bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavy Metal Effects on the Metabolic Activity of Elliptio complanata: A Calorimetric Method
Authors: Cheney Marcos A. , Criddle Richard S.
Published: July 2010

The effects of short time exposure to mercury (Hg2+), cadmium (Cd2+), and copper (Cu2+) ions on the metabolic activity of gill tissue from the freshwater bivalve Elliptio complanata were investigated by isothermal calorimetry and respirometry. Metabolic heat rates were altered following exposure of gill tissue to these ions over the concentration range from 10−6 to 10−3 M. The effects of metal ions on metabolic heat rates were metal ion specific and time and concentration dependent. Treatment of tissue with low concentrations of Hg2+ and Cu2+ for short times caused stimulation of metabolic heat rates. Longer exposures and higher concentrations caused inhibition. Cadmium was inhibitory under all conditions tested. Treatment of mitochondria isolated from gill and muscle tissues showed a similar pattern of stimulation of respiratory rate at low concentration and inhibition at higher concentration. Analysis of CO2, and O2 from the headspace gasses in the calorimeter ampule showed an enhancement of respiratory quotient (RQ, i.e., RCO2/RO2 where R = rate) following addition of 10−3 M Cd2+ for 30 min. The microcalorimetric method proved to be a useful technique to assess toxicity of heavy metals on the gills of a freshwater bivalve.
A Passive Flux Sampler for Measuring Ammonia Volatilization from Manure Storage Facilities
Authors: Sommer Sven G. , Sibbesen Erik , Nielsen Tina , Schjørring Jan K. , Olesen J. E.
Published: July 2010

An integrated horizontal flux technique was tested for quantification of ammonia (NH3) emission from manure storage. The method is based on a simple and inexpensive passive flux sampler consisting of two disconnectable glass tubes, coated on the inside with oxalic acid. The flux sampler is mounted at a minimum of three heights, 20 to 100 cm above the storage, on each of four masts, placed perpendicular to each other around the storage. The samplers continuously integrate the horizontal flux of NH3 at the various heights. After analysis of the NH3 content in the tubes facing the storage (exposed tubes) and surroundings (background tubes), the vertical flux of NH3 from the storage can be obtained by application of mass balance equations (micrometeorological mass balance technique). For the measurements of NH3 volatilization from slurry tanks or lagoons the technique is useful, because it is not affected by heterogenity in wind profiles and the masts with the passive flux samplers are placed on the periphery of the slurry store. The flux samplers were able to accurately quantify NH3 volatilization from slurry tanks. From above the rim of the slurry tank the horizontal net flux decline exponential with height. This may facilitate the calculation of the vertical flux of NH3. Bypass of NH3 between exposed and background tubes may occur during periods with high wind velocities (>10 m s−1) or when more than one‐fifth of the oxalate in the exposed tube has reacted. However, if bypass occurs, a good estimate of NH3 volatilization can still be obtained by addition of exposed and background tubes, because the NH3 flux from storage are usually much greater than the flux from surroundings. Bypass due to high net horizontal fluxes of NH3 can be avoided by reducing the measuring period or increasing the length of the tubes. Storm conditions with heavy rain can flood the flux samplers and spoil the measurements. Within the study NH3 volatilization from stored cattle slurry were measured eight times from October to December 1992. Daily loss rates of NH3 varied between 0.33 and 4.15 g NH3‐N m−2 d−1.
Herbicide and Nitrate Distribution in Central Iowa Rainfall
Authors: Hatfield J. L. , Wesley C. K. , Prueger J. H. , Pfeiffer R. L.
Published: July 2010

Herbicides are detected in rainfall; however, these are a small fraction of the total applied. This study was designed to evaluate monthly and annual variation in atrazine (6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine), alachlor (2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide), metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide), and NO3‐N concentrations in rainfall over Walnut Creek watershed south of Ames, IA. The study began in 1991 and continued through 1994. Within the watershed, two wet/dry precipitation samplers were positioned 4 km apart. Detections varied during the year with >90% of the herbicide detections occurring in April through early July. Concentrations varied among events from nondetectable amounts to concentrations of 154 μg L−1, which occurred when atrazine was applied during an extremely humid day immediately followed by rainfall of <10 mm that washed spray drift from the atmosphere. This was a local scale phenomenon, because the other collector had a more typical concentration of 1.7 μg L−1 with an 8‐mm rainfall. Variation between the two collectors suggests that local scale meteorological processes affect herbicide movement. Yearly atrazine deposition totals were >100 μg m−2 representing <0.1% of the amount applied. Nitrate‐N concentrations in precipitation were uniformly distributed throughout the year and without annual variation in the concentrations. Deposition rates of NO3‐N were about 1.2 g m−2. Annual loading onto the watershed was about 25% of the amount applied from all forms of N fertilizers. Movement and rates of deposition provide an understanding of the processes and magnitude of the impact of agriculture on the environment.
Response of White Clover to Ozone in Different Environments
Authors: Heagle Allen S. , Reinert Richard A. , Miller Joseph E.
Published: July 2010

