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Research Project: Soil Erosion, Sediment Yield, and Decision Support Systems for Improved Land Management on Semiarid Rangeland Watersheds

Location: Southwest Watershed Research Center

2016 Annual Report

1a. Objectives (from AD-416):
Objective 1. Provide databases, knowledge, and information on 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 improved planning and evaluation of rangeland management practices.

1b. Approach (from AD-416):
This project addresses the need for rangeland decision tools to assess the climatic and conservation management effects on rangeland sustainability as affected by runoff and erosion. The Natural Resources Conservation Service (NRCS) has requested that the Rangeland Hydrology and Erosion Model (RHEM) be integrated with a watershed scale model for the Conservation Effects Assessment Project (CEAP). Techniques to assess natural drivers and management practice effects on rangeland hydrologic and erosion processes at the hillslope or ecological site scale are primarily qualitative. Techniques are needed to quantify erosion rates and processes, particularly under disturbed conditions where data are lacking. At larger scales, the impact of conservation structures on sediment dynamics is poorly understood. Tools are needed that integrate the effect of management practices implemented at the hillslope scale with watershed scale processes to assess their environmental impact and cost effectiveness. The general approach of this project is to develop databases, knowledge, and information that will be used to evaluate conservation practices and quantify the physical and effectiveness of those practices on reducing runoff and erosion at the hillslope and watershed scale. The expected outcomes of the research are 1. Databases and improved measurement techniques to quantify a) decadal-scale hillslope erosion rates, b). overland flow erosion for disturbed conditions, c) sediment transfers as impacted by conservation structures and d). landscape change; 2. Integration of RHEM and KINEROS2 in the GIS based AGWA framework for rangeland conservation practice assessment; and 3. A framework to assess effectiveness of conservation practices.

