R. K. Hubbard

USE OF FLOATING VEGETATION TO REMOVE NUTRIENTS FROM SWINE LAGOON WASTEWATER

Methods are needed to remove nutrients contained within wastewater lagoons. Potential exists for nutrient removal directly from lagoons if vegetation can be grown on floating mats in the lagoon and periodically harvested and removed. Vegetative cover of lagoons may also help reduce odor problems. A study was conducted to determine the feasibility of using floating mats of vegetation on swine lagoon wastewater. Wastewater from the University of Georgia swine wastewater lagoons was pumped to replicated tanks (1285 L) in which floating mats of vegetation were grown. The floating platforms were made of PVC pipe with attached wire screen and fibrous material into which the vegetation was sprigged. Three different wetland species were tested: cattail (Typha latifolia L.), soft rush (Juncus effuses), and maidencane (Panicum hematomon Schult ‘Halifax’). Full-strength wastewater, 1/2-strength wastewater, and an inorganic nutrient solution (1/4-strength Hoaglund solution) as a control were tested. The test was conducted as a modified batch process as opposed to a continuous flow through process. The modification was that every two weeks half of the volume of each tank was replaced with the appropriate solution of full-strength wastewater, 1/2-strength wastewater, or 1/4-strength Hoaglund solution so that nutrient concentrations would not be depleted. There were four replicate tanks of each nutrient solution for each wetland species, for a total of 36 tanks. Vegetation from the floating mats was harvested periodically by removing all vegetation above 5 cm of the base of the floating mat. Measurements were made at each cutting of the total biomass per tank, leaf area, and nutrient content (N, P, K) of the vegetative tissue. Growth responses were quite different among the three species. The cattail had tremendous growth during the spring and summer months. The growth rate of the rush was slow for the first year. It then died during summer of 2002 at both the 1/2-strength and full-strength wastewater, indicating that this species is not suitable for growth on floating mats in swine lagoon wastewater. Total nutrient removal by both the cattail and maidencane was primarily a function of total biomass produced. Over the length of the study, on full-strength wastewater, the cattail produced 16,511 g m-2 biomass and removed 534, 79, and 563 g m-2 of N, P, and K, respectively, while the maidencane produced 9751 g m-2 of biomass and removed 323, 48, and 223 g m-2 of N, P, and K, respectively. Results from this study indicate that potential exists for using floating platforms to grow cattail, maidencane, or possibly other yet to be identified plant species in wastewater lagoons for nutrient removal.

ASSESSMENT OF FOREST MANAGEMENT EFFECTS ON NITRATE REMOVAL BY RIPARIAN BUFFER SYSTEMS

A study was conducted to determine the impact of different forest management techniques on shallow groundwater quality in coastal plain riparian zones. Considerable past research had shown that riparian zones are effective in removing or assimilating nitrates entering from upslope agricultural fields via shallow lateral flow, but the impact of different forest management techniques on this process was unknown. The study was conducted at a site near Tifton, Georgia, on a second-order coastal plain stream. The riparian buffer system consisted of a grass buffer, a managed forest zone, and a forest zone adjacent to the stream. Three forest treatments were studied: mature forest (MF), clearcut (CC), and selective thinning (ST). Following a nine-month pretreatment period, trees were completely or selectively removed from the CC and ST treatments, respectively. Shallow groundwater quality was evaluated in networks of wells on transects extending downslope from the edge of the agricultural field to the stream. Results from the study showed that all three forest management treatments were effective in assimilating nitrate-nitrogen (NO3-N). Significant differences in NO3-N concentrations in the shallow groundwater between the three different treatments did not occur. The only statistically significant effect that was observed on groundwater quality was under the CC treatment, where solute concentrations (both NO3-N and chloride [Cl]) decreased after the tree cutting. This was attributed to a combination of effects including possible increased NO3-N uptake by rapidly growing vegetation, dilution associated with less evapotranspiration by young vegetation as compared to mature forest, and more throughfall of rainfall under the CC than under the other two treatments. No treatment effects were observed on ammonium-nitrogen (NH4-N) concentrations. Overall the study showed that regardless of forest management techniques, coastal plain riparian forests are effective in assimilating NO3-N.

Riparian Forest Buffer System Research at the Coastal Plain Experiment Station, Tifton, GA

