bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of Nitrate in Aquifer Microcosms by Carbon Additions
Authors: Obenhuber Donald C. , Lowrance Richard
Published: July 2010

Aquifer microcosms were used to examine the effects of NO−3 and C amendments on groundwater from the Claiborne aquifer. Nitrate concentrations of 12.17 mg L−1 in aquifer microcosms were reduced 0.92%/d to 5.84 mg L−1 by the addition of 10 mg C L−1 for 35 d. Nitrate disappearance correlated with increases in number of denitrifiers and dissolved N2O concentration and decreases in dissolved oxygen, suggesting biological denitrification. Nitrate/chloride ratios decreased in microcosms with 10 mg C L−1 added and then increased when the C addition was removed. Carbon additions of 0.4 mg C L−1 had no effect on the microbial or chemical properties of the microcosms. Nitrous oxide levels in wells sampling the Claiborne aquifer showed an increase with depth, indicating N2O production within the aquifer. Microcosms are useful tools to examine biological transformations of chemical contaminants in unconsolidated aquifer material. The remediation of NO−3 contaminated aquifers by organic infusion is possible and appears to be a function of microbial denitrification.
Coal Waste Reclamation using Automated Weathering to Predict Lime Requirement
Authors: Gitt M. J. , Dollhopf D. J.
Published: July 2010

Abandoned coal waste exhibits adverse physical and chemical properties which preclude vegetation establishment. Coal waste from a site in Montana was acidic (pH 2.8), black, 85% coarse fragments and had a low water holding capacity. Incorporation of cement kiln dust (CaO) and limestone (CaCO3) to 35 cm at rates recommended by a weathering procedure neutralized coal waste acidity in the surface 10 cm. Incorporating CaO to 100 cm neutralized coal waste to the 30‐cm depth. Seeded vegetation was healthy and vigorous where lime was applied, though percent canopy cover and aboveground production were low after 2 yr. Application of kiln dust five times the recommended rate significantly reduced plant performance. Application of coversoil significantly increased plant performance compared to sites without coversoil by providing a more suitable germination medium. Increasing coversoil application from 15 to 30 cm did not significantly increase plant performance. Depth of root penetration was a function of depth of lime incorporation and coversoil thickness. Root distribution was neither confined to nor concentrated in the coversoil. Root proliferation into limed coal waste was similar to that present in overlying coversoil.
Lysimeter Study of Nitrogen Fertilizer and Irrigation Rates on Quality of Recharge Water and Corn Yield
Authors: Prunty Lyle , Montgomery B.R.
Published: July 2010

Accrual of NO3‐N to groundwater as a result of agricultural practices is a focus of environmental concern. This inquiry was conducted to quantify precisely in a replicated experiment the rate of N loading to groundwater resulting from inputs of N and irrigation water to corn (Zea mays L.). Input levels were designed to balance potential for high production with minimum loading of NO3‐N to groundwater. Four large (2.4 by 2.4 m and 2.3 m deep) drainage lysimeters with reconstructed Hecla loamy fine sand (Aquic Haploborolls) were employed in this southeast North Dakota study. Grain yields at N fertilizer rates of 95 and 145 kg/ha were 10.3 and 11.3 Mg/ha, respectively. Differences in yield due to irrigation and irrigation by N interaction were nonsignificant. There was no residual effect of N fertilizer on yield. The higher irrigation rate caused increases in drainage of water within about 30 d. The higher rate of N fertilizer, however, was not reflected by increased concentration of NO3‐N in the drainage water until 325 d after application. The increased concentrations then persisted to 500 d. Flow‐weighted means of NO3‐N concentrations for this period were 8.6 and 12.3 mg/L for the low and high N rates, respectively. For this soil and climate, irrigation and N management can be tailored to produce NO3‐N concentrations below 10 mg/L with continuous corn. However, the 5:1 economic return produced by 50 kg/ha of incremental N fertilizer means that producers are unlikely to adopt the needed practices without incentives.
Site‐Specific Erosivity Evaluation of a Sierra Nevada Forested Watershed Soil
Authors: Guerrant D. G. , Miller W. W. , Mahannah C. N. , Narayanan R.
Published: July 2010

