Identification and Quantification of Base Flow Using Carbon Isotopes

Identification and Quantification of Base Flow Using Carbon Isotopes

Six surface water samples from locations along Otter Creek in Southeastern Montana and a groundwater sample from a nearby monitoring well completed in the Knobloch coal were analyzed for stable carbon isotope ratios. Along the length of its perennial reach, between the towns of Otter and Ashland, Ot...

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Bibliographic Details
Published in:Ground water Vol. 50; no. 6; pp. 959 - 965
Main Authors: Meredith, Elizabeth L., Kuzara, Shawn L.
Format: Journal Article
Language:English
Published: Oxford, UK Blackwell Publishing Ltd 01-11-2012
Ground Water Publishing Company
Subjects:
Aquifers
Base flow
Carbon
Carbon - analysis
Carbon isotopes
Carbon Isotopes - analysis
Coal
Creeks & streams
Environmental Monitoring - methods
Groundwater
Groundwater - analysis
Groundwater flow
Hydrology - methods
Isotopes
Mathematical analysis
Models, Theoretical
Montana
Rivers - chemistry
Seasons
Surface water
Water Movements
Water Pollutants, Chemical - analysis
Montana
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Summary:Six surface water samples from locations along Otter Creek in Southeastern Montana and a groundwater sample from a nearby monitoring well completed in the Knobloch coal were analyzed for stable carbon isotope ratios. Along the length of its perennial reach, between the towns of Otter and Ashland, Otter Creek crosses several coal outcrops, including the Knobloch coal zone. The carbon isotope ratio of the creek becomes progressively more similar to that of the Knobloch coal aquifer groundwater in samples collected downgradient from the town of Otter. The isotope ratio of the stream changes from −10.5 to −8.9‰ reflecting the influence of the coal‐aquifer base flow contribution, as represented by Knobloch coal groundwater, which has a carbon isotope value of +3.9‰. The dissolved inorganic carbon concentrations of the groundwater and surface water are similar (∼100 mg/L), which allowed the use of the simplified, first‐order, two‐end‐member mixing equation. Using carbon isotope ratios, calculations of the fraction of water contributed by coal aquifers indicate that approximately 11% of the surface water in Otter Creek at its mouth near Ashland was supplied by groundwater from the coal aquifers that crop out between Otter and Ashland. This study was conducted in December, when Otter Creek is at low flow. At times of higher surface flow, the contribution from groundwater base flow will be correspondingly smaller. This study illustrates that carbon isotopes can be an effective, low‐cost tool in base flow studies.
Bibliography:istex:812546870A8D500BDD4D0B6225664766A2F8802A
ArticleID:GWAT952
ark:/67375/WNG-3KBFBPMD-0
ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
content type line 23
ISSN:0017-467X
1745-6584
DOI:10.1111/j.1745-6584.2012.00952.x