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Shallow Groundwater Denitrification Rate Measurement by Acetylene Block
Author(s) -
Bragan R. J.,
Starr J. L.,
Parkin T. B.
Publication year - 1997
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/jeq1997.00472425002600060012x
Subject(s) - denitrification , groundwater , riparian zone , water table , hydrology (agriculture) , chemistry , nitrous oxide , environmental chemistry , environmental science , nitrogen , ecology , geology , geotechnical engineering , organic chemistry , habitat , biology
We field tested a short term, in situ method for measuring highly variable shallow groundwater denitrification rates using a methodology developed in an earlier, laboratory phase of this study. A pulse of tracer solution was injected and subsequently sampled within well clusters 50 cm in radius. The injectate contained dissolved acetylene (C 2 H 2 ) to block denitrification at the nitrous oxide (N 2 O) stage of reduction. Six well clusters were established at two depths along a riparian area transect through field, grass, and woodland ecotypes. Bromide tracer, C 2 H 2 , and accumulated N 2 O were monitored at sample wells downgradient from each injection well. Adequate C 2 H 2 concentrations (0.43 m M ) to block N 2 O reduction between injection and sample wells were attained in five of the six well clusters tested. Acetylene peak concentrations moved laterally an average of 19% more slowly than the Br peak, N 2 O peak concentrations an average of 8% after C 2 H 2 peaks. Highest denitrification rates of 2.8 and 3.3 mg N L −1 d −1 were observed near the surface of the water table within the grass buffer and riparian forest. Shallow groundwater denitrification rates in the adjoining field and 2 m deep into the saturated zone at all three ecotypes were <25% of the highest rates. Acetylene block procedures were thus used to determine in situ denitrification rates within a few days time with little disruption of soil structure or associated microbial communities. Portable equipment allows application at remote sites independent of line power and road access.