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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

In semiarid regions, thousands of small reservoirs provide the rural population with water, but their storage volumes and hydrological impact are largely unknown. This paper analyzes the suitability of weather-independent radar satellite images for monitoring small reservoir surfaces. The surface areas of three reservoirs were extracted from 21 of 22 ENVISAT Advanced Synthetic Aperture Radar scenes, acquired bimonthly from June 2005 to August 2006. The reservoir surface areas were determined with a quasi-manual classification approach, as stringent classification rules often failed due to the spatial and temporal variability of the backscatter from the water. The land-water contrast is critical for the detection of water bodies. Additionally, wind has a significant impact on the classification results and affects the water surface and the backscattered radar signal (Bragg scattering) above a wind speed threshold of 2.6 m x [s.sup.-1]. The analysis of 15 months of wind speed data shows that, on 96% of the days, wind speeds were below the Bragg scattering criterion at the time of night time acquisitions, as opposed to 50% during the morning acquisition time. Night time acquisitions are strongly advisable over day time acquisitions due to lower wind interference. Over the year, radar images are most affected by wind during the onset of the rainy season (May and June). We conclude that radar and optical systems are complimentary. Radar is suitable during the rainy season but is affected by wind and lack of vegetation context during the dry season. Index Terms--Bragg scattering, radar, remote sensing, reservoirs, resource management, water, water resources, West Africa.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2008.08.011 Byline: Nalini S. Rao (a)(b), Zachary M. Easton (a), Elliot M. Schneiderman (c), Mark S. Zion (c), David R. Lee (d), Tammo S. Steenhuis (a) Abbreviations: Best Management Practices, BMP; Dissolved Phosphorus, DP; Particulate Phosphorus, PP; Total Phosphorus, TP; Variable Source Areas, VSAs Abstract: Planners advocate best management practices (BMPs) to reduce loss of sediment and nutrients in agricultural areas. However, the scientific community lacks tools that use readily available data to investigate the relationships between BMPs and their spatial locations and water quality. In rural, humid regions where runoff is associated with saturation-excess processes from variable source areas (VSAs), BMPs are potentially most effective when they are located in areas that produce the majority of the runoff. Thus, two critical elements necessary to predict the water quality impact of BMPs include correct identification of VSAs and accurate predictions of nutrient reduction due to particular BMPs. The objective of this research was to determine the effectiveness of BMPs using the Variable Source Loading Function (VSLF) model, which captures the spatial and temporal evolutions of VSAs in the landscape. Data from a long-term monitoring campaign on a 164-ha farm in the New York City source watersheds in the Catskills Mountains of New York state were used to evaluate the effectiveness of a range of BMPs. The data spanned an 11-year period over which a suite of BMPs, including a nutrient management plan, riparian buffers, filter strips and fencing, was installed to reduce phosphorus (P) loading. Despite its simplicity, VSLF predicted the spatial distribution of runoff producing areas well. Dissolved P reductions were simulated well by using calibrated reduction factors for various BMPs in the VSLF model. Total P losses decreased only after cattle crossings were installed in the creek. The results demonstrated that BMPs, when sited with respect to VSAs, reduce P loss from agricultural watersheds, providing useful information for targeted water quality management. Author Affiliation: (a) Department of Biological and Environmental Engineering, 206 Riley-Robb Hall, Cornell University, Ithaca, NY 14853, United States (b) Department of Natural Resources, Fernow Hall, Cornell University, Ithaca, NY 14853, United States (c) New York City Department of Environmental Protection, Kingston, NY 12401, United States (d) Department of Applied Economics and Management, Warren Hall, Cornell University, Ithaca, NY 14853, United States Article History: Received 22 August 2007; Revised 31 July 2008; Accepted 24 August 2008

