27-3 Using Sr and U isotopic ratios to trace water flow paths and solute sources across irrigation seasons: understanding agrohydrology processes of Dryland Critical Zone in extensive agricultural areas of Idaho

Session: Environmental Geochemistry and Health (Posters)

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Agricultural irrigation alters hydrological cycles by redistributing surface and ground water, modifies Critical Zone elemental cycles, and impacts water quantity and quality due to land use changes. Here, we focus on understanding the agrohydrologic processes in the Dryland Critical Zone at an extensively irrigated agricultural area in south-central Idaho. The Snake River and the underlying Snake River Plain Aquifer are principal water sources for over 900,000 acres of farmland and 200,000 people in southern Idaho. The Snake River originates in Wyoming and runs across southern Idaho, providing water for irrigation in Kimberly, Idaho, our focus study area and, a region known for its agricultural activity. With increasing demand crop production for future population growth, monitoring water quantity and quality is a top priority. Previous research has not fully understood how the subsurface flows in the fractured basalt aquifer systems return excess water and nutrients from the agricultural fields back into the Snake River. For this study, different types of agricultural water samples were collected before, during and, after the irrigation season, from multiple locations along the Snake River in Kimberly, Idaho, including agricultural irrigation canals, regional groundwater wells, and underground tunnels. Water chemistry parameters (major, trace elements, and alkalinity) and isotope ratios of ⁸⁷Sr/⁸⁶Sr and ²³⁴U/²³⁸U systems were measured to improve our understanding of the infiltration depth, flow paths and directions, and residence time of the water source, and to allow for a clear picture of the irrigation practices and their effects on the flow and chemistry of natural river systems. An expected result is for the water to show evidence of fertilizer contamination and anthropogenic interference; however, water samples from July 2024 show the complete opposite. The samples provide an insight into enhanced weathering and how agriculture accelerates this process. The biggest indicator is the increase of bicarbonates and the decrease of ⁸⁷Sr/⁸⁶Sr and ²³⁴U/²³⁸U. Elements released in the weathering processes also have an increase in concentration, showing positive correlations with bicarbonates. With further research in the study, samples from previous years and pre- and post-irrigation seasons will allow further insight into the effects of agriculture on modern water systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7868

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