Little quantitative site‐specific infiltration, runoff, and erosion data for forested watershed soils of the Tahoe Basin are available. A Modular‐type rainfall simulator was used to examine these variables for the Cagwin (mixed Typic Cryopsamment) soil series. Three slope (0–15, 15–30, >30%) and four plot conditions (undisturbed with natural duff, undisturbed without natural duff, disturbed without natural duff, and disturbed with natural duff removed) were studied. Infiltration and runoff data were incorporated into a modified Philip's model whereas erosion data were incorporated into a general nonlinear model. Data sets were analyzed via nonlinear regression for slope and plot interaction. Slope had negligible effect on infiltration and runoff but had a significant effect on erosion. Plot condition had significant effects on infiltration, runoff, and erosion. Final infiltration rates ranged from 4.7 to 6.1 cm h−1, runoff ranged from 36 to 59% of the application rates, and cumulative interrill erosion ranged from 37.5 to 108.4 g m−2 for a simulated design storm of 8 to 10 cm h−1. The findings of this investigation were consistent with those of related quantitative investigations and indicate that the Cagwin soil has a low relative erosivity. Data from this study further suggest that previously applied models used to estimate potential erosion hazards of forested watershed soils may well result in over‐estimation of erosion potential.
Sediment Concentration of Interrill Runoff under Varying Soil, Ground Cover, Soil Compaction, and Freezing Regimes
Authors: Edwards Linnell M. , Burney J.R.
Published: July 2010

Sediment concentration (SC) was the focus of this study, which is part of a wider investigation into runoff volume and sediment mass. In the present study, SC of runoff was measured from three Prince Edward Island (Canada) soils (loam, sandy loam, and fine sandy loam surface texture) subjected to laboratory rainfall simulation to assess the effect of ground cover [winter rye (Secale cereale L.) or straw], subsoil compaction, and freezing (10 days' continuous freeze or daily freeze/thaw). Sediment concentration for the loam was 47 and 50% greater than the other soils. Straw cover gave SC of 23% < bare surface, and winter rye 25% < bare surface. Freezing treatment had no first‐order effect on SC but interacted with soil type and with ground cover. The loam showed 30% greater SC based on lower runoff volume with daily freeze/thaw than with continuous freeze. Freeze/thaw resulted in a 54% greater SC than continuous freeze. Freeze/thaw caused numerous surface cracks in the soil and enhanced internal drainage, thus resulting in less runoff than continuous freeze. A regression analysis of the relationship between SC and winter rye cover showed that variations in SC were dominated, 53%, by sediment mass (compared with 18% by runoff volume). Variations in rye cover were dominated, 49%, by leaf area (compared with 8% by leaf mass and 5% by root mass). Although this study found increasing SC to occur with subsurface soil compaction for all three soils, and the loam to be particularly susceptible to daily freeze/thaw, any adverse impact of these factors on erosion or erosion control was minimized with the use of winter rye or straw as ground cover.
Baseflow and Stormflow Transport of Nutrients from Mixed Agricultural Watersheds
Authors: Owens L. B. , Edwards W. M. , Keuren R. W.
Published: July 2010

Many of the reported nutrient losses from agricultural areas, especially where artificial subsurface drainage is not present, have been from surface runoff. In unglaciated, well drained silt loams in eastcentral Ohio, a portion of the infiltrated rainfall moves through the soil returning to the surface at springs or seep areas. Such return flow often creates a constant baseflow in multi‐hectare watersheds. The purposes of this study were to compare relative water and nutrient transports via storm runoff with amounts removed in continuous baseflow and to evaluate the influence of different management practices on such transport. Baseflow and storm runoff from four watersheds with different land use practices were measured, sampled, and analyzed for these comparisons. In two watersheds, 123 and 32.1 ha in size, containing woodland, pasture, and row crops, the majority of N moved from the watersheds in the storm runoff; however, 25 to 50% of the N transport was via baseflow. Using 10‐yr averages, 5.0 and 2.8 kg/ha of mineral N were annually transported from the 123‐ha watershed via 242 and 196 mM of storm runoff and baseflow, respectively; from the 32‐ha watershed, 3.6 and 3.2 kg/ha of mineral N were annually transported via 144 and 198 mm of storm runoff and baseflow, respectively. Mineral N transport from a 28.8‐ha poor practice pasture watershed and from a 17.7‐ha wooded watershed was less than above, but the proportions in storm runoff and baseflow were similar. Although stormflow was the larger transport pathway for nutrients leaving a watershed, a sizable portion of the nutrients can be carried with the baseflow. This comparison of watersheds in an unglaciated area indicates that there is a negligible difference in the quality of water leaving an unfertilized wooded area or unfertilized pasture or a watershed that receives fertilization on 55% of its area.
Fate of Volatile and Semivolatile Organic Chemicals in Soils: Abiotic Versus Biotic Losses
Authors: Anderson Todd A. , Beauchamp John J. , Walton Barbara T.
Published: July 2010