The value of research on effects of O3 done in greenhouse or field exposure systems is often questioned because chamber environments may affect plant response. Foliar injury, chlorophyll, and forage weight responses of two clones of white clover (Trifolium repens L.) to ambient O3 were compared for plants grown in charcoal‐filtered (CF) and nonfiltered air (NF) in greenhouse and open‐top field chambers and in ambient air (AA) plots at Raleigh, NC. One clone is sensitive to O3 (NC‐S), whereas the other is resistant (NC‐R). Comparisons of individual clone responses in CF vs. NF treatments in the greenhouse and in the field and the proportional response of the clones (defined as the NC‐S/NC‐R response ratio) were used to indicate the relative response to O3 in the different environments. Foliar injury and chlorophyll responses of NC‐S to O3 were similar in the NF greenhouse, NF open‐top chambers, and in AA. However, for individual harvests, the percentage decrease in NC‐S forage weight in NF compared with CF was 7 to 23% greater in the greenhouse than in open‐top chambers. The NC‐S/NC‐R forage ratios indicated that clover response to O3 in NF open‐top field chambers was the same as in AA. Large environmental differences between greenhouse and open‐top chambers apparently caused differences in plant responses to O3, whereas relatively small environmental differences between open‐top chambers and ambient air did not.
Estimating the Effects of Changing Land Use Patterns on Connecticut Lakes
Authors: Field Cathryn K. , Siver Peter A. , Lott Anne‐Marie
Published: July 2010

Changes in land use of 30 Connecticut lake watersheds between 1934, 1970, and 1990 were quantified using aerial photographs. Results were used with existing land use models to estimate changes in concentrations of total phosphorus (TP) and total nitrogen (TN) over the 56‐yr period. On average, the watersheds have increased in urban‐residential land cover from 2% in 1934 to 16% in 1990, and decreased in agricultural land from 20 to 7% during the same time period. The mean percentage of forested land has remained relatively constant. Based on the land use models of Norvell et al. (1979) and Frink (1991), the mean estimated total phosphorus concentration (eTP) increased from 15 μg L−1 in 1934 to 25 μg L−1 in 1990. The eTP concentrations increased in 26 of the 30 study lakes. In contrast, the mean estimated concentration of total nitrogen (eTN) increased only 20% from 374 to 450 μg L−1. Principal component analysis (PCA) was used to score each study lake according to its current trophic and ionic condition using chemical data from 1991 to 1993, and the results regressed against the 1990 land use types. Trophic scores were most highly correlated with forest cover, while ionic scores were most highly correlated with forest cover and the degree of urban‐residential land cover. The effect of water retention time is discussed. Land use models provide useful tools in the management of lakes.
Groundwater Vulnerability to Pesticide Contamination on a Regional Scale
Authors: Soutter Marc , Pannatier Yvan
Published: July 2010

Regional groundwater vulnerability maps that indicate the impact of leaching uncertainties, should be accompanied by maps expressing the probability of surpassing that index value. This case study presents first steps in a methodology for developing such an index and the probability of its value. Regionalization of piezometric data provided an estimate of the lacking water table depth at soil profiles. Monte‐Carlo simulations of pesticide fate on these soil profiles produced local distributions of a groundwater vulnerability index. Soil hydraulic properties were randomly generated using pedotransfer functions and experimental probability density functions of particle‐ size distribution and organic matter content. Medians of locally simulated distributions were then mapped to show the spatial distribution of groundwater vulnerability. It appeared that the resulting groundwater vulnerability map might be significantly affected by soil spatial variability, although soils are quite similar throughout the area. Deciles of the locally simulated distributions seem to show intrinsic coregionalization. This property could be used to build, over the whole area, an estimated groundwater vulnerability index distribution.
Input Parameter and Model Resolution Effects on Predictions of Solute Transport
Authors: Inskeep W. P. , Wraith J. M. , Wilson J. P. , Snyder R. D. , Macur R. E. , Gaber H. M.
Published: July 2010

Model predictions of solute transport using larger scale soil and climatic data sets may be useful for classifying mapping units based on their susceptibility to chemical leaching. However, model predictions based on input data sets with low spatial resolution may not accurately reflect transport processes occurring in situ. The goal of the current study was to compare several modeling approaches that might be applicable for classifying soil mapping units (1:24 000) according to their leaching potential to (i) model results based on detailed site‐specific measurements and (ii) observed data collected at a field site (Borollic Calciorthid) in southwestern Montana. Data from a 2‐yr field study of pentafluorobenzoic acid (PFBA), 2,6‐difluorobenzoic acid (DFBA) and dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) transport in fallow and cropped systems under two water application levels were compared to simulations obtained using the Chemical Movement in Layered Soils (CMLS) and Leaching and Chemistry Estimation (LEACHM) models. The resolution of model input parameters was varied based on sources of data. In Case 1, model inputs were obtained primarily from detailed soil profile characterization and site‐specific measurements of precipitation, irrigation, and pan evaporation. LEACHM predictions were also generated using estimated conductivity and retentivity functions from textural data obtained from the USDA‐NRCS Soil Survey (SSURGO) database (Cases 2 and 3). CMLS predictions were generated using (i) detailed site‐specific measurements (Case 1) and (ii) estimated volumetric water contents from textural data (SSURGO) and estimated daily precipitation and evapotranspiration (ET) from the Weather Generator (WGEN) and Montana Agricultural Potentials (MAPS) climate database (Cases 2 and 3). Comparison of observed and simulated mean solute travel times showed that (i) LEACHM and CMLS performed adequately with high‐resolution model inputs, (ii) model performance declined when field conditions were conducive to preferential flow, (iii) estimated Ks values from regression equations based on textural data were problematic for generating adequate predictions using LEACHM, and (iv) CMLS predictions were less sensitive to data input resolution, due in part to the fact that CMLS provides an oversimplified description of transport processes.
Incorporating Spatial Variability into GIS to Estimate Nitrate Leaching at the Aquifer Scale
Authors: Görres Josef , Gold Arthur J.
Published: July 2010

