Location: Water Quality and Ecology Research2010 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) has been transferred to the national repository. Changes in lake water quality and fish resources relevant to land use changes have been analyzed and documented, and evaluation of runoff from Conservation Reserve Program (CRP) areas and buffer strips continues. Field and laboratory studies were continued for the third year on the effects of soil amendment with industrial byproduct gypsum on crop yields and soil properties using soybean and cotton under different tillage systems. Soil water probes have been installed for the purpose of monitoring water contents during the growing season. Soil cores collected to a depth of five feet are being characterized for a range of physical and chemical properties. Watershed management, water availability, ecosystem restoration. Artificial streams were relocated to the University of Mississippi Biological Field Station in order to obtain water supply of acceptable quality, and additional recirculating streams were also installed and tested. Fish, water quality and physical data were collected from the Big Sunflower and Coldwater Rivers, which drain the intensively cultivated Mississippi Delta, concluding three and six years of study, respectively. Data analysis is targeted at finding links between water quality and ecological impairment. At sites adjacent to Coldwater River study reaches, a sixth and final year of data collection at degraded and restored backwaters is being completed. Evaluation of ecosystem restoration along a leveed floodway (Abiaca Creek, Mississippi) is continuing. 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. Influent and effluent nonpoint source pollutant loads were computed for one degraded backwater now being managed as a treatment wetland. This managed wetland was also used for an experiment involving measurement of the attenuation of pollution from an artificial runoff event contaminated with agrichemicals (sediment, nutrients, pesticides). At another site, studies of vegetated constructed wetlands in mitigating agrichemicals such as nutrients and pesticides in various combinations were completed. Several small-scale laboratory and field experiments were conducted to examine nutrient uptake effects by various species of aquatic plants. Field trials on the performance of small concrete weirs in mitigating nutrient flux from agricultural drainage ditches were conducted. Collaborative efforts have also taken place to incorporate stream metabolism studies with current research activities. Sites were selected for a long-term study of water quality and aquatic ecology in three agricultural watersheds in the Mississippi Delta based on analyses of watershed soils, land use, topography and hydrologic features.
1. Effects of Farmland Conversion to Forest Measured. The federal Conservation Reserve Program (CRP) has resulted in billions of dollars invested in removing cultivated lands from production for conservation purposes, but environmental effects have rarely been quantified. ARS scientists in Oxford, MS, showed that conversion of 280 ha of cropped land to trees in the Mississippi Delta reduced the concentration of sediments and nutrient loads in runoff by an order of magnitude relative to adjacent sites with similar topography and soils that were under reduced tillage crop production. Associated positive impacts on the water quality of the receiving water body, Beasley Lake, have also been measured. These findings support future federal investment in the CRP.
2. Ditches Used to Remove Pesticides From Irrigation Runoff. Irrigation and storm water runoff from agricultural fields can contain pesticides, which can damage rivers, lakes and streams. An ARS scientist at Oxford, MS, working with colleagues at the United States Environmental Protection Agency, the University of California-Davis, and the USDA-Natural Resource and Conservation Service conducted field trials and bioassays to examine the reduction of pesticide levels in irrigation runoff from California alfalfa and tomato fields when the runoff was routed through vegetated drainage ditches. In alfalfa field runoff, chlorpyrifos concentration was decreased by 20% from the inflow to the ditch outflow. In the case of tomato field runoff, permethrin concentration was decreased by 67% and there was a 35% reduction in suspended sediment concentration from inflow to the ditch outflow. However, ditch outflows were still toxic to test animals. This research is directly useful to producers required to mitigate pesticide concentrations in runoff.
3. New Device Developed to Study Degradation of Pesticides by Naturally-occurring Bacteria. Bacteria have been shown to play a valuable role in degrading pesticides in the environment, but little work has been done with bacteria present in sediment and plants commonly found in vegetated agricultural drainage ditches. Laboratory studies of bacterial action require small chambers (bioreactors) that can be modified to fit closely mimic the ditch environment. ARS scientists in Oxford, MS, along with collaborators at the University of Mississippi developed a single-stage gradostat reactor and used it to study the action of bacteria found in the root zone of wetland plants on the pesticide, lambda-cyhalothrin. This new tool will greatly enhance the study of processes responsible for pesticide processing in drainage ditches and other edge-of-field environments.
