A method was developed to calculate site-specific soil-test phosphorus (STP) limits at the soil polygon scale for agricultural land in Alberta. The method uses a quantitative approach for determination of STP limits based on: (1) the relationship between STP and total phosphorus (TP) in runoff developed from field data collected in Alberta conditions; (2) the estimated runoff potential using the Water Erosion Prediction Project (WEPP) model; and (3) hypothetical watershed-scale TP runoff water quality objectives (TPRWQOs) of 0.5 and 1.0 mg L^-1. The calculated STP limits were variable among soil polygons within each watershed. Variability was directly related to the runoff potential among soil polygons and the selected TPRWQOs. As runoff potential from soil polygons within a watershed decreased, the allowable TP in the runoff increased, which in turn resulted in higher STP limits. The TPRWQO value of 0.5 mg L^-1 resulted in STP limits of 60 mg kg^-1 or less in the top 15 cm of soil for 84% of the land within the agricultural area of Alberta. However, when a TPRWQO value of 1.0 mg L^-1 was used, 43% of the agricultural area had STP limits of 60 mg kg^-1 or less. The STP calculations can be refined by further investigation of watershed-scale TPRWQO for Alberta, by application of digital elevation model data in runoff modeling, and by determination of the contribution of base flow to the total flow volume from a watershed.

---

 
The form of phosphorus (P) transported in snowmelt and rainfall runoff has important implications for implementation and assessment best management practice.  Processes governing P export differ between the frost-melt (FM) and frost-free (FF) periods.  In this study, a systems approach was used on three hydrologically isolated hill-slope tracts (3.7 x 36.6 m) where natural snowmelt and rainfall runoff samples were collected.  All fields were planted in corn (fall chisel plow) but had extremes in residue cover created by different corn harvesting schemes, which included grain (high residue), silage (low residue), and silage with fall manure application (intermediate).  Runoff samples were analyzed for total and volatile solids, particle size distribution, different forms of P (dissolved vs. particulate-bound), and P mass distribution in different size classes. The majority of P losses occurred in the particulate-bound form, as indicated by a strong total P versus total solids correlation for the FM (r² = 0.79) and FF (r² = 0.95) periods.  Residue treatments influenced total sediment loads and forms of P in both snowmelt and rainfall-runoff.  During the FF period, both sediment and P loss patterns were related to the percent residue cover (highest cover produced the lowest load).  In contrast, mixed residue cover/manuring effects were observed in snowmelt runoff.  In snowmelt, the highest sediment P concentrations were obtained from the manured site whereas the presence of crop residue (corn-grain site) resulted in P losses dominated by the dissolved organic form.

---

Using SWAT to Model and Target Upland Areas in the Fort Cobb Basin

Phillip R. Busteed, Michael J. White, Daniel E. Storm, and Scott H. Stoodley

 

Department of Biosystems and Agricultural Engineering, Division of Agricultural Sciences and Natural Resources, Oklahoma State University and AMEC Earth & Environmental Water Quality Programs 

The primary purpose of this project was to estimate total phosphorus and sediment loads to the Fort Cobb Reservoir using the Soil and Water Assessment Tool (SWAT) model. A secondary goal was to target priority areas in which landowners would be recruited into a program that provided funds for land improvements to improve water quality. SWAT identified cropland as the primary source of sediment and nutrients in the basin. The Cobb Creek Basin sediment and phosphorus load from upland areas, as predicted by SWAT, was 190,000 Mg/yr and 133,000 kg/yr, respectively. Model results for sediment were extrapolated to a 30 meter grid for the basin using soils, land cover, and Digital Elevation Model data.  This was used to target the 5% of the basin with the highest sediment yield, which accounted for 31% of the total sediment load for the Fort Cobb Basin. Visits to fields marked as priority areas visually corroborated that the model was targeting highly erodible fields.

