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United States Department of Agriculture

Agricultural Research Service


Location: Southwest Watershed Research

2012 Annual Report

1a.Objectives (from AD-416):
The existing project objectives (as given below) reflect the redirection towards quantification of climate change effects: 1. Develop methods and techniques for quantifying natural and anthropogenic induced ephemeral-channel runoff and subsequent recharge in cooperation with U.S. Geological Survey Tucson Science Center under current and projected climate scenarios. 2. Develop methods and techniques to quantify and predict water budgets of riparian ecosystems under current and projected climate scenarios through direct measurements of evaporation and plant transpiration and predict water savings by removal of invasive mesquite vegetation. 3. Develop methods and techniques to explicitly quantify the spatial and temporal distribution of vegetation, land use, and infiltration reduction using remotely sensed methods to improve prediction of basin scale semi-arid water budget components.

1b.Approach (from AD-416):
Methods of investigation include field and laboratory experimentation, as well as the development and use of state-of-the-science watershed models and the use of remote sensing for watershed characterization. Satellite derived rainfall will be evaluated using raingages for large area rainfall estimation, the enhancement of recharge due to urbanization will be examined in adjacent, well instrumented, natural and residentially developed catchments. High-resolution remotely sensing and rainfall simulator experiments will be used to evaluate the capability to remote estimate infiltration rates on compacted and constructed surfaces common to development at the urban-rural interface. Remote spectral surface responses will be combined with energy balance models and radiative transfer theory to estimate surface water, carbon and energy fluxes based on observations from a network of five eddy-covariance and two Bowen ratio towers. A number of modeling components for the Automated Geospatial Watershed Assessment (AGWA) will be developed or enhanced to enable a more realistic representation of watershed processes and best management practices. AGWA will be migrated to both the internet and ARCGIS platforms to enhance usability and access. In addition we will quantify the physical mechanisms and component fluxes that are responsible for the observed ecosystem-scale water and CO2 fluxes. Scientists will carry out this research at sites located across both a riparian and an upland woody plant encroachment gradient. Continue existing research under objective #3, and add activities to develop methods and techniques to quantify and predict water budgets under current and projected climate scenarios through direct measurements of evaporation and plant transpiration, and predict water savings by removal of invasive mesquite vegetation.

3.Progress Report:
This the final report for project 5342-13610-010-00D terminated in Jan. 2012. This project is followed by project 5342-13610-011-00D (Ecohydrological Processes, Scale, Climate Variability, and Watershed Management). Over the 5 years of the project a number of important advances were made under all project objectives which all fall under NP211 – Component Area 5: Watershed Management, Water Availability, and Ecosystem Restoration. Under Objective 1 classification strategies were developed to obtain improved estimates of impervious area with high-resolution remotely sensed imagery to refine the estimate of groundwater recharge resulting from urbanization. An important factor in determining the increase in runoff resulting from urbanization beyond the addition of impervious area was the compaction of soils from site preparation. Increases in runoff from a well-monitored sub-division were successfully modeled with a new “Urban” modeling element incorporated into the KINEROS2 rainfall-runoff and erosion model. Under Objective 2 the Automated Geospatial Watershed Assessment (AGWA) tool was significantly enhanced and a new version was released. AGWA has become an accepted and trusted tool for watershed management by local, state and Federal agencies as well as numerous universities and private consultants with over 3000 registered users from 160 countries or territories. Under Objective 3 research results contradicted the commonly held hypothesis that there is a positive feedback between canopy cover and soil moisture that then explains the stability of woody vegetation patterns - a key finding to understand desertification. In the case of woody plant encroachment, the current paradigm that more ecosystem carbon sequestration would occur under such conditions was not supported due to an increase in the release of CO2 from enhanced soil microbial respiration. A number of important advances were made in climate, plant, water, and carbon cycle interactions as a result of invasive species (Lehmann Lovegrass) encroachment in the ARS Walnut Gulch Experimental Watershed (WGEW) due to a long-term drought. The structural difference of Lovegrass (small basal area as compared to native gramma grasses) resulted in several important feedbacks. The small basal area resulted in higher runoff velocities and the first measureable erosion is over 20 years. Soil water evaporation more than doubled over the growing season and carbon uptake and the ratio of post-storm evaporation to evapotranspiration was altered.

In addition, the MU completed a multi-year effort resulting in the publication of 20 papers in Water Resources Research describing and analyzing over 50 years of data collected at the WGEW. Substantial progress was also made in planning and conducting research and field experiments for the rangeland portion of the congressionally mandated NRCS Conservation Effects Assessment Project (CEAP). A major review of the importance of ephemeral and intermittent streams at the request of EPA in response to the 2006 Rapanos Supreme Court decisions as to whether these streams constitute “waters of the United States” under the Clean Water Act was completed.

