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ABSTRACT The movement of contaminants via colloidal transport mechanisms through the vadose zone to groundwater is of growing concern. Normally-immobile contaminants can enter an aquifer via colloid-facilitated transport, and pathogens... more
ABSTRACT The movement of contaminants via colloidal transport mechanisms through the vadose zone to groundwater is of growing concern. Normally-immobile contaminants can enter an aquifer via colloid-facilitated transport, and pathogens themselves (e.g. Cryptosporidium parvum) are colloidal in scale. Little is known about the complex pore-scale mechanisms of transport and retention of colloids in soils. Measurements of colloid and microbial transport have been typically limited to the evaluation of breakthrough curves from column experiments (which yield only an integrated signal of all retention processes in the column) or to the visualization in micromodels with limited applicability to realistic conditions. The objective of the work discussed here is to observe and model colloid transport and retention on the pore scale. Flow experiments were run in a horizontal flow chamber containing clean quartz sand as the porous medium. Synthetic fluorescent microspheres were used as easily-detected colloid surrogates. A syringe inlet pump and peristaltic outlet pump controlled the chamber moisture content and flow rate. The chamber was mounted under a Laser Scanning Confocal Microscope (Leica TCS SP2, 10x 0.40 UV objective) which allowed the acquisition of time series images and D reconstruction of pore-scale images. Three spectral channels were used to detect: 1) fluorescent microsphere emissions (500 to 540 nm) excited at 488 nm by an argon laser; 2) water phase emissions (555 to 650 nm) due to Rhodamine B stain excited at 543 nm by a green HeNe laser; and 3) reflectance of laser light at the grain surfaces. Three 8-bit images were detected simultaneously for every time step. The system is also capable of obtaining image stacks in the z-direction, which allow the determination of the position of attached colloids relative to the interface between air, water menisci, and solid grains. The 3D z-axis stacks reveal that the colloids are attaching at the air/water meniscus/solid (AWmS) interface, our term for the region where the water menisci diminish into a thin film covering the grains. Methods of digital image analysis are presented for quantification of the number and area of both moving and retained colloids. After thresholding the argon laser channel images (in which the microsphere location information is stored), binary images are obtained. The total number and area of white pixels in selected regions are counted for each image sequence. Pixels are counted as colloids attached to the AWmS interface when they appear at exactly the same location in sequential images, as determined by using a Boolean logical operator in a measurement loop. The difference between total and attached particles represents mobile (suspended) particles. The results show that once the first colloid is attached at the AWmS interface, the attachment rate increases until the number of locations where the colloids can be attached near other colloids becomes limiting. A Langmuir model is presented that is capable of predicting the observed colloid attachment processes. Forces acting on the colloids are discussed.
Research Interests: Materials Science, Time Series, Image Analysis, Soil moisture, Thin Film, and 15 moreDigital Image Analysis, 3-D Reconstruction, Groundwater Quality, Rhodamine B, Moisture Content, Porous Medium, Flow Rate, Vadose Zone Modeling, Image Sequence, Instruments and Techniques, Colloid, Breakthrough Curve, Binary Image, Cryptosporidium parvum, and Facilitated transport
To understand the movement and retention of colloids in the vadose zone, it is crucial to investigate processes on the pore scale. Experiments were carried out using a confocal laser scanning microscope which allows acquisition of time... more
To understand the movement and retention of colloids in the vadose zone, it is crucial to investigate processes on the pore scale. Experiments were carried out using a confocal laser scanning microscope which allows acquisition of time series images as well as D reconstruction of pore-scale images. Hydrophilic (carboxylated latex) and hydrophobic (polystyrene latex) colloids in aqueous solution stained with rhodamine B were injected into a small horizontal flow chamber packed with fine or coarse quartz sand. The chamber was situated under the microscope which used three spectral channels: a 488 nm (argon) line excites the colloid fluorescence, a 543 nm green (HeNe) line excites rhodamine B fluorescence, and a transmitted light channel that delineates the sand grains. This offers the possibility of finding suitable thresholds for detecting colloidal micropheres and the water phase. Methods of digital image analysis are presented which determine the number and area of moving and retained colloids. The results can be used to verify simulation model parameters concerning colloid transport, such as quantitative measurements for determining collision efficiencies.