Disappearance of 15 volatile and semivolatile organic compounds was determined in a mixture added to two different soil types, a Captina silt loam (Typic Fragiudult) and McLaurin sandy loam (Typic Paleudults), using experimental procedures to distinguish abiotic losses from biological degradation over a 7‐d period. Losses due to volatilization were quantified and mass balances were calculated for each compound. Standard USEPA and National Institute of Occupational Health and Safety (NIOHS) methods were used for sample handling, storage, and analysis. The compounds (methyl ethyl ketone; tetrahydrofuran; chlorobenzene; benzene; chloroform; carbon tetrachloride; p‐xylene; 1,2‐dichlorobenzene; cis‐1,4‐dichloro‐2‐butene; 1,2,3‐trichloropropane; 2‐chloronaphthalene; ethylene dibromide; hexachlorobenzene; nitrobenzene; and toluene) were applied to the soil in a mixture such that the concentration of each chemical was 100 mg/kg soil (dry wt.). The headspace of the soil samples and matched sterile (autoclaved) controls, which were incubated in the dark at 20 °C in stoppered jars fitted with charcoal traps, was flushed daily to maintain aerobic conditions and to trap vapors. Apparent half‐lives for the 15 organic compounds ranged from < 2 to 11.3 d and showed good agreement with published values in the few instances where they were available. Rapid disappearance due to abiotic factors was observed for all chemicals during the 7‐d period. Although short‐term spike and recovery analyses yielded consistently reproducible recovery for all compounds, careful attempts to account for all losses, including the use of 14C‐toluene, were unsuccessful. Nonreversible sorption and preanalysis storage conditions were considered as contributors to this inability to achieve a mass balance. On the basis of these results, we strongly advise positive accounting for all test compounds and degradation products at the conclusion of studies involving volatile and semivolatile compounds.
Modeling the Influence of Sorption and Transformation on Pesticide Leaching and Persistence
Authors: Boesten J. J. T. I. , van der Linden A. M. A.
Published: July 2010

Pesticide leaching to ground water at 1 m depth and pesticide persistence in the plow layer were calculated with a mathematical model for a sandy soil continuously cropped with maize (Zea mays L.) and exposed to weather conditions in a temperate climate. The pesticide was applied in spring. In the model, water flow was described by Darcy's law and water uptake by the crop was included. Dally averages of meteorological conditions (rainfall, evapotranspiration, soil temperature) were used as input. The model assumes first‐order transformation, equilibrium sorption (Freundlich equation), and passive plant uptake. Pesticide leaching and persistence were calculated as a function of pesticide sorption (characterized by the organic‐matter/water distribution coefficient, Kom) and of transformation rate. It was found that pesticide leaching is very sensitive to both Kom and the transformation rate: changing Kom or the transformation rate by a factor of 2 changes the fraction of the dose leached typically by about a factor of 10. Pesticide persistence in the plow layer was found to be sensitive to Kom at low transformation rates and sensitive to the transformation rate at high Kom values. Additional calculations showed that autumn application results in much higher leaching of nonsorbing pesticides with short half‐lives than spring application (difference of two orders of magnitude).
Effects of Long‐Term 2,4‐D and MCPA Field Applications on the Soil Breakdown of 2,4‐D, MCPA, Mecoprop, and 2,4,5‐T
Authors: Smith A. E. , Aubin A. J.
Published: July 2010

Under laboratory conditions, the rates of breakdown of (14C)2,4‐D (2,4‐dichlorophenoxyacetic acid), (14C)MCPA (4‐chloro‐2‐methylphenoxyacetic acid), (144C)mecoprop (2‐[4‐chloro‐2‐methylphenoxy]propionic acid), and 2,4,5‐T (2,4‐5‐trichlorophenoxyacetic acid) in soils from Canadian prairie field plots, 6 wk after receiving the 43rd annual application of 2,4‐D formulations or the 37th annual treatment with MCPA, were compared with those in soils from untreated plots. Loss of 2,4‐D and MCPA was faster in soils that had received continuous applications with the appropriate herbicide than in soil from the control plots. There was some indication that (144C)2,4‐D was dissipated more rapidly from soils treated annually with MCPA than from the control soils, though breakdown was slower than in soil from the 2,4‐D‐treated plots. In contrast, (14C)MCPA breakdown in the 2,4‐D‐treated plots was similar to that in untreated soils. Breakdown of (14C)mecoprop and 2,4,5‐T in the 2,4‐D and MCPA‐treated soils was very similar to that in the control soils. Thus, there was no support for the phenomenon of cross‐enhancement. Forty‐eight weeks after the last herbicide applications, the field soils still maintained their ability to degrade 2,4‐D or MCPA more rapidly than soil from untreated control plots.
Separation of Gaseous and Particupate Dry Deposition of Sulfur at a Forest Edge in Denmark
Authors: Beier Claus
Published: July 2010

