Location: Water Quality and Ecology Research2009 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 has been assembled for the watershed of Beasley Lake, one of the watersheds selected for concentrated analysis within the Conservation Effects Assessment Program (CEAP). Data are being transferred to the national repository, and data have also been used in validation of the AnnAGNPS model. Monitoring of lake water quality and fish resources and evaluation of runoff from CRP areas and buffer strips continues. 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. Field and laboratory studies were continued on the effects of soil amendments derived from industrial byproducts, (FGD gypsum and ferrihydrite) on soil quality, runoff quality, and crop production. Specifically, 80 plots were amended with five rates of FGD gypsum and planted. Yields were estimated at the end of the growing season. Experimental field plots were set up in preparation for the initial planting of no-till cotton. Integrated soil erosion and sedimentation technologies. Soil and sediment samples were collected and analyzed in support of a sediment source identification study. A supply of soil was prepared for studies on effects of gypsum on infiltration. Watershed management, water availability, ecosystem restoration. Artificial streams have been constructed, but organism survival tests have been postponed due to difficulties in obtaining water supply of adequate quality. The artificial streams are being relocated to a site with better water supply. Fish, water quality and physical data were collected from the Big Sunflower and Coldwater Rivers, which drain the intensively cultivated Mississippi Delta. Data will be used to examine links between water quality and ecological impairment. Coldwater River studies are also targeted at effects of ecological restoration of river backwaters and their use as nonpoint source management measures. Evaluation of ecosystem restoration along a leveed floodway has been initiated. Water quality protection systems. Toxicology studies using an invertebrate, Hyallela azteca, and sediments from river backwaters were completed. The efficacy of using grassed fields versus bare soil for mitigating pesticide contamination of runoff was studied by collecting and analyzing samples of water, sediment and plant tissue. Studies examining use of weirs in vegetated drainage ditches to mitigate runoff contamination continued. Experiments were conducted testing the effects of such weirs on nutrient loads in simulated runoff. Resilience of herbaceous plant species in drainage ditch environments was evaluated, and the relative efficacy of various species in mitigating nutrients and pesticides was measured. An experiment involving an artificial runoff event contaminated with agrichemicals (sediment, nutrients, pesticides) into a managed wetland was completed, and analyses are underway. One part of this effort involves examination of the effects of herbicide pollution on nutrient uptake by algae.
1. Weedy Drainage Ditches Reduce Nonpoint Source Pollution. Phosphorus leaving farm fields in storm runoff can contaminate rivers, lakes, ponds and downstream marine environments. The ability of six aquatic plants commonly found in agricultural drainage ditches to attenuate nutrient concentrations in runoff water was tested. It was found that no plant species was more efficient than the others at decreasing nutrients; however, vegetated systems reduced concentrations of soluble reactive phosphorus more than the unvegetated controls did. This is an important discovery for conservation leaders who are working with landowners in decreasing the amount of nutrients leaving their fields.
2. Native Wetland Plant Turns Drainage Ditches into Phosphorus Magnets. Pollution of rivers, lakes and the ocean by nutrients that are washed from fields is a global problem. Using vegetated drainage ditches is an economical and environmentally sound way to help alleviate this pollution, but little is known regarding which ditch characteristics produce the best results. Nutrient assimilation performances of two common plant species found in drainage ditches, Bacopa monnieri (water hyssop) and Leersia oryzoides (rice cutgrass), were compared in an eight-week greenhouse experiment. Both plants were subjected to a range of flooding regimes. Rice cutgrass was able to immobilize phosphorus more as it was subjected to increased water levels. Water hyssop did not show a similar response. This research provides farmers and conservationists information useful for managing drainage ditches to clean up nutrient-rich agricultural runoff.
3. Vegetated Drainage Ditches Mitigate Insecticide Pollution from Runoff and Spray Drift. Studies have shown that insecticide runoff and spray-drift are important sources of water pollution. Drainage ditches are common agricultural landscape features that previously have been simply viewed as water management tools. Studies were conducted in South Africa and the Mississippi Delta (USA) on both runoff and spray drift events, and on the ability of ditches to remove harmful insecticides. Mathematical models were derived from field data to provide tools for managing ditches to obtain pollution control benefits. This information will provide farmers and conservationists a basis for incorporating this management practice into farm plans.
4. Stream Erosion is as Important as Water Quality to Biological Integrity. Current federal legislation mandates regulation of stream water quality to meet concentration targets referred to as “total maximum daily loads,” ostensibly to safeguard ecological values. The same legislation mandates development of remedial strategies for non-attaining streams. Strategies for agricultural and mixed-cover watersheds usually focus on management of nonpoint source pollution derived from land use. Long-term studies of streams in two Mississippi watersheds showed that many processes responsible for degradation of stream biological resources are tightly linked to channel erosion driven by channelization, but only indirectly reflect land use. The two streams drained watersheds of similar size, soils, and topography, but one was rapidly eroding while the other was stable and flanked by forested floodplain wetlands. The eroding stream was characterized by much flashier hydrology, had significantly worse water quality, and supported only half as many fish species as the stable stream. These results suggest that degradation of physical habitat and perturbation of stream hydrology by channel erosion contribute to a syndrome of ecological degradation. Ecological engineering of stream corridors must focus at least as much energy on mediating hydrologic perturbations as on pollutant loadings.
