Location: Water Quality and Ecology Research2011 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
A comprehensive data set for the watershed of Beasley Lake, one of the watersheds selected for the Conservation Effects Assessment Program (CEAP), was developed, used for validation of the AnnAGNPS watershed model, and has been transferred to the national repository. Changes in the lake water quality and fish associated with land use changes have been analyzed and documented, and evaluation of runoff from Conservation Reserve Program (CRP) areas and buffer strips completed. At other sites, cotton and corn production areas were monitored to determine effects of tillage and residue management, and edge-of-field best management practices on soil herbicide concentrations and runoff quality were evaluated. Field and laboratory studies were completed on the effects of soil amendments (ferrihydrite and gypsum) on soil quality and crop production. Two sets of artificial streams were established at the University of Mississippi Biological Field Station, and experimentation initiated. Fish, water quality, and physical data were collected from two major rivers which drain the intensively cultivated Mississippi Delta for multiple years. Data analysis revealed links between water quality and ecological impairments. At sites adjacent to Coldwater River study reaches, water quality and ecological data were collected from degraded and restored backwaters for six years. Data collection for evaluation of ecosystem restoration along a leveed floodway (Abiaca Creek, Mississippi) was also completed. Studies were initiated to ascertain nutrient limitation in low-gradient bayou systems in the Mississippi Delta. A project was initiated to monitor the efficacy of sediment retention ponds in trapping agrichemicals. Influent and effluent nonpoint source pollutant loads were computed for a natural wetland managed to provide runoff treatment. This managed wetland was also used for an experiment involving measurement of the attenuation of pollution from three artificial runoff events contaminated with agrichemicals. One part of this effort involved examination of the effects of herbicide pollution on algal nutrient uptake. Studies of constructed wetlands in mitigating nutrients and pesticides in various combinations were completed. Experiments were conducted to examine pesticide and nutrient uptake by various species of aquatic plants. Field trials on the performance of vegetation and small weirs in agricultural drainage ditches in mitigating pesticide and nutrient flux were conducted. The efficacy of using rice fields for mitigating pesticides was studied. Sites were selected and instrumented for a long-term study of water quality and aquatic ecology in three agricultural watersheds in the Mississippi Delta. Bioassay toxicology studies of sediments from river backwaters were completed. The efficacy of using conservation tillage and cover crops for mitigating nutrients in runoff was studied. Resilience of herbaceous plant species in drainage ditch environments was evaluated.
1. Management practices restored lake water quality. Billions are spent annually on best management practices (BMPs) to control water quality impacts of crop production, but benefits are rarely quantified. ARS scientists in Oxford, MS, measured long-term improvements in the quality of a natural lake receiving runoff from a heavily cultivated watershed after BMP implementation. During the last 15 years, BMPs were installed within crop fields and at field edges throughout the 915 ha watershed, including 113 ha enrolled into Conservation Reserve Program (CRP) and planted to trees. Over a 14-year period, sediment and nutrient levels (except for dissolved phosphorus) decreased annually, and algae populations and water clarity increased. Improvements were most pronounced in spring. These findings provide scientific basis for future investments in conservation programs supporting land retirement and BMP establishment.
2. Rice fields may be managed to provide additional benefits. Runoff or irrigation return flows from agricultural lands often contain harmful concentrations of pesticides. ARS researchers in Oxford, MS, showed that aqueous diazinon and atrazine concentrations decreased about 80% in water passing through a rice field. Based on current ecological economic values for water quality improvement, it was determined that the water treatment value of the rice was almost triple that of the actual market value of rice if it had been harvested as a typical crop (based on current commodity prices). Such valuation of ecosystem services is necessary to stimulate implementation of sustainable practices.
3. Soil phosphorus saturation due to heavy fertilization accelerates pollution. Farmers can use fertilizers containing phosphorus to boost yields, but elevated phosphorus levels in streams and lakes are detrimental to water quality. Links between the amount of fertilizer applied to a watershed and the amount of phosphorus subsequently lost from the land (“loads”) are poorly understood. ARS scientists from Oxford, MS, working with colleagues from the U.S. Environmental Protection Agency and the USDA-Natural Resources Conservation Service (NRCS), used AnnAGNPS model computer simulations of an Ohio watershed to quantify the extent to which long-term high fertilization rates accentuate phosphorus loads leaving the watershed. This dramatic change in load indicates that a “critical point” in soil phosphorus levels may exist beyond which phosphorus load increases dramatically. This finding is directly applicable by agencies and land managers implementing plans that include nutrient management practices and guidelines for agricultural watersheds.
4. Ditches retain and process pesticides. Agricultural drainage ditches are important components of water management infrastructure, but little is known about the persistence of pesticides in ditch waters. ARS researchers in Oxford, MS, working with scientists from Mississippi State University measured the presence of current and past-use pesticides in water and sediment in agricultural ditches across multiple seasons in four states along the Lower Mississippi River. They found that 87% of the samples were free from detectable levels of pesticides, although historic-use organochlorine pesticides (e.g., DDT) were still present at detectable concentrations in about 20% of the sediment samples. These findings demonstrate the potential for drainage ditch management to provide significant pollution control benefits by trapping and processing pesticides.
5. Increasing biofuel production increases pollution. Ethanol from corn (a type of biofuel) has been shown to be a useful alternative to some fossil fuel applications. Increasing biofuel production would require more corn production. ARS scientists from Oxford, MS, in collaboration with colleagues from the U.S. Environmental Protection Agency used the computer model AnnAGNPS to study environmental effects of increasing corn production in an Illinois watershed. They found that as corn production increased, total nitrogen losses increased 200 percent if all corn/soybean rotations were converted to continuous corn. This pilot study provides an important foundation for a regional modeling effort that will allow large-scale policy assessments.