Most widely used nonpoint source models associate pollutant loads almost exclusively with land use via pollutant export coefficients and some kind of runoff coefficient. Not surprisingly, the range of management options suggested by such models' simulations are largely linked to changes in land use. This problem is addressed by developing models of dissolved phosphorus (DP) mobility for specific agricultural sources: manure, fertilizers, soil/plant complexes, and impervious surfaces and those associated with baseflow P loads. These models are coupled with a spatially distributed hydrologic model, the variable source loading function model. The model was applied to a small (164 ha), upstate New York watershed and tested against 1996-2000 stream flow and DP data. The source-specific model required no direct calibration of parameters compared to eight parameters needed in a similar export coefficient type model. Both models predicted stream DP loads well but the source-specific model provided additional insights into, for example, how much DP in the stream was derived from accumulated soil P as opposed to direct leaching from manure. This type of information is necessary to develop and assess a full range of options for best management practices, especially those that involve nonstatic activities such as manure spreading. DOI: 10.1061/(ASCE)0733-9372(2009) 135:1 (25) CE Database subject headings: Phosphorus; Watersheds; Agriculture; Water pollution; Nonpoint pollution.

The most common form of onsite domestic wastewater treatment in the United States is the septic system. Although the design of these systems has been well established, no systematic evaluation of septic system performance exists for sloping hardpan soils. In this paper, we develop a simple hydrologic model for assessing the probability of failure for a set of hydrologic conditions, septic loading rates, and soil and landscape parameters that are readily available for sloping soils. To demonstrate the model capabilities, input data for a septic field of a two-person residence in the New York City drinking water basin in the Catskills was utilized. Our analysis showed that the saturated hydraulic conductivity, depth to the impermeable layer, and slope of the drain field are critical parameters to assess in the design and siting of these systems. We concluded that septic systems perform poorly in undulating landscapes where the hydraulic conductivity is low and the impermeable layer is close to the surface. Under prolonged rainfall conditions on these soils, the septic field and downslope field saturate, causing hydraulic failure of the septic system and saturation in the downslope field; as a result, effluent may be routed directly to streams via overland runoff. DOI: 10.1061/(ASCE)0733-9372(2006) 132:10(1289) CE Database subject headings: Hydrology; Evaluation; Slopes; Wastewater treatment; Waste disposal.

Fire is commonly used to establish and maintain pastures in the Amazon. Fire is also known to induce soil water repellency but few published data exist for the humid tropics. The objectives of this study were to characterise the intensity and spatial variability of water repellency on previously burned pasture soils in the Amazon, and its effect on the nutrient status of the forage grass Brachiaria brizantha (Hochst.) Stapf. Surface soils of pastures and forests in north-western Mato Grosso, Brazil, were found to exhibit soil water repellency using MED and WDPT tests. Soil water repellency was found only within 0-0.01 m of the mineral soil surface, with soil below 0.01 m found to be hydrophilic in all cases. Spatial variability of repellency was high for both pasture and forest soils. For pasture soils, soil water repellency was strongest on recently burned pastures, which exhibited some extremely high values (MED >8 M). Repellency decreased rapidly with time following burning. Increasing soil water repellency was associated with decreasing N:P ratios or B. brizantha above-ground biomass ([r.sup.2] = 0.66, P= 0.004). These findings indicate that soil water repellency and pasture productivity are inversely related. Since pasture abandonment fuels continued deforestation, disrupting the processes causing pasture degradation may lead to more sustainable land use in the Amazon. Additional keywords: hydrophobicity, Brachiaria brizantha, burning, N : P, Oxisol, Ultisol., Introduction Over 75% of Amazonian deforestation in the past 30 years has been directed towards the establishment of pastures (Fearnside 1996). The productivity of Amazonian pastures declines within 4-8 years [...]

