Does Shrub Removal Increase Groundwater Recharge in Southwestern Texas Semiarid Rangelands?

Abstract

Evapotranspiration (ET) is a key component limiting groundwater recharge past the root zone in semiarid regions. Vegetation management may alter groundwater recharge if ET is altered due to changes in vegetation type or cover. This study quantifies changes in groundwater recharge following vegetation cover change from native woodland to pasture in a semiarid region of southwest Texas. The Carrizo-Wilcox aquifer is a valuable groundwater resource in this area, where overuse by dependent farming practices has lowered aquifer levels significantly in the last 85 yr. Combining data from short-term (30 mo) monitoring of the changes in soil moisture and long-term (5-30 yr) changes in total soil chloride indicated deep drainage increased slightly where land had been cleared of vegetation. Annual recharge rates below rooting depths (standardized to 155 cm) averaged only 0.72 6 0.2 mm ? yr 21 (mean 6 SE) in areas not cleared of woody vegetation, as estimated by chloride mass balance. Upon clearing, 72% of the total chloride naturally occurring in the soil profile was flushed away within 30 yr, leading to an estimated 2.59 6 1.7 mm ? yr 21 additional recharge. Deep soil moisture in recently cleared land increased by up to 17% during the growing season of wet years (double the average rainfall) but did not increase in dry or normal precipitation years, providing supporting evidence that more water penetrated below the roots under certain environmental conditions. These results demonstrate that brush management can increase recharge by modest, but measurable, amounts depending on site-specific soil characteristics and degree of reduction in vegetation. Resumen La evapotranspiración (ET) es un componente clave que limita la recarga de agua subterránea más allá de la zona radicular en regiones semiáridas. El manejo de la vegetación puede alterar la recarga de las aguas subterráneas si se altera la ET por los cambios en la cubierta o el tipo de vegetación. Este estudio midió los cambios de la recarga del agua subterránea despue´s de los cambios en la cubierta de la vegetación de un bosque nativo a un pastizal en una región semiárida del suroeste de Texas. El acuífero de Carrizo-Wilcox es un recurso valioso de las aguas subterráneas en esta zona, donde el uso excesivo debido a las prácticas dependientes de la agricultura ha bajado significativamente los niveles acuíferos en los últimos 85 añ os. Combinando los datos de seguimiento a corto plazo (30 meses) de los cambios en la humedad del suelo y a largo plazo (5-30 añ os) en los cambios del total del cloruro de suelo indicaron que el drenaje profundo aumentó ligeramente en áreas donde la vegetación se había aclarado. Las tasas anuales de recarga debajo de la profundidad de la raíz (estandarizado a 155 cm) promedió sólo 0.72 6 0.2 mm ? añ o 21 en áreas no esclarecidas de vegetación leñ osa, estimado por el balance de masa de cloruro. Despue´s del aclareo el 72% del total del cloruro que ocurre naturalmente en el perfil del suelo fue removido entre 30 añ os, conduciendo a una estim...

Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

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Ecohydrology: Processes and Implications for Rangelands

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