Water Chemistry — Erhardt Isotope Geochemistry Laboratory

IDENTIFICATION OF THE CAUSES AND EXTENT OF ELEVATED METHANE CONCENTRATIONS IN THE GROUNDWATER OF EASTERN KENTUCKY

Anecdotal evidence indicated significant methane in private groundwater wells, posing a public safety risk. Previous researchers had found a north-south divide between high methane and high sulfate groundwater, and we postulated that isotopic characterization of these waters would clarify the methane sources. Working with the local Agricultural Extension offices, we identified 24 wells for sampling. Each homeowner was provided with a full characterization of their water chemistry at the end of the study.

To characterize each sample, a complete suite of geochemical measurements was measured, including δ13C and δD of methane, δ 34S of sulfate, δ13C values in DIC and DOC, δ18O and δD of water, and cation and anion chemistry. We found correlations between methane concentrations and isotopes, sulfate concentrations and isotopes, and distance from active mining and/or drilling activities. Most of the methane was isotopically biogenically sourced, with only limited occurrences of deeper, thermogenic methane. Additionally, relationships between δ 34S of sulfate and 1/sulfate concentration were consistent with sulfate reduction trends. Overall, we saw that locations in closer proximity to active mining, oil, and gas exploration had higher sulfate concentrations and reduced methane, consistent with the suppression of methanogenesis when the sulfur in local coal horizons is disturbed.

*Alvarez Villa, C., Fichtner, V., Fryar, A., Parris, T.M., Zhu, J., Webb, S.E., Munizzi, J.S., and Erhardt, A.M. Identification of the causes and extent of elevated methane concentrations in the groundwater of Eastern Kentucky. Planned submittal to Science of the Total Environment.

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WATER ISOTOPES IN UKRAINE

PhD Student Elizabeth Avery has measured precipitation, tap water, and surface water isotopes in Kyiv, Ukraine and surrounding areas as part of a Fullbright Fellowship.

Precipitation patterns in Ukraine as derived for water isotope analysis

North-central Ukraine is vulnerable to temperature increases and precipitation pattern changes associated with climate change. With water management becoming increasingly important, information on current water sources and moisture recycling is critically needed. Isotope ratios of oxygen (𝛿18O) and hydrogen (𝛿2H) in precipitation are sensitive to these variables and allow comparisons across the region. The 𝛿2H and 𝛿18O values from collected precipitation in Kyiv and Cherkasy in 2020 and published 3H data for Kyiv from the year 2000 show an influence of the North Atlantic Oscillation (NAO) and provide information about processes affecting precipitation along the storm trajectory. The 𝛿18O values also show a correlation with temperature, indicating that precipitation patterns may be affected by the rising temperatures in the region, as predicted by recent regional studies using Representative Concentration Pathway scenarios and the global climate model GFDL-ESM2M. When compared to backtracked storm trajectory and NAO data, clear relationships emerged between water isotope ratios, storm paths, and likely moisture recycling. Overall, 𝛿2H, 𝛿18O, 3H, and backtracked storm trajectory data provide more regional and local information on water vapor processes, improving climate-change-driven precipitation forecasts in Ukraine.

Variation of tap-water isotope ratios and municipal water sources across Kyiv city, Ukraine

Stable isotopes of water allow researchers to examine water pathways and better understand spatial and temporal variability in mixtures of municipal water sources. In regions such as Kyiv (Ukraine), with a water supply that is vulnerable to the effects of climate change, pollution, and geopolitical conflict, such understanding is critical for effective water management. Trends in stable isotope values and water sources can function as a confirmation of municipal data. Additionally, these data can provide an early signal for the effects of climate change on these sources, reducing uncertainty from physical measurements.

For this study, tap water, surface water, and groundwater were collected over 14 months in Kyiv and nearby Boryspil, Brovary, and Boyarka and measured for hydrogen (d2H) and oxygen (d18O) stable isotopes. The stable isotope values from the tap water for each district show a general seasonal trend in water sources, with more groundwater used in the supply in the winter for most districts. Spatially, groundwater use increases from south to north in the left-bank districts in Kyiv city and groundwater use generally decreases from south to north in the right-bank districts. As precipitation patterns shift and temperatures increase, the reliance on particular water sources may need to shift as well. Overall, d2H and d18O data provide a baseline expectancy for current water use throughout the year and, from this, deviations can be assessed early.