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Hydrological Impacts of Mesquite Encroachment in the Upper San Pedro Watershed
Citation:
Nie, W., Y. YUAN, W. G. KEPNER, C. L. ERICKSON, AND M. JACKSON. Hydrological Impacts of Mesquite Encroachment in the Upper San Pedro Watershed. JOURNAL OF ARID ENVIRONMENTS. Elsevier Science Ltd, New York, NY, 82(0):147-155, (2012).
Impact/Purpose:
Extensive invasions of mesquite into grassland or/and savannas occurred throughout the arid and semi-arid regions of the world over the last several decades or earlier [Briggs et al., 2007; Goslee et al., 2003; Shiferaw et al., 2004; van Klinken et al., 2006]. The conversion of grassland into mesquite can generate many environmental consequences through altering nutrient and water cycling, changing carbon storage, enhancing climate variability, and reducing biodiversity [Ceballos et al., 2010; Jackson et al., 2002; Schlesinger et al., 1990; Walvoord et al., 2003; Zeng et al., 1999]. Specifically, considering that water is a limited resource in the ecosystem of these regions, hydrological responses to mesquite invasion will directly impact human beings and the local ecosystem. Impacts of landuse changes on hydrology in regions with mesquite encroachment have been investigated [Hernandez et al., 2003; Miller et al., 2007]. However, simultaneous changes for multiple land uses enhance the difficulties of quantifying the effects of mesquite invasion on hydrological cycling. To address this issue, the Soil and Water Assessment Tool (SWAT) 2005 [Neitsch et al., 2005], a physically based hydrological model, was applied to simulate progressive invasions of mesquite into grassland using developed land use scenarios. The objective of this study is to quantify how mesquite encroachment influences the major hydrological processes at the basinal scale.
Description:
Invasion of mesquite into grassland occurs in water-limited ecosystems throughout the world. To assess hydrological consequences of mesquite invasion, the Soil and Water Assessment Tool (SWAT) was applied to simulate idealized progressive mesquite encroachments in the upper San Pedro watershed (U.S./Mexico). Results indicate that the average annual basinal evapotranspiration (ET) increases with mesquite invasion, while percolation, surface runoff, baseflow, and water yield decreases. The increase of ET leads to a non-ignorable decrease of water supply in the upper San Pedro watershed, because total runoff (water yield) and percolation are reduced by 16.5% and 9.9%, respectively. Thus, the negative impact of mesquite encroachment on water supply should be considered in future water resource planning and land use management. In addition, a non-linear response of hydrology to grassland removal was observed; hydrological processes changed markedly until more than 40% of grassland was removed. It indicated that the strongest increase of ET occurred in the early stage of invasion. Once mesquite invasion begins, the high transpiration demand of mesquite decreases soil moisture, enhances the capability of mesquite to compete with grassland, and in turn enforces the invasion. Consequently, to prevent desertification and protect the grasslands in the semiarid regions, mesquite should be controlled in its earliest stage of invasion.