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ABSTRACT Nitrous oxide (N2O) gas has been identified as an important contributor to atmospheric greenhouse effect. The largest agricultural N2O emissions are from fertilizer applications, tillage and livestock on farms. Livestock sources... more
ABSTRACT Nitrous oxide (N2O) gas has been identified as an important contributor to atmospheric greenhouse effect. The largest agricultural N2O emissions are from fertilizer applications, tillage and livestock on farms. Livestock sources include manure storage, handling, and land application, and N2O emissions from those manure management practices can be very significant. The development of manure best management practices to minimize the contribution of livestock to the global greenhouse effect requires knowledge of the environmental and atmospheric conditions that affect nitrous oxide emission rates. In this study we estimated nitrous oxide emissions from fresh dairy manure under several air exchange rates creating different oxic and anoxic conditions. During a three weeks period, gas flows with and without oxygen (compressed air and dinitrogen) at different rates were continuously passed through manure samples incubated at 25°C. Nitrogen transformations in manure and N2O emissions were quantified as a function of flow rate. We found that manure treatments involving exposure to the air could be significant source of nitrogen gaseous emissions. The rates and dynamics of N2O emissions were substantially impacted by oxygen and total ammoniac nitrogen content, which, in turn, was regulated by the aeration rate. The higher oxygen availability resulted from high aeration significantly enhanced nitrification and inhibited denitrification. Increasing airflow rates led to higher N losses through ammonia volatilization and, consequently, to the faster depletion of total N stock and reducing potential for N2O formation. N-N2O losses varied from 1.6 to 4.2% of manure total nitrogen content. The maximum N2O emissions were observed at moderate aeration rates.
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The effect of surfactant and ionic strength concentration on colloid transport through saturated or partially saturated media has typically been studied inferentially using breakthrough curves. In this work, we made pore-scale... more
The effect of surfactant and ionic strength concentration on colloid transport through saturated or partially saturated media has typically been studied inferentially using breakthrough curves. In this work, we made pore-scale observations in a small flow chamber to count colloids retained on the grain, air and liquid interfaces using a confocal microscope system and public domain image analysis software ImageJ. Stacks of images were analyzed for colloid retention in which the ionic strength and concentration of surfactant (nonionic Surfynol 485) were varied. The number of mobile (free in the water phase) colloids and attached colloids (retained at the surface of sand grains) for each image were quantified. We found that as ionic strength increased, the location where the colloids were retained changed from the air/water meniscus/solid (AWmS) interface to the water/solid (WS) interface. In addition, we observed that increasing the surfactant concentration reduced the retention of colloids due to decreased contact angle and surface tension.
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ABSTRACT Agriculture has been implicated as an important source of atmospheric nitrous oxide and ammonia emissions. In dairy areas the main source of N is due to the spreading of animal waste on the agricultural land. Fifty to eighty... more
ABSTRACT Agriculture has been implicated as an important source of atmospheric nitrous oxide and ammonia emissions. In dairy areas the main source of N is due to the spreading of animal waste on the agricultural land. Fifty to eighty percent of the excreted N from animals occurs in urine with the varying proportion depending on the diet. The main goal of the research was to quantify ammonia and nitrous oxide emissions from urine-treated soils and to relate these results to urinary N-transformation processes in soil. We studied effects of soil texture, air filled porosity, and rate of air exchange. Series of laboratory experiments were carried out in aerobic as well as anaerobic conditions in which synthetic urine was mixed with either fine and coarse sand. Ammonia and nitrous oxide were measured at the time intervals of 20 minutes up to 6 hours. The air flow rate ranged from zero to 2000 ml/min. As expected, most ammonia volatilized during the first hours of the experiment and was well correlated with moisture loss by evaporation. Ammonia volatilization and evaporation rates were greater for coarse rather than fine sand. Consequently the total nitrous oxide emission was higher for the fine sand because more ammonium was available for nitrification and subsequent denitrification. Under no air flow conditions, the input of denitrification to total nitrous oxide production was higher in the fine sand than in the coarse sand at the same moisture content. In all experiments, the most nitrous oxide was emitted within two ranges of oxidation-reduction potential: -50-50 with denitrification-dominant conditions and 250-400 mV with nitrification-dominant conditions.
