Location: Southwest Watershed Research2008 Annual Report
1a. Objectives (from AD-416)
Objective 1. Provide data bases, knowledge, and information of rangeland erosion at a range of spatial scales for the development, validation, and implementation of erosion decision tools. Objective 2. Develop decision tools including a rangeland specific hydrology and erosion model for the planning and evaluation of sustainable rangeland management.
1b. Approach (from AD-416)
This project addresses the lack of rangeland specific decision tools to quantify the climatic and management effects on the sustainability of rangelands as affected by runoff and erosion. In particular, the Natural Resources Conservation Service (NRCS) and other action agencies have requested a hydrologic and erosion model to contribute to the ecological site description and National Resource Inventory data bases, to assess the efficacy of conservation practices for the Conservation Security Program, and to provide estimates of runoff and erosion for rangeland monitoring and ranch planning. To address this, two objectives were identified: Objective 1. Provide data bases, knowledge, and information on rangeland erosion at a range of spatial scales for the development, validation, and implementation of erosion decision tools and Objective 2. Develop decision tools including a rangeland specific hydrology and erosion model for the planning and evaluation of sustainable rangeland management. Objective 1 consists of three elements on Erosion Processes, one on Conservation Structures, and one on Remote Sensing. The Erosion Processes elements addresses the quantification of the rates and amounts of erosion, sources and sinks of sediment, and biotic and aboitic influences on sediment yield at scales ranging from plot to small watershed. The resulting data and knowledge will be used to validate hydrologic and erosion relationships and for parameter estimation equations for the erosion model. The Conservation Structures element addresses delivering design criteria for local ranchers and provide the erosion model with data on conservation practices. The Remote Sensing element addresses providing parameter estimation for large scale applications of the erosion model and rangeland health assessments. Objective 2 consists of one element on an Erosion Model and one element on an Economic Decision Support System (EDSS). The Erosion Model will be developed for a wide range of erosion related applications, ranging from parameterizing the NRCS ecological site descriptions to ranch planning. The EDSS will be used to calculate the cost benefit ratios of upland conservation management. Formerly 5342-66000-004-00D & 5342-12660-003-00D (4/07).
3. Progress Report
50 years of data (precipitation, runoff, sediment, weather, soil moisture, vegetation, carbon and water flux, remote sensing, and geographic data) collected at the USDA-ARS Walnut Gulch Experimental Watershed (WGEW) were made available to the public via an Internet data base and documented with the publication of a special section of 20 papers in Water Resources Research, one of the premier journals in hydrology. Significant progress was also made in planning and conducting research for the rangeland portion of the congressionally mandated Natural Resources Conservation Service (NRCS) Conservation Effects Assessment Project (CEAP) in collaboration with ARS locations at Reno, NV, Boise, ID, Las Cruces, NM, and Temple, TX, national and state NRCS, United States Forest Service at Moscow, ID, and NASA Ames, CA. Planning elements included selection of large watersheds (8 digit HUCs) for evaluation of conservation management practices at a range of scales and coordinating with NRCS at the national level on the implementation of the newly developed Rangeland Hydrology and Erosion Model (RHEM) to quantify hydrologic and erosion processes for Ecological Site Descriptions. Research elements included developing a new rangeland specific erosion equation and new experimental protocols for the evaluation of the RHEM model. A CEAP related project with Co-PI’s including scientists from the MU, University of Arizona, Tucson and University of Wyoming, Laramie was funded by CSREES. In addition, Dr. Mark Nearing gave a keynote presentation at the ISCO Conference in Hungary detailing the rangeland CEAP project to leaders in soil water conservation from around the world. The effects of a long-term drought on plant mortality and subsequent replacement by an invasive species within the WGEW on the watershed runoff and erosion response has been observed. The impact of this disturbance on runoff and erosion has been quantified using data from both the long WGEW data record and rainfall simulator experiments and studies are underway to evaluate the effect on the water balance and vegetation community respiration rates. The results from this study will be valuable in evaluating the potential effects of climate change on vegetation communities in the arid southwest US. The MU has made significant contributions to technology transfer in the form of WEB based natural resource tools including WEPPCAT (effects of climate change on erosion rates) and Facilitator (a multi-objective decision support system) for use by the scientific community, educators, land-use agencies, and policy makers. The management unit was heavily involved in organizing the annual international conference of the Soil and Water Conservation Society held in Tucson in late July. This project is part of the USDA-ARS NP # 211: Water Availability and Watershed Management. The research carried out under this project plan addresses Problem Area 4 - Integrated Soil Erosion and Sedimentation Technologies, Product 2 – Sediment Yield Data Bases., Product 5 – Best Management Practices.