5. Water Treatment Byproduct Clarifies and Cleans Sediment-polluted Waters. Water bodies impacted by agricultural runoff often experience elevated levels of suspended fine clay sediment and sorbed chemical contaminants. Resulting turbidity has negative aesthetic impacts and limits photosynthesis in aquatic systems. Clarification by gravity settling in natural environments is exceedingly slow or nonexistent. A series of laboratory experiments showed that addition of as little as 10 mg/L of ferrihydrite, a naturally-occurring mineral obtained as a byproduct of water treatment plants, was effective in reducing turbidity for a range of pH conditions, and especially for pH values below 5.77. These findings may be useful in developing strategies to restore aquatic systems degraded by fine sediment pollution.
6. Natural Wetlands May be Managed to Provide Ecological Services. Lowland river corridors, which often support intensive cultivation, also often contain relatively large, numerous floodplain wetlands in the form of sloughs, filled lakes, meander scars and backwaters. These wetlands are known to support processes that trap and process contaminants, but strategies for managing specific sites have rarely been developed. A 25 m x 500 m slough tributary to the Coldwater River in northern Mississippi was modified by constructing a water control weir, and pollution control capacity was tested by routing water dosed with three pesticides into the wetland to simulate a runoff event. Pesticide levels decreased sharply with downstream distance and time, completely disappearing after 56 days. No discharge occurred to the river during the study period. A series of bioassay experiments was run by exposing a common aquatic insect, Hyallela azteca, to water and sediment from the wetland. Tests confirmed above results regarding water concentrations. Significant insect mortality occurred using water collected at the upstream end of the wetland during the first two hours of the test, but not at any time using water from the downstream site. These results may be used to advance the science of managing natural wetlands within agricultural landscapes to control pollution.
7. Lake Sediments Only Slightly Polluted by Current use Pesticides. Contamination of lakes by pesticides and attendant biological impacts are a concern in areas dominated by row-crop agriculture. Surface sediments were collected from three sites in each of five lakes and analyzed for 17 current- and historic-use pesticides. Three of the lakes were in a relatively pristine national wildlife refuge, while the other two were polluted by agricultural runoff. Biological impacts were assessed by exposing a common aquatic insect, Hyallela azteca, to sediments for 28 days. Although some sediment contamination by historic-use pesticide was found at all sites, current use pesticides were detected at only three of the 15 sites. Animal survival was similar in mud from all lakes, but animals grew more slowly in mud from one of the polluted lakes. Survival rates paralleled pesticide concentrations. These findings provide important feedback for scientists developing strategies to control pesticide pollution of aquatic systems.
8. Rice Fields may be Used as Water Treatment Systems. Contamination of surface waters by pesticides is a growing concern, and innovative mitigation strategies are needed. Water amended with diazinon was discharged through two rice paddies post-harvest and simultaneously through non-vegetated control ponds. Bottom sediments collected near rice paddy outflow points had diazinon concentrations that were >77% lower than those near the inflow, while control levels differed <2% between inflow and outflow. These results indicate diversion of pesticide contaminated runoff through post-harvest rice fields holds potential as a low-cost, environmentally efficient mitigation practice and provide a foundation for additional studies.
9. Conservation Tillage Effective in Mississippi Delta. Although conservation tillage has been found to have significant positive effects on soil and water quality, relatively limited information is available concerning the effects of conservation tillage in the Mississippi Delta.Analysis of soils collected from two Mississippi Delta watersheds before and after conservation tillage showed that conservation tillage enhanced soils, with higher organic matter and nutrients such as P, K, Ca, and Mg. These findings may be applied to promote the use of conservation tillage in the Mississippi Delta and similar regions and thereby reduce nonpoint source pollution.
10. Mississippi Delta Stream Nutrient Levels are Low Relative to Mississippi River Basin. Plant nutrients such as nitrogen and phosphorus are entering coastal marine systems from rivers at greatly elevated rates, causing excessive growth of algae and triggering episodes of oxygen depletion when the algae die and decay. Available data regarding the concentrations of nitrogen and phosphorus in streams draining the Yazoo River watershed of Mississippi were compiled and summarized. It was found that the Yazoo River watershed retains most of the nutrients that are input into it, and exported water generally carries lower concentrations of nutrients than the receiving stream, the Mississippi River. However, watershed nutrient concentrations are several times higher than water quality criteria set by the US Environmental Protection Agency for this region. The watershed may be divided into two nearly equally-sized regions, the intensively cultivated Delta, and the mixed land use Hills. Levels of both nutrients tend to be three to four times higher in the Delta than in the Hills. Delta nutrient concentrations peak strongly in spring when agricultural fertilizers are applied and stream flows are highest. Concentrations of nitrogen in Hill streams do not exhibit seasonal patterns, but mean monthly phosphorus levels are correlated with mean monthly discharge. This information is useful to land managers seeking to develop strategies for controlling nutrient pollution at the landscape scale.
Yuan, Y., Locke, M.A., Bingner, R.L. 2008. Annualized Agricultural Non-Point Source Model Application for Mississippi Delta Beasley Lake Watershed Conservation Practices Assessment. Journal of Soil and Water Conservation 63(6): 542-551.