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... Texture Effect. Olga Singurindy, Brian K. Richards * , Marina Molodovskaya and Tammo S. Steenhuis Dep. of Biological and Environmental Engineering, Riley-Robb Hall, Cornell Univ., Ithaca, NY 14853 * Corresponding author... more
... Texture Effect. Olga Singurindy, Brian K. Richards * , Marina Molodovskaya and Tammo S. Steenhuis Dep. of Biological and Environmental Engineering, Riley-Robb Hall, Cornell Univ., Ithaca, NY 14853 * Corresponding author (bkr2{at}cornell.edu). Received 16 May 2006. ...
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... solid dairy manure. ... Field under footprint was estimated according to landscape features and predominant wind direction, and sampling unit and 3-D anemometer were installed at the height of 3 m, following the rule of... more
... solid dairy manure. ... Field under footprint was estimated according to landscape features and predominant wind direction, and sampling unit and 3-D anemometer were installed at the height of 3 m, following the rule of fetch/measurement height ratio of 100:1. Time lag between ...
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Research Interests: Chemistry, Kinetics, Environmental Monitoring, Confocal Microscopy, Medicine, and 15 moreMultidisciplinary, Environmental science and technology, Porosity, LaTeX, Air, Porous Media, Colloids, Polystyrene, Particle Size, Film Thickness, Colloid, Environmental, Geologic Sediments, Breakthrough Curve, and Polystyrenes
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The distribution of colloid particles onto interfaces in partially saturated media was investigated by using a pore scale visualization technique which consists of a small horizontal chamber and a Leica Confocal Scanning Microscope.... more
The distribution of colloid particles onto interfaces in partially saturated media was investigated by using a pore scale visualization technique which consists of a small horizontal chamber and a Leica Confocal Scanning Microscope. Synthetic hydrophilic (carboxylated latex) and hydrophobic (polystyrene latex) microspheres with diameters of 1 mu m were applied using a 1.5 ml/min steady flow rate. Quartz sand of two different sizes (fine and coarse) and glass beads were used as media. For the hydrophilic colloids, we observed retention at the Air/Water meniscus/Solid (AWmS) interface for both sizes of sand grains and glass beads. The colloids were retained at the AWmS interface where the water menisci diminished to a thin water film on the grain surface, and the film thickness approximately equals to the colloid diameter. This mechanism can be explained by additional capillary potentials exerted on colloids, pulling them out from the menisci. Mechanisms for hydrophobic colloids differed slightly. When glass beads were used as media, retention occurred at the AWmS and the solid-water interface. However, with sand grains as media, the retention of hydrophobic colloids mostly occurred at the solid-water interface and only to an insignificant amount at the AWmS interface. The greater retention of hydrophobic colloid at the solid-water interface is due to irregularities in sand grain surfaces (compared to the smoother glass beads). This factor seems to play an insignificant role in the retention of hydrophilic colloids.
