Location: Water Quality and Ecology Research2012 Annual Report
1a. Objectives (from AD-416):
Develop and refine conservation technologies for implementation within agricultural watersheds that improve water quality and ecosystem function, contribute to TMDL and nutrient criteria development, and conserve natural resources by (1) evaluating farm and land management systems in Beasley Lake Conservation Effects Assessment Project (CEAP) watershed that are intended to reduce erosion, conserve soil, improve receiving water quality, and protect ecological resources; (2) determining the effectiveness of conservation practices for improving water and soil quality within the Yazoo River Basin to meet Total Maximum Daily Load criteria; (3) developing a database for Beasley Lake CEAP watershed that contains water, soil, ecological, and land management results from research conducted at field, farm, and watershed scales for assessment of conservation practices applicable to the Yazoo River Basin; (4) validating and quantifying uncertainties of model predictions for Beasley Lake CEAP watershed; (5) determining essential abiotic and biotic relationships required to effectively restore streams impaired by physical habitat degradation as defined by Total Maximum Daily Load criteria; and (6) assessing effects of conservation practices on off-site water quality for improved TMDL and nutrient criteria decision-making in agricultural watersheds impaired by non-point source pollution.
1b. Approach (from AD-416):
There is extensive literature on agricultural conservation practices aimed at protecting water quality and ecological integrity. Most of this work, however, is based on small-scale studies, and findings often are not easily scaled up due to complex interactions at the whole-farm, watershed, and landscape scales. Therefore, effects of widespread implementation of conservation measures (i.e. BMPs) have not been demonstrated. Continued work is needed on assessing individual innovative BMPs. Furthermore, realistic ecological restoration experiments require additional work at the prototype scale. To address these issues, natural resource (water, soil, and biological quality) responses to conventional and innovative conservation measures will be studied across a range of scales to provide support for the goals of the Clean Water Act of 1972 (and its amendments) and the Farm Security and Rural Investment Act of 2002. This research will focus on quantifying and assessing impacts associated with conservation practice implementations in an economically efficient manner to reduce nutrient, pesticide, and sediment loadings to the nation's surface waters necessary to produce sustainable ecosystems. This plan calls for a set of complementary experiments dealing with physical, chemical, and ecological processes at a range of scales from the laboratory bench to the watershed.
3. Progress Report:
Effectiveness of conservation practices. A comprehensive data set for the watershed of Beasley Lake, one of the watersheds selected for concentrated analysis within the Conservation Effects Assessment Program (CEAP) continues to be assembled. The data set includes soils, cropping patterns, cultural practices, topography, climate, water quality, and LIDAR. These data are being input on the STEWARDS (Sustaining the Earth's Watersheds: Agricultural Research Data System) data base. Monitoring of lake water quality and fish populations and evaluation of runoff from Conservation Reserve Program and buffer areas continues. Aerial multi-spectral data were acquired in summer 2011 and will be collected again in 2012. Watershed management, water availability, ecosystem restoration. Experiments on the transport of bacteria associated with bottom sediments in artificial streams have been completed. Currently, experiments on effects of suspended sediment concentration on fish growth are underway in the artificial streams. Research on the Big Sunflower and Coldwater Rivers have been published. Chronic hypoxia was found to reduce species diversity in the Big Sunflower River. A manuscript on the evaluation of ecosystem restoration along a leveed floodway (Abiaca Creek, Mississippi) is nearing completion. Two of three sites were identified for research of tailwater recovery systems using storage reservoirs. Studies will aid in understanding impacts of water availability (water quantity) in Mississippi Delta watersheds. Instrumentation is being purchased and prepared for installation. Water quality protection systems. Monitoring and assessing the effects of sediment retention ponds in trapping agrichemicals (sediment, nutrients, pesticides) was initiated in December 2009 and continues. Results were published from study using a managed backwater wetland to attenuate sediment, nutrients, and pesticides in artificial runoff. Several small-scale laboratory and field experiments were conducted to examine nutrient and pesticide uptake effects by various species of aquatic plants. Water quality and ecological monitoring are continuing in three agricultural watersheds in the Mississippi Delta.
