Comparison of Denitrification Activity Measurements in Groundwater Using Cores and Natural-Gradient Tracer Tests
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- 作者：Richard L. Smith ; Stephen P. Garabedian ; and Myron H. Brooks
- 刊名：Environmental Science & Technology
- 出版年：1996
- 出版时间：December 1996
- 年：1996
- 卷：30
- 期：12
- 页码：3448 - 3456
- 全文大小：597K
- 年卷期：v.30,no.12(December 1996)
- ISSN：1520-5851
文摘
The transport of many solutes in groundwater isdependent upon the relative rates of physical flow andmicrobial metabolism. Quantifying rates of microbialprocesses under subsurface conditions is difficultand is most commonly approximated using laboratorystudies with aquifer materials. In this study, wemeasured in situ rates of denitrification in a nitrate-contaminated aquifer using small-scale, natural-gradient tracer tests and compared the results withrates obtained from laboratory incubations withaquifer core material. Activity was measured usingthe acetylene block technique. For the tracer tests,co-injection of acetylene and bromide into the aquiferproduced a 30 µM increase in nitrous oxide after10 m of transport (23-30 days). An advection-dispersion transport model was modified to includean acetylene-dependent nitrous oxide production termand used to simulate the tracer breakthrough curves.The model required a 4-day lag period and arelatively low sensitivity to acetylene to match thenarrow nitrous oxide breakthrough curves. Estimatesof in situ denitrification rates were 0.60 and 1.51 nmolof N2O produced cm-3 aquiferday-1 for twosuccessive tests. Aquifer core material collectedfrom the tracer test site and incubated as mixed slurriesin flasks and as intact cores yielded rates that were1.2-26 times higher than the tracer test rateestimates. Results with the coring-dependenttechniques were variable and subject to the small-scale heterogeneity within the aquifer, while thetracer tests integrated the heterogeneity along a flowpath, giving a rate estimate that is more applicableto transport at the scale of the aquifer.