State Water Resources Research Institute Program (WRRI)
USGS Grant Number:
Start Date: 2009-09-01 End Date: 2012-08-31
Total Federal Funds: $226,890 Total Non-Federal Funds: $286,511
Principal Investigators: Chris Zou, Dave Engle, Sam Fuhlendorf, Don Turton, Rodney Will, Kim Winton
Abstract: Problem Statement: Land based water cycle and water supplies to streams and groundwater are heavily influenced by vegetation and vegetation change resulting from management. In the Great Plains, tallgrass prairie is rapidly transforming to woodland largely by the encroachment of eastern redcedar trees. Using Oklahoma as an example, of the 17 million acres of rangeland including prairie, eight million acres are currently overgrown with eastern redcedar. That number is increasing at an alarming rate equivalent to 762 acres per day. Given the speed, magnitude and extent of the observed and projected encroachment, a logical question is: how and will increases in eastern redcedar cover modify streamflow and raw water supplies in the Great Plains states where water shortages are increasing? Our understanding of such effects is limited to somewhat inconclusive results from studies on semiarid savanna ecosystems. Therefore, a climate and site-specific investigation focusing on mesic prairies of the Great Plains is urgently needed considering long-term water planning is ongoing for most of these affected states. Broad Project Objectives: The proposed project is a field-based, multiple-year collaborative research effort between Oklahoma State University and the USGS Oklahoma Water Science Center. The overall objectives are to develop an improved understanding of the effects of eastern redcedar encroachment in tallgrass prairie on water supply. Hypotheses to Be Tested: i). The encroachment of eastern redcedar in tallgrass priarie alters the dynamic response between precipitation and water loss through interception; ii). The encroachment of eastern redcedar increases rooting depth and alters seasonal water-use pattern, leading to increased overall transpirational water loss; and iii). Eastern redcedar encroachment will significantly reduce streamflow production at the watershed scale. Location of Research: Research will be conducted on the Oklahoma State University Range Research Station (OSURR) near Stillwater, OK. Several of the co-PIs have a history of research foci on this site. Methods: We will directly quantify components of the water budget of small watersheds in tallgrass prairie with and without eastern redcedar encroachment. Specifically, we will directly quantify the tallgrass prairie evapotranspiration (E/T) using an USGS-developed portable E/T chamber (Stannard 1988; Garcia et al. 2008) in conjunction with an indirect method using the soil water balance approach (Rodriguez-Iturbe and Porporato 2004). We will measure interception by tallgrasses using a method that directly quantifies both throughfall and stemflow (revised from Corbett and Crouse 1968). Transpirational water loss by eastern redcedar trees will be quantified using a sap flow technique (Granier 1985, 1987). Streamflow from each watershed will be measured using appropriately sized flumes. In order to apply our small watershed results to other watersheds in the region, we will apply watershed models such as Rangeland Hydrology and Erosion Model (Wei et al. 2008). Our results will be used to parameterize, calibrate and validate the models. Accomplishments/Deliverables: The research will provide quantitative information on the effect of eastern redcedar encroachment in tallgrass prairie on hydrologic processes in general and water yield at the watershed scale in particular. This information will be incorporated into extension and demonstration projects for forestry and rangeland programs. Peer-reviewed and extension publications will be developed and disseminated.