Joshua W. Faulkner

Evaluation of Two Langmuir Models for Phosphorus Sorption of Phosphorus-Enriched Soils in New York for Environmental Applications

The phosphorus (P) sorption isotherm experiment is a widely used tool in environmental applications for assessing soils vulnerability to P loss to runoff or drainage. The sorbed legacy P (S0) (i.e., the P retained in soils from previous P applications) participates in sorption processes but cannot readily be determined in a sorption experiment. Thus, it is important to accurately estimate S0 for P-enriched soils (e.g., the soils that heavily receive fertilizer, manure, farm wastewater, or sewage sludge). Two curve-fitting procedures (i.e., one-step method and two-step method) with Langmuir models have been used to estimate S0 and other sorption parameters, including the P sorption maxima (Smax), the bonding energy constant (k), and the zero-sorption equilibrium concentration (EPC0). This study evaluated these two methods on 16 samples of Langford, Volusia, and Mardin channery silt loam soils at surface (0-8 cm) and subsurface (61-91 cm) in New York. The results indicate that the two methods agreed well in estimating P sorption maxima, and the estimates of k were close. The S0 estimates by the two methods had a good agreement for surface soils but a poor agreement for subsurface soils, which may be of little concern because of small S0 of subsurface soils. Although the one-step method yielded greater EPC0 estimates, the EPC0 estimates by the two methods had an excellent linear correlation for P-enriched surface soils, suggesting that both methods could work equally if only the relative magnitudes of EPC0 among soils are needed. Overall, both methods are acceptable to fit the Langmuir isotherms.

Tracer movement through paired vegetative treatment areas receiving silage bunker runoff

The need for less resource-intensive agricultural waste treatment alternatives has lately increased. Vegetative treatment areas (VTAs) are considered a low-cost alternative to the collection and storage of various agricultural wastewaters. As VTAs become more widespread, the need for design guidance in varying climates and landscapes increases. The purposes of this study were to investigate runoff movement and nitrate-nitrogen concentrations within two VTAs and to use the results to improve VTA design and recommendations for management. Silage bunker runoff movement through the selected VTAs following a 7.8 mm (0.31 in) rainfall event was characterized using a chloride tracer. Both surface and subsurface runoff movement was analyzed using tracer concentrations and a simple binary mixing model. Results show that concentrated surface flow paths existed within both VTAs, and surface flow in general was more prevalent in the VTA that received a higher hydraulic loading. Rapid preferential flow to shallow monitoring wells was also observed. A shallow restrictive soil layer likely exacerbated surface flow but restricted runoff water and nitrate-nitrogen from leaching to deeper groundwater. The nitrate-nitrogen did not appear to be directly linked to runoff movement, but concentrations as high as 28 mg L−1 were observed in downslope surface flow in the wetter VTA. A more comprehensive VTA design process is called for that accounts for shallow soils and antecedent moisture conditions. Regular maintenance and design measures to prevent the formation of concentrated flow paths are also critical to the prevention of surface discharge.

Nutrient transport within three vegetative treatment areas receiving silage bunker runoff.

Silage bunker runoff can be a very polluting substance and is increasingly being treated by vegetative treatment areas (VTAs), but little information exists regarding nutrient removal performance of systems receiving this wastewater. Nutrient transport through the shallow subsurface of three VTAs (i.e. one VTA at Farm WNY and two VTAs at Farm CNY) in glaciated soils containing a restrictive layer (i.e., fragipan) was assessed using a mass balance approach. At Farm WNY, the mass removal of ammonium was 63%, nitrate was 0%, and soluble reactive phosphorus (SRP) was 39%. At Farm CNY, the mass removal of ammonium was 79% in the West VTA, but nitrate and SRP increased by 200% and 533%, respectively. Mass removal of ammonium was 67% in the East VTA at Farm CNY; nitrate removal was 86% and SRP removal was 88%. The East VTA received a much higher nutrient loading, which was attributed to a malfunctioning low-flow collection apparatus within the settling basin. Results demonstrate that nutrient reduction mechanisms other than vegetative uptake can be significant within VTAs. Even though increases in nitrate mass were observed, concentrations in 1.65m deep wells indicated that groundwater impairment from leaching of nitrate was not likely. These results offer one of the first evaluations of VTAs treating silage bunker runoff, and highlight the importance of capturing concentrated low flows in VTA systems.

