A closer look at nitrification in pelagic sediments.

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Abstract
Nutrient profiles in southwest Pacific interstitial solutions suggest that, in environments of oxic pelagic sedimentation, microbially mediated nitrification is recognizable as a 2-step process. During the 1st step partially oxidized nitrogenous intermediates accumulate in distinctive ammonia and nitrite maxima along with nitrate. During the 2nd step nitrification continues and all intermediate species are fully oxidized to nitrate. Both steps occur within a zone that corresponds in thickness to the biologically active surface layer. Similarly, experimental N regeneration from decomposition of plankton in seawater suggests that each step corresponds to a distinct reaction in the microbially mediated transformation of [organic] N .fwdarw. NH3 .fwdarw. NO2 .fwdarw. NO3. The resolution of distinct reaction zones in pore water nutrient profiles possibly depends on the nature and mode of supply of the organic matter undergoing nitrification, or reflects the spatial succession downcore of microbial populations capable of deamination, ammonium oxidation and nitrite oxidation, respectively. Finally, stoichiometric ratios of nutrients in the free water column reflect the same 2 steps of nitrification as delineated by the dissolved pore water species. Future pore water studies should include dissolved O2 measurements and accurate .SIGMA.CO2, PO4 and nitrogenous species profiles to verify and better quantify these separate steps in nitrification mechanism of oxic pelagic sediments.

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