We evaluated the effect of spatial variability of selected intrinsic soil properties and extrinsic management practices on the groundwater quality in the 330‐ha recharge area of a high yield well site in Rhode Island. The analyses were performed at different support scales, ranging from point level to a support level equal to the entire recharge area. We used a mass balance model that relates leaching from the vadose zone to long‐term estimates of NO3‐N concentration at the well. We used a GIS database and stratified sampling for both soil characterization and assessment of spatial variability of NO3 leaching. The LEACHA/N rootzone model was used in conjunction with Monte Carlo simulation to generate cumulative distribution functions (CDFs) for leaching from different land strata (given by combinations of soil type and land use). To simulate the spatial variability of properties that served as inputs to the root zone model, we used CDFs of spatial distributions of soil properties and CDFs of the spatial variability of fertilizer application rates within a field. These strata scale CDFs were then combined to generate CDFs of the NO3‐N concentrations at the well, i.e., at a recharge area support scale. Although considerable variability was found at a point support scale, the analyses generated a markedly lower variability at the recharge area support scale. The results suggest that GIS data bases generated at scales available to resource managers (i.e., 1:12 000 and 1:24 000) may be well suited to manage the water quality of large production scale wells.
Coupling Vadose Zone Models with GIS: Emerging Trends and Potential Bottlenecks
Authors: Tim U. Sunday
Published: July 2010

The capabilities of geographic information systems (GIS) to capture, edit, manipulate, analyze, and display spatial and nonspatial data have long been recognized. Since its initial development in the 1960s, GIS technology has been used extensively to generate and spatially organize large volumes of data to support modeling of contaminant transport in the vadose zone. In the literature, however, two constantly recurring themes have been, on one hand, the opportunities that GIS provide for sophisticated analysis and visualization of spatial data, and on the other hand, their inadequacy for research and application in many disciplines, including environmental modeling. In vadose zone modeling, the gap between user demands and the functional capabilities of GIS have become something of a cliché. An intensive research effort will be needed to couple vadose zone models with GIS. The extent to which such research is advantageous depends upon the benefits to be derived and the potential problems that can be encountered. This paper examines broad issues concerning the coupling of vadose zone models with GIS and emphasizes the emerging trends and potential bottlenecks. Application examples involving the coupling of some vadose zone models of nonpoint source pollution with GIS are described. The issues addressed will help to explain how to loosely, closely, or tightly couple models with GIS, and to hopefully stimulate more discussions and future research activities.
Movement of Nitrate Fertilizer to Glacial Till and Runoff from a Claypan Soil
Authors: Blevins D. W. , Wilkison D. H. , Kelly B. P. , Silva S. R.
Published: July 2010

Although water from 20 to 25% of shallow farmstead wells in northern Missouri has concentrations of nitrate (NO−3) exceeding 10 mg L−1 as nitrogen (N), many potential sources for this NO−3 are usually present. A field experiment was designed to trace and isolate the amount of a single application of N fertilizer lost to a glacial‐till aquifer and runoffrom a 400 m2 corn (Zea mays L.) plot with bromide (Br−) and isotopically labeled (15N) fertilizer. Soil at the plot is a Albaquic Hapludalf of the Adco Series containing a 61 cm claypan beneath 41 to 43 cm of topsoil. Groundwater levels ranged from 0.38 to 2.40 m below the land surface. Transport of water and NO−3 to the saturated zone was not substantially retarded by the claypan. Labeled‐N fertilizer accounted for as much as 8.6 mg L−1 of the NO−3 (as N) in groundwater, but only in the top 1 to 2 m of the saturated zone. After two growing seasons (16 mo), <2% of the labeled‐N fertilizer was lost to runoff, about 30% was in the saturated zone, 27.3% was removed with the grain, and about 5% remained in the unsaturated zone. A large part of the remaining labeled N may have been lost in gaseous N forms. The presence of labeled NO−3 only in the top 2 m of the aquifer, slow horizontal transport, and winter recharge indicate grass crops such as wheat (Triticum aestivum L.) or rye (Secale cereale L.) might be used to extract near‐surface N during the winter recharge period. Also, fall fertilizations can be expected to readily leach. Because groundwater concentrations of labeled NO−3 were still increasing after two growing seasons, rotation of crops requiring small N inputs could be expected to limit the cumulative effect of large annual fertilizer applications on groundwater.
Vapor‐Phase and Particulate‐Associated Pesticides and PCB Concentrations in Eastern North Dakota Air Samples
Authors: Hawthorne Steven B. , Miller David J. , Louie Peter K. K. , Butler Raymond D. , Mayer Gale G.
Published: July 2010

