1a. Objectives (from AD-416)
To quantify interactive effects of variable climate, dynamic land use, and land management, particularly conservation practices, on surface and subsurface water quality at the watershed scale. Specific objectives are: 1) Develop and implement a multi-site data system to organize, document, manipulate, and compile water, soil, management, and socio-economic data for assessment of conservation practices from ARS Benchmark watersheds; 2) Quantify water quality, water quantity, and soil quality effects of conservation practices across field to watershed scales within the Upper Washita River Watershed; and 3) Quantify accuracy and uncertainty in model output across field to watershed scales and incorporate this information into assessment tools. The anticipated result of the research are new methods to quantify environmental effects of conservation practices implemented on the landscape and tools to support future strategic placement of conservation practices on the landscape.
1b. Approach (from AD-416)
Multi-temporal land use data sets (both current and retrospective) will be developed for incorporation into watershed-scale hydrologic models to determine the effects of changing land use and management on model predictions. Geomorphic assessments and sediment source tracking will be conducted to determine potential sources and contributions of sediments from overland processes and stream banks. The historical and existing hydrologic, geomorphic, geologic, soil, climate, and land use and management conditions that govern the movement of water, sediment, and nutrients through selected sub-basins within the Upper Washita River watershed will be quantified. Hydrologic modeling studies will be conducted at multiple scales to monitor water quantity and quality responses to conservation practice implementation. The soil management assessment framework (SMAF), developed for mid-western soils and cropping conditions, will be used to evaluate the effects of management practices on soil parameters, and evaluate the hydrologic sensitivity to the soil parameters.
3. Progress Report
Scientists from the Grazinglands Research Laboratory (GRL), in cooperation with scientists from ARS' Hydrology and Remote Sensing Laboratory, completed a multi-decade satellite-based retrospective land use study in the Ft. Cobb Reservoir Experimental Watershed (FCREW) and Little Washita River Experimental Watershed (LWREW). These data sets will be used to complement the satellite-based land use study to address long-term land use changes/impacts on water resources. USGS was contracted to continue water quality sampling for six high-flow runoff events. For the fifth straight year, water samples were collected on a bi-weekly basis from 15 locations in the FCREW. The multi-year, bi-weekly water quality data set is being analyzed and manuscripts are being prepared to report results. GRL scientists in collaboration with scientists from Texas Institute for Applied Environmental Research (TIAER) – Tarleton State University used a whole-farm economic simulation model to simulate the farm profit impacts of no-till and conventional tillage as well as the status quo mix of tillage operations currently used in the watershed. Simulations were completed and a peer-reviewed manuscript is under review. GRL and USDA ARS Temple scientists developed a procedure that uses simple stream channel observations obtained by rapid geomorphic assessment (RGA) to parameterize the Soil and Water Assessment Tool (SWAT) model stream channel variables before calibrating SWAT for streamflow and sediment. A scientist from the GRL met with Kenyan scientists in Nairobi in August 2009 in connection with the UNESCO – HELP twinning project. The GRL scientist presented a short video of the reservoir sediment measurements using Acoustic Profiling System (APS) in Lake Crowder Reservoir, Oklahoma, 2009. Long-term climate analysis (1950-present) was completed for the Calera Aquifer region. A land-use map and crop management files were developed and incorporated into a SWAT project, which must still be calibrated. A ModFlow project was developed at the Bushland laboratory, and additional sources of input data were recently identified to allow calibration of that model in the future. Water policy and management scenarios for the Calera Aquifer were developed by consensus of the Mexican partners that will provide the basis for future simulation analyses. The ARS teams at El Reno and Bushland have entered into a joint effort to link surface and subsurface hydrologic models for application in the Ogallala, Rush Springs, and Calera aquifer assessments. GRL scientists carried out a bathymetric survey using the APS in Crowder Lake, located within the Fort Cobb Reservoir watershed. Data were analyzed to determine the long-term average annual sedimentation rates into the lake from the contributing/drainage area. This data was used to cross-check Crowder Lake sediment accumulation rate simulated by SWAT.
1. Spatial resolution of input data sets may impact SWAT performance. The level of uncertainty of input parameters in hydrologic models has a significant impact on model simulation accuracy and the uncertainty of the resulting model outputs. Two separate studies were conducted in the Fort Cobb Reservoir watershed, located in southwestern Oklahoma, to evaluate the impact of spatial resolution of precipitation and soils data sets on parameters and simulation accuracy of the Soil and Water Assessment Tool (SWAT), and watershed scale hydrologic model. The study findings indicated that varying precipitation data set input resolution impacted some SWAT calibration parameters at both the daily and monthly time scales, but only affected model performance at the daily time scale. Varying the input resolution of the soils input data set had less impact on model parameters and model performance. Precipitation input spatial resolution could impact the value of certain model parameters used to evaluate the effectiveness of some conservation practices, so caution is urged.
5. Significant Activities that Support Special Target Populations
The laboratory partnered with ARS laboratories at Lane, OK; Booneville, AR; and Fayetteville, AR, to develop and staff an exhibit for the Know Your Farmer, Know Your Food Conference and Gala Dinner in El Reno, Oklahoma, in July 2010. The Conference was attended by over 200 persons, the majority being small- to mid-sized farmers, institutional food professionals, and extension or outreach specialists. The project's capacity in soil and water quality assessment was included in the exhibit.
Moriasi, D.N., Starks, P.J. 2010. Effects of the resolution of soil dataset and precipitation dataset on SWAT2005 streamflow calibration parameters and simulation accuracy. Journal of Soil and Water Conservation Society. 65(2):63-78.