6. Aquatic vegetation cleans up pollution. Wetlands may be used to trap and process pollutants in agricultural runoff, but little is known about the optimal types of aquatic vegetation for such remediation. ARS scientists in Oxford, MS, examined two species of aquatic plants, singly and in combination, and found that vegetated wetlands with both vegetated conditions were highly efficient in removing nitrogen and pesticide (permethrin) concentrations from wetland surface water. Although differences in efficiencies between the two aquatic plant species were observed, plant biomass appeared to be the most important factor influencing pollutant removal efficiencies. These findings are directly applicable for developing guidelines for designing and managing wetlands to control nonpoint source agricultural pollution.
7. Ecological significance of low oxygen concentrations in rivers. Rivers and streams in intensively cultivated, low-relief watersheds often experience periods when dissolved oxygen concentrations fall below minimum levels set by state regulators. Ecological literature contains varied information about the effects of such conditions on fish. ARS researchers in Oxford, MS, showed that fish communities in the Big Sunflower River, Mississippi, were sensitive to dissolved oxygen levels, with several species disappearing from collections obtained when oxygen levels were low. These results contribute to ongoing deliberations regarding requirements for modification of farming activities to improve stream water quality conditions in agricultural landscapes.
8. Impact of agricultural pollutant mixtures on algae. Nutrients and herbicides often simultaneously enter lakes and streams through agricultural runoff, but it is not clear how mixtures of plant growth stimulators and inhibitors alter algal growth in receiving waters. ARS researchers in Oxford, MS, used a new infrared microspectroscopy technique to assess the physiological response of individual algae from natural communities following exposure to atrazine and nutrient mixtures. They found that algal community response will depend on its composition, as each species studied had unique reactions. For example, nutrients inhibited the negative impact of atrazine in some species, while atrazine and nutrients both stimulated growth in others. This study developed an analytical method to bridge the gap between laboratory toxicity tests and field observations of algae, and can be used to develop predictions of how agricultural pollutants will alter aquatic microbial communities.
9. Traditional channelization produces deleterious effects. Historically, river channel management in agricultural valleys has included channel straightening and enlargement to alleviate flooding, but these measures frequently cause accelerated erosion upstream and sediment deposition downstream. Watersheds disturbed by channelization are difficult to stabilize, and creative approaches are needed that consider ecological effects and sediment transport considerations. ARS researchers in Oxford, MS, showed that a traditional $1.1 million 2003 rechannelization project on the Yalobusha River in northern Mississippi triggered channel instability during the last days of its construction and ultimately provided no flood control benefits. This analysis provides an instructive example for planners and designers of future river management projects.
10. Wetlands may be managed to trap phosphorus. Runoff and streams draining agricultural areas often have elevated phosphorus concentrations that trigger algal blooms and water quality degradation downstream. ARS researchers in Oxford, MS, found that the concentration of bioavailable phosphorus in the wetland bottom sediments decreased in portions of the wetland that were consistently underwater as opposed to sites that were subjected to cycles of wetting and drying. These findings suggest that managing wetlands to maintain flooded conditions can decrease the bioavailability of phosphorus in wetland sediments receiving agricultural runoff. These results contribute to science needed to manage natural wetlands receiving agricultural runoff to retain phosphorus and reduce downstream impacts.
11. Nitrogen levels often control algal accumulation in streams. Excessive nutrient concentrations in runoff from agricultural lands can stimulate runaway growth of algae in downstream channels, lakes, and wetlands, and may lead to depressed dissolved oxygen levels, which are harmful to fish and other animals. ARS researchers in Oxford, MS, showed that algal biomass and productivity at a majority of studied sites in the Mississippi Delta could be controlled by decreasing the input of nitrogen. Algal response to nutrients varied based on the type of habitat-channel, wetland or lake. These findings may be applied to tailor nutrient control strategies to a given landscape to maximize water quality benefits with available resources.
12. Long term study links lake water pesticide levels to land management. Pesticides applied to crops may pose a hazard to the ecology of adjacent water bodies, but links between conservation and cropping practices and risk are poorly understood. ARS researchers in Oxford, MS, studied an oxbow lake receiving runoff from fields in the Mississippi Delta for ten years. Over the ten-year study period, risk (computed using measured lake water concentrations of 13 pesticides) to lake aquatic animals and algae was greatest when fields were primarily in conventional tillage cotton and was reduced by transferring lands from cotton production to either reduced tillage soybeans or cottonwood trees (under the Conservation Reserve Program). Placing fields in conventional-till milo and corn for one year resulted in intermediate risk levels. These results are of interest to regulatory agencies and the pesticide industry by providing a basis for quantifying benefits of conservation practices.
13. Compensatory mitigation policies for streams reviewed. 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. However, little is known about the return on these investments. An ARS researcher in Oxford, MS, working with a colleague at the University of North Carolina, found that most stream restoration projects focus on relatively short reaches of channel, but conditions occurring over larger spatial domains seem to govern most ecological attributes. Therefore, benefits due to most restoration projects are not detectible. Based on these findings, they provided specific recommendations for modifications of existing policy on compensatory stream mitigation such as inclusion of measurable performance standards and greater flexibility in the size and location of mitigation projects. These results are directly applicable to concerned citizens, legislators and conservation agencies charged with developing and implementing mitigation policies.
Cullum, R.F., Locke, M.A., Knight, S.S. 2010. Effects of conservation reserve program on runoff and lake water quality in an oxbow lake watershed. Journal International Environmental Application and Science. 5:318-328.