Discharge variability for an artesian spring of the Edwards Aquifer: Comal Springs (1933–2007)

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Abstract

Daily discharge volumes of Comal Springs, the largest artesian spring of the Edwards Aquifer (EA) in Central Texas, were utilized to characterize the flow of Comal Springs for the period of record spanning 1933–2007. The influence of water extraction (pumping) on discharge characteristics during the record was examined and found to be statistically significant for both volume and variability of spring discharge (p < 0.01). Pumping explains approximately a quarter of the variation in annual discharge (r2 = 0.25) and nearly a third of the daily variability (r2 = 0.32) within the Comal Springs discharge record.

Statistically significant teleconnections to flow are demonstrated within the discharge record of Comal Springs. The El Niño-Southern Oscillation (ENSO, as measured by the Southern Oscillation Index) and the Pacific Decadal Oscillation (PDO) are shown to exhibit statistically significant correlations with annual mean flow from Comal Springs. PDO modulation of ENSO results in mean flow anomalies of 21.9% between extreme quintile years. The Atlantic Multi-decadal Oscillation (AMO) appears to exert influence based on the magnitude of the index value, irrespective of its positive or negative condition (p < 0.01), with the highest quintile (based on magnitude) years correlating with strong positive flow anomalies. A composite index was developed which combines the AMO, PDO and SOI. The extreme quintile years of this index demonstrate a 32.4% divergence in flow (p < 0.01) while demonstrating a stronger skill at capturing negative flow anomalies than positive anomalies.

Precipitation data, at 4-km spatial resolution, were utilized to examine the temporal and spatial correlation of water input to the EA with rates of average monthly discharge from Comal Springs. The spatial dependence of the correlation between precipitation and Comal Springs discharge indicates significant seasonal variability. Overall, the correlation between precipitation and discharge is significant for spring, summer and fall seasons and not significant for winter. Copyright © 2009 Royal Meteorological Society

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