1a. Objectives (from AD-416)
The Natural Resources Conservation Service (NRCS) and the Agricultural Research Service (ARS) have agreed to work together, as part of the national Conservation Effects Assessment Project (CEAP) initiative to quantify the environmental benefits of conservation practices at the watershed scale. The project plan detailed in this document represents one of 12 ARS CEAP watersheds established under the national CEAP initiative to address conservation and environmental research issues. Objectives of the project are to: 1) develop and implement a data system to organize, document, manipulate, and compile water, soil, management, and socio-economic data for assessment of conservation practices at field, farm, and watershed scales for the Mark Twain Lake watershed; 2) measure and quantify water quality, water quantity, and soil quality effects of conservation practices at the field, farm, and sub-watershed scale for the Mark Twain Lake; and 3) validate models, quantify uncertainties in model output, and conduct analyses with hydrologic models at field, farm, and watershed scales, and develop methodologies and decision support tools for application on watersheds within the Mark Twain Lake watershed.
1b. Approach (from AD-416)
This research will focus on developing tools and techniques to quantify the impact of implementing conservation practices within a watershed in the most economically efficient manner to achieve sustainable and targeted reductions of nutrients, sediment, herbicide, and pathogen loadings to the Salt River/Mark Twain Lake basin. The research encompasses the following approaches: 1) participation in the development of the STEWARDS database; 2) conduct water quality monitoring to characterize the hydrologic balance and nutrient/chemical loading to Mark Twain Lake; 3) conduct studies at field and plot scales to determine the effectiveness of various conservation practices and cropping systems to reduce nutrient, sediment, and herbicide transport; 4) develop a real-time PCR (RT-RCR) method for quantitation of pathogenic water-borne bacterial species; 5) use the SWAT model to evaluate conservation practices and conservation systems abilities to reduce nutrient, sediment, pesticide, and pathogen loadings in agricultural watersheds; and 6) apply the SWAT model to improve surface water quality assessment and planning.
3. Progress Report
In 2011, only seven of the original 13 sites in the Salt River monitoring network were installed. The sites were chosen on the basis of whether or not they supported on-going ARS research and a new NRCS Mississippi River Basin Initiative project within Goodwater Creek Experimental Watershed (GCEW). In addition, three new sites were established in southeastern Missouri within the Little River Drainage District to begin assessing nutrient and sediment transport in this intensive agricultural area. Over the last year, the Cropping Systems Water Quality Research Unit water quality lab received 1,078 samples for nutrient, herbicide, and sediment analyses. Conservation Effects Assessment Project (CEAP) activities in 2011 included completion of three full years of seasonal data collection for a streambank erosion project at 34 sites located in Crooked and Otter Creek watersheds (both watersheds are located within the Salt River Basin). Another of our CEAP-related activity involves identification of vulnerable areas within fields and watersheds that should be targeted for conservation practices. One such effort focused on identifying the vulnerable areas within our 30 research plots at Centralia using indices developed for claypan soils. The vulnerable areas identified by the claypan indices were then used to create two targeted switchgrass cropping systems in which 25% of the plots were planted to switchgrass and the remainder of the area is to be used for grain production. Assessing the water quality impacts of these new cropping systems was included in the current draft of our new NP211 project plan. The first phase of field studies to evaluate the impacts of vegetative buffer strips on reducing the transport of herbicides and veterinary antibiotics has been completed, with some lab analyses still pending. Preliminary results from the first two years have been published as well as related growth chamber studies demonstrating the ability of grasses and poplar trees to enhance contaminant degradation in the rhizosphere. Calibration and validation of the Soil and Water Assessment Tool model for GCEW has been completed for flow, sediment, and dissolved nutrients. The effects of management practices in the watershed have been analyzed, and up-scaling of the models to larger watersheds are near completion. The Precision Agriculture System work at the Centralia Field 1 site continued under this project, with nearly 7 years of field data collected. Lastly, a two-part series of papers were published documenting 15 years of herbicide data from GCEW. The papers led to the development of an index that accounts for the annual variation in atrazine loads and, showed that changes in herbicide usage and 2nd quarter stream flow had the greatest effect on trends in concentration and annual mass transport.