Throughfall deposition of SO2−4 and Na+ to a spruce [Picea abies (L.) Karst.] forest edge in Denmark was measured during 1 yr. The deposition of both SO2−4 and Na* was highly elevated at the forest edge with Na+ showing the steepest gradient. Using Na+ as a model‐substance for the deposition of particles and assuming that 6 to 24% of the SO2−4‐deposition in throughfall inside the stand originated from particles, the relative contribution of particulate and gaseous S to the throughfall deposition at the forest edge could be estimated. The deposition of particulate S showed a strong dependence on the distance to the forest edge. Thus, particulate S contributed 25 to 100% of the net throughfall deposition under the front tree, whereas particulate S only contributed 6 to 24% inside the stand. The gaseous deposition showed a more moderate dependence on the forest edge and did not exceed the change in leaf area index.
Heavy Metal Extractability in Long‐Term Sewage Sludge and Metal Salt‐Amended Soils
Authors: Bell Paul F. , James Bruce R. , Chaney Rufus L.
Published: July 2010

Heavy metals applied to agricultural soils as soluble salts are usually considered more plant available in the short‐term than equivalent amounts of metals applied to soil in sewage sludge. Slow soil chemical processes over several years, however, may change the forms, extractability, and bioavailability of metals. To determine the long‐term changes in forms of Cd added to a soil, Cd and other heavy metals were extracted with several solutions from a Christiana fine sandy loam (Typic Paleudult; clayey, kaolinitic, mesic) Ap horizon 8 or 9 yr after application of sewage sludge or CdCl2. Cadmium was applied at the rate of 21 kg ha−1 either as a component of sewage sludge or as CdCl2 in 1978 and 1979, respectively. In 1987, the distribution of Cd and other metals among soil fractions was operationally defined using the following selective dissolution and total metal analyses techniques: 10 mM Ca(NO3)2 (soluble); 5 mM DTPA (diethylenetriaminepentaacetate)‐10 mM CaCl2‐100 mM triethanolamine (TEA), pH 7.5 (exchangeable/organically complexed); 100 mM NH2OH·HCl‐10 mM HNO3 (pH 2) (Mn oxide bound); 100 mM NH2OH·HCl‐1M HNO3 (paracrystalline Fe oxide bound); and aqua regia dissolution (total soil metal). The percentages of total soil Zn, Mn, and Fe extracted by DTPA and Ca(NO3)2 from the sludge or salt‐amended soils were much less (<4%) than the percentages for Cd (47–60%), indicating greater potential mobility for Cd than for the other metals, regardless of the form of Cd added originally. A larger percentage of total soil Cd was extracted with the paracrystalline iron oxide fraction of the sludge‐amended soil (35%) than in the salt‐amended soil (23%). This greater apparent Cd association with Fe oxides in the sludge‐amended soil may have been due to the greater quantity of paracrystalline Fe oxides in that soil (843 vs. 616 mg Fe kg−1 for the sludge and salt‐amended soils, respectively). Compared to the sludge‐amended soil, the salt‐amended soil had a higher percentage of Cd in the soluble and exchangeable fractions (60 vs. 47%) and nearly equal percentages in the residual fraction (15%), suggesting, at the same total soil Cd concentration (5 mg kg−1 in 1987), plant‐available Cd would be greater from the salt‐amended soil. The sludge addition apparently enhanced retention of Cd in an iron oxide pool, relative to the soluble and exchangeable forms.
Dissipation of Clopyralid and Picloram in Soil and Seep Flow in the Blacklands of Texas
Authors: Bovey R. W. , Richardson C. W.
Published: July 2010

The dissipation, leaching and movement of clopyralid (3,6‐dichloro‐2‐pyridinecarboxylic acid) and picloram (4‐amino‐3,5,6‐trichloro‐2‐pyridinecarboxylic acid) were determined in soil and subsurface water after spray application of the herbicides to the surface of an area overlying a shallow perched water table in the Blacklands of Texas. A 1:1 mixture of the monoethanolamine salt of clopyralid and the tri‐isopropanolamine salt of picloram was applied at 0.56 kg a.i./ha each in May 1988 and June 1989 on the same area. Approximately 90 d after treatment, >99% of the clopyralid and >92% of the picloram had dissipated. Most herbicide was detected in the upper 30 cm of soil. No herbicide was detected in subsurface water from the area treated in 1988, but concentrations of <6 mg/m3 of clopyralid and <5 mg/m3 of picloram were detected in subsurface water collected 11 and 41 to 48 d after treatment in 1989.
Formation and Transport of Deethylatrazine in the Soil and Vadose Zone
Authors: Adams C. D. , Thurman E. M.
Published: July 2010

Atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) and two degradation products were monitored at seven depths in the soil and vadose zone throughout the growing season in two experimental plots in which corn (Zea mays L.) was grown. The soils in these plots were a Kimo silty clay loam (clayey over loamy, montmorillonitic, mesic, Fluvaquentic Hapludoll) and a Eudora silt loam (course, silty, mixed, mesic, Fluventic Hapludoll). The purpose this field study was to identify and quantify the mobile and persistent degradation products of atrazine that comprise the input, or “source term,” to groundwater resulting from the application of atrazine to the soils. The formation of deethylatrazine (2‐amino‐4‐chloro‐6‐isopropylamino‐s‐triazine) and deisopropylatrazine (2‐amino‐4‐chloro‐6‐ethylamino‐s‐triazine) was monitored at vurious depths using suction lysimeters to determine the relative proportions at which these compounds enter the aquifer. Deethylatrazine was the major degradation product of atrazine identified in the soil water and appeared to enter the underlying aquifer at a concentration of 5.0 µg/L, which was greater than the concentration of atrazine entering the aquifer. Deisopropylatrazine also was detected in the soil water, bnt only in minor concentrations relative to atrazine and deethylatrazine. Because deethylatrazine was the major degradation product in the unsaturated zone, the deethylatrazine‐to‐atrazine ratio (DAR) may be a good indicator of transport of atrazine through the soil. The hypothesis is proposed that the DAR may be used to distinguish point‐source from nonpoint‐source contamination of an aquifer.
Effect of Growth Stage on Soybean Response to Chronic Ozone Exposure
Authors: Heagle Allen S. , Miller Joseph E. , Rawlings John O. , Vozzo Steven F.
Published: July 2010

Four cultivars of soybean [Glycine max (L.) Merr., cv. Forrest, Davis, Bragg, and Ransom] were exposed to chronic doses of O3 in open‐top field chambers to determine if a relationship exists between growth stage and yield response to O3. The season was divided into four 31‐d quarters (Q1–Q4) in which plants were exposed either to charcoal‐filtered air (C) or to nonfiltered air with O3 added (N). Sixteen different quarterly sequences represented all possible combinations of the C and N treatments. The mean 31‐d O3 concentration (7 h d−1 mean) in the N treatment was almost identical at 96 to 98 nL L−1 (ppb) for each quarter. In the sequence with N during all four quarters (NNNN), plants were exposed from emergence to physiological maturity. Mean yields in the NNNN treatment, expressed as a percentage of yield in the CCCC treatment ranged from 44% for Forrest (56% loss) to 70% for Bragg (30% loss). Ozone exposure during mid‐ to late‐growth stages generally caused a greater yield decrease than exposure during early growth stages. Models to estimate O3‐yield relationships were developed separately for each cultivar using seasonal and quarterly O3 statistics. A statistical comparison for relative goodness‐of‐fit between these two models was not possible. However, the models based on the quarterly O3 values provided estimates with less absolute deviation from the observed data than models based on seasonal O3 values. Models based on quarterly O3 values generally confirmed that the relative effect of O3 during a given quarter was related to when the pod‐fill stage occurred. For example, with the early‐maturing Forrest, pod fill occurred mainly during Q3 so O3 stress during Q3 had the greatest effect. For the later‐maturing Bragg, pod fill occurred mainly during Q4 so O3 stress during Q4 had the greatest effect.
Agronomic Effectiveness of Wood Ash as a Source of Phosphorus and Potassium
Authors: Erich M. Susan
Published: July 2010

Wood ash is a residual material produced when wood is burned for energy production. It is a useful soil amendment because it raises soil pH and has the potential to supply plant nutrients. The two studies described in this paper were designed to assess the plant availability of P and K in wood ash. Both studies compared nutrient uptake by corn (Zea mays L.) grown in the greenhouse in wood ash—amended soils to nutrient uptake from fertilizer‐amended soils. The wood ashes used were chemically characterized for available P and soluble K content by ammonium citrate extraction, as well as for total P and K. In addition wood ash‐ and fertilizer‐amended soils from the P availability study were extracted with Bray‐1, Olsen, and NH4OAc solutions after harvest. Wood ashes were found to be more similar to conventional P fertilizer materials when the amendments were compared on a citrate‐extractable P basis than when they were compared on a total P basis. For K there was little difference between ash and fertilizer sources, whether they were compared on a total K or a citrate‐extractable K basis. The buffered NH4OAc (pH 3.0) extract was adequate for determining K availability in wood ash—amended soils, but inadequate with regard to P availability in these soils. The buffered solution may have dissolved residual wood ash and released P that was not actually plant‐available. Either the Bray‐1 or the Olsen extract provided a relative measure of P availability that was consistent for both fertilizer‐ and wood ash—amended soils.
Growth and Elemental Content of Two Tree Species Growing on Abandoned Coal Fly Ash Basins
Authors: Carlson Claire L. , Adriano Domy C.
Published: July 2010

