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United States Department of Agriculture

Agricultural Research Service


Location: Southwest Watershed Research

2010 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
Rainfall simulator experiments continued at fire recovery & other ecological sites in southeastern Arizona. An upgraded Walnut Gulch Rainfall Simulator was constructed for ARS Reno to be used in collaborative rangeland research on the Rangeland Hydrology & Erosion Model (RHEM) & the rangeland Conservation Effects Assessment Project (CEAP). Field experiments have been implemented to determine the impact of low-tech rangeland erosion control methods on sediment reduction, soil moisture, & vegetative response. Initial research results have been submitted for publication, & additional measurements will be ongoing to determine long-term impacts with respect to regional rainfall & climate patterns. Sediment transport studies conducted at Walnut Gulch have been completed to characterize channel bed characteristics with respect to transported sediment & to quantify the combined fine & coarse transported loads for individual storm events. In combination, these two areas of research are producing important information for land management agencies & funding agencies interested in rangeland restoration strategies that focus on sediment reduction. RHEM was tested by ARS & NRCS to determine if the output reproduced observed & expected trends in runoff & erosion rates for a wide range of rangeland ecosystems. As a result of the tests, modifications were made to the parameter estimation procedures & implemented in the model. At the request of NRCS, two projects, one at the National Resource Inventory (NRI) scale & one at the watershed scale, were completed for inclusion in the USDA Resources Conservation Report for 2011. For the first project, RHEM was used to estimate erosion rates at 10,000 NRI points in 17 western states. In collaboration with ARS locations in Reno, NV & Boise, ID & NRCS at the state & national level, each of the points was parameterized to develop input for the model. The model output was used to create maps showing areas of erosion rates > 2 t/ha in order to identify areas where the sustainability of rangeland resources may be at risk. The second project was a collaboration between the MU, ARS Boise & Reno, & the University of Arizona & used the Automated Geospatial Watershed Assessment (AGWA) tool to quantify the effects of urbanization & several rangeland management practices (brush conversion, buffer strips, fire, & stock tanks) on runoff & erosion on four 10-12 digit HUC's (Walnut Gulch and Upper San Pedro, AZ, Rock Creek, NV, & Reynolds Creek, ID). A framework to evaluate the benefits and costs of planning at several ranches and the San Pedro watershed scale was developed by linking Soil Survey Geographic (SSURGO) map units with their corresponding ecological site, assigning each site to a state (from that ecological site's state and transition model), associating each state with a stream of ecosystem service benefits, and comparing the benefits with the cost of transitioning from the given state to a state with more benefits. Although at this stage there is uncertainty in every step, having a framework allows for a start at analyzing the costs and benefits of conservation planning.

4. Accomplishments
1. Report of current rates of soil erosion across the western United States: The Soil and Water Resources Conservation Act report of the USDA is due to be completed in 2011. ARS scientists at the Southwest Watershed Research Center in Tucson, AZ used the Rangeland Hydrology and Erosion Model (RHEM) to calculated soil loss across 17 western states with data collected by the Rangeland National Resources Inventory (NRI) between 2003 and 2006 at over 10,000 sites. The model output was analyzed to estimate the average annual and the 2-, 10-, 25- and 50- year return period sediment yield to provide estimates of the vulnerability of the site to accelerated soil loss. The data are being used to create maps representing annual hillslope soil loss of the western United States in order to illustrate areas with accelerated soil loss (>2 ton/acre) that will likely lead to unsustainable plant communities and a loss of ecosystem goods and services. The findings of this study will be reported in the Soil and Water Resources Conservation Act report of the USDA in 2011.

2. Impact of an invasive grass species on erosion and sediment yield: As a result of a prolonged drought in the mid 2000's, a large proportion of the native grass species was replaced by an invasive grass species, Lehmans Lovegrass, over large portions of the Walnut Gulch Experimental Watershed (WGEW) near Tombstone, AZ. A study by ARS Scientists in Tuscon, AZ, was conducted using the WGEW's long term rainfall, runoff, and sediment yield data base and rainfall simulator data for a small watershed to quantify the effect of the Lehmans Lovegrass invasion on the hydrologic function and site stability of the watershed. It was shown that during the transition period low cover on the hillslopes and adjacent swale caused an increase in erosion and sediment yield. After the Lehmans Lovegrass was established, hillslope erosion remained elevated but revegetation in the swale caused much of the hillslope eroded sediment to be deposited, resulting in a decrease in watershed sediment yield. These results highlight the importance of topographic features in controlling watershed function under changing climatic conditions.

3. Non-engineered rock structures for improving degraded rangelands. ARS researchers in Tucson, Arizona conducted a study to measure and document soil moisture response to loose rock structures and wire bound rock structures in comparison with untreated control sites during the first rainfall season following construction. A field experiment was conducted on a degraded alluvial fan in southeastern Arizona where erosion control structures were built on three small ephemeral channels. Significantly more soil moisture was present through the soil profile on channel banks were found in association with both loose rock and wire bound check dams in comparison with controls sites. These results quantify this response and will be useful in designing rangeland restoration strategies that rely on soil moisture to improve vegetative cover.

4. Sediment yield and transport in semiarid watersheds. Sediment data collected at sufficient resolution to characterize yield and transport are rare in semiarid watersheds. To address this data and information gap, ARS researchers in Tucson, Arizona have conducted field experiments on the Walnut Gulch Experimental Watershed to characterize small watershed sediment processes. Research results describe particle patch dynamics and transport of both fine and coarse sediment particles and will be applied to understand the impacts of rangeland treatments and the potential of land management actions to alter sediment processes in rangeland watersheds.

Review Publications
Nichols, M.H., Ruyle, G.B., Nourbakhsh, I.R. 2009. Very High Resolution Panoramic Photography to Improve Conventional Rangeland Monitoring. 62:579–582.

Vasquez-Mendez, R., Ventura-Ramos, E., Oleschko, K., Hernandez-Sandoval, L., Parrot, J., Nearing, M.A. 2010. Soil erosion and runoff in different vegetation patches from semiarid Central Mexico. Catena. 80: 162–169.

Smith, R.E., Quinton, J., Goodrich, D.C., Nearing, M.A. 2010. Soil-Erosion Models: Where do we Really Stand? Short Communication (Discussion) on the papers by Wainwright et al. (2008a, b, c). Earth Surface Processes and Landforms. p. 1-5.

Yuill, B., Nichols, M.H. 2010. Patterns of grain-size dependent sediment tranpsort in low-ordered, ephemeral-channels. Earth Surface Processes and Landforms. p. 1-13.

Last Modified: 2/23/2016
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