1. Herbicide transport trends in Goodwater Creek experimental watershed. Farmers in the Midwestern United States continue to rely on soil-applied herbicides for row-crop weed control, and herbicide contamination of surface waters, especially in runoff-prone watersheds, remains an environmental problem. ARS scientists at Columbia, Missouri analyzed 15-year (1992 to 2006) trends in five common herbicides in Goodwater Creek Experimental Watershed (GCEW). The scientists also developed a simple index that explained annual variation in herbicide transport from planting progress, runoff events, and soil dissipation rate. Trends were apparent only for those herbicides that had phased in or out of use (metolachlor, alachlor, and acetochlor). No trends were discernable for atrazine and metribuzin, despite substantial education and extension efforts in the region, especially for atrazine management. This work, combined with previously published ARS research on the vulnerability of restrictive layer soils to herbicide transport, has gained widespread recognition among other federal agencies (Environmental Protection Agency and United States Geological Survey) and atrazine registrants as critical to understanding the spatial variation in atrazine contamination across the Corn Belt. Specifically, both agencies have expressed interest in the index, the Environmental Protection Agency has used the atrazine data during re-registration, and the United States Geological Survey has acknowledged the importance of restrictive soil layers in their new Watershed Regressions for Pesticides (WARP) model for the corn belt (WARP-CB), instead of applying the national WARP model in the region.
2. Vegetative buffer strips reduce transport of organic contaminants in surface runoff. The effectiveness of vegetative buffer strips (VBS) for reducing the hydrologic transport of herbicides and veterinary antibiotics (VAs) requires a combination of altered surface hydrology to initially trap contaminants followed by enhanced soil degradation. Two separate, but related, studies were conducted by ARS scientists in Columbia, Missouri, and University of Missouri researchers. One study investigated the effectiveness of different grass species for reducing the transport of herbicides and VAs in surface runoff and the other investigated the ability of several grass species to promote the breakdown of atrazine in soil. The results showed that all VBS significantly reduced the transport of herbicides and VAs in surface runoff, with native grasses (i.e., Eastern gamagrass and switchgrass) most effective for reducing herbicide transport and tall fescue most effective at reducing VA transport. Relationships developed to relate buffer size and pollutant transport provide needed design criteria for effective implementation of VBS. In the second study, all grasses tested showed significant increases in atrazine breakdown compared to soil without plants, with eastern gammagrass, smooth bromegrass, and switchgrass showing the greatest ability to enhance soil breakdown of atrazine. Overall, these studies demonstrated that VBS are an effective conservation practice for reducing the off-site movement of herbicides and VAs. Land management agencies (e.g., USDA- Natural Resources Conservation Service and State conservation agencies) and landowners can use this research to implement VBS designs that will effectively protect water resources from non-point source pollution.
3. Novel application of the pathogen module in Soil and Water Assessment Tool (SWAT). In 2001, a pathogen module was inserted in SWAT, a computer simulation program that simulates the movement of water and pollutants in agricultural watersheds. An ARS scientist in Columbia, Missouri collaborated with scientists from the French Institute for the Exploration of the Sea (IFREMER) to use the SWAT model to simulate pathogen transport in a coastal watershed and estimate the impacts of contamination on shellfish production by linking SWAT to a hydrodynamic model of the coastal waters. The results confirmed that direct bacteria inputs into streams had a major impact on the model results, in part because of the bacteria sampling protocol that over-characterizes dry weather conditions. The research indicates the need for stream sampling procedures during wet weather. This application expands the range of application of SWAT and shows that alternative agricultural practices can reduce the risk of shellfish contamination.
4. Characterization of performance measures for agricultural pollution control. Current soil and water conservation programs consist primarily of compensating farmers for implementing pre-defined best management practices without considering their site specific cost-effectiveness. An alternative approach, performance-based incentives, consists in payments attached to a specified environmental performance, for example reduction in nutrient loss from a field or reduction in stream loading at the mouth of a watershed. The performance evaluation requires the definition of a performance measure used to calculate the payments. In order to enable rational comparison of this approach with conventional approaches, an ARS scientist from Columbia, Missouri, collaborated with scientists from different institutions to characterize performance measures adopted or considered by watershed stakeholders in several states and identify the issues related to the selection of a measure: scale at which the performance is measured, modeling versus monitoring, and feedback to the farmer. Performance measures can then be integrated in decision support tools for implementing practices where they are most cost effective. Watershed managers, policy makers, and extension agents can consider this information to make informed choices among proposed approaches toward improving water quality in streams affected by agricultural nonpoint source pollution.
