Louis S. Saporito

Using Flue Gas Desulfurization Gypsum to Remove Dissolved Phosphorus from Agricultural Drainage Waters

High levels of accumulated phosphorus (P) in soils of the Delmarva Peninsula are a major source of dissolved P entering drainage ditches that empty into the Chesapeake Bay. The objective of this study was to design, construct, and monitor a within-ditch filter to remove dissolved P, thereby protecting receiving waters against P losses from upstream areas. In April 2007, 110 Mg of flue gas desulfurization (FGD) gypsum, a low-cost coal combustion product, was used as the reactive ingredient in a ditch filter. The ditch filter was monitored from 2007 to 2010, during which time 29 storm-induced flow events were characterized. For storm-induced flow, the event mean concentration efficiency for total dissolved P (TDP) removal for water passing through the gypsum bed was 73 ± 27% confidence interval (α = 0.05). The removal efficiency for storm-induced flow by the summation of load method was 65 ± 27% confidence interval (α = 0.05). Although chemically effective, the maximum observed hydraulic conductivity of FGD gypsum was 4 L s(-1), but it decreased over time to <1 L s(-1). When bypass flow and base flow were taken into consideration, the ditch filter removed approximately 22% of the TDP load over the 3.6-yr monitoring period. Due to maintenance and clean-out requirements, we conclude that ditch filtration using FGD gypsum is not practical at a farm scale. However, we propose an alternate design consisting of FGD gypsum-filled trenches parallel to the ditch to intercept and treat groundwater before it enters the ditch.

A comparison of phosphorus speciation and potential bioavailability in feed and feces of different dairy herds using 31p nuclear magnetic resonance spectroscopy.

An experiment was conducted to examine how potential phosphorus (P) bioavailability (inferred from speciation) differs in feed and feces collected in spring from four dairy herds representing different management systems: (i) total confinement with cows fed total mixed ration (TMR), (ii) total confinement with TMR plus P mineral supplement, (iii) a hybrid of confinement with TMR and pastoral grazing, and (iv) predominantly grazing with supplemental grains. A treatment was included that air dried feces to simulate conditions after dung deposition. Wet chemical techniques and solution (31)P nuclear magnetic resonance spectroscopy ((31)P-NMR) were used to identify P concentrations and compounds present in water (a surrogate for P in overland flow), dilute acid (0.012 M HCl, an estimate of P utilization by cattle), or NaOH-EDTA (a solution that maximizes the organic P extraction) extracts of feed and feces. In general, P concentration in feces paralleled P in feed. Air drying feces decreased water-extractable P by 13 to 61% largely due to a decrease in orthophosphate, whereas NaOH-EDTA-extractable P increased by 18 to 48%. Analysis of dilute HCl was unsuccessful due to orthophosphate precipitation when pH was adjusted to 12 for (31)P-NMR. In water extracts, more P was in bioavailable diester-P forms, undetectable by colorimetry, than in NaOH-EDTA extracts. In feed, orthophosphate dominated (46-70%), but myo-IHP varied with feed (<10% in forage samples but 43% in a TMR sample). The proportion of myo-IHP decreased in feces compared with feed via mineralization but decreased less in systems with a greater proportion of available P input (e.g., orthophosphate and phospholipids). Feed and drying effect the concentrations and forms of P in feces and their potential impact on soil and water quality. Although bioavailable P in feces from pasture-based and confined systems can be similar in spring, dung-P is distributed on a lower kg P ha(-1) rate in grazing systems. The best method to mitigate P loss from feces is to decrease P in feed.

Effect of direct incorporation of poultry litter on phosphorus leaching from coastal plain soils

Management of poultry litter on the Delmarva Peninsula is critical to reducing phosphorus losses to the Chesapeake Bay. New poultry litter incorporation technologies have shown promise at reducing phosphorus losses, but their effectiveness has not been tested in this environmentally sensitive region. This study evaluates subsurface leaching losses of three litter application methods, including surface broadcast, surface broadcast with disking, and subsurface litter incorporation with a novel litter incorporator developed by the USDA Agricultural Research Service. Cube-shaped soil lysimeters (61 × 61 × 61 cm [24 × 24 × 24 in]) were extracted from high phosphorus (P) (Mehlich-3 P is greater than 500 mg kg−1) agricultural soils on the University of Maryland Eastern Shore Research Farm near Princess Anne, Maryland, and were subjected to two rainfall simulation events that were separated by 11 semiweekly soaking-type irrigation events. The average cumulative total phosphorus loss was highest for the subsurface litter incorporation method (0.48 kg ha−1 [0.43 lb ac−1]) and was lowest for the no litter control (0.19 kg ha−1 [0.17 lb ac−1]). Particulate P loss among manure treatments ranged from 58% to 64% of total P loss. Total phosphorus losses were strongly correlated to total phosphorus concentration in the leachate (coefficient of determination [r2] ≥ 0.84), indicating availability of P in applied litter to be the primary control of P in leachate. Soil properties also impacted P leaching losses, with the soils possessing a higher sand content and having a shallower depth to the sandy subsoil, yielding higher cumulative total P losses (0.64 kg ha−1 [0.57 lb ac−1]). Although the subsurface litter incorporator increased total P leaching losses, a concern on the Delmarva Peninsula, opportunity exists to modify the subsurface incorporator design using zone tillage, potentially reducing the leaching losses.

