| DOI: | 10.2172/1253607
|
| 报告号: | 45266
|
| 报告题名: | Laboratory Experiments to Evaluate Matrix Diffusion of Dissolved Organic Carbon Carbon-14 in Southern Nevada Fractured-rock Aquifers |
| 作者: | Hershey, Ronald L.; Fereday, Wyatt
|
| 出版年: | 2016
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| 发表日期: | 2016-05-01
|
| 总页数: | 40
|
| 国家: | 美国
|
| 语种: | 英语
|
| 中文主题词: | 碳
; 碳酸酯
; 无机碳
; 有机碳
; 扩散
; 含水层
|
| 主题词: | CARBON
; CARBONATE
; INORGANIC CARBON
; ORGANIC CARBON
; DIFFUSION
; AQUIFERS
|
| 英文摘要: | Dissolved inorganic carbon (DIC) carbon-14 (14C) is used to estimate groundwater ages by comparing the DIC 14C content in groundwater in the recharge area to the DIC 14C content in the downgradient sampling point. However, because of chemical reactions and physical processes between groundwater and aquifer rocks, the amount of DIC 14C in groundwater can change and result in 14C loss that is not because of radioactive decay. This loss of DIC 14C results in groundwater ages that are older than the actual groundwater ages. Alternatively, dissolved organic carbon (DOC) 14C in groundwater does not react chemically with aquifer rocks, so DOC 14C ages are generally younger than DIC 14C ages. In addition to chemical reactions, 14C ages may also be altered by the physical process of matrix diffusion. The net effect of a continuous loss of 14C to the aquifer matrix by matrix diffusion and then radioactive decay is that groundwater appears to be older than it actually is. Laboratory experiments were conducted to measure matrix diffusion coefficients for DOC 14C in volcanic and carbonate aquifer rocks from southern Nevada. Experiments were conducted using bromide (Br-) as a conservative tracer and 14C-labeled trimesic acid (TMA) as a surrogate for groundwater DOC. Outcrop samples from six volcanic aquifers and five carbonate aquifers in southern Nevada were used. The average DOC 14C matrix diffusion coefficient for volcanic rocks was 2.9 x 10-7 cm2/s, whereas the average for carbonate rocks was approximately the same at 1.7 x 10-7 cm2/s. The average Br- matrix diffusion coefficient for volcanic rocks was 10.4 x 10-7 cm2/s, whereas the average for carbonate rocks was less at 6.5 x 10-7 cm2/s. Carbonate rocks exhibited greater variability in DOC 14C and Br- matrix diffusion coefficients than volcanic rocks. These results confirmed, at the laboratory scale, that the diffusion of DOC 14C into southern Nevada volcanic and carbonate aquifers is slower than DIC 14C. Because of the apparent sorption of 14C-labeled TMA in the experiments, matrix diffusion coefficients are likely even lower. The reasons for the higher than expected Br-/14C-labeled TMA are unknown. Because the molecular size of TMA is on the low end of the range in molecular size for typical humic substances, the matrix diffusion coefficients for the 14C-labeled TMA likely represent close to the maximum diffusion rates for DOC 14C in the volcanic and carbonate aquifers in southern Nevada. |
| URL: | http://www.osti.gov/scitech/servlets/purl/1253607
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| Citation statistics: |
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| 资源类型: | 研究报告
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/42131
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| Appears in Collections: | 过去全球变化的重建
影响、适应和脆弱性
科学计划与规划
气候变化与战略
全球变化的国际研究计划
气候减缓与适应
气候变化事实与影响
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| 1253607.pdf（3343KB） | 研究报告 | -- | 开放获取 | | View
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| Recommended Citation: | |
Hershey, Ronald L.,Fereday, Wyatt. Laboratory Experiments to Evaluate Matrix Diffusion of Dissolved Organic Carbon Carbon-14 in Southern Nevada Fractured-rock Aquifers. 2016-01-01.
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