Modeling the transport of chemicals is challenging due to the presence of preferential flow paths and the input data needed to describe these paths. We propose a simple equation that can predict the breakthrough of solutes without excessive data requirements under steady state flow conditions. In our generalized preferential flow model (GPFM), the soil is conceptually divided into a distribution zone and a conveyance zone. The distribution zone acts as a linear reservoir resulting in an exponential loss of solutes through preferential flow paths from this zone. In the conveyance zone, the transport of solutes is described with the convective-dispersive (CD) equation. Input data required are the apparent water content of the distribution zone, and solute velocities and dispersivities in the conveyance zone. The model is tested with chloride breakthrough curves (BTCs) resulting from three sets of experiments performed with steady state artificial acid rainfall at different intensities applied sequentially using duplicate columns filled with undisturbed soil or sand both exhibiting preferential flow. The model is able to describe the breakthrough of solutes with physically meaningful parameters through coarse sand with fingered flow and through undisturbed soil cores. In coarse sand, water and solutes flow only through the fingered flow paths in the conveyance zone. In undisturbed columns there is both flow through the matrix and preferential flow paths, and two velocities in the conveyance zone are needed to simulate the breakthrough curves.

While the rapid transport of nonadsorbed chemicals is relatively well understood, preferential transport of adsorbable chemicals including P requires further study. Our objective was to characterize subsurface P transport in glaciated soils of the northeastern USA. Large intact columns from five soils with differing structures were subjected in duplicate to both synthetic acid rainfall at a low rate simulating natural rainfall, and ponded water for observing saturated flow. The rain was enriched with inorganic and organic P after baseline conditions were established. Drainage water P concentrations were measured and adsorption isotherms were determined. Type of flow was characterized using Cl breakthrough curves and visualizations of blue dye patterns. Baseline P concentrations in drainage water were 0.02 to 0.04 mg [L.sup.-1]. At low flow rates, P appeared in the drainage water soon after application of either inorganic or organic P for the silt loam soil (firm, moderate coarse prismatic parting to moderate medium subangular blocky structure) in which preferential flow paths carried most of the water flow. In contrast, the soils in which matrix type flow dominated (weak fine granular or weak medium subangular blocky structures) had little or no increase in drainage water P. However, under ponded conditions all soils exhibited preferential flow and rapid P breakthrough. Elevated P concentration in the drainage water could not be explained by the P adsorption strength with the possible exception of the sandy loam soil, where the outflow P concentration was consistently low. Variation in flow rate in conjunction with soil structure satisfactorily explained elevated concentrations of dissolved inorganic and organic P in drainage water from surface applied P.

Watersheds, in many parts of the world, consist of sloping soils with a dense subsoil at shallow depth. Very few measurement techniques exist for realistically determining hydraulic properties in situ on these hillside soils. A hillslope infiltrometer, open at the bottom, top, and downhill sides, was developed that can measure the vertical saturated conductivity of the horizon sequence and lateral hydraulic conductivity of the horizon most conductive to water. The infiltrometer was tested on the steeply sloping soils in Honduras. Increasing rainfall intensities were applied and lateral flow rate was measured in several troughs at the downslope end of the hillslope infiltrometer. Vertical infiltration rates for the horizon sequence and lateral conductivity were calculated at each rainfall rate after steady state conditions were established. The hillslope infiltrometer proved useful in the characterization of subsurface flow on the steep slopes in Honduras.

Water-repellent soils occur all over the world and affect both groundwater pollution and crop yield. The finger-like wetting patterns in these soils have many similarities with unstable wetting fronts in coarse-grained sandy soils. Our objectives were to study the water movement in water-repellent sand and to examine how the theory for unstable wetting fronts applies to water-repellent sands. Infiltration experiments, in which moisture content and matric potentials were measured, were carried out in slab chambers with identical sands but with different levels of water repellence. Soil water characteristics were determined in separate experiments. Infiltration in the hydrophilic soil resulted in a uniform and horizontal front. All water-repellent sands showed a fingered flow pattern. For negative water-entry values, water infiltrated without delay. For positive values, water entered the soil only after the depth of the ponded water equaled or exceeded the water-entry pressure, which increased with increasing repellency. The finger widths predicted with the unstable flow theory agreed rather well with the observed values. In general, the research showed that the wetting patterns of water-repellent sands depended directly on the soil water characteristic curve. This implies that the type of wetting front and risk to groundwater pollution can be predicted based on laboratory-measured soil hydraulic properties.