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Very few direct observations have been made of colloid transport in unsaturated porous media. Studies have typically been limited to the evaluation of breakthrough curves from column experiments. Because breakthrough curves give only an... more
Very few direct observations have been made of colloid transport in unsaturated porous media. Studies have typically been limited to the evaluation of breakthrough curves from column experiments. Because breakthrough curves give only an integrated response, differing and sometimes conflicting colloid retention mechanisms have been proposed. To assess the validity of proposed mechanisms, we carried out pore scale visualization technique
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ABSTRACT: The line transect method of measuring crop residue cover was tested twice in the field for variation in results obtained by different people. By the second test, observers attained a high degree of precision in their results.... more
ABSTRACT: The line transect method of measuring crop residue cover was tested twice in the field for variation in results obtained by different people. By the second test, observers attained a high degree of precision in their results. Variation in field residue cover exceeded variation among observers. Consequently, to obtain accurate results it is more important to have multiple measurements than it is to have multiple observers.
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ABSTRACT Eutrophication due to anthropogenic phosphorus (P) sources is a persistent and critical national water quality problem. Although agricultural land is a recognized nonpoint source (NPS) of P, current risk assessment tools and best... more
ABSTRACT Eutrophication due to anthropogenic phosphorus (P) sources is a persistent and critical national water quality problem. Although agricultural land is a recognized nonpoint source (NPS) of P, current risk assessment tools and best management practices for addressing P are limited by our incomplete understanding of the processes controlling P mobility. The Cornell Soil and Water Laboratory and Ecohydrology Research Groups are pursuing a campaign of projects focused on improving our understanding of the ecohydrological factors - both natural and anthropogenic - that control P mobility. Specific projects are designed to identify specific roles of microbial ecology, soil chemistry, and landscape position or propensity to soil-saturation on P transport potential. This presentation synthesizes findings across these projects that access our best understanding of ecohydrological controls on P mobility and highlight persistent challenges in unraveling this puzzle as well as implications for land management.
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The detrimental loss of N from N fertilizers is a serious environmental problem of modern agriculture. Amongst the threats that elevated N use poses to the environment, the increase in net N2O production is of special concern, due to its... more
The detrimental loss of N from N fertilizers is a serious environmental problem of modern agriculture. Amongst the threats that elevated N use poses to the environment, the increase in net N2O production is of special concern, due to its persistent atmospheric effect as a greenhouse gas and as a contributor to ozone destruction. Long-term monitoring of N2O flux was conducted on a mid-size dairy farm in central New York to determine N2O emission levels from agricultural practices that are common for the region. The technique used was Tunable Diode Laser Absorption Spectrometer (TDLAS) coupled with 3D sonic anemometer; continuous eddy flux observations were conducted throughout three years on an alfalfa field in 2006, corn field in 2007, and on a split alfalfa/corn site in 2008 (ongoing). All fields were fertilized after/before growing seasons with dairy manure only. The results showed highly variable, instantaneous nature of N2O flux, with peak values reached after strong and sharp increases in both soil moisture and temperature. Manure spreading affected N2O fluxes only when factors of temperature and moisture were not limiting: at temperatures below 5°C, manure spreading had no pronounced effect on the N2O release. Average flux values were higher for corn (0.059mug m-2 s-1) then for alfalfa (0.045mug m-2 s-1), which was possibly related to manure application during spring thaw and its further incorporation with the plowing on the corn field. The greatest flux value for 2006-2007 of 0.76mug m-2 s-1 was also observed for the corn field during a spring thawing event.
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Phosphonate‐based herbicides are extensively used in agriculture. Glyphosate was long considered immobile in soils due to strong complexation with metal oxides, but detection in agricultural effluents and surface waters points to... more
Phosphonate‐based herbicides are extensively used in agriculture. Glyphosate was long considered immobile in soils due to strong complexation with metal oxides, but detection in agricultural effluents and surface waters points to glyphosate mobilization and transport. In particular, mechanisms of glyphosate adsorption and subsequent mobility from runoff‐prone soils enriched in quartz have not been fully elucidated. Here we used theoretical and experimental approaches to gain new insights on the soil mobility of glyphosate and two other phosphonate herbicides, glufosinate and fosamine. Molecular modeling simulations of optimized adsorbate complexes of the phosphonate herbicides with quartz and montmorillonite revealed Ca‐enhanced interactions for all three herbicides at both mineral interfaces, weak binding of Na‐complexed phosphonate herbicides on quartz, and more favorable interactions for glufosinate and fosamine with Na‐montmorillonite than for glyphosate. We conducted adsorption...
