Quantification of Ammonia-Oxidizing Bacteria and Factors Controlling Nitrification in Salt Marsh Sediments

Abstract

To elucidate the geomicrobiological factors controlling nitrification in salt marsh sediments, a comprehensive approach involving sediment geochemistry, process rate measurements, and quantification of the genetic potential for nitrification was applied to three contrasting salt marsh habitats: areas colonized by the tall (TS) or short (SS) form of Spartina alterniflora and unvegetated creek banks (CBs). Nitrification and denitrification potential rates were strongly correlated with one another and with macrofaunal burrow abundance, indicating that coupled nitrification-denitrification was enhanced by macrofaunal burrowing activity. Ammonia monooxygenase (amoA) gene copy numbers were used to estimate the ammonia-oxidizing bacterial population size (5.6 ؋ 10 4 to 1.3 ؋ 10 6 g of wet sediment ؊1 ), which correlated with nitrification potentials and was 1 order of magnitude higher for TS and CB than for SS. TS and CB sediments also had higher Fe(III) content, higher Fe(III)-to-total reduced sulfur ratios, higher Fe(III) reduction rates, and lower dissolved sulfides than SS sediments. Iron(III) content and reduction rates were positively correlated with nitrification and denitrification potential and amoA gene copy number. Laboratory slurry incubations supported field data, confirming that increased amounts of Fe(III) relieved sulfide inhibition of nitrification. We propose that macrofaunal burrowing and high concentrations of Fe(III) stimulate nitrifying bacterial populations, and thus may increase nitrogen removal through coupled nitrification-denitrification in salt marsh sediments.

Evaluation of nitrogen sources in the Urias lagoon system, Gulf of California, based on stable isotopes in macroalgae

“…Although little research has been done on these processes in subtropical coastal environments, we maintain that coupling occurs in the Urías system when conditions are stable (e.g., dry-cold season), as has been observed in other coastal ecosystems (Dollhopf et al 2005). Coupling occurs mainly in areas where mangroves grow, where the oxygen released from the roots promotes nitrification close to the anoxic sediment zone, in turn stimulating denitrification (Ottosen et al 1999).…”

“…Aunque el estudio de estos procesos en ambientes costeros subtropicales es muy limitado, nosotros sostenemos la hipótesis del acoplamiento en el sistema de Urías en épocas con condiciones estables (e.g., en la época seca-fría), como ha sido observado en otros ecosistemas costeros (Dollhopf et al 2005). Dicho acoplamiento ocurre mayormente en las áreas con manglar, donde el oxígeno liberado desde las raíces fomenta la nitrificación cerca de la zona anóxica de los sedimentos, estimulando a su vez la desnitrificación (Ottosen et al 1999).…”

“…Tampoco la fijación biológica de N produce fraccionación isotópica (Swart et al 2008). Por otro lado, suponemos que el NO 3 -producido por nitrificación está acoplado al proceso de desnitrificación (Dollhopf et al 2005).…”

“…Neither does biological N fixation produce isotopic fractionation (Swart et al 2008). On the other hand, we assume that NO 3 -produced by denitrification is associated with the denitrification process (Dollhopf et al 2005).…”

Seasonal oxygen, nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns

“…As a consequence, at this site denitrification rates were highest in the winter when the temperatures were the lowest, and mostly supported by nitrification-denitrification. Nitrifying microorganisms have been shown to grow slower than denitrifiers both in sediments and in bioreactors (Dollhopf et al 2005;Duan et al 2009). Our findings suggest that the nitrifying microorganisms in this sediment either grew as rapidly as the denitrifying bacteria despite the low temperatures or that a large dormant nitrifying population was reactivated as oxygen concentrations increased.…”