1. Drainage ditches tell history of pesticide transport. Drainage ditches surrounding agricultural fields are conduits for storm and irrigation runoff, linking the production landscape to rivers, lakes, and other water bodies. An ARS scientist from Oxford, MS, in collaboration with scientists from Mississippi State University analyzed seasonal sediment and water samples from eight ditches throughout the Lower Mississippi Alluvial Valley. Results demonstrated that pesticide concentrations in sediments were an order of magnitude higher (150-300 ug kg-1) than those in water samples (6-14 ug L-1). Additionally, out of all collected samples, approximately 87% were below detection limits for the 17 current and past-use pesticides examined. This lack of pesticide prevalence highlights the improved conditions in aquatic systems adjacent to agriculture and a potential decrease in toxicity associated with pesticides in the agricultural landscapes in the Lower Mississippi Alluvial Valley.
2. Ecological impacts lessened by managed wetlands. Water quality has been shown to be improved by the use of natural and constructed wetlands, but fewer studies have examined the ecological impacts these systems have on resident biota. Simulated runoff amended with three pesticides (atrazine, S-metolachlor, and permethrin), as well as nitrogen and phosphorus was delivered into the managed wetland. ARS scientists in Oxford, MS, found that sediments and nutrients showed little variation at the outflow (500 m) whereas pesticide concentrations peaked within 48 h, but those concentrations were less than 15% of the peak concentrations at the inflow. Hyalella azteca survival significantly decreased within 48 h of the start of the experiment up to 300 m due to permethrin concentrations. These study results are of interest to regulatory and other action agencies examining effectiveness of constructed wetlands as a conservation practice to improve and sustain receiving river and lake water quality.
3. Aquatic plants in ditches retain nutrients. Hypoxia in the Gulf of Mexico has been a growing concern for decades. Several management practices (constructed wetlands, drainage ditches, riparian zones, etc.) rely on vegetation to help mitigate nutrients from agricultural runoff water. ARS scientists in Oxford, MS, discovered that vegetated systems lowered total nitrogen loads in runoff water by more than 50%, significantly more than systems without vegetation. Two particular aquatic plant species were more effective than others in lowering nitrogen loads in water. These findings demonstrate the importance of vegetation in management practice design for nutrient reduction which will aid in reduction of the Gulf's hypoxic zone.
4. Sediment source identification to target conservation needs. Because pollutants are most often associated with fine sediment sizes eroded from upland fields, identification of sediment sources is important for targeting areas of the watershed that are the greatest contributions of pollutants and may require a change in management systems. ARS scientists in Oxford, MS, developed an accurate index for each soil typed mapped in the Walnut Gulch Experimental Watershed. Suspended sediment collections taken from the mouths of each subwatershed allowed scientists to discover shrub dominated subwatersheds were more highly erodible than those subwatersheds dominated by grasses. This research permits site specific location of best management practices to more fully help protect water quality of the entire watershed.
5. Stream restoration needed on larger scale. Many of the Nation's stream ecosystems are badly degraded, and billions of dollars are spent annually to restore or rehabilitate these systems as required by the Clean Water Act. ARS scientists in Oxford, MS, along with scientists from the University of North Carolina, reviewed existing published literature providing data on the effectiveness of stream restoration projects. It was found that most stream restoration projects focus on relatively short reaches of channel, while watershed land use controls ambient water quality and hydrology which control other functional attributes. This scale of restoration or modification has limited benefits within the broader landscape context. In order to achieve higher standards for actual and measurable physical, chemical, or biological improvement, greater flexibility in location and size may be required.
6. Soil microbes change in altered landscape. Constructed wetlands in agricultural drainage waterways can serve as a best management practice for removal of nutrients and pesticides. ARS scientists from Oxford and Stoneville, MS, documented plant and microbial communities prior to wetland construction and for the following two years. Wetland plants quickly colonized in the new construction area, and the microbial community quickly adapted to the altered hydrology, taking on many of the same characteristics as the reference wetland studied. Within the newly constructed wetland, the abundance of fungi and gram-negative bacteria rapidly decreased, while a noted increase in gram-positive and overall bacteria was observed. These results demonstrate the constructed wetland microbial community had higher overall metabolic activity than either the reference wetland or the adjacent upland area. This demonstrates the ecosystem services function of the constructed wetland.