Assessing manure management strategies through small-plot research and whole-farm modeling

Plot-scale experimentation can provide valuable insight into the effects of manure management practices on phosphorus (P) runoff, but whole-farm evaluation is needed for complete assessment of potential trade offs. Artificially-applied rainfall experimentation on small field plots and event-based and long-term simulation modeling were used to compare P loss in runoff related to two dairy manure application methods (surface application with and without incorporation by tillage) on contrasting Pennsylvania soils previously under no-till management. Results of single-event rainfall experiments indicated that average dissolved reactive P losses in runoff from manured plots decreased by up to 90% with manure incorporation while total P losses did not change significantly. Longer-term whole farm simulation modeling indicated that average dissolved reactive P losses would decrease by 8% with manure incorporation while total P losses would increase by 77% due to greater erosion from fields previously under no-till. Differences in the two methods of inference point to the need for caution in extrapolating research findings. Single-event rainfall experiments conducted shortly after manure application simulate incidental transfers of dissolved P in manure to runoff, resulting in greater losses of dissolved reactive P. However, the transfer of dissolved P in applied manure diminishes with time. Over the annual time frame simulated by whole farm modeling, erosion processes become more important to runoff P losses. Results of this study highlight the need to consider the potential for increased erosion and total P losses caused by soil disturbance during incorporation. This study emphasizes the ability of modeling to estimate management practice effectiveness at the larger scales when experimental data is not available.

A protocol for conducting rainfall simulation to study soil runoff.

Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hr after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been prewetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.

Transport of dissolved trace elements in surface runoff and leachate from a Coastal Plain soil after poultry litter application

The application of poultry (Gallus gallus domesticus) litter to agricultural soils may exacerbate losses of trace elements in runoff water, an emerging concern to water quality. We evaluated trace elements (arsenic [As], mercury [Hg], selenium [Se], and zinc [Zn]) in surface runoff and leachate from an agricultural soil with and without poultry litter application. Litter from a commercial operation was applied by three methods—broadcast application, subsurface placement, and broadcast application followed by disking—to no-till soils with a history of receiving litter. Soil monolith lysimeters (61 by 61 by 61 cm)(24 by 24 by 24 in) were extracted from each of the treatments and subjected to rainfall simulation (1 hour, 61 mm h−1 [2.4 in hr−1]) 15 and 42 days after litter application. Broadcasting poultry litter significantly increased concentrations (mg L−1) and loads (g ha−1) of As and Zn in runoff during the first event relative to other application methods. Notably, incorporating litter, either by disking after broadcasting or by subsurface placement, lowered As and Zn in runoff to near background levels by the second event, and there were no significant differences in As and Zn between any of the treatments. While Hg and Se were detected in runoff, they likely derived from edaphic sources as they were not detected in the litter nor did they differ significantly between treatments. Results point to poultry litter as a temporary source of some trace elements to runoff. This source can be readily controlled by adjusting application method.

Estrogen Transport in Surface Runoff from Agricultural Fields Treated with Two Application Methods of Dairy Manure

This study compares two methods of dairy manure application-surface broadcast and shallow disk injection-on the fate and transport of natural estrogens in surface runoff from 12 field plots in central Pennsylvania. Ten natural surface runoff events were sampled over a 9-mo period after fall manure application. Results show that the range of estrogen concentrations observed in surface runoff from the broadcast plots was several orders of magnitude higher (>5000 ng L) than the concentrations in runoff from the shallow disk injection plots (<10 ng L). Additionally, the transport dynamics differed, with the majority of the estrogen loads from the surface broadcast plots occurring during the first rainfall event after application, whereas the majority of the loads from the shallow disk injection plots occurred more than 6 mo later during a hail storm event. Total estrogen loads were, on average, two orders of magnitude lower for shallow disk injection compared with surface broadcast. Independent of the method of manure application, 17α-estradiol and estrone were preserved in the field for as long as 9 mo after application. Overall, injection of manure shows promise in reducing the potential for off-site losses of hormones from manure-amended soils.