4. Aquatic Plants in Drainage Ditches Retain Pesticides. Pesticides applied to agricultural fields may be washed off due to irrigation or storm events. In conjunction with scientists from Mississippi State University, ARS scientists in Oxford, MS, demonstrated that retention of pesticides used in rice production could be increased by managing the plants and residence time in wet and dry experimental basins (mesocosms). This study used vegetated and non-vegetated mesocosms to simulate retention of fipronil by ditches in initially dewatered (dry) and impounded (inundated) conditions. The vegetated mesocosms significantly reduced loads and concentrations of fipronil, fipronil sulfone and sulfide in both inundated and dry hydrological conditions. The inundated condition reduced greater than 50% of influent fipronil concentrations and between 60-70% of fipronil loads, significantly higher than the dry condition (10-32% concentration and load). Results suggest that ditch and wetland management strategies that increase chemical or water residence time as well as maintain a diverse vegetation assemblage will significantly improve pesticide retention and protect downstream aquatic ecosystems.
5. Weirs in Drainage Ditches Enhance Pollution Control. Agricultural water pollution control by drainage ditches is directly related to water residence time in ditches, but these channels must also provide water drainage. ARS scientists in Oxford, MS, working with scientists from Mississippi State University and Arkansas State University showed that low concrete weirs could be used to manage ditches for improved hydraulic residence time with minimal impacts on water drainage. Results showed that ditches with weirs reduced higher amounts of dissolved inorganic phosphate (71% vs. 66%), total inorganic phosphate (60% vs. 12%), nitrate-N (96% vs. 76%) and ammonium (-47% vs. -53%) than ditches without weirs. These results provide a foundation for future research on ditch weir design and maintenance.
6. Energy Industry Byproduct an Effective Alternative to Agricultural Lime. The success of conservation tillage management systems imposed on highly erodible soils is, in large part, dependent upon the application of lime and fertilizer amendments. However, lime effects in no-till systems can be less than adequate due to its slow solubility. ARS researchers in Oxford, MS, found that fluidized gas desulfurization (FGD) gypsum, a byproduct of coalfired power plants, was an attractive alternative to lime for no-till cotton on a highly erodible loess soil due to its high calcium and sulfur contents, and its much greater solubility than lime. Results indicated that FGD gypsum can potentially increase yields of no-till cotton by improving soil water conditions and providing a readily available source of sulfur, a limiting nutrient in many cotton soils. These findings could improve productivity of no-till cotton in the Mid South region.
7. Energy Industry Byproduct Found to be a Valuable Soil Amendment. Soils with high sodium contents (sodic soils) occur extensively in the lower Mississippi River Valley states of Arkansas, Louisiana, Mississippi, and Tennessee where they create management problems due to their high erodibility and dispersive nature, and salt toxicities that restrict plant growth. Such soils may be remediated with high calcium content material, such as mined gypsum, but this is too costly to use on large acreages. ARS scientists in Oxford, MS, showed that fluidized gas desulfurized (FGD) gypsum produced by coal-fired power plants was at least as effective as mined gypsum for sodium-affected, dispersive soils. The data show that the addition of FGD gypsum, at rates as low as 1.5 tons/acre, produced statistically significant improvements in infiltration rates and lower runoff and soil loss rates. These findings could lead to beneficial use of FGD gypsum for economical soil remediation resulting in reductions in offsite water quality impacts.
8. New Soil Amendment not Harmful to Aquatic Ecosystems. Fluidized gas desulfurization (FGD) gypsum is a popular agricultural soil amendment, but its soluble components may be transferred with agricultural runoff into receiving waters. Effects on biota are unknown. ARS scientists in Oxford, MS, working with scientists at Arkansas State University showed that even elevated concentrations of FGD gypsum were not toxic to four common freshwater aquatic invertebrates. These findings may accelerate the use of FGD gypsum for increasing profitability of production on certain problem soils.
9. Effects of Agricultural Runoff on Rice. Pesticide runoff from agricultural fields can damage rivers, lakes and streams. A newly suggested management practice is to divert agricultural runoff into rice fields before releasing water into rivers and lakes, but the effects of pollutants in the runoff on the rice are not well known. ARS scientists in Oxford, MS, showed that rice germination was not affected by pesticide exposure, but shoot growth decreased in response to metolachlor/atrazine mixture, diazinon, and lambda-cyhalothrin exposure. These results will help scientists determine if diversion through rice fields is a plausible future management option.
10. Natural Wetlands May be Used as Water Pollution Controls. Sediments and pesticides leaving croplands in runoff degrade downstream aquatic resources and have been linked to the expansion of hypoxic zones in the Gulf of Mexico and elsewhere. ARS researchers in Oxford, MS, demonstrated that natural riverine wetlands may be managed to yield improved trapping and retention of nonpoint source pollutants. An existing 1-ha wetland receiving runoff from 350 ha of cultivated land was modified by the construction of water control structures. The wetland cell retained about 18% of input suspended sediment, 24% of phosphorus, and 29% of nitrogen inputs. Results will be helpful to those developing criteria for design of management systems for natural wetlands in the agricultural landscape, allowing another option for reducing effluent nutrient loads.
