Print PageArundo donax L. is a tall perennial grass that has invaded and come to dominate riparian zones throughout the southwestern United States. Arundo forms large, dense stands and transpires large amounts of water to support its high rate of growth and is therefore expected to have a major impact on riparian zone hydrology. Understanding the hydrologic impacts of Arundo invasion is currently limited, in part, by uncertainties associated with Arundo dependence on deep water sources. We report here results from a study designed to understand how Arundo’s access to groundwater varies across riparian zones, the causes of this variation, and how this might impact spatial variability in Arundo transpiration. We used natural-abundance stable isotopes of oxygen and hydrogen to determine the water sources of Arundo along four approximately 100-meter transects perpendicular to the Rio Grande in southwest Texas. Surface soil water, river water, groundwater, precipitation and rhizome samples were collected every month during 2010 summer to understand the range of isotopic variability in our system and mixing models were used to estimate Arundo dependence on surface soil moisture or groundwater.
Results/Conclusions
Our results suggest that proximity to the river and smaller vertical distances from groundwater tend to increase use of the groundwater resource. Across sites and in mid-summer, the isotopic compositions of groundwater and river water are not significantly different, which indicates a close interaction between the river and groundwater. In this case, we didn’t find a relationship between depth to groundwater and transpiration rate.