---

 Targeting High Nonpoint Source Contributing Areas in the Turkey Creek Basin

Michael J. White, Daniel E., Storm, Scott Stoodley, and Phillip R. Busteed

Sediment is the number one pollutant in Oklahoma’s surface waters. Erosion from upland and riparian areas can be reduced by best management practice (BMP) implementation.  Funding for BMP implementation is provided by Section 319(h) of the Clean Water Act.  Through this program, the Oklahoma Conservation Commission (OCC) has finite funding available to implement BMPs throughout Oklahoma watersheds.  To most efficiently use these funds, it is necessary for the OCC to quantitatively target areas with the highest potential for water quality improvement.  The focus of this project was to identify target areas within the Turkey Creek Basin.  Targeting in upland areas was performed using the Soil and Water Assessment Tool (SWAT) model.  The SWAT model was applied to a high resolution data set (10 meter) and operated in a 10 m grid-cell mode to predict sediment and phosphorus loads spatially across the Turkey Creek Basin.  These SWAT model predictions were used to identify areas which potentially contribute disproportionate amounts of sediment and phosphorus per unit area. These areas are typically the best places to implement practices which reduce non-point source pollution.

---

Upland and In-stream Phosphorus Modeling for the Illinois River Basin

Michael J. White, Daniel E., Storm, Brian Haggard, and Phillip R. Busteed

Department of Biosystems and Agricultural Engineering, Division of Agricultural Sciences and Natural Resources, Oklahoma State University and Department of Biological and Agricultural Engineering, University of Arkansas

 

The Illinois River basin covers approximately 1,600 square miles and is divided nearly equally by the Oklahoma/Arkansas border.  The Illinois River is arguable Oklahoma’s most valued scenic river. The basin has been a hot bed of legal activity since 1982, reaching even the US Supreme Court in 1992.  Oklahoma recently set a 0.037 mg/l phosphorus criterion for scenic rivers.  Point source dischargers and the application of poultry litter are often blamed as the chief sources of phosphorus in the Illinois River.  The primary purpose of this project was to predict reductions in poultry litter application and point source phosphorus discharges which will be required to meet the 0.037mg/l Oklahoma criterion. The 0.037 mg/l criterion is calculated as a geometric mean, which tends to be more sensitive to baseflow concentrations and less influenced by short duration runoff events.  Reducing nonpoint source phosphorus loads has only a minor impact the geometric mean, but is critical to meeting the beneficial uses for Lake Tenkiller. A secondary goal of this project was to evaluate the phosphorus load to Lake Tenkiller under differing point and nonpoint scenarios.

---

PPM Calculator:  A Tool for Pasture Phosphorus Management

Michael J. White, Daniel E. Storm, Michael D. Smolen, and Hailin Zhang

Departments of Biosystems and Agricultural Engineering and Plant and Soil Sciences Division of Agricultural Sciences and Natural Resources, Oklahoma State University

The Phosphorus Pasture Management (PPM) Calculator was developed to assist in designing and evaluating pasture management practices to reduce Phosphorus losses. It can be used to evaluate the effect of commercial fertilizer and/or animal waste application, cattle stocking rates, and forage management in grazing and hay production systems.  The PPM Calculator predicted phosphorus loss in kg/ha/yr can be used to evaluate management alternatives.  It can also be used to aid in the implementation of a TMDL if the user has a target rate for P-loading. The PPM calculator is an interface for the SWAT model, implemented on a field basis.  The user-interface allows easy application, with input choices tailored to the specifics of the area such as rainfall, soil types, and land use parameters. User options include fertilizer and litter application rates and timing, animal stocking rates and timing, and management alternative such as removing cattle from a field when the grass is grazed down to a predetermined level. If the SWAT model has been calibrated to the watershed, the PPM Calculator will utilize the calibration to reduce the uncertainty in the model predictions.

---

Riparian Corridor Analysis Using Remote Sensing

Laura E. Christianson, Meagan Armstrong Smith, Daniel E. Storm, and Michael J. White  

Department of Biological and Agricultural Engineering, Kansas State University and Department of Biosystems and Agricultural Engineering Division of Agricultural Sciences and Natural Resources, Oklahoma State University

 

The Oklahoma Conservation Commission has begun using satellite imagery with water quality modeling to identify potential critical source areas of pollutants.  Identification of these source areas aids in implementation of best management practices for targeted Oklahoma watersheds. To more efficiently use available funds, it is necessary for the Oklahoma Conservation Commission to quantitatively target areas with highest potential for water quality improvement.  The objective of this research was to compare the accuracy of SPOT and Landsat imagery with aerial photography to identify land covers thought to be critical sources of erosion in riparian corridors. The study area was Turkey Creek, a 108,000 ha watershed in northwest Oklahoma.  Aerial photography was used to manually digitize 2400 ha of riparian corridor and used as a truth layer for comparing the satellite images. Land cover percentages for each type of image were calculated and compared. In addition, a statistical method using weighting factors was used to help identify the location and magnitude of critical errors.   We concluded that manual classification using aerial photography was the best option for areas up to twice the study size.  For areas that exceed this critical size, we recommend Landsat as the best satellite option. 