Recent attention has focused on riparian forest buffer systems for filtering sediment, nutrients, and pesticides entering from upslope agricultural fields. Studies in a variety of physiographic areas have shown that concentrations of sediment and agrichemicals are reduced after passage through a riparian forest. The mechanisms involved are both physical and biological, including deposition, uptake by vegetation, and loss by microbiological processes such as denitrification. Current research by USDA-ARS and University of Georgia scientists at Tifton, GA is focusing on managing riparian forest buffer systems to alleviate agricultural impacts on the environment. The underlying concept for this research is that agricultural impact on streams is best protected by a riparian forest buffer system consisting of three zones. In consecutive upslope order from the stream these zones are (1) a narrow band of permanent trees (5–10 m wide) immediately adjacent to the stream channel which provides streambank stabilization, organic debris input to streams, and shading of streams, (2) a forest management zone where maximum biomass production is stressed and frees can be harvested, and (3) a grass buffer strip up to 10 m wide to provide control of coarse sediment and to spread overland flow. Several ongoing projects at Tifton, GA are focusing on using riparian forest buffer systems as filters. A forest management project is testing the effects of different management practices on surface and ground water quality. This project includes three different forest management practices: mature forest, selectively thinned forest, and clearcut. In a different study a natural wetland is being restored by planting frees. The effectiveness of this wetland on filtering nutrients from dairy wastes which are being applied upslope is being evaluated. At this same site, a pesticide study is being conducted on the side opposite to where dairy wastes are applied. An overland flow-riparian buffer system using swine lagoon waste is evaluating the effectiveness of different vegetative treatments and lengths of buffer zones on filtering of nutrients. In this study three vegetative treatments are compared: (1) 10 m grass buffer and 20 m riparian forest, (2) 20 m grass buffer and 10 m riparian forest, (3) 10 m grass buffer and 20 m of the recommended wetland species maidencane. Waste is applied at the upper end of each plot at either a high or low rate, and then allowed to flow downslope. The three zone riparian forest buffer system is being used for the Riparian Ecosystem Management Model (REMM). This model, which is currently under development at Tifton, GA, is a computer simulation model designed to reduce soil and water degradation by aiding farmers and land use managers in decision making regarding how best to utilize their riparian buffer system. Both information currently being collected in field studies and development of the REMM are innovative farm-level and forestry technologies to protect soil and water resources.

Subsurface Flow Patterns in a Riparian Buffer System

Matric potential was measured in a grass and forest riparian buffer system adjacent to a cropped field in the Georgia Coastal Plain. The soil in the adjacent cropped field is a Tifton loamy sand, containing an argillic subsurface horizon with plinthite at approximately 1 m which has been shown to restrict vertical infiltration and induce lateral flow. Two years of matric potential data and measurements of soil hydraulic characteristics were examined to evaluate and quantify unsaturated water flow in the riparian buffer. The lowest soil matric potential occurred at the grass/forest interface, and the greatest surface infiltration occurred within 10 m downslope of the same interface. The area of low matric potential was likely due to water uptake by trees. Water flowed laterally through the unsaturated soil into the riparian area from the upland field, apparently induced by low vertical conductivity in the subsurface and driven by the high water demand of the forest.

Links among Nitrification, Nitrifier Communities, and Edaphic Properties in Contrasting Soils Receiving Dairy Slurry

Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy (Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha(-1). Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.

RIPARIAN ECOSYSTEM MANAGEMENT MODEL (REMM): II. TESTING OF THE WATER QUALITY AND NUTRIENT CYCLING COMPONENT FOR A COASTAL PLAIN RIPARIAN SYSTEM

The Riparian Ecosystem Management Model (REMM) was used to simulate nitrogen (N), phosphorus (P), and carbon (C) cycling and transport in a Coastal Plain riparian buffer system near Tifton, Georgia. The riparian buffer consisted of zone 3 (grass next to a row crop field); zone 2 (mature pine forest downslope from zone 3); and zone 1 (hardwood forest downslope from zone 2, adjacent to a stream). Uncalibrated simulation results for a five-year period were compared to measured values for the same time period at the research site. In general, simulated water table nutrient concentrations were within one standard deviation of observed values on an annual basis. Surface runoff loads exiting zone 3 for most N and P forms were simulated within one standard deviation of the observed. In contrast zone 2, surface runoff loads for inorganic N species were an order of magnitude lower than observed. Although some of the surface runoff differences (observed vs. simulated) were large in relative terms, the overall trends within the riparian buffer were generally well-represented and differences were not large in absolute terms. Simulated values for one of the most important processes responsible for effectiveness of riparian zones — denitrification, were within the range of those observed. Much of the temporal dynamics of the observed data were also captured in the REMM simulations. Certain constraints of the model use are discussed, but REMM appears to be useful for representing many of the specific processes and general trends in riparian ecosystem buffers.

Protocols for Nationally Coordinated Laboratory and Field Research on Manure Nitrogen Mineralization

Abstract The National Program structure of USDA‐ARS provides an opportunity to coordinate research on problems of national and global significance. A team of USDA‐ARS scientists is conducting nationally coordinated research to develop predictions of manure N availability to protect water quality and improve farm solvency. Experimental design and research protocols were developed and used in common across all participating locations. Laboratory incubations are conducted at each location with a minimum of three soils, three temperatures, two wetting/drying regimes, and two manure treatments. A soil from the central United States (Catlin silt loam, fine‐silty, mixed, superactive, mesic Oxyaquic Argiudoll) is used as an internal reference across all locations. Incubation data are compiled across locations to develop generalized predictions of manure nitrogen mineralization (Nmin). Field validation data are then obtained by monitoring nitrogen (N) transformations in manure‐amended soil cores equipped with anion exchange resin to capture leached nitrate. This field data will be used to compare laboratory‐based predictions with field observations of Nmin in each soil, climatic zone, and manure type represented. A Decision Support System will then be developed for predicting manure N mineralization across ranges in soil, climate, and manure composition. Protocols used by this research team are provided to 1) document the procedures used and 2) offer others detailed information for conducting research on nutrient transformation processes involving collaboration across locations or complementary research between laboratory and field environments.