7. Tillage practices can affect shallow groundwater resources. Success of maintaining good production of corn grown annually on sloping land with a shallow water restrictive layer is based on the assumption that the tillage management can aid in conserving soil and soil moisture and also control weeds. Concerns were expressed that conservation tillage practices, which significantly reduce erosion, might result in contamination of shallow groundwater resources. ARS scientists in Oxford, MS, found that conservation tillage had only minor detrimental effects on the water quality in runoff and shallow groundwater and promoted more soil water for crop use during the growing season than conventional tillage practices. Additionally, no-till practices produced higher corn yields than conventional tillage practices due to soil moisture conservation. Results from this research will provide action agencies and extension personnel with additional guidance for making tillage and pesticide management practices for farmers utilizing sloping land for continuous corn production.
8. Variable water level affects phosphorus retention in wetlands. Excessive nutrients travelling down the Mississippi River are contributing to the Gulf of Mexico hypoxic zone. Natural and constructed wetlands are a suggested conservation practice to help decrease transport of nutrients downstream. ARS scientists in Oxford, MS, along with scientists from Mississippi State University discovered that wetland sediments exposed to longer periods of water inundation decreased the amount of phosphorus released into the water column. Water-extractable (bioavailable) phosphorus concentrations significantly decreased over time at sites with the most inundation. These findings suggest wetlands in the Lower Mississippi River Valley can be managed hydrologically to improve phosphorus retention on site.
9. Weirs in drainage ditches enhance nutrient retention. Nutrients applied to agricultural fields may be washed off due to irrigation or storm events. In conjunction with scientists from Mississippi State University and Arkansas State University, ARS scientists in Oxford, MS, demonstrated nitrate reductions were significantly different between weir and no weir treatments based on ditch residence time. Low-grade weirs increase the travel time for nutrient-rich runoff to reach receiving systems, thereby allowing natural processes to improve water quality. Results from this study will assist watershed planners and other interested parties in devising nutrient reduction strategies for the Gulf of Mexico.
10. Controlled drainage improves water quality. Drainage ditches efficiently move water off the production landscape and into downstream rivers and lakes. Unfortunately, this rapid transport can also result in significant amounts of sediment, nutrients, and pesticides being delivered to the water bodies. An ARS scientist in Oxford, MS, working with colleagues from Arkansas State University and Mississippi State University determined through implementation of controlled drainage structures, the impact of "first flush" effects on rivers and lakes from nutrient runoff could be significantly decreased. These findings are critical to the success of the Mississippi River Healthy Basin Initiative and targeted decreases of the Gulf of Mexico hypoxic zone.
11. Tiered, collaborative strategies needed to help improve Gulf of Mexico. ARS scientists in Oxford, MS, are working with local, state, and federal partners to address the serious water quality issue of hypoxia in the Gulf of Mexico. Successful frameworks for addressing hypoxia must include tiered collaboration starting on the field with the stakeholder (farmer) and travelling all the way through to federal cooperation. Frameworks must cross state boundaries and work toward a common goal. Strategic implementation plans for states draining into the Gulf should be compatible, comparable, and consistent if successful nutrient reduction is to occur.
12. Outside the box thinking for pesticide mitigation. For the last 13 years, ARS scientists in Oxford, MS, have conducted studies utilizing natural vegetation (phytoremediation) in aquatic systems - constructed wetlands, drainage ditches, and now rice fields - to help clean agricultural runoff containing pesticides and excessive nutrients. Efforts have been made to design practices which are environmentally successful, but still economically feasible for the farmer to implement. Vegetated drainage ditches show the most promise in pesticide and nutrient reductions, with relatively little cost to the farmer. The potential for using rice as a phytoremediation "crop" is currently being examined.
13. Lake water quality improves with watershed BMP installation. Beasley Lake Watershed is a 915 hectare intensively-farmed Mississippi Delta watershed. The oxbow lake, Beasley Lake, was sediment impaired resulting in poor sport fishing and degraded water quality. Over the course of 14 years, ARS scientists in Oxford, MS, monitored lake water quality following installation of watershed-wide management practices within-field, at the edge-of-field, as well as enrollment in the Conservation Reserve Program. Reduction of nutrients and solids resulting in improved water quality and sport fisheries have been noted over the evaluation period. Results will provide action agencies and landowners with information to improve and sustain lake and flood plain water quality using conservation practices.Shields Jr., F.D., Knight, S.S. 2011. Significance of riverine hypoxia for fish: The case of the Big Sunflower River, Mississippi. Journal of the American Water Resources Association. 48(1):170-186. DOI:10.1111/j.1752-1688.2011.00606.x