Location: Southwest Watershed Research2012 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.
3. Progress Report:
This is the final report for Project 5342-12660-004-00D terminated in February 2012 and replaced by new Project 5342-12660-005-00D. For additional information, see the new project report. Over the life of the five year project, basic knowledge of semi-arid rangeland sediment yield processes was increased and significant progress was made on decision support systems for evaluating rangeland conservation practices. Two methods of identifying primary sediment source areas at soil mapping unit scales were developed. One method involves rare earth element oxides that are tagged to surfaces of the watershed and tracked as the soil moves through the watershed to the outlet. The other method quantifies soil erodibility in terms of a soil aggregation index to calculate a potential sediment yield index for individual soil types on a watershed. Rainfall simulator experiments on grassland wildfire sites showed that erosion rates increased immediately after a fire and decreased to pre-fire levels after three to four years. Data bases from the experiment were used to develop flow erosion parameter estimation equations for the Rangeland Hydrology and Erosion Model (RHEM). An analysis of Walnut Gulch Experimental Watershed (WGEW) data showed that the erosion rates are much greater than rates typically reported for rangelands of Arizona and that a large fraction of the sediment is the result a few large storms. The erosion rates appeared to be related both to the vegetation and the general geology of the area. Drought induced invasion of Lehmanns lovegrass at WGEW caused increased runoff and erosion at the hillslope scale but a swale on the watershed limited sediment delivery to the watershed outlet and thus net sediment yield. A study of loose rock and wire/bound check dams showed that both retain sufficient soil moisture to support rangeland restoration efforts to reduce bare soil. A new approach was developed to derive roughness data from satellite-based radar images to produce a quantitative roughness map that can be directly assimilated into hydrologic models. Significant progress was made in the development of RHEM. The model is based on an extensive set of measured data that has been collected over the past 20 years and is accessible via the internet. It requires only information that is commonly collected by or available to rangeland scientists and managers. At the request of NRCS, the model was used to analyze 10,000 National Resource Inventory (NRI) points in 17 western states for the 2011 USDA Resources Conservation Report. A framework was developed for evaluating upland rangeland management for Arizona consisting of a statewide spatial database describing ownership, grazed or ungrazed, a preliminary map of ecological sites, NRCS supported conservation practices, Parameter Evaluation Regression Independent Slopes Model (PRISM) historical climate estimates, slope, aspect, burned areas, and remotely sensed cover estimates. PRISM precipitation and temperatures for the previous three winter and summer seasons, slope, and aspect were able to explain over 75% of the variability in remotely sensed annual cover estimates on grazed rangelands.
1. Climate change impact on rangeland erosion in the southwestern United States. A study was completed by ARS researchers in Tucson, AZ, to evaluate the potential impacts of precipitation changes on soil erosion and surface water runoff in southeastern Arizona that will occur as a result of rainstorms. We used the outputs from seven models of climate change for the projected time periods of the 2050s and 2090s in order to run a model to assess what these changes might be compared to 1970 through 1999 conditions, and the USDA-ARS Rangeland Hydrology and Erosion Model (RHEM). Our results suggested no significant changes in annual precipitation across the region, but projected mean annual runoff and soil loss approximately doubled. These dramatic increases in runoff and soil loss were attributed to the increase in the frequency and intensity of extreme events. Predicted erosion from shrub communities increased more than that for other plant communities under the three scenarios. This is a problem, because future increasing runoff and soil erosion could accelerate the transitions of grassland to shrublands or to more eroded states that has already been occurring on the area over the past century.
2. High resolution photography to monitor rangeland ecosystem changes. Very high resolution gigapixel photography is increasingly being used to support a broad range of ecosystem and physical process research because it offers an inexpensive means of simultaneously collecting information at a range of spatial scales. Recently, methods have been developed to incorporate temporal scaling based on commercially available hardware and new software to create very high resolution zoomable time-lapse imagery. However, use of the hardware is limited by the need for access to AC power. ARS researchers in Tucson, Arizona, modified the power system and built a weatherproof housing for field use an deployed the system at a remote field site in southern Arizona. Images collected every two hours during a one month time period were stitched and the resultant panoramas were used to create a time-lapse video that can be zoomed to display high-resolution spatial detail. This type of photography will be useful for both capturing legacy data and for supporting a broad range of hypothesis driven research.
3. Decision support for tile-drained agriculture. ARS scientists from the Southwest Watershed Research Center, National Laboratory for Agriculture and the Environment, and the Agricultural Systems Research Unit demonstrated an approach linking production and water quality monitoring data, the Root Zone Water Quality Model (RZWQM) simulation model, the DevTreks economic budgeting tool, and the Facilitator decision support tool to rank management systems in northeastern Iowa. We considered the effects of tillage, crop rotation, cover crops, and Nitrogen (N) application method, timing, and amount for the 30 long term simulations on net returns and N loading in ranking management systems. The rankings from simulated results were very similar to those from the observed results from both an onsite and offsite perspective. This research demonstrates a systematic and integrated approach to link the field monitored data with physically based simulation models and budgeting tools to address water quality problems in tile-drained agriculture.
4. New tools to enhance rangeland management. America’s rangelands cover about 80% of the western U.S. and provide habitat for wildlife, recreational opportunities, forage for livestock, a source of minerals and raw materials, and water resources for irrigating crops and the rapidly urbanizing western states. New Decision Support Tools (DSTs) that are easy-to-use, incorporate ecological concepts and rangeland management practices, use readily available data, and are designed to represent rangeland hydrologic and erosion processes have been developed and enhanced for rangeland management. They include the RHEM (Rangeland Hydrology and Erosion Model) and the Automated Geospatial Watershed Assessment tool (AGWA). RHEM is applicable at the hillslope scale. AGWA enables application of RHEM at the watershed scale, allowing assessments of larger areas. These tools are being employed to assess the effectiveness of conservation practices as part of the Congressionally requested Conservation Effects Assessment Program.
5. Semi-desert grassland responses to extreme precipitation events. Climate change models predict an increase in the intensity and frequency of extremely large precipitation events. A critical feature modulating how such large rains will affect ecosystem and watershed processes in these water limited systems is dependent on vegetative cover. By utilizing plot-level water and carbon gas exchange measurements, ARS scientists at the Southwest Watershed Research Center were able to show that levels of net ecosystem carbon uptake did not differ between high- and low-cover desert grassland plots, principally due to plant biomass constraints to ecosystem respiration in low cover grasslands. These findings are important because they suggest spatial and temporal variation in grassland productivity may be reduced under climate regimes of larger, more widely spaced storms that are predicted to increase across the S.W. United States.
Zhang, Y., Nearing, M.A., Wei, H. 2011. Effects of antecedent soil moisture on runoff modeling in small semiarid watersheds of southeastern Arizona. Hydrol. Earth Syst. Sci., 15: 3171–3179.