Vapor‐phase and suspended particulate (<50 µm) samples were collected on polyurethane foam (PUF) and quartz fiber filters in rural North Dakota to determine the air concentrations of pesticides in an area where agriculture is a primary source of semivolatile pollutants. Samples were collected at two sites from 1992 to 1994 that were at least 0.4 km from the nearest farmed fields and known application of pesticides, and analyzed for 22 different organochlorine, triazine, and acid herbicide pesticides. Fourteen pesticides were found above the detection limits (typically <1 pg/m3). The most prevalent species found in the PUF extracts were endosulfan I and II (6,7,8,9,10,10‐hexachloro‐1,5,5a,6,9,9a‐hexahydro‐6,9‐methano‐2,4,3‐benzodioxathiepin 3‐oxide, exo‐ and endo‐isomers, respectively) at <1 to 2200 pg/m3 and <1 to 500 pg/m3, respectively, trifluralin (2,6‐dinitro‐N,N‐dipropyl‐4‐trifluoromethylaniline) at 3 to 700 pg/m3, and 4,4′‐DDE (1,1‐dichloro‐2,2‐bis‐(4‐(chlorophenyl)ethylene) at 6 to 200 pg/m3. The most prevalent pesticides in filter extracts included carbofuran (2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranyl methylcarbamate) at <0.5 to 470 pg/m3, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐l,3,5‐triazine) at <0.4 to 46 pg/m3, 2,4‐D ((2,4‐dichlorophenoxy)acetic acid) at <0.4 to 1800 pg/m3, and chlorothalonil (2,4,5,6‐tetrachloro‐1,3‐benzenedicarbonitrile) at <13 to 7800 pg/m3. Concentrations of polychlorinated biphenyl (PCB) congeners were much lower (<50 pg/m3 in all cases) than many of the pesticides. These results demonstrate that pesticides are among the most prevalent chlorinated semivolatile pollutants present in rural North Dakota, that significant transport of pesticides occurs both in the vapor‐phase and on suspended particulate matter, and that blown soil may be a significant mechanism for introducing pesticides into surface and ground waters.
Observed and Simulated Solute Transport Under Varying Water Regimes: II. 2,6‐Difluorobenzoic Acid and Dicamba
Authors: Pearson R. J. , Inskeep W. P. , Wraith J. M. , Gaber H. M. , Comfort S. D.
Published: July 2010

Significant interest in the fate of agrichemicals in soils has prompted the development of several transport simulation models. Our primary objective was to evaluate the simulation model LEACHM for predicting the fate of dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) and a nonreactive tracer, 2,6‐difluorobenzoic acid (2,6‐DFBA) in fallow and cropped (barley, Hordeum vulgare L.) systems under different water application levels. A field study (1992) was conducted using in situ soil columns on a Borollic Calciorthid (Brocko silt loam, Gallatin Co., MT). Dicamba (14C‐labeled) and 2,6‐DFBA were surface applied at rates of 0.26 and 112 kg ha−1, respectively. Solute concentrations were measured at three depths (0.36, 0.66, and 0.96 m) using porous cup lysimeters for 70 d following chemical application. Time‐moment analysis of observed solute breakthrough curves (BTCs) generally showed increasing travel times with increasing soil depth and decreasing water application. Dicamba transport was similar to 2,6‐DFBA, with the exception that 40 to 60% of applied dicamba was degraded during transport. The distribution of 14C remaining in the soil columns showed that the primary degradate of dicamba, 3,6‐dichlorosalicylic acid (DCSA), was confined primarily to surface samples (0–0.2 while dicamba was found only at lower depths. This is consistent with a much higher sorption coefficient (Koc) determined for DCSA relative to dicamba. Comparison of observed and predicted (LEACHM) solute BTCs suggested that preferential solute transport occurred especially under high and medium water regimes. Finally, data from three field seasons at the same site suggest that the timing of chemical application relative to initial soil water content and plant stage, the presence of root channels, and temporal changes in soil hydraulic properties in the absence of tillage may significantly affect the degree of preferential flow and subsequent agreement between predicted and observed BTCs.
Growth Response of Barley on Unweathered Fly Ash‐Amended Soil
Authors: Salé L. Y. , Naeth M. A. , Chanasyk D. S.
Published: July 2010

A clay loam topsoil that tends to form surface crusts was mixed with unweathered fly ash from a western Canada power plant in mixtures ranging from 0 to 100% fly ash (v/v). Barley (Hordeum vulgare L. var. Leduc) was grown on the mixtures in a greenhouse to examine the potential for phytotoxicity caused by trace elements in the fly ash. Plant emergence was delayed when ≥6.25% fly ash was added to the soil, however, it was not reduced unless ≥25% fly ash was added. The addition of 6.25 and 12.5% fly ash increased both plant height and grain yield while 25% fly ash produced similar plant heights and grain yields as the 0% fly ash treatment. Boron toxicity symptoms were evident in treatments with ≥6.25% fly ash and B accumulated in silage and straw to levels in excess of amounts considered adequate for most plant species. There was no reduction in yield, however, unless ≥50% fly ash was added to the soil. Adding ≤25% fly ash increased Se concentrations favorably in the grain, straw, and silage. Fly ash increased plant Mo concentrations to alter Cu/Mo such that it could be a concern for ruminant diets.
Response of European Chestnut to Varying Calcium/Aluminum Ratios
Authors: Zysset M. , Brunner I. , Frey B. , Blaser P.
Published: July 2010

