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Isotope Fractionation of 15 N and 14 N in Microbiological Nitrogen Transformations: a Theoretical Model
Author(s) -
Focht D. D.
Publication year - 1973
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1973.00472425000200020017x
Subject(s) - nitrate , nitrification , fractionation , chemistry , ammonium , isotope fractionation , denitrification , nitrogen , isotopes of nitrogen , isotope , stable isotope ratio , environmental chemistry , chromatography , organic chemistry , physics , quantum mechanics
The kinetics for first‐order multisequence reactions are derived for microbial fractionation of 14 N and 15 N isotopes. The isotope effect accounts for unreacted substrate becoming progressively enriched in the heavier isotope due to preferential utilization of the lighter isotope by microorganisms. Consequently, during denitrification nitrate becomes enriched in 15 N as its concentration diminishes. This inverse proportional relationship is expressed as a hyperbolic function, y = ax −b . Similar curves are derived for nitrate originating from ammonification and/or nitrification. Regression coefficients for a straight line approximation are better than −0.98, but not as good as the actual coefficients for the derived hyperbolic equations. A negative regression “line” for nitrate occurs for all denitrification reactions during isotope discrimination. Nitrate originating from caesin, ammonium, and nitrate are respectively less enriched in 15 N for equal nitrate concentration due to ammonium and nitrate being initially enriched in 14 N during ammonification and nitrification, respectively.