Lithologic influences on groundwater recharge through incised glacial till from profile to regional scales: Evidence from glaciated Eastern Nebraska

摘要

[1] Variability in sediment hydraulic properties associated with landscape depositional and erosional features can influence groundwater recharge processes by affecting soil-water storage and transmission. This study considers recharge to aquifers underlying river-incised glaciated terrain where the distribution of clay-rich till is largely intact in upland locations but has been removed by alluvial erosion in stream valleys. In a stream-dissected glacial region in eastern Nebraska (Great Plains region of the United States), recharge estimates were developed for nested profile, aquifer, and regional scales using unsaturated zone profile measurements (matric potentials, C1~- and ~3H), groundwater tracers (CFC-12 and SF_6), and a remote sensing-assisted water balance model. Results show a consistent influence of till lithology on recharge rates across nested spatial scales despite substantial uncertainty in all recharge estimation methods, suggesting that minimal diffuse recharge occurs through upland glacial till lithology whereas diffuse recharge occurs in river valleys where till is locally absent. Diffuse recharge is estimated to account for a maximum of 61% of total recharge based on comparison of diffuse recharge estimated from the unsaturated zone (0-43 mm yr~(-1)) and total recharge estimated from groundwater tracers (median 58 mm yr~(-1)) and water balance modeling (median 56 mm yr~(-1)). The results underscore the importance of lithologic controls on the distributions of both recharge rates and mechanisms.