Larry M. Hauck

APPLICATION OF SWAT FOR THE UPPER NORTH BOSQUE RIVER WATERSHED

Agriculture, including livestock production, has been implicated as a major source of pollution to streams and lakes. This study was conducted to assess the effect of dairy production on water quality within Upper North Bosque River Watershed (UNBRW) of north central Texas. The UNBRW encompasses an area of approximately 93 250 ha and included 94 dairies at the time of the study. A river basin model (Soil and Water Assessment Tool, SWAT) was applied in two phases. During the first phase, SWAT was validated for the baseline condition within UNBRW. The baseline condition within UNBRW was simulated from 1988 through 1996; model output was compared to flow, sediment, and nutrient measurements for 11 stream sites within the watershed for the period of October 1993 to July 1995 for SWAT model validation. The Nash-Sutcliffe coefficient evaluating model efficiency of SWAT for predicting average monthly flow, sediment, and nutrient loading (organic-N, NO3-N, organic-P, and PO4-P) at 11 stream sites over the validation period ranged from 0.65 to 0.99, indicating reasonable predicted values. SWAT also adequately predicted monthly trends in average daily flow, sediment, and nutrient loading over the validation period with Nash-Sutcliffe coefficients ranging from 0.54 to 0.94 except for NO3-N which had a value of 0.27. Nutrient loadings were consistently highest in the subwatersheds with the most dairies operations. In phase two, to evaluate the effect of dairies, SWAT was executed by replacing the manure waste application fields with grassland. The results from this phase of study indicate that loading from the watershed could be reduced about 33% for total-N (organic-N plus NO3-N) and 79% for total-P (organic-P plus PO4-P) in the UNBRW if dairy waste application fields were replaced by grassland. Empirical equations based on the output with and without dairy loading were developed to illustrate the impact of cow density and percent area covered by dairy waste application fields on sediment and nutrient loading.

APPLICATION OF A WATERSHED MODEL TO EVALUATE MANAGEMENT EFFECTS ON POINT AND NONPOINT SOURCE POLLUTION

A Total Maximum Daily Load (TMDL) program has been initiated in the North Bosque River Watershed in Texas, USA, where point and nonpoint sources of pollution are of a concern. The Soil and Water Assessment Tool (SWAT), which had been validated for flow and sediment and nutrient transport, was applied to quantify the effects of Best Management Practices (BMPs) related to dairy manure management and municipal wastewater treatment plant effluent. Results are presented for the period from 1960 through 1998 for three sites along the North Bosque River. Results are presented as annual time–weighted concentrations (average of the daily load divided by daily flow over a year) and annual flow–weighted concentrations (total cumulative load divided by total cumulative flow over a year). The wastewater treatment plant BMPs resulted in greater improvement in time–weighted instream soluble phosphorus concentrations than dairy BMPs. On the other hand, dairy BMPs made greater differences in flow–weighted concentrations. This study showed that SWAT could be a useful tool for studying the effects of alternative management scenarios for pollution control from point and nonpoint sources in large watersheds.

The Agricultural Policy Environmental EXtender (APEX) Model: An Emerging Tool for Landscape and Watershed Environmental Analyses

The Agricultural Policy Environmental eXtender (APEX) model was developed by the Blacklands Research and Extension Center in Temple, Texas. APEX is a flexible and dynamic tool that is capable of simulating a wide array of management practices, cropping systems, and other land use across a broad range of agricultural landscapes, including whole farms and small watersheds. The model can be configured for novel land management strategies, such as filter strip impacts on pollutant losses from upslope cropfields, intensive rotational grazing scenarios depicting movement of cows between paddocks, vegetated grassed waterways in combination with filter strip impacts, and land application of manure removal from livestock feedlots or waste storage ponds. A description of the APEX model is provided, including an overview of all the major components in the model. Applications of the model are then reviewed, starting with livestock manure and other management scenarios performed for Livestock and the Environment: A National Pilot Project (NPP), and then continuing with feedlot, pesticide, forestry, buffer strip, conservation practice, and other management or land use scenarios performed at the plot, field, watershed, or regional scale. The application descriptions include a summary of calibration and/or validation results obtained for the different NPP assessments as well as for other APEX simulation studies. Available APEX Geographic Information System–based or Windows-based interfaces are also described, as are forthcoming future improvements and additional research needs for the model.

