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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2010.03.019 Byline: Joshua W. Faulkner, Zachary M. Easton, Wei Zhang, Larry D. Geohring, Tammo S. Steenhuis Abstract: 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. Author Affiliation: Department of Biological and Environmental Engineering, Cornell University, 62 Riley-Robb Hall, Ithaca, NY 14850, USA Article History: Received 16 September 2009; Revised 16 March 2010; Accepted 27 March 2010

Phosphorus flux from agricultural landscapes to surface waters may cause eutrophication. In the northeastern United States, P transport largely depends on P sorption of soils in variable source areas or in land treatment systems. Soil redox fluctuation commonly occurs in these areas. Nevertheless, the effect of soil redox on P sorption has been variable in the literature. This study investigated P sorption of an organic-rich northeastern glaciated silt loam (Langford) under air-dried, field-wet, and reduced conditions using batch P sorption experiments. Additionally, the influence of farm wastewater on soil P sorption was studied. Major results indicated that soil reduction increased the maximum amount of P that can be sorbed ([S.sub.max]) and decreased the aqueous P concentration at which P sorption and desorption are equal ([EPC.sub.0]), both determined from a modified Langmuir isotherm model. The slightly reduced field-wet soils had no significant difference in [S.sub.max] due to limited soil reduction. Using the diluted wastewater as the sorption solution matrices instead of 0.01 mol [L.sup.-1] KCl solution, the soils generally exhibited greater [S.sub.max] and lower [EPC.sub.0] except for the [EPC.sub.0] of a reduced surface soil, implying more complex P sorption in the field. Identified P sorption mechanisms include phosphate precipitation, ligand exchange with organic matter, and adsorption onto Fe hydroxides. Transformation of Fe compounds during soil reduction is primarily responsible for the changes in soil P sorption. Abbreviations: DOC, dissolved organic carbon; ICP-AES, inductively coupled plasma-atomic emission spectrometry; OM, organic matter; SRP, soluble reactive phosphorus; TC, total carbon; TN, total nitrogen; VSA, variable source area; VTA, vegetative treatment area. doi:10.2136/sssaj2009.0123

Many U.S. states require farmers to evaluate the risk of P loss from farm fields using P site assessment tools, such as the Phosphorus Index (P‐Index). The simplicity of the P‐Index allows for users with various backgrounds to utilize the tool; however, the P‐Index may be limited in its ability to reliably predict P losses across variable farm terrain, for instance where saturation‐excess runoff generation dominates. The objective of this study was to identify potential improvements that could be made to the Vermont P‐Index (VT P‐Index) by comparing VT P‐Index predictions of P loss with those of a model that considers topographic controls on P transport. Scenarios with varying P management strategies were developed and modeled for corn (Zea mays L.) silage production fields in a small agricultural watershed (360 ha) located in Vermont using both the VT P‐Index and a modified version of the Soil and Water Assessment Tool (SWAT). Modeled outputs from both the VT P‐Index and SWAT were aggregated based on topographic index (TI) class and compared for the directional agreement of P risk assessments and relative annual average dissolved and particulate P losses. The P‐Index nutrient management recommendations gave higher P loss risk ratings than SWAT for 94% of the 120 unique scenario combinations simulated. Results from this study suggest that the VT P‐Index could improve its ability to support farm nutrient management planning by incorporating topographic controls on runoff production into its estimation of P transport. Core Ideas: Consideration of topographic factors can improve estimation of dissolved P loss in the VT P‐Index.Best management practice effectiveness can be increased in the VT P‐Index by accounting for VSA hydrology.Generally, the VT P‐Index resulted in a higher risk of P loss rating than SWAT‐VSA. [ABSTRACT FROM AUTHOR]

Phosphorus flux from agricultural landscapes to surface waters may cause eutrophication. In the northeastern United States, P transport largely depends on P sorption of soils in variable source areas or in land treatment systems. Soil redox fluctuation commonly occurs in these areas. Nevertheless, the effect of soil redox on P sorption has been variable in the literature. This study investigated P sorption of an organic-rich northeastern glaciated silt loam (Langford) under air-dried, field-wet, and reduced conditions using batch P sorption experiments. Additionally, the influence of farm wastewater on soil P sorption was studied. Major results indicated that soil reduction increased the maximum amount of P that can be sorbed (Smax) and decreased the aqueous P concentration at which P sorption and desorption are equal (EPC0), both determined from a modified Langmuir isotherm model. The slightly reduced field-wet soils had no significant difference in Smax due to limited soil reduction. Using the diluted wastewater as the sorption solution matrices instead of 0.01 mol L-1 KCI solution, the soils generally exhibited greater Smax and lower EPC0 except for the EPC∅ of a reduced surface soil, implying more complex P sorption in the field. Identified P sorption mechanisms include phosphate precipitation, ligand exchange with organic matter, and adsorption onto Fe hydroxides. Transformation of Fe compounds during soil reduction is primarily responsible for the changes in soil P sorption. [ABSTRACT FROM AUTHOR]