scholarly journals Groundwater residence time estimates obscured by anthropogenic carbonate

2021 ◽  
Vol 7 (17) ◽  
pp. eabf3503
Author(s):  
Alan M. Seltzer ◽  
David V. Bekaert ◽  
Peter H. Barry ◽  
Kathryn E. Durkin ◽  
Emily K. Mace ◽  
...  
Keyword(s):  
Residence Time ◽  
Open System ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Soil Amendments ◽  
Flow Models ◽  
Time Estimates ◽  
Drinking And Irrigation ◽  
Carbonate Soil ◽  
Agricultural Regions

Groundwater is an important source of drinking and irrigation water. Dating groundwater informs its vulnerability to contamination and aids in calibrating flow models. Here, we report measurements of multiple age tracers (14C, 3H, 39Ar, and 85Kr) and parameters relevant to dissolved inorganic carbon (DIC) from 17 wells in California’s San Joaquin Valley (SJV), an agricultural region that is heavily reliant on groundwater. We find evidence for a major mid-20th century shift in groundwater DIC input from mostly closed- to mostly open-system carbonate dissolution, which we suggest is driven by input of anthropogenic carbonate soil amendments. Crucially, enhanced open-system dissolution, in which DIC equilibrates with soil CO2, fundamentally affects the initial 14C activity of recently recharged groundwater. Conventional 14C dating of deeper SJV groundwater, assuming an open system, substantially overestimates residence time and thereby underestimates susceptibility to modern contamination. Because carbonate soil amendments are ubiquitous, other groundwater-reliant agricultural regions may be similarly affected.

scholarly journals Comparison of 14C Collected by Precipitation and Gas-Strip Methods for Dating Groundwater

Radiocarbon ◽  
2016 ◽  
Vol 58 (3) ◽  
pp. 491-503 ◽  
Author(s):  
Kotaro Nakata ◽  
Takuma Hasegawa ◽  
Teruki Iwatsuki ◽  
Toshihiro Kato
Keyword(s):  
Residence Time ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Precipitation Method ◽  
Strip Method ◽  
Naoh Solution ◽  
C Value ◽  
The Difference ◽  
Predicted Values

AbstractDissolved inorganic carbon (DIC) in groundwater is used to estimate the residence time based on radiocarbon concentration. DIC is usually extracted by a gas-strip or precipitation (SrCO3 or BaCO3) method. In this study, the gas-strip and precipitation methods of DIC were applied to both artificially prepared NaHCO3 solutions and natural groundwater to estimate the certainty of the two methods for 14C dating. 14C values obtained by the gas-strip method for NaHCO3 solutions with distinct salinity, DIC, and 14C concentrations were close to the theoretically predicted 14C value based on the 14C value of NaHCO3 powder. Conversely, the 14C value obtained by the precipitation method always showed higher values than the predicted values. The difference in 14C value between the gas-strip and precipitation methods was assumed to be caused by the contamination of modern carbon in the NaOH solution used in the precipitation method. The contamination of modern carbon derived from the NaOH solution during precipitation was found to range from less than 1 mg/L to about 1 mg/L. The applicability of the precipitation method for groundwater should be considered carefully according to the DIC, 14C concentration of groundwater, and purpose of the study being conducted.

A Survey of the 14C Content of Dissolved Inorganic Carbon in Chinese Lakes

Radiocarbon ◽  
2017 ◽  
Vol 60 (2) ◽  
pp. 705-716 ◽  
Author(s):  
Taibei Liu ◽  
Weijian Zhou ◽  
Peng Cheng ◽  
G S Burr
Keyword(s):  
Steady State ◽  
Simple Model ◽  
Residence Time ◽  
Surface Waters ◽  
Lake Water ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Water Cycle ◽  
Average Residence Time ◽  
Exchange Character

AbstractWe present radiocarbon (14C) measurements of dissolved inorganic carbon (DIC) from surface waters of 11 lakes, widely distributed in China. Surface lake water DIC F14C values show distinct differences, and we relate these to the physical exchange character (“open” or “closed”) of each lake. Open lakes studied here generally have lower DIC F14C values than closed lakes. We present a simple model of a lake water cycle to calculate an average residence time for each lake. Comparisons between lake DIC F14C and average residence time shows that the DIC F14C increases with the average residence time and reflects a steady-state.

Factors influencing the growth of Mougeotia in experimentally acidified mesocosms

2000 ◽  
Vol 57 (3) ◽  
pp. 538-547 ◽  
Author(s):  
Jennifer L Klug ◽  
Janet M Fischer
Keyword(s):  
Inorganic Carbon ◽  
Phytoplankton Community ◽  
Dissolved Inorganic Carbon ◽  
Abiotic Factors ◽  
Minor Role ◽  
Little Rock ◽  
Factors Associated ◽  
Phytoplankton Communities ◽  
Mesocosm Experiments ◽  
Potential Factors

Acidification causes profound changes in species composition in aquatic systems. We conducted mesocosm experiments in three northern Wisconsin lakes (Trout Lake, Little Rock - Reference, Little Rock - Treatment) to test how different phytoplankton communities respond to acidification. Major differences exist among these lakes in water chemistry and phytoplankton community composition. In each lake, three pH treatments (control, press (sustained pH 4.7), and pulse (alternating pH 4.7 and ambient pH)) were maintained for 6 weeks. We observed a striking increase in species in the genus Mougeotia in all systems. Mougeotia is a filamentous green alga often found in acidified lakes. The magnitude of the Mougeotia increase differed among lakes and treatments, and we used an autoregressive model to identify potential factors responsible for these differences. Our results suggest that biotic factors such as competition with other algae played a relatively minor role in regulating Mougeotia dynamics. Instead, pH and abiotic factors associated with changes in pH (e.g., dissolved inorganic carbon) were important predictors of Mougeotia dynamics.

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