Urea Release by Intermittently Saturated Sediments from a Coastal Agricultural Landscape

Urea-N is linked to harmful algal blooms in lakes and estuaries, and urea-N-based fertilizers have been implicated as a source. However, the export of urea-N-based fertilizers appears unlikely, as high concentrations of urea-N are most commonly found in surface waters outside periods of fertilization. To evaluate possible autochthonous production of urea-N, we monitored urea-N released from drainage ditch sediments using mesocosms. Sediments from a cleaned (recently dredged) drainage ditch, uncleaned ditch, forested ditch, riparian wetland, and an autoclaved sand control were isolated in mesocosms and flooded for 72 h to quantify urea-N, NH-N, and NO-N in the floodwater. Sediments were flooded with different N-amended solutions (distilled HO, 1.5 mg L NH-N, 3.0 mg L NH-N, 2.6 mg L NO-N, or 5.1 mg L NO-N) and incubated at three water temperatures (16, 21, and 27°C). Urea-N concentrations in mesocosms representing uncleaned and cleaned drainage ditches were significantly greater than nonagricultural sediments and controls. While flooding sediments with N-enriched solution had no clear effect on urea-N, warmer (27°C) temperatures resulted in significantly higher urea-N. Data collected from field ditches that were flooded by a summer rainstorm showed increases in urea-N that mirrored the mesocosm experiment. We postulate that concentrations of urea-N in ditches that greatly exceed environmental thresholds are mediated by biological production in sediments and release to stagnant surface water. Storm-driven urea-N export from ditches could elevate the risk of harmful algal blooms downstream in receiving waters despite the dilution effect.

Persistence and Surface Transport of Urea-Nitrogen: A Rainfall Simulation Study

Studies of harmful algal blooms and associated urea concentrations in the Chesapeake Bay and in coastal areas around the globe strongly suggest that elevated urea concentrations are associated with harmful algal blooms. The observed increased frequency and toxicity of these blooms in recent decades has been correlated with increased agricultural use of N inputs and increased use of urea as a preferred form of commercial N. This rainfall simulation study sought to assess the potential for different N fertilizers and manures to contribute to urea in runoff from a Coastal Plain soil on the Eastern Shore of Maryland. Under worst-case conditions, ~1% of urea-N applied as commercial fertilizer and surface-applied poultry litter was lost in runoff in a simulated rainfall event, roughly equivalent to a 1-yr return period rain storm in the study area, 12 h after application. Cumulative urea-N losses, including four subsequent weekly rainfall events, approached 1.7% from urea-N fertilizer containing a urease inhibitor. Urea-N loss from incorporated poultry litter was negligible, and losses from dairy manure were intermediate. These losses are likely confined to hydrological contributing areas that extend several meters from a drainage ditch or stream for storms with frequent recurrence intervals. Cumulative dissolved N losses in runoff (urea-N + ammonium-N + nitrate-N) as a proportion of total applied plant-available N were <5%, suggesting that most of the applied N was lost by other pathways or was immobilized in soil. Results also highlight the potential for simple management options, such as shallow incorporation or timing, to greatly reduce urea runoff losses.

A Protocol for Collecting and Constructing Soil Core Lysimeters.

Leaching of nutrients from land applied fertilizers and manure used in agriculture can lead to accelerated eutrophication of surface water. Because the landscape has complex and varied soil morphology, an accompanying disparity in flow paths for leachate through the soil macropore and matrix structure is present. The rate of flow through these paths is further affected by antecedent soil moisture. Lysimeters are used to quantify flow rate, volume of water and concentration of nutrients leaching downward through soils. While many lysimeter designs exist, accurately determining the volume of water and mass balance of nutrients is best accomplished with bounded lysimeters that leave the natural soil structure intact. Here we present a detailed method for the extraction and construction of soil core lysimeters equipped with soil moisture sensors at 5 cm and 25 cm depths. Lysimeters from four different Coastal Plain soils (Bojac, Evesboro, Quindocqua and Sassafras) were collected on the Delmarva Peninsula and moved to an indoor climate controlled facility. Soils were irrigated once weekly with the equivalent of 2 cm of rainfall to draw down soil nitrate-N concentrations. At the end of the draw down period, poultry litter was applied (162 kg TN ha(-1)) and leaching was resumed for an additional five weeks. Total recovery of applied irrigation water varied from 71% to 85%. Nitrate-N concentration varied over the course of the study from an average of 27.1 mg L(-1) before litter application to 40.3 mg L(-1) following litter application. While greatest flux of nutrients was measured in soils dominated by coarse sand (Sassafras) the greatest immediate flux occurred from the finest textured soil with pronounced macropore development (Quindocqua).