Differences in aboveground tissue concentrations of trace elements were assessed for sweetgum (Liquidambar styraciflua L.) and sycamore (Platanus occidentalis L.) growing on two abandoned coal fly ash basins and a control soil (Fuquay sand; loamy, siliceous, thermic Arenic Plinthic Kandiudult; pH = 4.99). The “wet basin” (pH = 5.58) had originally received precipitator ash in an ash‐water slurry, while the “dry basin” (pH = 8.26) had received both precipitator and bottom ash in dry form. In general, trees from the wet basin exhibited elevated trace element concentrations in comparison to the controls, while the dry basin trees exhibited reduced concentrations. One of the most striking differences in elemental concentrations among the ash basin and control trees was observed for Mn, with the control trees exhibiting concentrations orders of magnitude greater than the ash basin trees. Differences in foliar trace element concentrations among the sites can generally be explained by differences in substrate trace element concentrations and/or substrate pH. While trees from the wet ash basin generally had the highest trace element concentrations, these trees also attained the greatest height and diameter growth, suggesting that the elevated trace element concentrations in the wet basin substrate are not limiting the establishment of these two species. The greater height and diameter growth of the wet basin trees is presumably a result of the greater water‐holding capacity of the substrate on this site. Differences in growth and tissue concentrations between sweetgum and sycamore highlight the importance of using more than one species when assessing metal toxicity or deficiency on a given substrate.
A Simple Effects Analysis of the Effects of Phosphogypsum Application on Phosphorus Transport to Runoff Water and Eroded Soil Sediments
Authors: Korentajer L. , Henry P. C. , Eisenberg B. E.
Published: July 2010

Phosphorus contamination of surface waters as a result of land application of phosphogypsum (PG—a soil amendment containing orthophosphate‐P) has not yet been investigated. A laboratory rainfall simulator study was conducted to assess the initial and residual effects of PG application on P transport to runoff water and eroded soil sediments. The experiment was carried out using three soils of various dispersivity and four rates of PG application (0, 2, 5, and 10 Mg ha−1, in three replicates). Simulated rainfall was applied during three consecutive wet‐dry cycles consisting of a 1‐h rainfall event followed by a 4‐ to 6‐d drying period. A split‐plot design was used, consisting of soils and rates of PG application as the main plot treatments, and the storm as the split‐plot treatment. A simple effects analysis was used to interpret the interactive effects between storms, PG rate, and soils. The beneficial effects of PG in reducing the amounts of runoff and sediment yield depended on the soil dispersivity. In a highly dispersive soil the positive effect was apparent at the lower rates of application (<5 Mg ha−1) and gradually leveled off at the higher application rates. Conversely, on a soil with low dispersivity the beneficial effect of PG was obtained only at the higher rates of application (>5 Mg ha−1). Differences in response to the PG application were explained in terms of the complementary effects of PG on chemical dispersion and mulching. The effects of PG decreased in subsequent storms indicating a progressive removal of PG from the soil surface by runoff and downward percolation. The orthophosphate‐P concentrations in the runoff were generally much greater than 0.025 mg L−1, which is considered as the threshold concentration limiting algae proliferation in surface waters. Phosphorus removal by runoff and erosion gradually decreased in subsequent storms. The data indicated that P experts were determined by the combined effect of PG rate on the amounts of labile P available for transport, and its effects on the amounts of runoff and sediment yield. The results of the study suggesthat application of high PG rates may resalt in P being exported to the waterways adjacent to the site of application and hence it may contribute to the enhanced eutrophication of the waterways.
Cellulose Decay in Natural and Disturbed Peatlands in North Carolina
Authors: Bridgham Scott D. , Richardson Curtis J. , Maltby Edward , Faulkner Stephen P.
Published: July 2010

Carbon cycling is central to nutrient dynamics and accretion rates in wetlands. Drainage and conversion of wetlands has been occurring at an accelerating rate. This paper compares decay rates in natural and disturbed peatlands in the southeastern USA and examines relationships between edaphic factors and decay rates. Cellulose decay rates (as tensile strength loss of cotton fibers) were used to compare decomposition potentials in these peatlands. A 1984 pilot experiment included undisturbed short pocosin and several sites under various stages of agricultural conversion. A spring 1987 experiment included an increasing nutrient availability gradient in undisturbed communities from short pocosin to tall pocosin to gum swamp, drained pocosin with natural vegetation remaining, and pocosin converted to pine forestry and agriculture. In the 1984 experiment, disturbed sites had decay rates approximately nine times greater than undisturbed pocosin. In the 1987 experiment, disturbed sites had decay rates from 1.8 to 10.3 times natural sites. The greatest decay rates occurred in the agricultural site with its high nutrients, less acidic conditions, and relatively low soil moisture. Drained pocosin had the next highest decay rates, although pH and nutrients were low. Pine (Pinus taeda L.) forestry had intermediate rates of decay, while undisturbed sites had low rates. The more nutrient‐rich, but wet and low pH, gum swamp site had similar or slightly higher rates than the pocosin sites. Drainage, relieving excessive soil moisture and the resultant anaerobiosis, was the dominant factor explaining the greater decay rates in the disturbed sites. Other factors, such as nutrient availability and low pH, may have had secondary effects on cellulose decay. Rates were also compared to a global data set based on potential evapotranspiration. Natural sites have rates very close to those predicted, while disturbed sites have much higher rates (1.9–4.4 × predicted).
Estimating Nutrient Exports to Estuaries
Authors: Frink Charles R.
Published: July 2010