Environmental benefits and economic costs of manure incorporation on dairy waste application fields.

Model simulations performed representing dairies in a 93000 ha watershed in north central Texas suggest that manure incorporation results in reduced phosphorus (P) losses at relatively small to moderate cost to producers. Simulated manure incorporation with a tandem disk on fields double-cropped with sorghum/winter wheat resulted in up to 33, 45, and 37% reductions in per hectare sediment-bound, soluble, and total P losses in edge-of-field runoff, relative to simulated surface manure applications. The effects of incorporation were evaluated at three different manure application rates. On aggregate across all three manure application rates, significant declines in P losses were obtained with incorporation except for sediment-bound P losses under the N-based manure application rate scenario. We found that the practice of incorporating manure shortly after it has been broadcast on the soil surface could help reduce P losses in such situations where P-based rates alone prove inadequate. The cost the producer incurs when manure is incorporated is on average about 1% of net returns when manure is applied at the N rate and 2-3% when it is applied at alternative P-based rates. In practice the costs could be lower because producers may substitute the manure incorporation operation for a tandem disk operation performed prior to manure application. As more and more dairy producers switch to the use of sorghum and corn silage in dairy rations and consequent on-farm production of these forages, the practice of manure incorporation may help to reduce phosphorus losses resulting from dairy manure applications to fields with these forage crops.

APPLICATION OF APEX FOR FORESTRY

This study was conducted to determine if the Agricultural Policy/Environmental Extender (APEX) model could reasonably replicate the effects of silvicultural practices on streamflow and loading of sediments and nutrients. APEX was modified to enhance factors associated with forestry conditions such as rainfall interception by canopy, litter, subsurface flow, nutrient movement, and routing enrichment ratios. Historical data from the Alto watershed forestry project in east Texas were used to calibrate and test APEX. The historical data included measured flow, sediment losses, and nutrient (NO3-N, organic N, total N, PO4-P, organic P, and total P) losses from nine small (2.6 to 2.7 ha) watersheds, with three replicates of each of the following treatments: (1) clearing, shearing, windrowing, and burning (SHR); (2) clearcutting, roller chopping, and burning (CHP); and (3) undisturbed control watersheds (CON). In addition, the modified APEX model was applied to two of the watersheds to demonstrate its capabilities in simulating an important sediment source (roads) and an effective best management practice (streamside management zones, or SMZs). The simulated and measured storm runoff, peak flow rates, and average annual sediment and nutrient losses were in reasonable agreement. Simulated storm runoff per mm of rainfall increased six times for SHR and five times for CHP watersheds during the first post-treatment year as compared to CON watersheds. Consequently, the sediment concentration increased about 13 times for SHR and doubled for CHP watersheds. The nutrient loading also increased during the first post-treatment year in SHR and CHP watersheds. However, storm runoff and sediment and nutrient losses were reduced during the second post-treatment year due to rapid vegetation growth. Storm runoff, along with sediment and nutrient losses from both SHR and CHP watersheds, approached those of CON watersheds during the fourth and fifth post-season years. In general, the modified APEX performance was reasonable considering that forestry losses are generally one or two orders of magnitude lower than agricultural losses. Further APEX simulations demonstrated that SMZs decreased the average annual runoff and sediment loss, while forest roads along with greater slope increased runoff and sediment loss from forested land.

Effect of brush control on evapotranspiration in the North Concho River watershed using the eddy covariance technique.

