Texas). Mar. Ecol. Prog. Ser. 237, 41-50. 

Dettmann, E.H. (2001) Effect of water residence time on annual export and denitrification of nitrogen in estuaries a model analysis. Estuaries 24, 481-490. 

Nowicki, B.L., Kelly, J.R., Requintina, E., and van Keuren, D. (1997) Nitrogen losses through sediment denitrification in Boston Harbor and Massachusetts Bay. Estuaries 20, 626-639. 

Rysgaard, S., Thastum, P., Dalsgaard, T., Christensen, P.B., and Sloth, N.P. (1999) Effects of salinity on NH4+ adsorption capacity, nitrification, and denitrification in Danish estuarine sediments. Estuaries 22, 21-30. 

Seitzinger, S.P. (1987) Nitrogen biogeochemistry in an unpolluted estuary The importance of benthic denitrification. Mar. Ecol. Prog. Ser. 41, 177-186. 

Yoon, W. B., and Benner, R. (1992) Denitrification and oxygen consumption in sediments of two south Texas estuaries. Mar. Ecol. Prog. Ser. 90, 157-167. 

It is obvious that sedimentary denitrification and water-column nitrification seem to be the major N2O formation processes. However, the yield of N2O from both processes strongly depends on the local O2 concentrations, thus dissolved O2 is the key factor regulating N2O production (and its subsequent emissions to the atmosphere). Additionally, N2O distributions in estuaries show a pronounced seasonal variability. 

Magalhaes, C. M., Joye, S. B., Moreira, R. M., Weibe, W. J., and Bordalo, A. A. (2005). Effect of salinity and inorganic nitrogen concentrations on nitrification and denitrification rates in intertidal sediments and rocky biofifins of the Douro River estuary, Portugal. Water Research 9, 1783—1794. 

Trimmer, M., NichoUs, J. C., and Deflandre, B. (2003). Anaerobic ammonium oxidation measured in sediments along the Thames Estuary, United Kingdom. Appl. Environ. Microbiol. 69, 6447—6454. Tyrrell, T., and Lucas, M. I. (2002). Geochemical evidence of denitrification in the Benguela upweUing system. Continent. Shelf Res. 22(17), 2497—2511. 

Wang, F. H., Juniper, S. K., Pelegri, S. P., andMacko, S. A. (2003). Denitrification in sediments of the Laurentian Trough, St. Lawrence Estuary, Quebec, Canada. Estuarine Coastal and Shelf Science. 57(3), 515-522. 

Nowicki, B. L., Requintina, E., Van Keuren, D., and Portnoy, J. (1999). The role of sediment denitrification in reducing groundwater-derived nitrate inputs to Nauset Marsh estuary. Cape... 

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