The response of European chestnut (Castanea sativa Mill.) to varying Ca/Al ratios of 10, 1, 0.1, and control (no Al added) in nutrient solutions with constant concentrations of 1 mmol L−1 Ca was investigated in a greenhouse experiment. The various Ca/Al ratios did not cause a significant effect on biomasses of roots, stems, shoots, and total plants. At a Ca/Al ratio of 0.1, however, a lower number of leaves with lengths >15 cm, a decreased biomass of leaves, an increased root/shoot ratio, and a decreased fine root ratio (roots with diameters <1 mm/root with diameters 1–2 mm) were observed. Elemental analyses of Al and base nutrient cations in roots and leaves revealed that increased Al concentrations reduced the uptake of Ca and Mg, but not the uptake of K. Aluminum concentrations were much higher in fine roots than in leaves, clearly indicating that only a minor amount of root Al was transported into leaves. This finding was supported by EDX analyses and microscopic data, where Al in fine roots was mainly detected in epidermal and cortical cells, but to a lesser extent in cells of the stele. The comparison of the results from the greenhouse experiment with field data from southern Switzerland suggests that there is no current risk originating from low Ca/Al ratio in the soil solution for European chestnut at the field site.
Elevated Atmospheric Carbon Dioxide in Agroecosystems Affects Groundwater Quality
Authors: Torbert H. A. , Prior S. A. , Rogers H. H. , Schlesinger W. H. , Mullins G. L. , Runion G. B.
Published: July 2010

Increasing atmospheric carbon dioxide (CO2) concentration has led to concerns about global changes to the environment. One area of global change that has not been addressed is the effect of elevated atmospheric CO2 on groundwater quality below agroecosystems. Elevated CO2 concentration alterations of plant growth and C/N ratios may modify C and N cycling in soil and affect nitrate (NO3−) leaching to groundwater. This study was conducted to examine the effects of a legume [soybean [Glycine max (L.) Merr.]] and a nonlegume [grain sorghum [Sorghum bicolor (L.) Moench]] CO2‐enriched agroecosystems on NO3− movement below the root zone in a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split‐plot design replicated three times with plant species (soybean and grain sorghum) as the main plots and CO2 concentration (∼360 and ∼720 µL L−1 CO2) as subplots using open‐top field chambers. Fertilizer application was made with 15N‐depleted NH4NO3 to act as a fertilizer tracer. Soil solution samples were collected weekly at 90‐cm depth for a 2‐yr period and monitored for NO3−‐N concentrations. Isotope analysis of soil solution indicated that the decomposition of organic matter was the primary source of NO3−‐N in soil solution below the root zone through most of the monitoring period. Significant differences were observed for NO3−‐N concentrations between soybean and grain sorghum, with soybean having the higher NO3−‐N concentrations. Elevated CO2 increased total dry weight, total N content, and C/N ratio of residue returned to soil in both years. Elevated CO2 significantly decreased NO3−‐N concentrations below the root zone in both soybean and grain sorghum. The results of this study indicate that retention of N in organic pools because of elevated atmospheric CO2 could reduce the nitrate concentration in groundwater beneath agroecosystems as indicated by NO3− movement.
Nitrate Removal in Stream Riparian Zones
Authors: Hill Alan R.
Published: July 2010

This review considers the role of stream riparian zones in regulating the transport of nitrate (NO−3) in groundwater flow from uplands to streams. The current consensus is that most riparian zones effectively remove NO−3 from subsurface water. However, research has not focused on the relationship between hydrology and chemistry within the context of the riparian zone hydrogeologic setting. Most riparian zones that remove NO−3 occur in landscapes with impermeable layers near the ground surface. In this setting, small amounts of groundwater follow shallow horizontal flow paths that increase water residence time and contact with vegetation roots and organic‐rich riparian soils. Limited research suggests that riparian zones have less effect on NO−3 transport in hydrogeologic settings where groundwater has little interaction with vegetation and sediments because flow occurs mainly across the surface, or at depth beneath the riparian zone before discharging to the stream. Considerable uncertainty surrounds the relative importance of vegetation uptake and microbial denitrification in NO−3 removal from subsurface water in riparian zones. Plant NO−3 uptake requires the presence of the root zone below the water table. Information is lacking on the vertical distribution and seasonal dynamics of fine root biomass in relation to water table fluctuations. High denitrification rates have been reported in 0 to 10 cm surface soils of riparian zones in the USA, France, and New Zealand. However, rapid NO−3 removal from groundwater also occurs in riparian locations where the water table is always >0.5 m below the surface. Denitrification at depth within the saturated zone has been studied to a limited extent and has been found not to occur at some sites. An interdisciplinary approach in which patterns of NO−3 depletion and the role of NO−3 removal processes are related to groundwater flow paths is needed to provide a better understanding of NO−3 regulation in riparian zones.
Chemical and Biological Characterization of Organic Matter during Composting of Municipal Solid Waste
Authors: Chefetz Benny , Hatcher Patrick G. , Hadar Yitzhak , Chen Yona
Published: July 2010

Composting of municipal solid waste (MSW) was studied in an attempt to elaborate transformations of organic matter (OM) during the process and define parameters for the degree of maturity of the product. Composting was performed in 1‐m3 plastic boxes and the following parameters were measured in 13 samples during 132 d of composting: temperature, C/N ratio, ash content, humic substance contents, and fractions (humic acid, fulvic acid, and nonhumic fraction‐HA, FA, and NHF, respectively). Spectroscopic methods (CPMAS 13C‐NMR, DRIFT) were used to study the chemical composition of the OM. A bioassay based on growth of cucumber (Cucumis sativus L. cv. Dlila) plants was correlated to other parameters. The C/N ratio and ash content showed a typical high rate of change during the first 60 d and reached a plateau thereafter. The HA content increased to a maximum at 112 d, corresponding to the highest plant dry weight and highest 1650/1560 (cm−1/cm−1) peak ratios calculated from DRIFT spectra. 13C‐NMR and DRIFT spectra of samples taken from the composting MSW during the process showed that the residual OM contained an increasing level of aromatic structures. Plant‐growth bioassay, HA content, and the DRIFT spectra indicated that MSW compost described in this study, stabilized and achieved maturity after about 110 d.
Long‐Term Fate of Nitrogen from Annual Feedlot Manure Applications
Authors: Chang C. , Janzen H. H.
Published: July 2010

