Denitrification and N2O effluxes in the Bothnian Bay (northern Baltic Sea) river sediments as affected by temperature under different oxygen concentrations

Abstract

Denitrification rates and nitrous oxide (N 2 O) effluxes were measured at different temperatures and for different oxygen concentrations in the sediments of a eutrophied river entering the Bothnian Bay. The experiments were made in a laboratory microcosm with intact sediment samples. 15 N-labelling was used to measure denitrification rates (Dw). The rates were measured at four temperatures (5, 10, 15 and 20°C) and with three oxygen inputs (\0.2, 5, and 10 mg O 2 l -1 ). The temperature response was highly affected by oxygen concentration. At higher O 2 concentrations (5 and 10 mg O 2 l -1 ) a saturation over 10°C was observed, whereas the anoxic treatment (\0.2 mg O 2 l -1 ) showed an exponential increase in the temperature interval with a Q 10 value of 3.1. The result is described with a combined statistical model. In contrast with overall denitrification, the N 2 O effluxes from sediments decreased with increasing temperature. The N 2 O effluxes had a lower response to oxygen than denitrification rates. The N 2 O/N 2 ratio was always below 0.02. Increased temperatures in the future could enhance denitrification rates in boreal river sediments but would not increase the amount of N 2 O produced.

Denitrification: an ecosystem service provided by salt marshes

“…On the whole, denitrification is influenced by multiple interacting variables (Seitzinger 1988, Thompson 1995, Cornwell et al 1999, Piña-Ochoa & Ál -varez-Cobelas 2006, Silvennoinen et al 2008), which may result in an inherent variability under identical experimental conditions. The present study showed that there is a significantly higher contribution of Spartina maritima marshes to N removal during winter.…”

“…Nitra te concentration, availability of easily degradable organic carbon, oxygen availability, temperature, light, and wa ter retention time are some of the physical-chemical factors influencing denitrification rates in these eco systems (Thompson 1995, Cornwell et al 1999, Piña-Ochoa & Álvarez-Cobelas 2006, Silvennoinen et al 2008. Indirectly, sulfide concentration may also affect denitrification: for sulfide concentrations within a certain range, nitrification is suppressed, which consequently affects denitrification (Seitzinger 1988).…”

Nitrogen enrichment and the emission of nitrous oxide from streams

“…No effect [Strauss et al, 2002;Strauss et al, 2004] Increased temperature Denitrification Increase to maximum [Silvennoinen et al, 2008a] Decrease [Silvennoinen et al, 2008a] Unknown Increase [Garcia-Ruiz et al, 1998b;Martin et al, 2001] No effect [Martin et al, 2001] Nitrification Increase [Starry et al, 2005] Decrease [Maag and Vinther, 1996] c Unknown No effect [Kemp and Dodds, 2002] Increased oxygen Denitrification Decrease [Kemp and Dodds, 2002;Silvennoinen et al, 2008a] Depends on temperature, range of O 2 [Silvennoinen et al, 2008a] Unknown Increase [Cavigelli and Robertson, 2000] c , [Betlach and Tiedje, 1981] c , [Weier et al, 1993] c Nitrification Increase [Kemp and Dodds, 2002] Decrease [Goreau et al, 1980] c ; [Khalil et al, 2004] c Unknown Increased pH Denitrification Increase [Müller et al, 1980] c Decrease [Cavigelli and Robertson, 2000]…”

N2O Production and Removal in Streambed Sediments: Understanding Physicochemical Influences on N2O Fluxes From Agricultural Streams on the Eastern Shore of Virginia

“…These values allow us to quantify how efficiently the sediment beneath the stream is able to bring denitrification to full completion which provides a much more holistic picture of (Blackmer & Bremner, 1978). This effect has been seen not only in closed-system laboratory investigations, but has been confirmed in soils and hyporheic sediments where they have shown a positive correlation between NO 3 -and N 2 O concentrations and N 2 O yields (Blackmer & Bremner, 1978;Weier et al, 1993;Hedin et al, 1998;Silvennoinen et al, 2008a;Beaulieu et al, 2011). Within the columns, there was not a difference in the amount of NO 3 -removed resulting from each initial NO 3 -concentration; however, there was significantly more N 2 O produced, which suggests that the inhibitory effect of NO 3 -on the reduction of N 2 O to N 2 was at play.…”

“…The LINX II study points to the existence of a significant undefined source of N 2 O in streams that results in waters supersaturated with respect to N 2 O. A sediment-column study investigating hyporheic exchange effects on benthic N 2 O fluxes found similar values of 7.5 to 124 µg N 2 O-N m -2 h -1 (Silvennoinen et al, 2008a).…”