The majority of land-derived N is removed from coastal environments through nitrate respiration processes, denitrification and anammox.  Despite the importance of nitrate respiration to the overall nitrogen cycle in coastal marine ecosystems and the significance of temperature as a physical control, surprisingly few studies have addressed the impacts of temperature on nitrate respiration.  We have been studying the mechanisms and controls of N removal in permanently cold sediments collected in the fjords of Svalbard, Norway, for the past five years.  As for other biogeochemical processes, rates of denitrification and anammox in cold (1-2 oC) Arctic sediments approach those measured in temperate marine sediments. Denitrifying bacteria were isolated and shown to follow a psychrotolerant to psychrophilic growth response.  Most recently, we have investigated the temperature regulation of microbial communities that mediate nitrogen removal in nearshore permeable sediments over a 50� latitudinal gradient at subtropical (Gulf of Mexico), temperate (Wadden Sea), and Arctic (Svalbard) sites.  Total N2 production rates from intact core incubations ranged widely according to environmental conditions.  While denitrification predominated at all sites, anammox comprised up to 12% of nitrogen removal at a temperate site.  Porewater advection was shown to have a substantial impact on N2 production at all sites, with rates up to 12 times higher under conditions simulating advective transport.  Denitrification potential rates had the highest optimum temperature (Topt) in subtropical sediments and decreased with latitude.  The apparent activation energy of denitrification was two-fold higher in subtropical versus temperate and arctic sediments, indicating a mesophile-dominated community.  A seasonal increase in the Topt was also observed for the temperate site in the summer.  The temperature response of anammox activity closely followed denitrification at Arctic and temperate sites, but anammox was not detected at subtropical sites.  Results reveal adaptation of N2-producing bacterial communities to in situ temperatures in permeable sediments.

Controls of the microbial nitrogen cycle in marine sediments and implications for global climate change

245th National Meeting (2013)

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