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Soils accumulate heavy metals when sewage sludge is applied to land for disposal or intended beneficial use. Because of the concern over the environmental danger that these sludge-borne metals could represent if mobilized, many studies... more
Soils accumulate heavy metals when sewage sludge is applied to land for disposal or intended beneficial use. Because of the concern over the environmental danger that these sludge-borne metals could represent if mobilized, many studies have been performed in an attempt to clarify the different factors that contribute to metal solubility, plant uptake and leachability. The objectives of this study were to determine if two independent factors soluble organic chelators and preferential flow paths enhanced metal mobility through soil. 2 2 2 3 2 Dilute solutions containing CdCl , ZnCl , CuCl , and Pb(NO ) were applied to soil columns with a rainmaker, and leachate metals and chloride concentrations were measured. For four columns, the input metal concentrations (mg L ) were 7.25 Cd, 4.55 Zn, 3.51 Cu, and 13.85 Pb. With four -1 other columns, the solution also contained dissolved organic matter so that the metals were organicallycomplexed, and input metal concentrations (mg L ) were 6.30 ...
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Phosphorus (P) transfer from the landscape to receiving waters is an important environmental concern because these diffuse losses may cause widespread water quality impairments which can accelerate freshwater eutrophication. Phosphorus... more
Phosphorus (P) transfer from the landscape to receiving waters is an important environmental concern because these diffuse losses may cause widespread water quality impairments which can accelerate freshwater eutrophication. Phosphorus (P) mobilization from soil to surface and subsurface flow paths is controlled by numerous factors, and thus it can vary greatly with time and landscape scale. To determine whether P
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Research Interests: Chemistry, Leaching, Environmental Chemistry, Environmental Pollution, Medicine, and 15 moreMultidisciplinary, Soil Pollution, Percolation, Mobility, Sewage sludge, Metal Complexes, Ground Water, Drinking Water, Preferential Flow, Leachate, Lysimeter, Environmental, Soil Profile, Soil Texture, and Land Application
ABSTRACT The introduction of microbial pathogens into the environment from untreated manure represents a threat to water quality and human health. Thus, understanding the effect of manure management strategies is imperative to effectively... more
ABSTRACT The introduction of microbial pathogens into the environment from untreated manure represents a threat to water quality and human health. Thus, understanding the effect of manure management strategies is imperative to effectively mitigate the inadvertent release of pathogens, particularly in subsurface environments where they can be transported through macropores to the groundwater or through agricultural tile line to open water bodies. The production of cell-surface biomolecules is also suspected to play an important role in the environmental survival and transport of enterobacterial pathogens. This study collected Escherichia coli samples from three dairy farms with artificial tile drainage systems and active manure spreading in the Central New York region over a three-month period. Sampling targeted four potential source locations on each farm: (i) cow housing, (ii) manure storage facilities, (iii) field soil, and (iv) subsurface drainage effluent. Over 2800 E. coli isolates were recovered and consequently analyzed for the cell surface components, cellulose and curli, traits associated with increased environmental survival, altered transport and pathogenicity. The E. coli isolates from locations i-iii displayed highly variable curli and cellulose-producing communities, while isolates collected from subsurface runoff on each farm had stable curli and cellulose production communities over all sampling dates. Furthermore, the method of manure application to the fields influenced the population characteristics found in drainage effluent isolates. Incorporation of manure into the soil was correlated to isolate populations largely deficient of curli and cellulose; whereas farms that only surface-applied manure were correlated to isolate populations of high curli and cellulose production. The production of curli and cellulose has previously been shown to be a response to environmental stress on the cell. Therefore, incorporation of manure directly into the soil appears to minimize environmental stresses, like UV radiation, desiccation and temperature fluctuation, typically found on the soil surface. Our findings indicate that E. coli strains above the surface are largely diverse, until they enter subsurface environments where specific extracellular characteristics are likely advantageous for survival and/or transport.