Animal wastes are a valuable soil amendment, but when rates of application exceed crop nitrogen (N) requirements, N can leach into groundwater or be lost to the atmosphere. The prediction of optimum manure application rates, however, is complicated by the mineralization of organic N that accumulates with repeated manure applications over many years. The objective of this study was to determine the N balance in soils receiving long‐term, repeated manure applications, as influenced by application rate and moisture regime. A N balance was constructed for a site at Lethbridge, AB, in which various rates of 1‐ to 2‐yr‐old manure (up to 180 Mg ha−1 yr−1) have been applied annually to irrigated and nonirrigated Chernozemic (Typic Haploboroll) clay loam since 1973. Under nonirrigated conditions, all of the N applied in manure was accounted for by crop uptake, soil organic N (Kjeldahl N), and soil NO3‐N. Losses of N via leaching or volatilization were small. Under irrigation, however, particularly at higher rates of manure application, appreciable amounts of N were lost by leaching and volatilization. The proportion of manure N mineralized was independent of application rate and irrigation regime. During a period of almost 20 yr, about 56% of the N applied in manure was mineralized. This estimate permits more quantitative estimation of manure application rates that exploit the agronomic value of manure without risk of adverse environmental effects under similar climatic conditions.
Nitrous Oxide and Carbon Dioxide Fluxes from a Bare Soil Using a Micrometeorological Approach
Authors: Wagner‐Riddle C. , Thurtell G. W. , King K. M. , Kidd G. E. , Beauchamp E. G.
Published: July 2010

Increasing atmospheric carbon dioxide (CO2) and nitrous oxide (N2O) levels have prompted research on management of the soil C and N pools. The impact of C and N fertilizer addition on N2O and CO2 field emissions is not clear. We determined N2O and CO2 fluxes from a 1‐ha bare soil plot using micrometeorological methods with the objective of evaluating the effect of management practices (cultivation, irrigation, fertilizer, and sucrose applications) on the relative importance of both trace gases. Research was conducted at the Elora Research Station (Typic Hapludalf) in Ontario, Canada, over 7 mo. The N2O concentration gradients were measured using a Tunable Diode Laser Trace Gas Analyzer and the CO2 gradients using an Infra‐Red Gas Analyzer. The transport coefficients were calculated using a Bowen Ratio Energy Balance and two wind profile approaches. These three approaches resulted in similar hourly fluxes. Daily N2O fluxes for nonevent periods were 12 ng m−2 s−1 in 1991, and 2 ng m−2 s−1 in the summer of 1992, while CO2 fluxes before treatments in 1991 were 0.18 mg m−2 s−1. Sucrose addition (420 kg C ha−1) resulted in the highest N2O and CO2 daily emissions measured during the experiment at 3100 ng m−2 s−1 and 0.5 mg m−2 s−1, respectively. Peak emissions of 250 ng N2O m−2 s−1 were measured after wetting of dry soil (WFP < 0.4) through irrigation in 1991, and rain in 1992. Application of ammonium sulfate (100 kg N ha−1) and irrigation increased N2O emissions to 75 ng m−2 s−1, with a smaller effect caused by two subsequent irrigations on wet soil (WFP > 0.6). Carbon dioxide fluxes varied between 0.01 and 0.5 mg m−2 s−1 being the predominant gas contributing to an equivalent CO2 global‐warming potential, but addition of sucrose increased the contribution of N2O to twice the contribution of CO2. The combined effect of C and N additions (e.g. manure and legume) on the N2O emissions in irrigated or high rainfall areas should be considered in the efforts of atmospheric C sequestering.
Estimating Polyacrylamide Concentration in Irrigation Water
Authors: Lentz R. D. , Sojka R. E. , Foerster J. A.
Published: July 2010

One practice used to control irrigation‐induced erosion amends irrigation furrow inflows with water‐soluble, anionic polyacrylamide (PAM) at low concentrations (0.25–10 mg L−1). Researchers wish to determine the fate of PAM, once added to furrow water streams. We developed and tested an instrumented flocculation test for quantifying PAM concentration in irrigation water. A kaolinite mineral standard is mixed with a PAM‐amended water sample, agitated, then placed in a spectrophotometer. The PAM concentration in the suspension was correlated with settling‐related transmittance changes. One highly correlated (r = 0.91–0.98) parameter, the time needed to initiate suspension clearing (clarity‐shift inflection, CSI), was used as the procedure endpoint. The procedure was sensitive to variations in the amount of kaolinite added, and sample volume, water salinity, and original sediment content. A 10% change in these factors altered measured CSIs by 10 to 50%. The sediment affected CSI by increasing the sample's dissolved organic C concentration. The procedure detected as little as 0.1 mg L−1 PAM dissolved in irrigation water; in samples containing >4 mL settled sediment per liter, the PAM detection limit was approximately 0.25 mg L−1. Precision ranged from ±0.06 to 0.11 mg L−1 for 0 to 2.5 mg L−1 PAM and ±0.39 to 0.86 mg L−1 for 2.5 to 10.0 mg L−1 PAM. The PAM concentration in runoff from irrigated furrows equaled that of the inflow stream after 3 h continuous treatment at 10 mg L−1. The CSI test provides a simple and accurate method of determining polyacrylamide in surface waters.
Transient Multicomponent Gas‐Phase Transport of Volatile Organic Chemicals in Porous Media
Authors: Amali S. , Rolston D. E. , Yamaguchi T.
Published: July 2010