3. Progress Report:
This project is carried out under National Program 211 - Water Availability and Watershed Management. The first objective of this project is associated with National Action Plan Components 2 - Erosion, Sedimentation and Water Quality Protection ; the second objective with Component 3 - Improving Conservation Effectiveness. This report summarizes progress through FY16 corresponding to the 60th month milestones listed in the five-year project plan. In addition to this project, scientists in the Management Unit (MU) provided significant contributions to the NP 211 National Action Plan for the new 211 project cycle. The MU currently has two (2) projects under NP 211: this project and Project No: 2022-13610-010-00D, "Ecohydrological Processes, Scale, Climate Variability, and Watershed Management". In consultation with our Area Director and the NP 211 National Program Leader, we agreed that these two projects will be combined in the next 211 cycle. A combined project plan has been developed and reviewed by the Area office and is currently pending review through the Office of Scientific Quality Review. From a personnel perspective, one long open category 1 scientist vacancy was filled this fiscal year. The new scientist reported to our laboratory August 8, 2016. Progress on Objective 1 was made in quantifying the decadal scale erosion rate and its short-term variability in a semi-arid environment. Ecological Site Descriptions (ESD) are currently being developed and mapped for the western states of the U.S. These ESDs describe the different potential plant communities that can exist on a piece of land, based on the type of soils, topography, and climate at that location. The State and Transition Model concept describes not only the types of ecological plant communities that can be found on a particular ecological site, but also the drivers that cause one plant community to shift to another. For many ecological sites soil erosion can play a significant role in how one plant community transitions to another, for example, as a site degrades from a healthy condition to a poor one. In this study we used two existing tools to measure soil erosion at different time scales in order to better understand the role that soil erosion might play in such transitions. We measured soil erosion using an isotopic technique with Caesium-137 (137Cs) as an average over approximately the last 50-60 years, and with a rainfall simulator, which characterizes erosion at essentially a single point in time. We learned that the measurements at a single point in time could vary quite a lot depending on the conditions at the location at that point in time, for example, if the measurements are made shortly after a fire. The longer term 137Cs measurements probably have more meaning in terms of characterizing the long-term differences in soil erosion rate as a function of plant community, but the rainfall simulator measurements are more useful to identify processes that have the potential to impact the ecological system and potentially cause a change in the state of the site. Additional progress on Objective 1 was made in implementing new photographic methods to discover previously undocumented erosion processes on the Walnut Gulch Experimental Watershed. A method for using very-high temporal resolution ground-based time-lapse photography to capture short-duration flash floods and gully head evolution was developed and implemented at an eroding rangeland site. As expected, mass wasting and headcut plunge pool erosion were the most frequently observed erosion mechanisms. High temporal resolution time-lapse photography was critical for identifying subsurface erosion processes that preceded that largest geomorphic change at the site. In the absence of time-lapse images piping would not have been identified as an erosion mechanism responsible for advancing the gully headwall at this site. Identification of specific erosion processes is a first step toward advancing simulation model representation of rangeland landscapes. We quantified the impacts of the conservation structures such as porous rock check dams on watershed sediment transfers. Rock check dams were constructed in 2004 on two small watersheds and their impacts have been measured for the past decade. Although their influence on reducing watershed outlet runoff appears to affect small flows and is short-lived, they have a substantial impact on reducing channel grades and inducing sediment deposition. Significant progress was made on Objective 2 to develop the Rangeland Hydrology and Erosion Model (RHEM) Risk Assessment Tool. The purpose of the tool is to evaluate and illustrate the risk of excessive runoff and soil erosion on rangeland sites relative to desired or optimal rangeland conditions. A user of the web tool will run various alternative scenarios of land conditions for a particular rangeland site, including a user defined “baseline”, desired, or good condition alternative. Statistics are used to define low, medium, high, and very high yearly rates of erosion determined from the baseline condition. From that starting point, other scenarios, or possible site conditions, are compared. This tool is an important addition to the current web-based RHEM model interface. There are many possible uses for the tool, but one that is currently being undertaken is for the development of Ecological Site Descriptions (ESDs). ESDs are formal documents being developed across the United States by the Natural Resources Conservation Service, Forest Service, and Bureau of Land Management that describe hydrologic and vegetation function of land resources, particularly for grazing lands. This tool will greatly facilitate the process of developing ESDs. The tool was developed by ARS scientists in Tucson, Arizona.

4. Accomplishments
1. Development of the Rangeland Hydrology and Erosion Model (RHEM) Risk Assessment Tool. Prediction technologies are critical for managing rangeland resources. ARS scientists in Tucson, Arizona, developed the RHEM tool to evaluate and illustrate the risk of excessive runoff and soil erosion on rangeland sites relative to desired or optimal rangeland conditions. The tool is implemented through a website where the user can run various alternative scenarios of land conditions for a particular rangeland site, including a user defined “baseline”, desired, or good condition alternative. Statistics are used to define low, medium, high, and very high yearly rates of erosion determined from the baseline conditions against which other scenarios, or possible site conditions, are compared. In addition, this tool will greatly facilitate the process of developing Ecological Site Descriptions which are formal documents that are currently being developed in a large and active program across the United States by the Natural Resources Conservation Service, Forest Service, and Bureau of Land Management to describe the hydrologic and vegetation functions of land resources, particularly for grazing lands.