NITROGEN ASSIMILATION BY RIPARIAN BUFFER SYSTEMS RECEIVING SWINE LAGOON WASTEWATER

A three-year study was conducted to determine the feasibility of using riparian buffer systems to assimilate nitrogen (N) from swine lagoon effluent. Replicated 30 ×4 m plots were established at the interface of a pasture and riparian forest. Wastewater from the third lagoon of the University of Georgia Coastal Plain Experiment Station main swine research unit was applied to each plot by overland flow from tanks at the top end of each plot. The wastewater, which contained an average N concentration of 160 mg L–1 N, primarily as ammonium (NH4-N), was applied to the plots at two different rates (either once per week [1 ×, 1285 L/plot] or twice per week [2 ×, 2570 L/plot]). Three different vegetative buffer treatments were evaluated: (1) 10 m grass buffer draining into 20 m existing riparian zone vegetation; (2) 20 m grass buffer draining into 10 m existing riparian zone vegetation; and (3) 10 m grass buffer draining into 20 m maidencane (Panicum hematomon). The effects of the wastewater on surface runoff and groundwater quality were evaluated by transects of surface runoff collectors, suction lysimeters, and shallow groundwater wells which extended from the top to the bottom of each plot. Data analyses showed differences due to wastewater application rate and distance downslope from the wastewater application pipe. Nitrogen concentrations increased over time at the top ends of the plots but showed little increase at the bottom ends of the plots. Overall, all three vegetative treatments were successful in assimilating N from the wastewater. The study showed that riparian buffer systems, where wastewater is applied by overland flow, can be effective in assimilating N contained within lagooned animal wastes.

Chemical Transport from Coastal Plain Soils Under Simulated Rainfall: L Surface Runoff, Percolation, Nitrate, and Phosphate Movement

ABSTRACT Astudy was conducted to determine amounts and rates of surface runoff, percolation, nitrate and phosphate movement from the upper root zone of three upland Coastal Plain soils. Surface soil samples of Greenville sandy clay loam. Red Bay loamy sand, and Bonifay sand were packed into rectangular stainless steel boxes equipped with surface runoff and percolate collection devices. The soils ranged in clay content from 29.3% to 3.6%, and represented a range of soil textures commonly found in the Coastal Plain. Simulated rainfall was applied to each soil at high (125 mm/hr), medium (75 mm/hr), or low (43 mm/hr) intensities. Surface runoff rates varied from none to about 100 mm/hr depending on soil texture, crusting and sealing, and rainfall intensity. Percolation was found to be the major water-loss pathway on the sandier soils at the lower rainfall intensities. Surface runoff was the major water-loss pathway at the high rainfall intensity on the Bonifay sand (69.8%), and for all three rainfall intensities on the Greenville sandy clay loam. The study showed that percolation is the major pathway for NO3-N movement from the upper root zone of the sandier Coastal Plain soils. Some PO4 moved with percolation on the two sandier soils, but not on the clayey soil. Nitrate and PO4 movement from the clayey soil was primarily in surface runoff. Comparison of NO3-N and PO4 movement predictions made by the GLEAMS model with actual observations showed that the model worked best on the sandier soils. The study indicates that care should be taken to avoid applying NO3-N and PO4 when probability for immediate intense rainfall is great.

Floating Vegetated Mats for Improving Surface Water Quality

Contamination of surface and ground waters is an environmental concern. Pollution from both point and nonpoint sources can render water unsuitable for use. Surface waters of concern include streams, rivers, ponds, lakes, canals, and wastewater lagoons. Lagooned wastewater from confined animal feeding operations (CAFOs) represents an extreme in water quality problems. Wastewater lagoons are used for primary treatment which includes settling of solids and loss of gases by volatilization. Additional methods are often used to treat the wastewater from the lagoons. These methods include passing the wastewater through constructed wetlands, where both plant uptake and biological processes such as denitrification remove or retain nutrients, and application of the wastewater to agricultural or forestry land. A new concept for improving surface water quality including that of wastewater lagoons is to grow vegetation on floating platforms in the water body. Little research has been conducted in this area, although this technology basically is application of hydroponics using floating platforms for the vegetation which then utilizes nutrients contained in the contaminated waters. Research conducted by USDA-ARS and the University of Georgia at Tifton, GA has focused on determining the feasibility of growing vegetation to produce biomass and remove nutrients from contaminated surface water bodies. The research has shown that different plant species can be found to grow on floating platforms in a range of different water qualities. In the most contaminated water tested thus far, anaerobic swine lagoon wastewater, it was determined that plants remove nutrients to their maximum capacity such that total removal of nutrients from the water body is a function of biomass produced. This chapter explains the concepts and techniques involved in using floating vegetated mats on contaminated water bodies for nutrient removal, reports results from completed studies, discusses ongoing projects, and identifies research needs for this emerging technology.