Liquid mixtures of volatile organic chemicals (VOCs) contaminating many soil and groundwater sites give rise to multicomponent mixtures of their vapors. Column studies were conducted to characterize multicomponent diffusive transport of TCE and benzene vapors through air‐dry sand. The vapors diffused from their liquid mixture source at one end of the column to the other end where their concentration was maintained at zero by flowing clean air across the column. Simulations based on Stefan‐Maxwell equations of vapor diffusion predicted that the TCE and benzene multicomponent steady‐state flux densities should be 6.7 and 5.5% higher than the predictions based on Fick's law, respectively. The measured steady‐state multicomponent mass flux densities were higher than Fick's law estimates by 4.5 to 10.6 and 3.9 to 10.0% for TCE and benzene, respectively. These results show that multicomponent equations should be used to predict the steady‐state flux densities in a multicomponent VOC vapor mixture. During the transient phase of the experiments, use of Fick's law led to adequate predictions of flux density and concentration. A transient transport model based on Fick's law and a multicomponent, nonlinear adsorption model predicted measured TCE and benzene concentrations along the column in both experiments more accurately than a model based on a single‐species linear isotherm, which underpredicted vapor concentrations for both species. The magnitude of the underestimation was less for benzene, which is less strongly adsorbed at low concentrations than TCE. The linear adsorption isotherm adequately predicted concentrations at the early stages of the experiment when low concentrations were predominant.
Impact of Land‐Applied Tertiary‐Treated Effluent on Soil Biochemical Properties
Authors: Schipper Louis A. , Williamson J. C. , Kettles H. A. , Speir T. W.
Published: July 2010

Land application is increasingly used for the disposal and treatment of effluents. We investigated how irrigation of tertiary‐treated domestic effluent influenced 14 soil biochemical properties in a Monterey pine (Pinus radiata D. Don) forest on volcanic soils. The soils were irrigated with either effluent or water at two loading rates (49 and 74 mm wk−1). Surface soils (0–5 cm) were collected from the effluent‐irrigated and adjacent nonirrigated control sites annually for 3 yr and for 2 yr from the water‐irrigated sites. Effluent irrigation significantly (P < 0.05) increased several soil properties including pH, invertase activity, denitrification, mineralizable N, and extractable nitrate. These increases were not observed in the water‐irrigated soils suggesting that the changes resulted from effluent chemistry rather than additional water loading. Phosphatase activity decreased with both water‐ and effluent‐irrigation. No changes were observed in total N, total C, basal respiration, microbial biomass, sulfatase activity, or extractable ammonium in the effluent‐ and water‐irrigated soils. Both rates of effluent application had the same effect on soil properties indicating that the threshold rate that changed soil properties was ≤49 mm of effluent per week.
Off‐Target Deposition of Pesticides from Agricultural Aerial Spray Applications
Authors: Bird Sandra L. , Esterly David M. , Perry Steven G.
Published: July 2010

Drift of pesticides at the times of aerial spray application is a source of concern because of potential impacts on human health, contamination of crops and livestock, and endangerment of sensitive ecological resources. A substantial body of information from field trials aimed at evaluating off‐target deposition of pesticides from aerial spray applications was analyzed. Forty‐five trials previously reported in the open literature were extrapolated and normalized and quantitatively compared to trials performed during the summer of 1992 in Plainview, TX, by the Spray Drift Task Force (SDTF). In general, the results observed in the SDTF studies are consistent with those reported in the open literature. Both sets of data show median values of pesticide deposition dropping from ∼5% of the nominal application rate at 30 m downwind to ∼0.5% at 150 m during low‐flight applications. Based on results from these trials and others reported in the literature, droplet size is consistently the primary application variable controlling off‐target drift during low‐flight applications. Application of a fine spray with a volume median diameter (VMD) <200 µm in an oil‐based carrier, typical of ultra‐low volume (ULV) applications, can yield up to a 10‐fold increase in off‐target drift, whereas use of solid stream nozzles producing a relatively coarse spray (VMD > 500 µm) can reduce drift 10‐fold relative to conventional application equipment producing a medium spray (VMD ∼300 µm). Off‐target drift increases with increasing wind speeds, but the magnitude of the effect is less significant than effects of droplet size. The SDTF trials were performed under neutral to unstable atmospheric conditions and the effects of stability for this range of conditions were not distinguishable from the effects of wind speed. In previously reported studies under a wider range of conditions, stability effects are most significant 100 m downwind and beyond with an increase in deposition of more than 10‐fold reported on occasion between unstable and very stable conditions. Currently, pesticide use labels restrict application during strongly stable atmospheric conditions and during high winds. In conjunction with these weather‐related restrictions, clear specification of nozzles and operating conditions is the best approach for effective control of off‐site drift and deposition from aerial applications.
Mitigation Alternatives to Decrease Nitrous Oxides Emissions and Urea‐Nitrogen Loss and Their Effect on Methane Flux
Authors: Delgado J. A. , Mosier A. R.
Published: July 2010