1. New satellites map crop type and monitor crop and soil condition. For decades, satellite imagery has played a unique and important role in farm management, but new satellites using radar technology promise even more information at 3-day frequency during day, night, and even under cloudy conditions. We found that the time-series data provided by recently launched radar sensors was suitable for distinguishing crop types, monitoring crop phenology, and capturing rapid changes in soil moisture condition. These results contribute to mission planning by providing information to balance the cost of additional sensor capabilities and the benefit to farm managers. These findings have been incorporated into the design of the European Space Agency Sentinel-1 mission for classifying and monitoring agricultural crops.

2. Cool-season performance of invasive and native grasses. Previous research has suggested the success of introduced South African grasses in invading Southwestern U.S. desert grasslands is their potential utilization of cool-season rains. Native perennial grasses are not thought to use cool-season rains, extensively. ARS scientists at the Southwest Watershed Research Center demonstrated, contrary to this expectation, that some native grasses were better able to sustain higher levels of whole plant carbon uptake, and had higher water use efficiency, during exceptionally wet winter/spring conditions associated with a Southern Oscillation/El Nino event than a highly successful South African invasive. These findings suggest that the invasive success of this grass is not supported by effective winter rain use. Predicted reductions in cool-season precipitation and increasing temperatures may facilitate the further spread and continued dominance of South African grasses across southwestern United States semi-desert grasslands.

Review Publications
Krishnan, P., Meyers, T., Scott, R.L., Kennedy, L., Heuer, M. 2012. Energy exchange and evapotranspiration over two temperate semi-arid grasslands in North America. Agricultural and Forest Meteorology. 153: 31-44.

Blonquist, J., Montzka, S., Munger, J.W., Yakir, D., Desai, A., Dragoni, D., Griffis, T., Monson, R., Scott, R.L., Bowling, D. 2011. The potential of carbonyl sulfide as a proxy for gross primary production at flux tower sites. Journal of Geophysical Research. 116: 1-18.

Nearing, G., Moran, M.S., Scott, R.L. 2012. Coupling diffusion and maximum entropy models to estimate thermal inertia. Remote Sensing of Environment. 119:222-231.

Cavanaugh, M.L., Kurc, S.A., Scott, R.L. 2011. Evapotranspiration partitioning in semiarid shrubland ecosystems: A two-site evaluation of soil moisture control on transpiration. Ecohydrology. 4:671-681.

Chen, M., Zhuang, Q., Cook, D., Coulter, R., Pekour, M., Scott, R.L., Munger, J., Bible, K. 2011. Quantification of terrestrial ecosystem carbon dynamics in the conterminous United States combining a process-based biogeochemical model and MODIS and AmeriFlux data. Biogeosciences. 8:2665-2688.

Jackson, T.J., Bindlish, R., Cosh, M.H., Zhao, T., Starks, P.J., Bosch, D.D., Moran, M.S., Seyfried, M.S., Kerr, Y., Leroux, D., Goodrich, D.C. 2012. SMOS validation of soil moisture and ocen salinity (SMOS) soil moisture over watershed networks in the U.S. IEEE Transactions on Geoscience and Remote Sensing. 50:1530-1543.

Snyder, K.A., Scott, R.L., Mcgwire, K. 2012. Multiple year effects of a biological control agent (Diorhabda carinulata) on Tamarix (saltcedar) ecosystem exchanges of carbon dioxide and water. Agricultural and Forest Meteorology. 164:161-169.

Hamerlynck, E.P., Scott, R.L., Barron-Gafford, B., Cavanaugh, M.L., Moran, M.S., Huxman, T. 2012. Cool-season whole-plant gas exchange of exotic and native desert semiarid bunchgrasses. Plant Ecology. 213:1229–1239. DOI 10.1007/s11258-012-0081-x.

Cable, J., Barron-Gafford, G., Ogle, K., Pavao-Zuckerman, M., Scott, R.L., Williams, D., Huxman, T. 2012. Shrub encroachment alters sensitivity of soil respiration to temperature and moisture. Journal of Geophysical Research. 117:1-11.

5. Burba, G., Schmidt, A., Scott, R.L., Nakai, T., Kathilankal, J., Fratini, G., Hanson, C., Law, B., Mcdermitt, D., Eckles, R., Furtaw, M., Velgersdyk, M. 2012. Calculating CO2 and H2O eddy covariance fluxes from an enclosed gas analyzer using an instantaneous mixing ratio. Global Change Biology. 18:385-399.

Yan, H., Wang, S., Billesbach, D., Oechel, W., Zhang, J., Meyes, T., Martin, T., Matamala, R., Baldocchi, D., Bohrer, G., Dragoni, D., Scott, R.L. 2012. Global estimation of evapotranspiration using a leaf area index-based surface energy and water balance model. Remote Sensing of Environment. 124:581-595. doi:10.1016/j.rse.2012.06.004.

Last Modified: 4/19/2014
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