Nutrient export coefficients for Long Island Sound were estimated by relating measured concentrations of N and P in 33 Connecticut lakes to land use in their watersheds. This approach does not require that watersheds represent a single category of land use, but rather uses the lake to integrate contributions from all sources. These estimates were then compared with those obtained from an extensive review of the literature. The results suggest that current models with a sediment transport component tend to overestimate N and P exports from agricultural land and underestimate exports of N and P from wooded and urban land. These differences are likely attributable to greater transport of nutrients in the soluble phase than predicted by such models. Moreover, efforts to reduce erosion may not be effective in preventing losses of nutrients, particularly N, where increased infiltration may actually increase N exports. In conclusion, it appears that more emphasis should be placed on management strategies to reduce leaching losses of N, with less emphasis on structural practices to reduce erosion.
Can Aquatic Macrophytes Mobilize Technetium by Oxidizing Their Rhizosphere?
Authors: Sheppard S.C. , Evenden W.G.
Published: July 2010

Technetium (Tc) is very mobile in aerated surface environments, but is essentially immobile and biologically unavailable in anaerobic sediments. Aquatic macrophyte roots penetrate anaerobic sediments, carrying O2 downward and frequently creating oxidizing conditions in their rhizosphere. We hypothesized that this process could mobilize otherwise unavailable Tc, possibly leading to incorporation of Tc into human or animal foods. Through experiments with rice (Oryza sativa L.), and with a novel artificial macrophyte root, we concluded that this pathway is unlikely to be important for annual plants, especially in soils with a high biological oxygen demand. The relatively slow oxidation of Tc limited its mobilization by short‐lived root systems.
Fate of Heavy Metals in an Abandoned Lead‐Zinc Tailings Pond: II. Sediment
Authors: Sidle Roy C. , Chambers Jeanne C. , Amacher Michael C.
Published: July 2010

Distribution of Cu, Zn, Cd, and Pb in sediments within a 14‐ha‐abandoned, Pb‐Zn tailings pond in north central New Mexico was investigated. Tailings were higher in heavy metals and fines in the south portion of the pond largely related to depositional patterns. Metals concentrations in surface deposits (above tailings) decreased across the pond from east to west, probably due to fluvial processes, surface disturbance by offroad vehicles, and surface erosion deposits. The two wet meadow soil/vegetation types at the south end of the pond had higher levels of heavy metals in surface soil and subsoil than the more xeric soil/vegetation types in the mid‐ to upper (north) portions of the pond. Ratios of total Cu, Zn, Cd, and Pb concentrations in surface soils to underlying and surface tailings, and ratios comparing the south and north portions of the pond, indicate that the relative order of mobility is Cd > Zn > Cu > Pb. Although chemical processes are partly controlling the distribution of metals within the pond, fluvial processes are at least as important. The amount and distribution of extractable metals in surface deposits overlying tailings can be used to determine topsoiling requirements for revegetation of the south end of the pond. The distribution of total metals in the upper 1.5 m of the pond suggests that surface water should be routed around the east side of the pond to prevent erosion of contaminated deposits and pollution of groundwater.
Soil Adsorption of Neutral and Anionic Forms of a Sulfonamide Herbicide, Flumetsulam
Authors: Fontaine D. D. , Lehmann R. G. , Miller J. R.
Published: July 2010

The binding of a weakly acidic herbicide (N‐2, 6‐difluorophenyl‐5‐methyl‐1,2,4‐triazolo(1,5a)pyrimidine‐2‐sulfonamide) to soil is presented as an ionization of the weak acid in solution, and the partitioning of both the anionic and neutral forms of the compound into the soil organic matter. This theoretical description is combined with experimentally determined bulk adsorption constants to give the organic C adsorption constants (Koc) for neutral (650 ± 40 L kg–1) and anionic (12 ± 1 L kg–1) forms of the molecule. Additional experiments with four soils adjusted to different pH levels gave an average Koc of 750 L kg±1 for the neutral form. Describing the soil sorption as a combination of anionic and neutral forms provided an adequate description of the measured sorption.
Laboratory Weathering of Combusted Oil Shale
Authors: Essington M. E.
Published: July 2010