Plant roots and soil biota require [O.sub.2] to function normally. When the soil [O.sub.2] is depleted, it must be replaced by [O.sub.2] from the atmosphere. The transport occurs primarily by gaseous diffusion. Although [O.sub.2] diffusion has been researched in homogeneous soils, and in tight clay soils with cracks, little is known about the effects of macropores on [O.sub.2] transport in typical agricultural soils. In this study we examined the impact of large pores on [O.sub.2] concentration in a sandy loam soil. Experiments were carried out with homogeneous and simulated-macropore columns with a steady-state rainfall of 3 cm [d.sup.-1] in which the [O.sub.2] concentration in the soil matrix and in the macropore was measured at 15-cm vertical intervals. The diameter of each column was 20 cm and the height was 105 cm. Groundwater depth was systematically varied between 30 and 105 cm. Soil water content did not vary with distance above the water table for the 30-, 60-, and 90-cm groundwater depths. While both the soil water for the entire column and the [O.sub.2] concentration from the surface to the 30-cm depth was the same for the homogeneous and macropore columns, the [O.sub.2] penetrated deeper in the macropore column and was 4% greater below the 30-cm depth in the macropore column than for the homogeneous column.

The often rapid arrival of pesticides at the ground water has been explained by the concept of preferential movement of water and solutes through the soil. To facilitate understanding of these transport processes, a drainage study was conducted by applying a nonadsorbed tracer to plots drained by subsurface drains. Three management practices were employed: no-till, conventional-till, and conventional-till with incorporation of the tracer. The plots were irrigated with 71-203 mm of water. Drainage line outflow and tracer concentration in the outflow were monitored for up to 52 hr. The resulting soil profiles were analyzed for tracer concentration. The main effect of plowing and incorporating the tracer was a more uniform concentration in the resulting profile. A simple mixing-layer model was used to predict the rate at which the tracer was transported out of the root zone into the layers below. The model was found to be in reasonable agreement with drainage outflow patterns, especially from the incorporated plots. These results may be helpful for future development of best-management practices for controlling the effects of agriculture on environmental pollution.

Simple methods for predicting runoff from watersheds are important in engineering practice, particularly in flood forecasting and water-balance calculation. In this paper, we illustrate that the often used SCS runoff curve-number approach in its most elementary form can be derived from assuming that only the saturated areas contribute to direct runoff. With this approach the initial abstraction or the amount of water required before runoff starts is equal to air-filled pore space per unit area for the most shallow soil in the watershed. Air-filled pore space throughout the year was calculated with aid of the simple water balance employing the Thornthwaite-Mather procedure for the most shallow soil in the watershed. By plotting the effective precipitation defined as the amount of precipitation minus the initial abstraction against the observed runoff for two watersheds in Australia and three in the northeastern United States we found that the SCS curve-number equation in its elementary form fitted the data well.

A new high-resolution quantitative method of examining quick alterations of the fluid amount present in porous media, was provided by synchrotron X-rays at the Cornell High Energy Synchrotron Source. This method is founded on controlling X-ray absorbance alterations in sand volumes crossed by an acute, highly collimated synchrotron X-ray beam. This method helps assess the physical and chemical characteristics of a rapid flow field in porous media.

Robust and noninvasive techniques for in situ measurement of soil water content are essential for monitoring and research of many hydrologic processes. Although in situ measurement of soil water content by means of a soil's electric and dielectric properties has been explored extensively, the use of ground-penetrating radar (GPR) for this purpose is not well established. We compared the soil's dielectric constant as measured by GPR and time domain reflectometry (TDR) and its relationship to water content determined independently in auger holes. We propose a calibration equation relating soil water to GPR-measured dielectric constants. The difference in calibration equations between GPR and TDR was partially attributed to the difference in frequency ranges in which TDR and GPR operate and the zero offset of the GPR.

The term 'groundwater pollution' typically brings to mind contaminants--pesticides, solvents, and excess nutrients, among others--that are either soluble in water or are fluids themselves, percolating downward through the soil. However, [...]

For us it was a routine test and demonstration of the preferential flow of water through soil: apply an inch or two of water containing blue food coloring to the [...]