11. Riverine Backwater Ecosystem Restored. Ponds, lakes, and wetlands on floodplains next to rivers are an important component of riverine ecosystems, but are becoming increasingly rare in agricultural landscapes due to sedimentation and flood control activities. ARS scientists in Oxford, MS, restored a floodplain backwater along the Coldwater River in northern Mississippi by adding a water control structure and observed improvements in water quality, fish habitat, and fish populations relative to an adjacent untreated backwater over a four year period. The restored backwater experienced increased summer water depth, moderation of severe diurnal water quality fluctuations, and reductions in concentrations of solids (~70%), nutrients (~30%-60%), and chlorophyll a (~50%). Fish species richness, numbers and biomass were unchanged following rehabilitation, but trophic structure shifted away from omnivorous species and toward predators, making the treated site less similar to the degraded reference. Similar changes did not occur in the untreated site. These findings are of interest to land managers interested in riverine aquatic ecosystem restoration and management.
12. River Restoration Priorities Identified. Rivers draining the Mississippi Delta and other major floodplains used for agricultural production have great ecological potential, but suffer from extreme degradation due to water pollution, water extraction, channelization and removal of riparian vegetation and large wood. Based on a three-year study of the Big Sunflower River, ARS scientists in Oxford, MS, found that physical habitat remediation is unlikely to be effective until water quality issues producing chronic low dissolved oxygen concentrations are addressed. Low-head weirs support relatively dense and diverse fish assemblages and thus provide local habitat enhancement, but may create stagnant zones upstream due to backwater effects that exacerbate low dissolved oxygen problems. This research is useful to water resource managers working with river systems in intensely cultivated floodplains.
13. Phosphorus Control Strategies Suggested. The Mississippi Delta (flood plain of Mississippi River) is an important agricultural region of the United States, and high phosphorus (P) loss from the region has been an environmental concern because of potential water quality problems in streams and lakes linked to P loads. ARS scientists in Oxford, MS, showed that applying P fertilizer in the spring rather than the fall may reduce soluble P loss during the dormant season; in addition, conservation practices can reduce total P loss associated with soil loss. These findings are useful to producers, extension personnel and regulatory agencies charged with safeguarding water quality.
14. Stream Ecosystem Structure Affects Nutrient Retention. Stream fishes can have strong effects on ecosystem processes through the consumption of algae and invertebrates, and excretion of nutrients that feed algal growth. However, varying flooding and drying patterns and different fish communities across streams makes it difficult to generalize fish impact. An ARS scientist in Oxford, MS, worked with colleagues at Kansas State, South Dakota State and Southern Illinois Universities and developed a conceptual model of the influence of stream fish on algal populations. A series of experiments was conducted using fish groups with different feeding styles (bottom-feeders and water column-feeders) following floods and drying in prairie streams. Fish impacts should be greatest shortly after a disturbance when algal and invertebrate communities are less complex and their biomass is low relative to fish biomass. These findings assist scientists to predict the consequences of biodiversity loss in streams with variable or human-modified disturbance patterns.
15. Flood Impacts on Stream Ecosystems Measured. Stream flow patterns in many parts of the U.S. are predicted to change with a changing climate, with one key result being more frequent and intense floods that have the potential to interact with pollution to disrupt aquatic food webs. An ARS scientist at Oxford, MS, working with scientists at Kansas State and Southern Illinois Universities measured stream recovery dynamics for 35 days after a simulated flood in large outdoor mesocosms under a gradient of six nutrient loadings crossed with six population densities of algae-eating fish and developed a model for predicting post-flood algal growth and nutrient fluxes. The model shows how nutrient loads and fish populations can influence nutrient flux and how the relative strength of each factor is largely dependent on stream environmental conditions. These results are directly applicable to understanding how changes in stream biodiversity are affecting stream services such as retaining and processing nutrients.
16. Algal Response to Nutrient Pollution Measured. In addition to increasing the amount of algae in a stream, nutrient pollution can change algal species composition, which can lead to communities dominated by species that are less edible by higher level organisms, less efficient at removing nutrients, or produce toxins. Measuring how individual species in natural algal communities respond to nutrient levels is difficult because it is not easy to separate species in large enough quantities for standard nutritional measurements. An ARS scientist in Oxford, MS, worked with scientists at Kansas State University and John Jay College at the City University of New York and used infrared microspectroscopy to measure the responses of single algal cells to changes in nutrient availability. It was found that the two most abundant species in a biofilm differed in their physiological responses and that algal colonies with more individuals responded faster to changing nutrients. These observations are useful to scientists trying to predict how increases, or decreases, in nutrient pollution will impact algal communities in regards to species composition and nutrient uptake.