Nitrous oxide (N2O) and methane (CH4) are greenhouse gases that are contributing to global warming potential. Nitrogen (N) fertilizer is one of the most important sources of anthropogenic N2O emissions. A field study was conducted to compare N‐use efficiency and effect on N2O and CH4 flux, of urea, urea plus the nitrification inhibitor dicyandiamide (U + DCD), and a control release fertilizer, polyolefin coated urea (POCU) in irrigated spring barley (Hordeum vulgare L.) in northeastern Colorado. Each treatment received 90 kg urea‐N ha−1 and microplots labeled with 15N‐fertilizer were established. Average N2O emissions were 4.5, 5.2, 6.9, and 8.2 g N ha−1 d−1 for control, U + DCD, POCU, and urea, respectively. During the initial 21 d after fertilization, N2O emissions were reduced by 82 and 71% in the U + DCD and POCU treatments, respectively, but continued release of N fertilizer from POCU maintained higher N2O emissions through the remainder of the growing season. No treatment effect on CH4 oxidation in soils was observed. Fertilizer 15N found 50 to 110 cm below the soil surface was lower in the POCU and U + DCD treatments. At harvest, recovery of 15N‐fertilizer in the plant‐soil system was 98, 90, and 85% from POCU, urea, and U + DCD, respectively. Grain yield was 2.2, 2.5, and 2.7 Mg ha−1 for POCU, urea, and U + DCD, respectively. Dicyandiamide and POCU showed the potential to be used as mitigation alternatives to decrease N2O emissions from N fertilizer and movement of N out of the root zone, but N release from POCU does need to be formulated to better match crop growth demands.
Long‐Term Decomposition of Grass Roots as Affected by Elevated Atmospheric Carbon Dioxide
Authors: van Ginkel J. H. , Gorissen A. , van Veen J. A.
Published: July 2010

Carbon input into the soil and decomposition processes under elevated CO2 are highly relevant for C sequestering in the soil. Plant growth and decomposition of root material under ambient and elevated atmospheric CO2. concentrations were monitored in wind tunnels. Grass roots (Lolium perenne L.) were homogeneously 14C‐labeled at 350 and 700 −L L−1 CO2 and at two N levels to obtain roots of different qualities. This root material was mixed with fresh loamy sand and transferred to four wind tunnels to observe its decomposition in bare soil and as affected by plant growth (L. perenne) at ambient CO2 and elevated CO2 for two growing seasons. After the second growing season, elevated CO2 had stimulated shoot and root growth by 13 and 92%, respectively. The CO2 and N concentrations at which the grass roots had been grown affected the decomposition rate. After the first growing season, the overall decomposition of 700 roots was 19% lower than that of 350 roots. The 14C‐labeled microbial biomass in the soil with 700 roots was higher (44%) compared with 350 roots. After the second growing season, the decomposition of 700 low N roots was 14% lower than that of 350 low N roots, whereas the decomposition of the high N roots was unaffected. The 14C‐labeled microbial biomass in the soil with 700 roots was still higher (30%) than with 350 roots. The combination of higher root yields at elevated CO2 combined with a decrease in root decomposition will lead to a longer residence time of C in the soil and probably to a higher C storage.
Understanding Phytotoxicity Thresholds for Trace Elements in Land‐applied Sewage Sludge
Authors: Schmidt J. P.
Published: July 2010

Sewage sludge contains trace elements. With repeated sludge applications as crop fertilizer, these trace elements may accumulate in the soil to phytotoxic concentrations. My objective was to assess the scientific basis for the current cumulative loading limits for Cu, Ni, and Zn in land‐applied sewage sludge. An overview of the USEPA's phytotoxicity risk assessment, the basis for these loading limits, was presented, discussed, and compared in the context of the underlying principles of phytotoxicity thresholds. I concluded that EPA phytotoxicity thresholds in immature plants were arbitrarily selected, and extrapolations to field applications of sewage sludge were not substantiated. Variability in plant accumulation rates and soil sorption capacities of trace elements were not adequately considered in the EPA analysis. Because of the assumptions, simplifications, and extrapolations introduced into the phytotoxicity analysis, the final results, that is, EPA's cumulative loading limits for Cu, Ni, and Zn, are not substantiated by the analysis. The phytotoxicity analysis does not represent an appropriate application of underlying scientific principles. A more appropriate basis for regulating trace element applications in sewage sludge would reflect an understanding of site‐specific characteristics, possibly including concentration limits for trace elements in plant tissue, soil, and/or groundwater. Additional research would be required to substantiate EPA's conclusions about the cumulative pollutant loading limits, as derived from EPA's phytotoxicity risk assessment.
Soil Microorganisms in Soil Cleanup: How Can We Improve Our Understanding?
Authors: Holden Patricia A. , Firestone Mary K.
Published: July 2010

Successful in situ biodegradation must depend on microbial catalysis as well as physical transport. While there has been much effort directed toward understanding vadose zone transport processes, our understanding of the microbial ecology of the indigenous catalysts limits our ability to manage biodegradation processes in soil. The environmental factors commonly listed as controlling in situ biodegradation are water, oxygen, redox potential, nutrients, pH, and temperature. Simplistic statements concerning the environmental determinants of in situ biodegradation may reflect a naive understanding of microbial ecology and may in fact direct management efforts in inappropriate directions. We discuss what we need to know about soil microbial ecology to elevate in situ biodegradation to a reliable and well‐understood remediation option. We need to know the following: What controls the presence of the desired metabolic capability; the distribution of degrading communities relative to contaminant source; and what controls activities of relevant communities?