Geochemical Recharge Estimation and the Effects of a Declining Water Table

Abstract

The High Plains aquifer (HPA) is one of the largest aquifers in the world and is critical for agricultural production in the United States. In Kansas, irrigation using the HPA has resulted in steep groundwater declines. Unexpected water-level response to pumping recovery in the northwestern Kansas portion of the HPA was recently observed, indicating a previously unknown source of recharge. The goal of this research was to investigate water movement and vadose zone chemical inventories to constrain recharge pathways and rates to the aquifer. Detailed geochemical profiles at a cored site indicated displaced chloride, bromide, nitrate-nitrogen (NO 3 -N), and sulfate reservoirs-likely mobilized by the onset of on-site irrigationbelieved to have commenced in 1984. Water in the vadose zone beneath the predevelopment water table (36-63 m below ground surface) is remnant groundwater left as the water table declined. Thus, assumptions of a chloride mass balance are not valid in this zone. These results indicate irrigation return flow has yet to travel through the vadose zone to recharge the aquifer at this location. Calculated chemical transit times through the profile to the predevelopment water table exceed the start of irrigation at the site, and groundwater radiocarbon ages on the order of 3000 yr BP provide further evidence against substantial irrigation return to the aquifer. These data establish evidence for complicated flow paths through the vadose zone to the aquifer and argue against broad, diffuse recharge to the aquifer. Future studies in the area should investigate focused recharge pathways to identify recharge sources.

Groundwater Withdrawals Under Drought: Reconciling GRACE and Land Surface Models in the United States High Plains Aquifer

“…The wells show water level in the utilized aquifer. In KS, this aquifer lies beneath a shallow, low permeability alluvial aquifer that can inhibit groundwater recharge (Gurdak & Roe, 2010;Katz et al, 2016;McMahon et al, 2006). Noah-MP does not distinguish between these aquifers.…”

In Situ and GRACE‐Based Groundwater Observations: Similarities, Discrepancies, and Evaluation in the High Plains Aquifer in Kansas

“…Water occurrence and movement in the vadose zone, and resulting saturated-zone recharge, are important to the interpretations made in this work and have been studied using geochemistry (e.g., Butler Jr. et al, 2014;Katz et al, 2016;McMahon et al, 2004McMahon et al, , 2006 and groundwater modeling (e.g., Gurdak et al, 2008;Keese et al, 2005;Liu et al, 2012). These works suggest that the time required for water infiltrated at land surface to reach the saturated zone of the HPA is as short as 20 years in preferential flow areas, averages close to 50 years, and can exceed 400 years (e.g., Katz et al, 2016;Liu et al, 2012;McMahon et al, 2006). Recent analysis indicates a strong relation between climate, groundwater pumping, and HPA groundwater levels (Whittemore et al, 2016).…”

“…The High Plains aquifer (HPA) in the Central United States is one of the most heavily used aquifers in a semiarid climate in the world (e.g., Butler Jr. et al, 2013;Katz et al, 2016;Longuevergne et al, 2010;McMahon et al, 2006;Stanton et al, 2011). As one of the world's largest and most economically vital freshwater aquifers, the HPA underlies an area where long-term water availability is at risk due to groundwater pumping and climate change (e.g., Crosbie et al, 2013;Whittemore et al, 2016).…”

Quantifying the impact of lagged hydrological responses on the effectiveness of groundwater conservation

“…However, the relative contributions of vertical and lateral flows to net inflow are poorly understood (Butler et al, 2016(Butler et al, , 2020b.While recent work has found that reductions in aquifer net inflow can decrease the effectiveness of groundwater conservation programs over time (Butler et al, 2020b), it is highly uncertain how the mechanisms, timescales, and magnitudes of lagged responses from different water balance components vary. For example, estimates of the magnitude and transit time for groundwater recharge vary dramatically over the HPA due to thick unsaturated zones (Gurdak et al, 2008;Katz et al, 2016;McMahon et al, 2006;Zell & Sanford, 2020). As a result, we do not know which lagged responses may impact overall groundwater sustainability, nor the timescales and controlling processes.…”