17. Impacts of Pesticides in Sediment on Aquatic Animals Assessed. Sediments in water bodies receiving runoff from cultivated lands are often contaminated with pesticides, and effects on resident species are not well known. ARS scientists in Oxford, MS, conducted experiments that showed contaminated lake sediments had subtle but perhaps important effects on a common aquatic invertebrate animal, Hyalella azteca. They analyzed sediments from a natural lake in the Mississippi Delta and found fourteen pesticides. Invertebrates exposed to mixtures of pesticides in these sediments did not experience mortality, but did exhibit pesticides in their tissues and growth impairment that were related to higher pesticide levels. These results are of interest to regulatory and other agencies and the pesticide industry by providing additional information to improve and sustain lake and flood plain water quality and overall environmental quality using conservation practices.
18. Constructed Wetlands Serve as Effective Buffers for Herbicides from Cropped Land. Runoff from cropped lands often carries pollutants such as pesticides. ARS scientists in Oxford, MS, showed constructed wetlands can improve downstream water quality though sequestration or processing of pollutants. They constructed a multi-cell wetland in a Mississippi Delta agricultural watershed to serve as a buffer between farmed land and a lake, and they evaluated herbicide moving through the constructed wetland during a simulated runoff event. Atrazine and fluometuron concentrations in the first (shallower, non-excavated) cell averaged 7- and 14-fold greater, respectively, than those in the second cell following simulated runoff, indicating entrapment in the second cell. Atrazine and fluometuron concentrations in the shallower cell decreased 32 and 22%, respectively, 9 days following simulated runoff, indicating either degradation or sorption to soil or wetland flora. Results from this study are directly useful to producers, action agencies and others seeking to design buffers to protect water bodies from agricultural pollutants.
19. Wetland Plants Reduce Toxicity of Polluted Waters. Agricultural runoff is often contaminated with nutrients and pesticides that are toxic to organisms in receiving waters. ARS scientists in Oxford, MS, working with scientists from Mississippi State University found that a constructed wetland reduced the initial toxicity of simulated storm-event agricultural runoff more than a similar sized holding basin without wetland plants. Simulated runoff was amended with two pesticides, diazinon and permethrin, and two nutrients, nitrogen and phosphorus, on a common aquatic crustacean, Hyalella azteca. The study showed that plants were better at decreasing the effects of nutrients and pesticides within the first 5 hours, but no differences between the wetland and unvegetated holding basin were noted for longer periods. Nutrient and pesticide contaminated water had to be retained in the constructed wetland for 21 days to remove toxicity. These results are of interest to regulatory and other agencies and the pesticide industry by providing additional information to improve and sustain river, stream and lake water quality and overall environmental quality using vegetated constructed wetlands as an effective conservation practice.
20. Nitrogen Loads Reduced by Subsurface Drainage Management. Effects of conservation and management practices on nitrogen losses to surface waters are poorly quantified, and more information is needed to address the effects of increased levels of biofuels production. ARS scientists in Oxford, MS, implemented the Annualized Agricultural Non-Point Source Pollution computer model to simulate the Upper Auglaize watershed in Ohio with the objective to assess the effects of agricultural conservation practices on water quality. Modeling showed that wider drain spacing and shallower depths to drain reduced nitrogen loadings. In addition, nitrogen loadings could be significantly reduced by controlling subsurface drains from November 1 to April 1 of each year. These findings are helpful to producers, land managers, and action and regulatory agencies charged with reducing nitrogen loads in streams and rivers.
21. Watershed Modeling Technology Used for Assessing and Predicting Conservation Effects at the Watershed Scale. Federal, state and local governments spend large sums on conservation practices, but often the benefits of these efforts are not measured. Analysis of conservation effects on downstream water quality at the watershed scale typically requires a combination of monitoring and numerical modeling. ARS scientists in Oxford, MS, tested the Annualized Agricultural Non-Point Source watershed model, AnnAGNPS, to analyze a Kansas watershed and developed a list of recommendations for calibrating and using AnnAGNPS in similar efforts elsewhere. A list of needed model enhancements, such as a baseflow feature that addresses the percolation into the vadose zone, groundwater movement, and interception of the top of the water table by the channel was also developed. The modeling application underscored the importance of ephemeral gully erosion to downstream water quality. These findings should guide future research and development of watershed models for assessing conservation effects.
Moore, M.T., Kroger, R., Cooper, C.M., Cullum, R.F., Smith, S., Locke, M.A. 2009. Diazinon reduction and partitioning between water, sediment and vegetation in stormwater runoff mitigation through rice fields. Pest Management Science. 65: 1182-1188.