Nitrogen in rock: Occurrences and biogeochemical implications

Abstract

[1] There is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations. Nitrogen-bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification. Nitrogen in rock originates as organically bound nitrogen associated with sediment, or in thermal waters representing a mixture of sedimentary, mantle, and meteoric sources of nitrogen. Rock nitrogen concentrations range from trace levels (<200 mg N kg À1 ) in granites to ecologically significant concentrations exceeding 1000 mg N kg À1 in some sedimentary and metasedimentary rocks. Nitrate deposits accumulated in arid and semi-arid regions are also a large potential pool. Nitrogen in rock has a potentially significant impact on localized nitrogen cycles. Elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen. In some environments, nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems (more nitrogen available than required by biota). Nitrogen saturation results in leaching of nitrate to surface and groundwaters, and, where soils are formed from ammonium-rich bedrock, the oxidation of ammonium to nitrate may result in soil acidification, inhibiting revegetation in certain ecosystems. Collectively, studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems.

Origin of first cells at terrestrial, anoxic geothermal fields

“…In addition, elimination of a water molecule from ammonia salts of carboxylic acids could also yield amides, in particular, formamide from ammonia formate. As noted earlier, exhalations of geothermal fields contain high amounts of ammonia (55); part of this ammonia is of nonsedimentary origin (110) and could have been present already in the primordial geothermal vapor. Formate and other carboxylic acids would also have been produced at anoxic geothermal fields (as detailed earlier).…”

Occurrence of nitrate in Tanzanian groundwater aquifers: A review

“…Natural sources of nitrate in the groundwater include leaching and oxidation of nitrogenous compounds incorporated in rocks (Holloway and Dahlgren 2002) and fixation by leguminous plants and microorganisms (Edmunds and Smedley 1996). According to Holloway and Dahlgren (2002), rock nitrogenous compound concentrations range from trace levels to above 200 mg-N/kg in granites and may exceed 1,000 mg-N/kg in some sedimentary and meta-sedimentary rocks. In many aquifers, background concentration of nitrate is less than 1 mg/l (West 2001;Wendland et al 2005).…”

Organic nitrogen chemistry during low-grade metamorphism

“…Analytical data from different studies are not always directly comparable due to differences among various wet-chemical digestion and combustion techniques (see Holloway and Dahlgren, 2002). Total N determination was therefore performed via complete Dumas combustion at high temperature in addition to ASTM D3179 (i.e., Kjeldahl-Gunning analysis) because wet-chemical methods are unable to fully digest N org in metamorphic organic matter.…”