Use of geochemical tracers for estimating groundwater influxes to the Big Sioux River, eastern South Dakota, USA

Neupane, Ram P.; Mehan, Sushant; Kumar, Sandeep

Use of geochemical tracers for estimating groundwater influxes to the Big Sioux River, eastern South Dakota, USA | Utilization de traceurs géochimiques pour évaluer les apports d’eau souterraine dans la rivière Big Sioux, dans l’est du Dakota du Sud, Etats-Unis d’Amérique Utilización de trazadores geoquímicos para estimar la afluencia de agua subterránea al río Big Sioux, al este de Dakota del Sur, EEUU 利用地球化学示踪剂估算流入美国南达科他州东部Big Sioux河的地下水通量 Uso de traçadores geoquímicos para estimar a descarga das águas subterrâneas para o Rio Grande Sioux, região leste de Dakota do Sul, EUA

2017

Neupane, Ram P. | Mehan, Sushant | Kumar, Sandeep

Understanding the spatial distribution and variability of geochemical tracers is crucial for estimating groundwater influxes into a river and can contribute to better future water management strategies. Because of the much higher radon (²²²Rn) activities in groundwater compared to river water, ²²²Rn was used as the main tracer to estimate groundwater influxes to river discharge over a 323-km distance of the Big Sioux River, eastern South Dakota, USA; these influx estimates were compared to the estimates using Cl⁻ concentrations. In the reaches overall, groundwater influxes using the ²²²Rn activity approach ranged between 0.3 and 6.4 m³/m/day (mean 1.8 m³/m/day) and the cumulative groundwater influx estimated during the study period was 3,982–146,594 m³/day (mean 40,568 m³/day), accounting for 0.2–41.9% (mean 12.5%) of the total river flow rate. The mean groundwater influx derived using the ²²²Rn activity approach was lower than that calculated based on Cl⁻ concentration (35.6 m³/m/day) for most of the reaches. Based on the Cl⁻ approach, groundwater accounted for 37.3% of the total river flow rate. The difference between the method estimates may be associated with minimal differences between groundwater and river Cl⁻ concentrations. These assessments will provide a better understanding of estimates used for the allocation of water resources to sustain agricultural productivity in the basin. However, a more detailed sampling program is necessary for accurate influx estimation, and also to understand the influence of seasonal variation on groundwater influxes into the basin.

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