---

Targeting High Phosphorus Loss Areas in the Spavinaw Creek Basin

Michael J. White, Daniel E. Storm, and Phillip R. Busteed

Department of Biosystems and Agricultural Engineering, Division of Agricultural Sciences and Natural Resources, Oklahoma State University

Using USEPA 319(h) funds, the Oklahoma Conservation Commission provides cost-share for landowners who implement soil and water conservation measures. Due to limited funding, only a small fraction of a basin can be included in such programs. The goal of this project was to define priority areas in the Oklahoma portion of the Spavinaw Creek basin, located in northeast Oklahoma.  Landowners in these targeted areas can be contacted and recruited into the cost-share program. Spavinaw Creek is the largest stream in the Lake Eucha basin.  Fields in the Spavinaw Creek basin have received phosphorus from poultry litter application for many years. This excess phosphorus contributes to water quality problems in Lake Eucha.  The SWAT (Soil and Water Assessment Tool) model was applied to a very high resolution data set to predict how phosphorus loads varies across the Spavinaw Creek basin.  These SWAT model predictions were used to identify areas which potentially contribute a disproportionate amount of phosphorus per unit area. These areas are typically the best places to implement practices which reduce phosphorus loss.

---

The watershed of Lake Allatoona in North Georgia includes the Etowah River and eleven smaller rivers.  Lake Allatoona is classified as in transition to eutrophic and the state has placed a cap on annual phosphorus (P) loads to the lake.   Our objective was to develop a watershed-scale model of P transport to Lake Allatoona using the Soil Water Assessment Tool (SWAT).  We calibrated SWAT using data from a USGS gauge station on the Etowah River with daily flow and approximately monthly samples of sediment and P concentrations from 1992-1996.  We also used monthly samples of flow, sediment concentration, and P concentration collected on each of the major tributaries in a Clean Lakes Study conducted from 1992-1996.  Land use data was from 1992.  The dominant land use was forest ranging from 79.9 to 95.2% of the area among watersheds.  Next was pasture land use (1.5-11.2%), and then low density residential land use (0-10.9%).  Pasture land use consisted, for the most part, of combined poultry and beef cattle operations.  We used county averages of soil test P (Mehlich-1) from the UGA soil test lab to estimate initial soil labile P content (using a regression equation we developed between STP and anion exchange resin P).  Mehlich-1 STP county averages for pasture landuse ranged from 50 to 238 lb/ac for 1992-1996.  The mean annual load of total P to Lake Allatoona predicted by SWAT was 122,229 kg/yr, which was about 77% of the state cap.  Point sources accounted for 10.0% of the total P inputs to streams, pasture land use accounted for 47.2%, forest land use accounted for 28.9%, and urban land use accounted for 9.5%.  Among the major landuse categories, pasture had the highest annual export per hectare for total P (1.83 kg/ha/yr).  Urban land use was intermediate (0.57 kg/ha/yr) and forest land use had the lowest annual export per hectare (0.15 kg/ha/yr).  We estimated P delivery ratio's from the difference between the model predictions of P loads entering the streams and the P loads reaching the lake.  The average delivery ratio was 90% indicating that P uptake lengths were very long.

---

Best management practices (BMPs) have proven to be an effective means of reducing non-point source contaminant loading to surface waters at the field and farm scale. To a great extent, the effectiveness of BMPs depends on their location relative to hydrologically sensitive areas, as greater reductions can be obtained when BMPs are correctly sited. However, very little research has explored the cost effectiveness of pollutant reduction using BMPs on farms. BMPs designed for farm fields often include strategies such as filter strips, nutrient management plans, seasonal manure spreading, prescribed grazing, and livestock exclusion from streams. The following costs are associated with each BMP: an installment cost, a maintenance cost and an opportunity cost. The benefits associated with each BMP include its effectiveness in reducing P loading in runoff, as well as farm level benefits. The effectiveness can range in value based on site characteristics. We are currently creating a tool to facilitate on-farm decisions in order to minimize cost and maximize the benefits associated with BMP placement, constrained by field and farm level aspects, cost-share agreements, nutrient loading restrictions, and the physical aspects of the farmland itself. The research will use detailed cost and hydrological information from farms in the Cannonsville, New York watershed to build an optimization model that will determine the cost-minimizing and benefit-maximizing way to select BMPs and the optimal areal extent to which they should be implemented. The results will have implications for farm and watershed level strategic decisions concerning water quality management in agricultural watersheds.

