Temple, TX, United States
Temple, TX, United States

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Yen H.,Texas A&M University | Lu S.,University of Aarhus | Feng Q.,Purdue University | Wang R.,U.S. Environmental Protection Agency | And 8 more authors.
Water (Switzerland) | Year: 2017

The Soil and Water Assessment Tool 2012 (SWAT2012) offers four sediment routing methods as optional alternatives to the default simplified Bagnold method. Previous studies compared only one of these alternative sediment routing methods with the default method. The proposed study evaluated the impacts of all four alternative sediment transport methods on sediment predictions: the modified Bagnold equation, the Kodoatie equation, the Molinas and Wu equation, and the Yang equation. The Arroyo Colorado Watershed, Texas, USA, was first calibrated for daily flow. The sediment parameters were then calibrated to monthly sediment loads, using each of the four sediment routing equations. An automatic calibration tool-Integrated Parameter Estimation and Uncertainty Analysis Tool (IPEAT)-was used to fit model parameters. The four sediment routing equations yielded substantially different sediment sources and sinks. The Yang equation performed best, followed by Kodoatie, Bagnold, and Molinas and Wu equations, according to greater model goodness-of-fit (represented by higher Nash-Sutcliffe Efficiency coefficient and percent bias closer to 0) as well as lower model uncertainty (represented by inclusion of observed data within 95% confidence interval). Since the default method (Bagnold) does not guarantee the best results, modelers should carefully evaluate the selection of alternative methods before conducting relevant studies or engineering projects. © 2017 by the authors.

Finzel J.A.,Great Basin | Seyfried M.S.,U.S. Department of Agriculture | Weltz M.A.,Great Basin | Kiniry J.R.,Soil and Water Research Laboratory | And 2 more authors.
Rangeland Ecology and Management | Year: 2012

Leaf area index (LAI) is defined as the one-sided area of leaves above a unit area of ground. It is a fundamental ecosystem parameter that is a required input of process-based plant growth and biogeochemical models. Direct measurement of LAI is the most accurate method, but is destructive, time-consuming, and labor-intensive. LAI is highly variable in time and space on sagebrush-steppe rangelands, and a rapid, nondestructive method is desirable to understand ecosystem processes. The point-intercept method is nondestructive and has been demonstrated to provide accurate LAI estimates, but the method is time-consuming. LAI measurement with the Accupar ceptometer (Decagon Devices, Pullman, WA) is nondestructive and faster than the point-intercept method, but has not been evaluated on sagebrush-steppe rangelands. The objective of this study was to evaluate the ceptometer for measurement of LAI in sagebrush-steppe rangelands. Ceptometer and point-intercept LAI data were collected at six sites in sagebrush-steppe rangelands and the values were compared. We found that 1) ceptometer LAI data were consistently greater than point-intercept LAI data, 2) ceptometer data were much more variable than the point-intercept data based on standard deviations, and 3) the overall correlation between the two methods was very weak (r 2=0.15). The much greater ceptometer LAI values were, at least partly, due to the large woody component of the vegetative cover. We attribute the high variability of ceptometer-measured LAI to high instrument sensitivity of the angle of the instrument relative to the sun. © 2012 Society for Range Management.

Radcliffe D.E.,University of Georgia | Keith Reid D.,Agriculture and Agri Food Canada | Blomback K.,Swedish University of Agricultural Sciences | Bolster C.H.,U.S. Department of Agriculture | And 14 more authors.
Journal of Environmental Quality | Year: 2015