This paper reports on a project that was designed to study changes in total water budget with implementation of brush control in two adjacent mesquite-dominated experimental sites, wherein one site received brush control treatment and the other served as an untreated site. The two sites, each consisting of about 80 ha (200 ac), are located within the North Concho River watershed near San Angelo, Texas. Evapotranspiration (ET) from the sites was measured with the eddy covariance technique beginning in April 2005. The field data indicated that the measured ET at the mesquite-treated site was lower than that of the untreated site during the mesquite growing season (May to October). For instance, the largest difference in ET (about 25%) in measured ET between the treated and untreated sites was recorded during the peak mesquite growing season in 2008. The higher ET measured at the untreated site suggests that there is great potential for increasing water yield by eliminating the water uptake by mesquite trees, through a brush control approach in the North Concho River watershed. For example, based on 952 daily ET measurements (from 9:00 a.m. to 6:30 p.m.), the experimental data indicated that during the four-year study, the mesquite-dominated untreated site had a net consumption of over 46 mm (1.8 in) more water than the treated site. In addition, extrapolation of the data set to include all days during the four-year study (1,370 days) indicated that the untreated site had a potential net consumption of about 71 mm (2.8 in) more water compared to the treated site. Truncation of the data set to include measurements obtained during only the months within the mesquite growing season (May to October) indicated that the untreated site had consumed more than 58 mm (2.3 in) more water than the treated site based on 513 daily measurements obtained during the four-year study. Extrapolation of the data set to account for missing values within the growing season (732 days) indicated that water consumption at the untreated site would be expected to potentially exceed that of the treated site by 90 mm (3.5 in) during the growing season months over the four year period.

Simulation of Nutrient Losses from Chicken Litter Applications in East Central Texas with APEX and SWAT

An increase in broiler chicken production has recently occurred in the Brazos-Navasota River Watershed (BNRW) in east central Texas. At present, over 8 million broiler chickens are produced annually in the Duck Creek Watershed (DCW), the most intensive production area of any of the BNRW sub-watersheds. Concern exists regarding the potential degradation of water quality within the BNRW due to nutrient runoff from land-applied broiler litter. Thus a simulation study was initiated to determine the potential impacts of current and alternative litter management practices. The application of Agricultural Policy eXtender (APEX) and the Soil and Water Assessment Tool (SWAT) models to assess water quality impacts for DCW baseline (current) conditions is reported here. The results of two simulation approaches are described: APEX run in combination with SWAT and SWAT without APEX.

Hydrologic and Water Quality Aspects of Using a Compost/Mulch Blend for Erosion Control

Construction projects often expose large amounts of soil to erosive forces of wind and rain. These areas must be stabilized and vegetated before a Notice of Termination can be submitted to regulators. The objectives of this project were to compare the stabilization performance of two types of compost wood mulch blend top dressing (low and high organic matter), a wood based hydromulch, and seeded bare soil and to determine the amount of sediment and nutrients exported from each type of treatment. Ten test plots ( 12.2×2.4  m2 ) were constructed at a quarry in Parker County, Texas and outfitted with runoff capture systems. Runoff quality and quantity was evaluated for 2 years after installation. Sediment discharge was reduced by 98% on the compost/mulch blend plots and about 75% with hydromulch treatment compared to bare plots. Treatments reduced nutrient loads, although runoff concentrations of nitrate and dissolved P from compost treated plots were often higher than from bare soil or hydromulch plots.

Macro-level analysis of CNMPs in the Ohio River Basin

The Comprehensive Economic and Environmental Optimization Tool – Macro Modeling System (CEEOT-MMS) was developed recently by researchers at the Texas Institute for Applied Environmental Research (TIAER) to help evaluate the implementation of agro-environmental policies or practices on large scales. CEEOT-MMS consists of a field-scale environmental model and a farm-level economic simulation model. Recently, CEEOT-MMS was applied to evaluate the impacts of alternative manure nutrient management options when implemented on all animal feeding operations (AFOs) in Texas. The model was also applied to study the impacts of changing herd sizes on the efficacy of various nutrient management practices, as well as the costs and effectiveness of implementing comprehensive nutrient management plans (CNMPs) on AFOs.

Impacts Of Changing Herd Sizes On The Effects Of Manure Application Rates

The Comprehensive Economic and Environmental Optimization Tool - Macro Modeling System (CEEOT-MMS) was developed by researchers at the Texas Institute for Applied Environmental Research (TIAER) to help evaluate the implementation of agro-environmental policies or practices on large scales. Recently, CEEOT-MMS was applied to evaluate the impacts of three alternative manure nutrient management options when implemented on all animal feeding operations (AFOs) in Texas. The three manure nutrient management options were manure application at the nitrogen uptake rate of receiving crops, manure application to supply all of crop phosphorus (P) requirements with manure ortho-P (a High P rate), and manure application to supply all crop P needs with manure total P (a Low P rate).