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Titre : An Investigation of Focused Aquifer Recharge in the Jornada Experimental Range Using Chloride as a Tracer

Auteur : Reuter, Sarah Elaine.

Université de soutenance : New Mexico Institute of Mining and Technology 

Grade : Master of Science in Hydrology 2020

[[ Résumé partiel
Recently published research has suggested that up to 20% of precipitation in a small (∼0.05 km2 ) piedmont watershed in the Jornada Experimental Range of southern New Mexico becomes deep percolation that leads to aquifer recharge. This finding, based on a watershed mass balance approach measuring precipi tation, runoff, evapotranspiration, and soil water storage change through time, challenges a prevalent understanding of Chihuahuan Desert ecohydrology that creosote shrubland prevents recharge. The potential management implications of this finding are consequential. Here I report on research designed to test for the hypothesized focused recharge in small, first-order channels by coring the sediment under two such channels and analyzing the chloride distribution with depth. If abundant recharge occurs then chloride should be flushed through the sediment to the groundwater, but if it does not then an accumulation, or bulge, of chloride should form at the most frequent depth of infiltration. To test the methodology, I also took two cores from flat interfluvial areas far from channels and one core from a 4-m-wide cobble-bed channel that almost certainly causes focused recharge. In addition to measuring chloride in the cores, I also measured gravimetric water content, soil water potential, and chloride to bromide ratios. The interfluve cores showed chloride concentrations that rose rapidly within 70 cm of the ground surface and remained high (∼8,000 mg/kg of pore water) through the remainder of the core, which confirms that chloride has accumulated in these non-recharging portions of the landscape. Water content was extremely low, with typical matric potential values of 6 MPa and a minimum value of 8.83 MPa, equivalent to 900 m of head. Collection of the large channel core was inhibited by the coarse nature of the channel sediment and most material was lost from the core barrel in retrieval, but the sediment that was obtained had an average chloride concentration of ∼100 mg/kg and had a matric potential of ∼0 MPa, which is effectively saturated.

Présentation et version intégrale (ProQuest)