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ABSTRACT Millions of hectares of marginal lands in the Northeast USA no longer used for agriculture are suitable for production of second-generation cellulosic bioenergy crops, offering the potential for regional bioenergy production... more
ABSTRACT Millions of hectares of marginal lands in the Northeast USA no longer used for agriculture are suitable for production of second-generation cellulosic bioenergy crops, offering the potential for regional bioenergy production without inducing food vs. fuel competition for prime farmland. Abundant water resources, close proximity between production and markets, and compatibility with existing agricultural systems all favor development in the region. Yet, little is known about how sustainable bioenergy crop production on marginal lands is regarding greenhouse gas emissions. In a 10-ha field trial on wet marginal soils in upstate New York, we are assessing the effect of land use change (from fallow land to perennial grass stands) on N2O and CH4 emissions. The deep clay loam is unsuited for row-crop agriculture because it is too dry in summer and too wet in winter. Monthly chamber campaigns were performed from April to November 2012 to monitor large scale (10-20 m resolution) differences caused by land cover type (n=4 for both switchgrass, reed-canary grass and a 50-yr unplowed control) across soil moisture gradients (n=5 soil moisture levels per replicate). Additional weekly campaigns assessed the smaller scale spatial and temporal variability in emissions at meter-scale. Here we present results of both the large and small-scale patterns in greenhouse gas emissions from this marginal soil, and discuss effects of soil properties and hydrologic conditions as potential drivers. Insight gained about the environmental impact of bioenergy crops can be used to assess the sustainability of using this region's underutilized land base for energy production.
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ABSTRACT Vegetative filter strips (VFS) are commonly used to reduce agricultural pollutants such as phosphorus (P) present in milkhouse wastewater and barnyard runoff. Although VFS can sometimes efficiently remove P, water flow and P... more
ABSTRACT Vegetative filter strips (VFS) are commonly used to reduce agricultural pollutants such as phosphorus (P) present in milkhouse wastewater and barnyard runoff. Although VFS can sometimes efficiently remove P, water flow and P sorption in a VFS used for treating milkhouse wastewater and barnyard runoff were found to be erratic due to preferential flow and reduced soil infiltration capacity. Several possible amendments were tested for P immobilization potential in the laboratory, including wollastonite (calcium metasilicate) and fly ash from a coal-fired power plant. Fly ash demonstrated superior P immobilization potential, with a Langmuir adsorption isotherm capacity of 10 mg g.-1. Fly ash was placed in the wastewater holding tank and in flow channels of an actual VFS, resulting in reduction of test well water ortho-P to ug L-1 (ppb) levels. Fly ash was shown to act in three ways: P adsorption, precipitation of P as Apatite, and co-precipitation of P during hydrolysis of Fe and Al. However, during summer P concentrations in observation wells was observed to be much higher than the influent wastewater in the VFS, particularly near the preferential flow path. Measurements of dissolved organic carbon (DOC), iron and total phosphorus indicate enhanced microbial activities during summer. As a result, anaerobic biodegradation of organic matter plays a great role in releasing P, Fe and Mn from adsorbed sites. It is believed that certain components of DOC (such as hydrophilic, hydrophobic and neutrals) are formed during anaerobic biodegradation of organic matter present in water and the VFS. These DOC components may interact with iron, aluminum, manganese, calcium etc. present in soil resulting in the concomitant release of elements together with adsorbed P. A practical management approach to reducing P during summer may involve relocating the preferred wastewater flowpaths in the VFS, as well as fresh applications of fly ash to the new flowpaths in order to avoid the release of adsorbed P by microbial processes.