Most phosphorus (P) modeling studies of water quality have focused on surface runoff loses. However, a growing number of experimental studies have shown that P losses can occur in drainage water from artificially drained fields. In this review, we assess the applicability of nine models to predict this type of P loss. A model of P movement in artificially drained systems will likely need to account for the partitioning of water and P into runoff, macropore flow, and matrix flow. Within the soil profile, sorption and desorption of dissolved P and filtering of particulate P will be important. Eight models are reviewed (ADAPT, APEX, DRAINMOD, HSPF, HYDRUS, ICECREAMDB, PLEASE, and SWAT) along with P Indexes. Few of the models are designed to address P loss in drainage waters. Although the SWAT model has been used extensively for modeling P loss in runoff and includes tile drain flow, P losses are not simulated in tile drain flow. ADAPT, HSPF, and most P Indexes do not simulate flow to tiles or drains. DRAINMOD simulates drains but does not simulate P. The ICECREAMDB model from Sweden is an exception in that it is designed specifically for P losses in drainage water. This model seems to be a promising, parsimonious approach in simulating critical processes, but it needs to be tested. Field experiments using a nested, paired research design are needed to improve P models for artificially drained fields. Regardless of the model used, it is imperative that uncertainty in model predictions be assessed. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Kendall J.R.A.,Ohio State University | Long D.S.,U.S. Department of Agriculture | Collins H.P.,Soil and Water Research Laboratory | Pierce F.J.,Washington State University | And 3 more authors.
Soil Science Society of America Journal | Year: 2015

Cellulosic ethanol commercialization promises to produce energy from agricultural biomass. Available biomass depends on plant net primary productivity (NPP) and crop type, which maintain total soil organic carbon (TOC). Effect of crop-type, residue removal, and NPP on ethanol yield and TOC levels were assessed by means of a three-pool C model derived from long-term soil incubation, acid hydrolysis, and curve fitting of a nonlinear regression model. A 2-yr field study consisting of three input regimes (Low, Medium, or High NPP), three crops [corn (Zea mays L), wheat (Triticum aestivum, L), and switchgrass (SG, Panicum virgatum L, cv. Blackwell)], and two harvest levels [residue removed (R) or residue not removed (NR)] was conducted near Prosser, WA, USA. After 2 yr, ethanol yield of all crops were similar under Low NPP while ethanol yield of SG under Medium and High NPP was significantly greater than that of corn or wheat under the same NPP. Switchgrass significantly contributed to active [mean residence time (MRT) < 7 d] and resistant (MRT > 500 yr) soil C pools. Other crops had net zero or significantly reduced C pools. During a transition to cellulosic energy production, SG will contribute to soil C maintenance across a range of potential net productivity. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All rights reserved.

Tuppad P.,Texas AgriLife Research Center | Kannan N.,Texas AgriLife Research Center | Srinivasan R.,Texas AgriLife Research Center | Rossi C.G.,Soil and Water Research Laboratory | Arnold J.G.,Soil and Water Research Laboratory
Water Resources Management | Year: 2010

The Bosque River Watershed in Texas is facing a suite of water quality issues including excess sediment, nutrient, and bacteria. The sources of the pollutants are improperly managed cropland and grazing land, dairy manure application, and effluent discharge from wastewater treatment facilities. Several best management practices (BMPs) have been proposed for pollution reduction and watershed protection. The overall objectives of this study were to demonstrate a modeling approach using Soil and Water Assessment Tool (SWAT) model to simulate various BMPs and assess their long-term impacts on sediment and nutrient loads at different spatial levels. The SWAT model was calibrated and validated for long-term annual and monthly flows at Valley Mills and for monthly sediment, total nitrogen (TN) and total phosphorus (TP) at Hico and Valley Mills monitoring locations. The BMPs including streambank stabilization, gully plugs, recharge structures, conservation tillage, terraces, contour farming, manure incorporation, filter strips, and PL-566 reservoirs were simulated in the watershed areas that met the respective practice's specific criteria for implementation. These BMPs were represented in the pre- and post-conditions by modifying one or more channel parameters (channel cover, erodibility, Manning's n), curve number (CN), support practice factor (P-factor), filter strip width, and tillage parameters (mixing efficiency, mixing depth). The BMPs were simulated individually and the resulting Hydrologic Response Units (HRUs), subwatershed, and watershed level impacts were quantified for each BMP. Sensitivity of model output values to input parameters used to represent the BMPs was also evaluated. Implementing individual BMPs reduced sediment loads from 3% to 37% and TN loads from 1% to 24% at the watershed outlet; however, the changes in TP loads ranged from 3% increase to 30% decrease. Higher reductions were simulated at the subwatershed and HRU levels. Among the parameters analyzed for sensitivity, P-factor and CN were most sensitive followed by Manning's n. The TN and TP outputs were not sensitive to channel cover. This study showed that the SWAT modeling approach could be used to simulate and assess the effectiveness of agricultural best management practices. © 2010 Springer Science+Business Media B.V.

