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 (δ2H) and oxygen (δ18O) 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, δ2H and δ18O data provide a baseline expectancy for current water use throughout the year and, from this, deviations can be assessed early.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43832-022-00021-x.

Use of isotopes in examining precipitation patterns in north-central Ukraine

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 vapour processes, improving climate-change-driven precipitation forecasts in Ukraine.

Preservation methods for the isotopic composition of dissolved carbon species in non-ideal conditions

RATIONALE

The stable carbon isotope compositions of dissolved inorganic carbon (δ¹³C_DIC) and dissolved organic carbon (δ¹³C_DOC) are readily affected by post-sampling microbial activity if not adequately preserved. Existing preservation methods require rapid chilling, analysis, and/or toxic chemicals, all challenging to use safely in the field and during remote field seasons. Therefore, a preservation method that is safe but also effective over a range of storage times is needed when sampling waters at very remote sites.

METHODS

Two samples, with different dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations, were filtered with a 0.2-μm filter and preserved with six different methods, mercuric chloride, copper sulfate, phosphoric acid, benzalkonium chloride, zinc chloride, hydrochloric acid, and a filter-only control. These samples were held at 4°C, 22°C, or 35°C. Regular measurement of the DIC and DOC δ¹³C values were made over the following 60 days for δ¹³C_DIC and 66 days for δ¹³C_DOC. RESULTS: Over the course of the experiment, mercuric chloride, copper sulfate, zinc chloride, and benzalkonium chloride resulted in δ¹³C_DIC fractionation at both 4°C and 22°C. Only filtering to 0.2 μm at the time of collection, with or without acidification with phosphoric acid, resulted in minimal isotopic fractionation at both 4°C and 22°C and over the entirety of the experiment. For δ¹³C_DOC values, only filtering to 0.2 μm minimized fractionation for both bulk and vial storage over 66 days at 22°C.

CONCLUSIONS

Filtering to 0.2 μm at the time of collection is more effective than the use of toxic chemicals for measuring δ¹³C_DIC and δ¹³C_DOC values. Phosphoric acid is as effective as only filtering for δ¹³C_DIC and may be ideal depending on sampling considerations. These results demonstrate not only that water samples can be preserved for δ¹³C_DIC and δ¹³C_DOC analysis for long periods, but that preservation is best accomplished with non-toxic or low-toxicity methods.