Springs on rangelands: runoff dynamics and influence of woody plant cover

Abstract

Abstract:To date, little effort has been devoted to understanding the nature of streamflow from dryland catchments where springs are found, and little is known about how changes in vegetation may alter that streamflow. But where they do occur in drylands, springs are important-ecologically as well as hydrologically. Areas that naturally support spring flow, such as those having an underlying karst geology, hold the most promise for increasing streamflow through control of woody plants. For rangelands, this possibility is a particularly appealing one. However, few studies have documented that such a method is effective (except in Mediterranean climates). For this reason, we studied runoff generation for a site on the Edwards Plateau of Texas: a first-order (19-ha) rangeland catchment supplied with intermittent streamflow from a spring at its base. Using hydrometric as well as isotopic characterization, we evaluated the extent to which runoff changed following removal of most of the woody plant cover (predominantly Ashe juniper). After monitoring streamflow for 4 years (two before plant removal and two following removal), we found that (1) streamflow increased following removal of juniper, by about 46 mm annually, except during the summer; (2) for the 4 years of observation, runoff made up about 22% of the water budget, with baseflow from the spring accounting for about half the total flow; and (3) hydrograph separation analysis conducted for two events following juniper removal indicated that pre-event water made up 25% and 50% of the runoff (these numbers represent lower bounds for the percentage of water derived from the spring during storm events). These findings are important, not only because they add to our understanding of runoff generation from spring-fed catchments, but also in particular because they demonstrate that where springs are present, decreasing woody plant cover may augment runoff.

Ecohydrology: Processes and Implications for Rangelands

“…We would expect higher hydrologic sensitivity where soils are sandy (Moore et al 2012;Dzikiti et al 2013), are deeply cracked (Richardson et al 1979), or are shallow and overlie fractured bedrock (Huang et al 2006). For many rangelands, the opportunities for deep drainage are quite limited, because of either climate or soils.…”

Long-term streamflow relations with riparian gallery forest expansion into tallgrass prairie in the Southern Great Plains, USA

“…That forestation may reduce streamflow in areas where subsurface flow is an important streamflow generation process appears axiomatic from the literature (Hibbert, 1983;Wilcox, 2002Huxman et al, 2005;Huang et al, 2006;Seyfried and Wilcox, 2006). Assuming other conditions remain the same, it seems logical that replacement of shallow-rooted grasses by deeply rooted trees could reduce streamflow if the latter were phreatophytic and transpired from aquifers or perched water tables inaccessible to shallow-rooted grasses.…”

Seasonal water use patterns of Juniperus ashei on the Edwards Plateau, Texas, based on stable isotopes in water

“…This question is of particular importance on the Edwards Plateau, where groundwater is a principal water source for municipalities, agriculture and the over 1.7 million people of San Antonio and surrounding smaller communities. Juniper may enhance evapotranspiration or reduce recharge by canopy interception, negatively impacting water resources; several field and modeling studies have attempted to quantify these effects with some studies showing adverse effects of junipers (Hester, 1996;Wright, 1996;Thurow and Hester, 1997;Owens et al, 2001;Wu et al, 2001;Brown and Raines, 2002;Bednarz et al, 2003;Afinowicz, 2004;Afinowicz et al, 2005;Huang et al, 2006;Lyons et al, 2006;Owens et al, 2006) with others finding negligible effects of juniper on water resources (Dugas et al, 1998 (third year of study); Wilcox et al, 2005Wilcox et al, , 2006. However, none of these studies address the primary source of water for junipers.…”