1. Fifty Years of Research and Data Collection: USDA ARS Walnut Gulch Experimental Watershed - Southwest Watershed Research Center Scientists completed a multi-year, unit-wide Data Access Project (DAP) with the goal to promote analyses and interpretations of historic and current WGEW data by improving data access. This special section of the Journal Water Resources Research and the associated Web site (http://www.tucson.ars.ag.gov/dap/) describe 50 years of data collection and the most recent research results at the USDA ARS Walnut Gulch Experimental Watershed (WGEW) in southeast Arizona. Ten of the twenty special section journal publications address the erosion, sediment yield, and ancillory data of the WGEW and well as providing experimental watershed history, metadata, data access and recent analysis results. The sediment data represents one of the few data sets of sediment yield for semi-arid rangelands at a range of scales. Along with the associated rainfall, runoff, soils, vegetation, and topographic data sets at WGEW, these data will be invaluable for developing and testing rangeland erosion and sediment yield models and assessment tools. NP 211 Problem Area 4 - Integrated Soil Erosion and Sedimentation Technologies, Product 2 – Sediment Yield Data Bases
2. Development of a rangeland hydrology and erosion model. Currently, there are no accepted or scientifically defensible tools to estimate the effects of climate, fire, and management on hydrology and erosion on rangelands. ARS scientists in the Southwest Watershed Research Unit in Tucson, AZ developed a new set of rangeland based sediment source terms for the Rangeland Hydrology and Erosion Model (RHEM) and performed parameter estimation analysis with rainfall simulator studies. These results have positive implications for the rangeland Conservation Effects Assessment Project, which is intended to make broad scale assessments of the benefits of federally-funded conservation practices on western US rangelands. RHEM will be used as the basic assessment tool for that project. NP 211 Problem Area 4 - Integrated Soil Erosion and Sedimentation Technologies, Product 5 – Best Management Practices.
3. Sediment Identification Techniques for Determining Sediment Source. Sediment is a major pollutant in many watershed streams and identification of sediment sources is critical to provide cost effective management to these watersheds and reduce sediment pollution. Using sediment identification techniques, ARS scientists in the Southwest Watershed Research Unit in Tucson, AZ determined that three subwatersheds on Walnut Gulch Experimental Watershed were contributing 86% of the sediment load from the watershed and that 65% of the stable carbon isotope leaving the watershed was from shrub plants that dominate the vegetation on the three subwatersheds. Land managers and landowners using the sediment identification techniques can now determine areas where they should focus their limited resources to produce the greatest reduction in sediment loads. NP 211 - Problem Area 4 - Integrated Soil Erosion and Sedimentation Technologies, Product 2 – Sediment Yield Data Bases.
4. Alternative future land cover scenarios used with hydrologic model to identify areas with potential erosion and water quality problems. There is critical need to assess, report, and forecast the life support functions of ecosystems to ensure we can maintain the sustainable nature of our environmental services and secure these resources into the future. Landscape metrics, in con¬junction with hydrological process models, were used, by ARS scientists in the Southwest Watershed Research Unit in Tucson, AZ, to examine the contribution of land use/land cover change to water and sediment yield and identify subwatersheds within the Willamette River Basin (Oregon, USA) that would be most affected in the year 2050 relative to three possible future growth and development scenarios which include inherent differences related to conservation, planning, and open development as compared to circa 1990 land cover. This study presents an integrated approach to identify areas with potential water quality problems as a result of land cover change projected by stakeholders within the basin;specifically, the impact of both urban and agricultural development in a large river basin. NP 211 Problem Area 4 – Integrated Soil Erosion and Sedimentation Technology, Product 2 – Sediment Yield Data Bases.
5. Sediment transport characteristics in semiarid channels. The full particle size distribution of sediment transported in low-order ephemeral channel is unknown. Sediment was collected by ARS scientists in the Southwest Watershed Research Unit in Tucson, AZ during runoff events for three seasons of flow on Walnut Gulch. The distribution of particles across the complete set of classes transported was quantified and related to channel and hydrologic characteristics. This data set will be critical for improving channel sediment transport models, such as those being proposed for the rangeland Conservation Effects Assessment Project program. This accomplishment is in association with: Hypothesis 1, NP211 Action Plan Component - Problem Area 4 - Integrated Soil Erosion and Sedimentation Technologies, NP Action Plan Problem Statement - Product 2 – Sediment Yield Data Bases
6. The impact of rock check dams on sediment, soil moisture, and vegetation Rock check dams are a common erosion control practice on rangelands. Their impact is anecdotally described, but there is little quantitative data describing their impact. Sediment retention, soil moisture, and vegetation were measure during a field experiment by ARS scientists in the Southwest Watershed Research Unit in Tucson, AZ to compare loose rock check dams with rock and wire structures on a rangeland pasture. This work provides quantitative information that will be useful for designing and implementing additional rangeland treatment using low tech erosion control structures. This accomplishment is in association with: Hypothesis 1 NP 211 Action Plan Component - Problem Area 4 - Integrated Soil Erosion and Sedimentation Technologies. NP Action Plan Problem Statement - Product 2 – Sediment Yield Data Bases.
5. Significant Activities that Support Special Target Populations
SWRC scientists are actively participating in a mentoring program through collaboration with the University of Arizona/NASA Space Grant Program. The program matches outstanding undergraduate students from underrepresented groups with mentors from the SWRC to work together on projects developed by mentors. The ultimate goal of the program is to "grow our own" scientists from underrepresented groups. Over the last four years, twelve students (Hispanic, African-American, women) have come through the program. This year two women completed the program under this project.
Skirvin, S., Kidwell, M., Biedenbender, S.H., Henley, F.P., King, D.M., Holifield Collins, C.D., Moran, M.S., Weltz, M.A. 2008. Vegetation Data, Walnut Gulch Experimental Watershed, Arizona, United States. Water Resources Research, Vol. 44, W05S08, doi:10.1029/2006WR005724.