Behrman K.D.,Soil and Water Research Laboratory | Behrman K.D.,University of Texas at Austin | Juenger T.E.,University of Texas at Austin | Kiniry J.R.,Soil and Water Research Laboratory | Keitt T.H.,University of Texas at Austin
Landscape Ecology | Year: 2015

Context: Expansion of bioenergy production is part of a global effort to reduce greenhouse gas emissions and mitigate climate change. Dedicated biomass crops will compete with other land uses as most high quality arable land is already used for agriculture, urban development, and biodiversity conservation. Objective: First, we explore the trade-offs between converting land enrolled in the U.S. Conservation Reserve Program (CRP) to switchgrass for biofuel production or preserving it for biodiversity. Next, we examine the trade-offs between agriculture, biodiversity, and biofuel across the central and eastern U.S. Methods: We compiled measures of biodiversity, agriculture, and biofuel from land cover classifications, species range maps, and mechanistic model output of switchgrass yield. We used a spatially-explicit optimization algorithm to analyze the impacts of small-to-large scale biomass production by identifying locations that maximize biofuel produced from switchgrass and minimize negative impacts on biodiversity and agriculture. Results: Using CRP land for switchgrass production increases the land area required to meet biomass goals and the species range area altered for birds, amphibians, mammals, and reptiles. When conversion is not limited to CRP, conversion scenarios including biodiversity and agriculture trade-offs require greater than 100 % more area for switchgrass to reach the same production goals. When land conversion scenarios do not include biodiversity, twice the range area for reptiles and amphibians could be altered. Conclusions: Land-use trade-offs between biofuel production, agriculture, and biodiversity exist and alter optimum location of land conversion for low-to-high biofuel levels. This highlights the need for systematic land-use planning for the future. © 2015 Springer Science+Business Media Dordrecht (outside the USA)

Francesconi W.,International Center for Tropical Agricuture | Smith D.R.,Soil and Water Research Laboratory | Flanagan D.C.,National Soil Erosion Research Laboratory | Huang C.-H.,National Soil Erosion Research Laboratory | Wang X.,Texas A&M University
Journal of Great Lakes Research | Year: 2015

Evaluation of USDA conservation programs are required as part of the Conservation Effects Assessment Project (CEAP). The Agricultural Policy/Environmental eXtender (APEX) model was applied to the St. Joseph River watershed, one of CEAP's benchmark watersheds. Using a previously calibrated and validated APEX model, the simulation of various conservation practices (single and combined) was conducted at the field scale. Seven variables [runoff, sediment, total phosphorus (TP), dissolved reactive phosphorus (DRP), soluble nitrogen (SN), tile flow, and soluble nitrogen in tile (SN-Tile)], were compared between the simulated practices. The field-scale outputs were extrapolated to the areas encompassed by the different conservation practices at the watershed scale. The speculative estimations are presented as percentage reductions compared to the baseline scenario. When single conservation practices were implemented, reductions were 39% for sediment, 7% for TP, and 24% for SN-Tile. In contrast, losses of DRP and SN increased by 5% and 57%, respectively. When the conservation practices were combined, percentage reductions increased for all variables. The total reductions for combined two and three practices were 68% and 91% for sediments, 35% and 74% for TP, 1% and 48% for DRP, -. 43% and 28% for SN, and 50% and 85% for SN-Tile. Negative reductions were due to the slightly higher DRP and SN loads in no-till, mulch-till, and conservation crop rotation practices, and their greater extent of incorporation at the watershed scale. Overall, the cumulative and combined effects of field conservation practices can help address the watershed's excess nutrient and sediment concerns and improve water quality. © 2015.

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