5. Significant Activities that Support Special Target Populations:

Review Publications
Oliveira, J., Dominguez, J., Nearing, M.A., Oliveira, P. 2015. A GIS-based procedure for automatically calculating soil loss from the Universal Soil Loss Equation: GISus-M. American Society of Agricultural and Biological Engineers. 31(6):907-917.
Polyakov, V., Nearing, M.A., Stone, J., Holifield Collins, C.D., Nichols, M.H. 2015. Quantifying decadal-scale erosion rates and their short-term variability on ecological sites in a semi-arid environment. Catena. 137:501-507.
Nearing, M.A., Unkrich, C.L., Goodrich, D.C., Nichols, M.H., Keefer, T.O. 2015. Temporal and elevation trends in rainfall erosivity on a 149 km2 watershed in a semi-arid region of the American Southwest. International Soil and Water Conservation Conference. 3:77-85.
Weltz, M.A., Jolley, L., Goodrich, D., Boykin, K., Nearing, M., Stone, J., Guertin, P., Hernandez, M., Spaeth, K., Pierson, F., Morris, C., Kepner, B. 2011. Techniques for assessing the environmental outcomes of conservation practices applied to rangeland watersheds. Journal of Soil and Water Conservation. 66(5):154A-162A.
Xie, Y., Yin, S., Liu, B., Nearing, M.A., Zhao, Y. 2016. Models for estimating daily rainfall erosivity in China. Journal of Hydrology. 535:547-558.
Pelletier, J., Nichols, M.H., Nearing, M.A. 2016. The influence of Holocene vegetation changes on topography and erosion rates: a case study at Walnut Gulch Experimental Watershed. Earth Surface Dynamics. 4:417-488.
Williams, C.J., Pierson Jr, F.B., Spaeth, K.E., Brown, J.R., Al-Hamdan, O.Z., Weltz, M.A., Nearing, M.A., Herrick, J.E., Boll, J., Robichaud, P.R., Goodrich, D.C., Heilman, P., Guertin, P.D., Hernandez, M., Wei, H., Hardegree, S.P., Strand, E.K., Bates, J.D., Metz, L., Nichols, M.H. 2016. Incorporating hydrologic data and ecohydrologic relationships in ecological site descriptions. Rangeland Ecology and Management. 69:4-19.
Weltz, M.A., Nouwakpo, S.K., Hernandez, M., Nearing, M.A., Stone, J.J., Armendariz, G.A., Pierson, F.B., Al-Hamdan, O., Williams, C.J., Spaeth, K.F., Wei, H., Heilman, P., Goodrich, D.C. 2015. USDA internet tool to estimate runoff and soil loss on rangelands: rangelands hydrology and erosion model. The Progressive Rancher. 8:24-25.
Webb, N.P., Herrick, J.E., Van Zee, J.W., Courtright, E.M., Hugenholtz, C.H., Zobeck, T.M., Okin, G., Barchyn, T.E., Billings, B.J., Boyd, R., Clingan, S., Cooper, B., Duniway, M., Derner, J.D., Fox, F.A., Havstad, K.M., Heilman, P., Laplante, V.K., Ludwig, N., Metz, L.J., Nearing, M.A., Norfleet, M., Pierson Jr, F.B., Sanderson, M.A., Sharratt, B.S., Steiner, J.L., Tatarko, J., Tedela, N., Toledo, D.N., Unnasch, R., Van Pelt, R.S., Wagner, L.E. 2016. The National Wind Erosion Research Network: Building a standardized long-term data resource for aeolian research, modeling and land management. Aeolian Research. 22:23-36.
Garbrecht, J.D., Nearing, M.A., Steiner, J.L., Zhang, X.J., Nichols, M.H. 2015. Can conservation trump impacts of climate change on soil erosion? An assessment from winter wheat cropland in the Southern Great Plains of the United States. Weather and Climate Extremes. 10(A):32-39. doi:10.1016/j.wace.2015.06.002.
Nichols, M.H., Polyakov, V.O., Nearing, M.A., Hernandez, M. 2016. Semiarid watershed response to low-tech porous rock check dams. Soil Science. 181(7):275-282. doi: 10.1097/SS.0000000000000160.
Nichols, M.H., Nearing, M.A., Hernandez, M., Polyakov, V. 2016. Monitoring channel head erosion processes in response to an artificially induced abrupt base level change using time-lapse photography. Geomorphology. 265:107-116.
Yin, S., Xie, Y., Liu, B., Nearing, M.A. 2015. Rainfall erosivity estimation based on rainfall data collected over a range of temporal resolutions. Hydrology and Earth System Sciences. 19(10):4113-4126. doi:10.5194/hess-19-4113-2015.