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United States Department of Agriculture

Agricultural Research Service


Location: Cropping Systems and Water Quality Research

2012 Annual Report

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:
Final report for 3622-12130-004-00D, which terminated in February 2012. Considerable progress was achieved during the project, with 33 peer-reviewed manuscripts, 17 conference proceedings, 9 theses, and 2 dissertations published. Major accomplishments over the 5 year project included: 1) Sustaining the Earth’s Watersheds, Agricultural Research Data System was developed to compile, document, and provide access to data from ARS research watersheds. 2) Vegetative buffer strips (VBS) were found to be effective at reducing hydrologic transport of nutrients, herbicides, and veterinary antibiotics (VAs). VBS were shown to enhance degradation of herbicides and VAs in soil by increasing microbial biomass and enzyme activities. Design criteria were also developed showing that buffer effectiveness decreased exponentially with decreasing buffer width. 3) New analytical methods for analysis of herbicides and their metabolites in soils and plants were developed in association with the VBS studies as new and sensitive methods were needed to support that research. Two new analytical methods were developed, one for the analysis of atrazine and its chlorinated metabolites in plants and the other for the analysis of isoxaflutole and its two primary metabolites in soils and plants. Both methods achieved detection limits that were one to two orders of magnitude more sensitive than previously published methods. 4) A model developed from plot-scale data reasonably estimated herbicide concentrations at the field scale (Field 1 nr Centralia, MO), particularly for atrazine. Inclusion of temperature and soil moisture into the plot-scale model significantly improved prediction of metolachlor concentrations at the field scale. The study also confirmed that atrazine and metolachlor losses were higher when the herbicides were not incorporated. 5) A calibrated and validated Agricultural Policy/Environmental eXtender (APEX) model of Field 1 was developed to relate the variability of contaminant transport within the field to spatial crop yield variability. Areas in the field that were vulnerable to herbicide and sediment losses correlated with the areas that had lower crop yields. This was an important result because management of the field to improve profitability could also result in improved water quality. 6) The Soil Water Assessment Tool (SWAT) model was improved to account for bacterial transport and to better simulate saturated conditions and lateral flow. In addition, a SWAT model of the Goodwater Creek Experimental Watershed was parameterized and calibrated using 15 years of flow and water quality data (1992-2006). The model was then scaled up to the major streams of the Salt River basin. 7) Two indices were developed that identify areas within Field 1 vulnerable to atrazine and sediment loss. These indices were developed as possible substitutes to the APEX model. Vulnerable areas identified with the indices strongly correlated to those areas predicted by APEX to have the greatest atrazine and sediment losses within the field. If generalized, this could prove a useful tool to target implementation of best management practices or alternative cropping systems.

4. Accomplishments
1. Contaminant transport in two central Missouri karst recharge areas. Karst hydrology is the most vulnerable groundwater setting for contamination by surface land use activities. A three-year study was conducted by ARS researchers at Columbia, MO, in two karst recharge areas to characterize the flow and contaminant transport of these cave systems prior to significant urbanization. Despite similarities in land use, geology, and weather, the quality of the water in the two cave streams was very different, with the Devils Icebox recharge area having significantly greater concentrations and total loads of nutrients, sediment, and herbicides than the Hunters Cave recharge area. Within the Devils Icebox recharge area, 94% of the row crop areas occurred on high runoff potential soils compared to only 57% for the Hunters Cave recharge area. Previous research has demonstrated that these high runoff potential claypan soils are especially problematic with respect to surface transport of contaminants. Because of these findings, a stakeholder-led watershed plan for the Bonne Femme watershed, which includes the two cave watersheds, was developed with the primary goal of improving water quality by implementing management practices for protection of karst recharge areas.

2. Delineating critical management areas within fields. Identifying the critical management areas within claypan soil fields is essential to maximize grain production and minimize environmental impacts. In this field-scale study conducted by ARS researchers at Columbia, MO, two indices that use readily available soil and landscape data were proposed for identifying field areas most vulnerable to losses of atrazine and sediment. A computer simulation model was used to provide estimates of crop yields and for prediction of sediment and atrazine losses within the field. The index values correlated well with the model simulated sediment and atrazine losses, and also with the lower corn yield areas of the field. Management scenarios were simulated that differentiated the management of the critical areas from the rest of the field. The developed indices were capable of identifying areas of higher environmental risk and lower productivity that could provide objective criteria for effective targeting of best management practices.

3. Streambank erosion in claypan soil watersheds. Stream water contamination by sediment remains a major environmental concern in the United States because soil deposited in streams results in impaired aquatic habitat and sedimentation of lakes and reservoirs. This study, conducted in collaboration with researchers at the University of Missouri, Iowa State University, and ARS at Columbia, MO, was undertaken to compare the streambank erosion rates of streams in the Crooked and Otter Creek watersheds, two claypan watersheds located in northeastern Missouri. Results showed that streambanks accounted for an average of 88% of the annual in-stream sediment and 23% of the total nitrogen exported from these watersheds. Thus, streambanks were the dominant source of sediment in these streams and a significant contributor to nitrogen transport. Improved management of riparian areas to decrease streambank erosion would result in significant water quality improvement in streams of the Central Claypan Areas.

4. Enhancing degradation of atrazine in root zone soils. 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 contamination of surface and ground water by atrazine and its breakdown products, which may be toxic to humans and aquatic life. In an effort to achieve more complete atrazine degradation in soil and prevent off-site transport, ARS researchers at Columbia, MO and University of Missouri researchers investigated the potential of adding a bacterium, Pseudomonas sp. strain ADP, to soils to enhance atrazine degradation. In this research, we tested the ability of a switchgrass rhizosphere (root zone soil) to sustain one of the degrading genes, atrazine-degrading gene (atzA), in soil compared to bulk soil with no plants. The results showed that switchgrass rhizospheres sustained a higher number of degrading genes than the control for about three weeks; the numbers were similar thereafter. In the presence of the degrading bacteria, more than 50% of the atrazine was completely broken down within seven days. The sustained gene numbers and high degradation rates observed indicated that the bacteria would be an effective addition to grass buffers for enhancing the degradation of atrazine and reducing stream and ground water contamination.

Review Publications
Lerch, R.N. 2011. Contaminant transport in two central Missouri karst recharge areas. Journal of Cave and Karst Studies. 73:99-113. DOI: 10.4311/jcks2010es0163.

Lin, C., Thompson, B.M., Hsieh, H., Lerch, R.N. 2011. Introduction of atrazine degrader to enhance rhizodegradation of atrazine. In: Goh, K., Bret, B., Potter, T.L., Gan, J, editors. Pesticide Mitigation Strategies for Surface Water Quality. Washington, DC: American Chemical Society. p. 139-154.

Willett, C.D., Lerch, R.N., Schultz, R.C., Berges, S.A., Peacher, R.D., Isenhart, T.M. 2012. Streambank erosion in two watersheds of the central claypan region. Journal of Soil and Water Conservation Society. 67:249-263.

Mugdal, A., Baffaut, C., Anderson, S.H., Sadler, E.J., Kitchen, N.R., Sudduth, K.A., Lerch, R.N. 2012. Using APEX to develop and validate physically-based indices for the delineation of critical management areas. Journal of Soil and Water Conservation. 67: 284-299.

Last Modified: 2/23/2016
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