---

The risk of phosphorus (P) loss from well-drained sandy soils can be primarily via vertical transport. Hence P retention capacity of the whole soil profile is pertinent to level of environmental risk associated with excess P application. Two site-specific approaches were developed to predict amounts of P that can be loaded to sandy soils before a given P concentration will ultimately be reached at a specified depth. A “capacity” approach involves calculating the mass of P addition that brings a given volume of soil to the change point threshold, or the mass of P potentially released at elevated concentrations if the soil is already above that threshold. The other approach uses P transport retardation and an iterative computer model to predict vertical P movement, deriving Kd from least-squares fitting of Freundlich equation parameters to a single-point P sorption assessment for a population of sandy soils. The capacity approach has proven more effective for soils with previous P loading, whereas the retardation approach provides a prediction of the time of P breakthrough and is less likely to be confounded by geologic phosphate. The approaches have had some laboratory testing and field validation and yield similar predictions for sandy soil materials. Protocols involve simple chemical analyses that should be feasible for routine environmental assessment of prospective application sites.

---

E. Schneiderman¹, M. Zion¹, P. Bishop², Z. Easton³, T. Walter³, T. Steenhuis³

¹New York City Department of Environmental Protection; ²New York State Department of Environmental Conservation; ³Department of Biological and Environmental Engineering, Cornell University.

Watershed model predictions for future conditions are common; but rarely are watersheds monitored long enough to test the predictions.  Fourteen years of storm event monitoring of the West Branch Delaware River at Beerston (WBDR), at the inlet to the Cannonsville Reservoir, affords such a test.  The Variable Source Loading Function (VSLF) model was used to investigate observed reductions in phosphorus loads at WBDR.  The model was calibrated and validated against streamflow and nutrient loading data for 1992-1999.  Nutrient load reductions due to non-point and point source watershed management were estimated by the model and tested against monitoring data for 2000-2004.  Substantial reductions in nutrient loads were predicted due to watershed management, but these predicted reductions for dissolved nutrients were much less than the observed reductions.  We attribute the additional observed reductions to substantial losses in agricultural land use and livestock that occurred from 1997 to 2004.  When nutrient concentrations in runoff in VSLF are further reduced by the decrease in livestock, predicted dissolved nutrient loads approach observed loads for the test period.  Particulate phosphorus predictions of loads after watershed reductions due to both watershed management and land use change were not observed in the test data.  It appears that dissolved nutrient loads are rapidly sensitive to changes in the watershed nutrient mass balance, as reduced livestock is accompanied by lower watershed nutrient inputs in feed and fertilizers.   Particulate nutrient response appears to be longer possibly due to slower transport of solids through the watershed.

---

The approach of the Indicator of Risk of Water Contamination by Phosphorus model (IROWC_P) aims to evaluate the risk of P being delivered to surface water from agricultural land at the Soil Landscape of Canada polygon and the watershed scales. Since its first application in 2000, major changes have been made to improve the IROWC_P. Thus, phosphorus sources and transport factors are now multiplicative rather than additive. Moreover, additional hydrological processes that are significant in Canadian agro-ecosystems have been integrated as a transport-hydrology component. The new transport-hydrology component includes the particulate and dissolved P transports (erosion, surface runoff and infiltration) as well as other factors accounting for hydrological connectivity between P sources and water bodies (topographic index, tile drainage, surface drainage and preferential flow). The main objective of this work was to assess the P transfer in agricultural watersheds of Quebec Province using agricultural census data. A second objective of this work was to validate the improved IROWC_P with Provincial Water Quality Monitoring data. Total P values measured at outlets of 16 agricultural watersheds in the province of Quebec (Canada) during the years 1981, 1986, 1991, 1996 and 2001 were used to test the corresponding risk of water contamination value calculated with the improved IROWC_P model. Pearson correlation analysis scenarios will be performed to adjust the improved IROWC_P sub-component weighting values. Those adjustments will be important to adapt the indicator to the overall Canadian regional conditions. Validation results of the improved IROWC_P model will be discussed.

