Regional oxygen reduction and denitrification rates in groundwater from multi-model residence time distributions, San Joaquin Valley, USA

JOURNAL OF HYDROLOGY

卷:543

Article

Green, Christopher T.¹  Jurgens, Bryant C.²  Zhang, Yong³  Starn, J. Jeffrey⁴  Singleton, Michael J.⁵  Esser, Bradley K.⁵ 

[1] US Geol Survey, 345 Middlefield Rd, Menlo Pk, CA 94025 USA

[2] US Geol Survey, Sacramento, CA USA

[3] Univ Alabama, Tuscaloosa, AL USA

[4] US Geol Survey, E Hartford, CT USA

[5] Lawrence Livermore Natl Lab, Nucl & Chem Sci Div, Livermore, CA USA

关键词: Oxygen reduction;    Denitrification;    Groundwater Residence time;    Multi-model analysis;    Regional water quality;   

DOI  :  10.1016/j.jhydrol.2016.05.018

来源: Elsevier

【 摘 要 】

Rates of oxygen and nitrate reduction are key factors in determining the chemical evolution of ground-water. Little is known about how these rates vary and covary in regional groundwater settings, as few studies have focused on regional datasets with multiple tracers and methods of analysis that account for effects of mixed residence times on apparent reaction rates. This study provides insight into the characteristics of residence times and rates of O-2 reduction and denitrification (NO3- reduction) by comparing reaction rates using multi-model analytical residence time distributions (RTDs) applied to a data set of atmospheric tracers of groundwater age and geochemical data from 141 well samples in the Central Eastern San Joaquin Valley, CA. The RTD approach accounts for mixtures of residence times in a single sample to provide estimates of in-situ rates. Tracers included SF6, CFCs, H-3, He from H-3 (tritiogenic He), C-14, and terrigenic He. Parameter estimation and multi-model averaging were used to establish RTDs with lower error variances than those produced by individual RTD models. The set of multi model RTDs was used in combination with NO3- and dissolved gas data to estimate zero order and first order rates of O-2 reduction and denitrification. Results indicated that O-2 reduction and denitrification rates followed approximately log-normal distributions. Rates of O-2 and NO3- reduction were correlated and, on an electron milliequivalent basis, denitrification rates tended to exceed O-2 reduction rates. Estimated historical NO3- trends were similar to historical measurements. Results show that the multi model approach can improve estimation of age distributions, and that relatively easily measured O-2 rates can provide information about trends in denitrification rates, which are more difficult to estimate. Published by Elsevier B.V.

【 授权许可】

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