5. Method for quantifying catabolic atrazine gene in soil. The corn herbicide atrazine has been widely used for weed control in U.S. corn production for decades, but public health and ecological concerns have been raised because of atrazine contamination of surface and ground water. Bioremediation is a strategy for cleaning up contaminated soils using micro-organisms, fungi, green plants or their enzymes. One strategy for degrading atrazine in soils has been the introduction of a known atrazine degrading bacteria. To track the activity and persistence of the added bacteria over time required new methodology aimed at quantifying the gene responsible for the initial breakdown of atrazine. Two DNA-based methods were investigated by ARS scientists in Columbia, Missouri and University of Missouri researchers, and one of them possessed the needed sensitivity to quantify this atrazine-degrading gene (atzA) in soils. This research provided the needed methodology for assessing the viability of the bacteria as a potential bioremediation strategy for decreasing contamination of water resources by this commonly used herbicide.
6. Delineating drainage areas for two Missouri show caves. Cave systems serve as habitat for unique and endangered species, and the groundwater quality in caves is especially vulnerable to contamination from surface land use activities. Onondaga Cave and Cathedral Cave are two large cave systems with active streams located along the Meramec River in the Ozarks region of Missouri. However, the sources of water to these caves, and the land use activities that may impact their water quality, were previously unknown. In this research, ARS researchers in Columbia, Missouri and Onondaga Cave State Park personnel used non-toxic dyes to trace the flow of water from the surface to the caves in order to determine the size of the drainage areas to the caves. The results showed that the drainage areas were approximately 9.3 square miles for Onondaga Cave and 3.5 square miles for Cathedral Cave; forest and grazed pasture are currently the most common land uses in both of these recharge areas. The knowledge gained from this research was incorporated into the cave management plans developed by Park personnel and will guide future land acquisitions and allow for educational programs and materials to be targeted to landowners within the recharge areas. The public can directly learn about this research as the supporting publication is available at the park and used by park staff to educate the public during guided tours of the caves.
7. Soil hydraulic properties are affected by long term management of the land. Soil maps available in the US describe the spatial range of the main soil series and associated databases give values for the properties of these soils without consideration of long term management. Soil samples in cooperation with the University of Missouri, ARS scientists from Columbia, Missouri obtained from two fields in Boone County, Missouri, with the same soil but extremely different long-term management. One field has been under continuous row crop cultivation for over 100 years while the other one is a native prairie that has never been tilled. Results showed that the soil from the row crop field was significantly more compact, less permeable and holding less water than the prairie soil. The research provided upper and lower boundaries of the soil hydraulic characteristics for this soil to be used in computer simulation models and improve the accuracy of their results.
8. Determination of the needed soil sample size to quantify redoxymorphic features. Soil redoximorphic features (SRF) are patches of different color soil material formed by the oxidation and reduction of iron and/or manganese during saturated conditions and provide information about past and present soil moisture regimes. Current methods to quantify these features require a lot of experience and the results are affected by external factors such as lighting. This accomplishment follows last year’s development of a method based on photographic images of soil samples for the objective quantification of SRF. To fully standardize the method, guidance was necessary relative to the minimum soil core needed so that measurements are independent of the sample size and account for spatial variations. Results of studies by ARS scientists in Columbia, Missouri, in cooperation with the University of Missouri, showed that, in claypan soils, soil cores 2” in diameter were necessary to accurately quantify the most useful features for soil delineation and wetland delineation in Northeastern Missouri. However, quantification of all features would require cores larger than 3” in diameter. The results indicated that this method could provide an objective assessment of SRFs but further study is required to determine the allowable uncertainty and corresponding core diameter.
9. Adsorption mechanisms of isoxaflutole degradates to iron and aluminum oxides. The herbicide, Balance, is a relatively new product marketed as a substitute for the most commonly used corn herbicide, atrazine. Recent studies by ARS scientist in Columbia, Missouri and the University of Missouri have shown that two of the Balance break down products, or degradates, were readily transported to shallow groundwater and based on their chemical properties are also likely to contaminant streams. One of the key mechanisms responsible for reducing the hydrologic transport of herbicides is their ability to bind to soil, a process referred to as sorption. The key objective of this study was to determine if iron and aluminum oxides can sorb the Balance degradates, diketonitrile (DKN) and benzoic acid (BA). Results showed that iron and aluminum oxides significantly sorbed both degradates, with slightly greater sorption to the iron oxides. Thus, metal oxides can help to reduce the transport of DKN and BA in acidic soils enriched with metal oxides, such as those common to the southern US. Land management agencies and growers can use this information to guide choices regarding the use of Balance to minimize its contamination of streams and shallow ground water.
Lerch, R.N., Sadler, E.J., Sudduth, K.A., Baffaut, C., Kitchen, N.R. 2010. Herbicide transport in Goodwater Creek experimental watershed: I. long-term research on atrazine. Journal of the American Water Resources Association. 47(2):209-223.