Phosphorus sorption and desorption properties of surface and subsurface horizons at three vegetative treatment areas in New York

Phosphorus (P) loss from intensive animal production farms to surface waters has drawn much attention in New York and elsewhere in the U.S. due to the role of P in surface water eutrophication. Vegetative treatment areas (VTAs) are alternative systems to treat farm wastewaters. P retention in the VTAs is partially dependent on soil properties. P sorption and desorption properties of surface and subsurface horizons of New York soils (Langford, Volusia, and Mardin) in three VTAs receiving dairy farm wastewaters were studied using batch experiments. Pearson correlation and stepwise linear regression show that soil organic matter (OM) is the most prominent soil property correlating with P sorption parameters. While OM is positively correlated with the P sorption maxima (Smax), it is also positively related to the sorbed legacy P (S0, the labile soil P from historical P additions), the zero-sorption equilibrium concentration (EPC0), and negatively correlated to the bonding energy constant (k). Relative to the surface soils, the subsurface soils generally had lower Smax and EPC0 as well as greater k. P desorption is related to similar soil properties correlating with S0 and EPC0, tapping the same labile soil P. The desorption can be lessened by decreasing soil moisture content or increasing contact time of the sorbed P with soils, following P sorption. Comparison between measured field P concentration and predicted EPC0 from the regression equation suggests that the P sorption study is a viable technique for qualitatively characterizing soil P loss, but not adequate in estimating field P concentrations. Implications on VTA design and management are discussed.

Evaluation of Two Langmuir Models for Phosphorus Sorption on Various Soils under Varied Conditions

Phosphorus (P) sorption isotherm experiment is a widely used tool in the field of agronomy for evaluating the availability of P for crop uptake, and in environmental studies for assessing the potential of P mobilization to runoff or drainage. For P-accumulated soils, the importance of accurately estimating the native sorbed P in a sorption study cannot be overemphasized. Surrogates measured experimentally by an extraction method and estimates from a curve-fitting procedure have both been employed in the past. This study evaluated two curve-fitting procedures, referred as linear approach and nonlinear approach, for 30 P sorption isotherms. The isotherms were determined for various soils under aerobic, slightly reduced, and highly reduced conditions. Estimated sorption parameters by the two approaches were compared in 1:1 linear scatter plots. Results indicated that the two approaches agree well in estimating P sorption maxima (Smax) under all tested conditions. Estimates of binding energy (k) were fairly close for aerobic and slightly reduced conditions (R2>0.976, slope=1.132 or 1.039, respectively), but not linearly correlated under highly reduced condition (slope=1.827, R2=-0.102). The native sorbed P (S0) estimates were relatively close for aerobic sorption (slope=1.055, R2=0.946), but differed significantly for slightly and highly reduced conditions (slope=1.914 or 1.402, and R2=0.983 or 0.616, respectively). The nonlinear approach estimated higher values of zero sorption equilibrium concentrations (EPC0), an indicator of a soil’s P loss potential. It was concluded that the nonlinear approach should be the preferred method since it does not assume isotherm linearity at a low concentration range.

Design and risk assessment tool for vegetative treatment areas receiving agricultural wastewater: preliminary results.

Vegetative treatment areas (VTAs) are commonly being used as an alternative method of agricultural process wastewater treatment. However, it is also apparent that to completely prevent discharge of pollutants to the surrounding environment, settling of particulates and bound constituents from overland flow through VTAs is not sufficient. For effective remediation of dissolved agricultural pollutants, VTAs must infiltrate incoming wastewater. A simple water balance model for predicting VTA soil saturation and surface discharge in landscapes characterized by sloping terrain and a shallow restrictive layer is presented and discussed. The model accounts for the cumulative effect of successive rainfall events and wastewater input on soil moisture status and depth to water table. Nash-Sutcliffe efficiencies ranged from 0.65 to 0.81 for modeled and observed water table elevations after calibration of saturated hydraulic conductivity. Precipitation data from relatively low, average, and high annual rainfall years were used with soil, site, and contributing area data from an example VTA for simulations and comparisons. Model sensitivity to VTA width and contributing area (i.e. barnyard, feedlot, silage bunker, etc.) curve number was also investigated. Results of this analysis indicate that VTAs should be located on steeper slopes with deeper, more-permeable soils, which effectively lowers the shallow water table. In sloping landscapes (>2%), this model provides practitioners an easy-to-use VTA design and/or risk assessment tool that is more hydrological process-based than current methods.

Investigating Event Nitrate Dynamics in Paired Vegetative Treatment Areas Receiving Silage Bunker Runoff Using a Simple Mixing Approach

Groundwater nitrate, often found in areas containing intensive agriculture, poses a human health risk at concentrations greater than 10 mg/L NO3--N. Vegetative Treatment Areas (VTAs) are alternative treatment systems that have been proposed and implemented for the treatment of silage bunker runoff and other agricultural wastewaters on Concentrated Animal Feeding Operations (CAFOs) and other farms. The objective of this study was to temporally and spatially characterize runoff movement and nitrate dynamics on the surface and in the groundwater within paired VTAs treating silage bunker runoff following a precipitation event. A conservative tracer was applied prior to rainfall, and tracer and nitrate concentrations were then monitored in surface-water collector and monitoring well networks in the VTAs. Preferential movement of runoff was observed on the surface and to the groundwater in both VTAs. Nitrate dynamics were localized within the VTAs and did not correlate well with runoff movement. Nitrate concentrations not attributable to bunker runoff in excess of 20 mg/L NO3--N were observed on the surface and in the shallow (61 cm) groundwater during the study. Observed groundwater nitrate concentrations were all less than 10 mg/L NO3--N at a 162 cm depth.