---

Cornell University, Biological and Environmental Engineering, B30 Riley-Robb Hall Ithaca, NY 14850-5701 (e-mail: ff35@cornell.edu).

Transport mechanisms, transformations, interactions, and dynamics of phosphorus (P) forms in freshwaters require accurate knowledge of the interaction between hydrology and biogeochemistry to understand the P transport process in surface and ground waters. Some stream waters may reach concentrations of several hundred μg l^-1 of soluble reactive P (SRP). Therefore, even if P sources are substantially reduced or eliminated, groundwater discharge to surface water may exceed critical thresholds under most conditions, and SRP contents in groundwater may become of great importance. In this paper the groundwater component, specifically subsurface flow, was studied. The research mainly focused on enhancing the understanding of SRP transport, changes in dissolved organic carbon (DOC), dissolved oxygen (DO), nitrate-N (NO3-N) concentrations, and depth to the groundwater table as well; as subsurface flow is an important pollution source of SRP loading into streams. We measured groundwater samples taken from piezometers installed in areas where the groundwater table is shallow in valley soils in the Catskill Mountains in central New York State. Sampling was done twice per month from November 2003 until April 2006. Low SRP concentrations were found with some peaks throughout the whole sampling time. Mean SRP concentrations found were 0.047 (n=227), 0.036 (n=158), 0.040 (n=182) and 0.038 (n=120) mg l^-1 for the Fall, Winter, Spring, and Summer, respectively. No significant linear relations were found between SRP and the depth to the groundwater table. However, some correlation was found between SRP and DOC.

---

Structural BMPs have been implemented throughout Cannonsville Reservoir Watershed (CRW) in an effort to maintain the reservoir as a potable water supply. However, continuous soil-P build-up resulting from farm P imports exceeding exports is believed to hinder long-term water quality control efforts. Addressing CRW's P imbalance problems while maintaining economic viability of the farms requires a system-level redesigning of farm management. One such strategy, Precision Feed Management (PFM), reduces soil-P build-up by limiting feed and fertilizer purchases while increasing high-quality forage production on the farm. This study used whole-farm simulation on two CRW dairy farms to assess effectiveness of several PFM variations in controlling off-farm P losses, reducing soil P build-up, and maintaining farm profitability. Model simulation of more accurate feeding (based on P in animal diets) integrated with increased productivity of grass-forage, and the proportion of forage in the diet, resulted in a farm P balance reduction of 64-75% and a soluble P loss reduction of 17%. Feed supplement purchases declined by 7.5 kg/cow/year for dietary mineral P, and by 285-442 kg/cow/year for grain and concentrates through adoption of the improved system. Moreover, when a land use conversion of corn to grass was coupled with precision feeding of P and improved forage management, whole-farm simulation predicted a reduction of 100g sediment-bound P/ha/yr in erosion for each 1ha of corn converted. The model also predicted slight increases in grain purchases to offset the reduction in corn silage, but no appreciable change in the farm P balance due to land use conversion. Such model-based studies done on a farm-by-farm basis are useful in complementing farm planners’ efforts in exploring innovative farming systems.

 

---

Parameter sensitivity and uncertainty in SWAT:
A comparison on 5 USDA-ARS watersheds

The SWAT parameter sensitivity and autocalibration module was tested on two northern and three southern USDA ARS experimental watersheds. These watersheds represent a range of climatic, physiographic, and land use conditions present in the United States. Sixteen parameters that govern basin, snow accumulation/melt, surface, and subsurface response in the model were evaluated. Average monthly streamflow over a 3-5yr period was calibrated against measured data for each watershed using mean square error. Sensitivity analysis results suggest that SWAT parameters governing surface runoff response due to rainfall are considerably more sensitive than those governing either subsurface runoff response to rainfall or streamflow response to snowmelt. The parameter uncertainty analysis showed that, on average, parameters in SWAT that primarily govern basin and surface runoff response exhibit percent-of-range solution spaces that are about one-half as large as those exhibited by parameters in the model that govern snow accumulation/melt or subsurface runoff response. In general, the selected space associated with parameter uncertainty was narrower for model simulations performed under wetter climatic conditions than for those under dryer conditions. These results are anticipated to aid watershed modelers and planners in preparing appropriately calibrated SWAT projects.

---

---

---