T194 Groundwater Influenced Ecosystems: Springs, Gaining Streams, and Terrestrial Ecosystems

Tuesday, 24 October 2017
8:00 AM - 12:00 PM
Room 615/616/617

USING THE GEOCHEMICAL KINETICS AND 87SR/86SR RATIOS OF A COMPLEX REWORKED AQUIFER TO IDENTIFY THE REGIONAL EXTENT OF INTERBASIN GROUNDWATER FLOW AND ITS IMPACT ON REGIONAL BASEFLOW GENERATION

Paper number: T194-3
Program: Technical Sessions
Time: 8:25 AM – 8:40 AM

Authors

Abstract

Interbasin groundwater flow (IGF) occurs when water that is recharged in one watershed or basin is discharged in an adjacent watershed or basin. IGF can therefore directly impact estimates of water and solute mass discharged from a watershed and consequently, skew estimates of watershed-scale weathering rates. It is extremely difficult to determine the regional (spatial) extent of IGF and its impact on streamflow and weathering processes in adjacent watersheds, because it is difficult to differentiate between solute mass originating within the watershed from solute mass transported into the watershed through IGF. Here we quantify the regional extent of IGF in watersheds draining the Tusas Mountains of northern New Mexico,

USA (sites where IGF has been shown to occur) using spatial trends in 87Sr/86Sr in springs and streams along with geochemical modeling using PHREEQC. 87Sr/86Sr ratios show a strong connection from the Canjilon watershed to the El Rito watershed, and suggest that the IGF connection likely extends to the Vallecitos watershed. Geochemical modeling informed using XRD analysis of aquifer mineralogy supports previous research showing that IGF from the Canjilon watershed is a dominant control on perennial flow in springs and streams in the adjacent El Rito watershed. However, the IGF connection to the Vallecitos watershed is weak to non-existent. The IGF connection to Vallecitos is largest during snowmelt, contributing as much as 20% of the water and solute mass to Vallecitos. However, the IGF contribution decreases to less than 5% during summer and fall months. Our methodology is different than most commonly employed mixing models because it accounts for the background geochemical evolution of IGF in addition to mixing with inputs from locally-recharged groundwater. When combined with 87Sr/86Sr ratios, this methodology is more robust and may offer capabilities to investigate the regional extent of IGF in other settings.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-300777

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