Proper management of large volumes of spent oil shale requires an understanding of disposal environment chemistry and mineralogy. Laboratory weathering is one method to rapidly and inexpensively assess the long‐term potential for spent oil shales to degrade the environment. The objective of this study was to examine the mineralogy and leachate chemistry of three combusted oil shales (two Green River Formation and one New Albany) in a laboratory weathering environment using the humidity cell technique. The mineralogy of the combusted western oil shales (Green River Formation) is process dependent. In general, processing resulted in the formation of anhydrite, lime, periclase, and hematite. During the initial stages of weathering, lime, periclase, and anhydrite dissolve and ettringite precipitates. The initial leachates are highly alkaline (pH > 10.5), saline, and dominated by Na, hydroxide, and SO4. As weathering continues, ettringite dissolves, gypsum and calcite precipitate, and the leachates are dominated by Mg, SO4, and CO3. Leachate pH is rapidly reduced to between 8.5 and 9 with leaching. The combusted eastern oil shale (New Albany) is composed of quartz, illite, hematite, and orthoclase. Weathering results in the precipitation of gypsum. The combusted eastern oil shale did not display a potential to produce acid drainage. Leachate chemistry was dominated by Ca and SO4. Element concentrations continually decreased with weathering. In a western disposal environment receiving minimal atmospheric precipitation, spent oil shale will remain in the initial stages of weathering, and highly alkaline and saline conditions will dominate leachate chemistry. In an eastern disposal environment, soluble salts will be rapidly removed from the spent oil shale to potentially affect the surrounding environment.
Treatment of Four Biorefractory Contaminants in Soils Using Catalyzed Hydrogen Peroxide
Authors: Tyre Bryan W. , Watts Richard J. , Miller Glenn C.
Published: July 2010

The treatment of soil contaminated with pentachlorophenol, trifluralin [2,6‐dinitro‐N, N‐dipropyl‐4‐(trifluoromethyl) benzenamine], hexadecane, and dieldrin (3,4,5,6,9,9‐hexachloro‐1a,2,2a,3,6,6a,7,7a‐octahydro‐2,7:3,6‐dimethanonaphth[2,3‐b]oxirene) using catalyzed hydrogen peroxide [H202 and iron(II)] was investigated in a soil of low development with organic C ranging from 2000 mg kg–1 to 16 000 mg kg–1. Soil treatment was conducted at pH 3 with 240 and 400 mg L–1 iron additions and 120 000 mg L–1 H2O2. Pentachlorophenol and trifluralin degradation rates decreased as a function of soil organic C content. However, soil organic C had no effect on the degradation rates of dieldrin and hexadecane. In addition, the four contaminants degraded at equal rates with soil containing organic C > 10 000 mg kg–1. The ratio of first‐order rate constants for contaminant degradation to hydrogen peroxide consumption (kcontaminant/kh2O2) was used as an empirical measure of treatment efficiency. These ratios were sensitive to both the soil organic C content and to the concentration of iron added during treatment. The efficiency ratios were highest for treatment with no iron addition; these data suggest that iron minerals and H2O2 provide a system in which Fenton‐like oxidations are catalyzed. The ability of iron minerals and H2O2 to oxidize pentachlorophenol was evaluated in goethite‐, hematite‐, and magnetite‐silica sand at pH 3. Pentachlorophenol was degraded in the mineral‐silica sand systems, which was verified by the loss of organic C and the stoichiometric recovery of chloride.
Predicting Nitrate Formation from Soil, Fertilizer, Crop Residue, and Sludge with Thermal Units
Authors: Honeycutt C. W. , Potaro L. J. , Halteman W. A.
Published: July 2010

Improved N utilization efficiency is a logical goal for reducing ground and surface water NO–3 contamination associated with various agricultural practices. Providing farmers with a tool for predicting NO–3 production from various N sources should allow for improved N utilization efficiency. This study was conducted to determine if soil thermal units (degree days) could be used to predict NO–3 formation from unamended soils and from soils amended with inorganic N, papermiil sludge, and crop residue. Fifteen studies were compiled from the literature where NO–3 formation had been temporally assessed over three or more temperatures. Data were compiled from three countries, nine states, eight soil orders, 38 soil series, and 473 soil × treatment combinations. Wide ranges in NO–3 concentration were found when assessed vs. days, owing to the various temperature treatments. However, this range was dramatically reduced for approximately 95% of the data files examined when NO–3 concentration was plotted vs. degree days. Nitrate concentration × thermal unit relationships were found to be soil‐specific, indicating this relationship should be determined for each soil or group of similar soils. Regression analyses of covariate data suggested that factors such as soil texture, pH, and climate may influence the nitrate × thermal unit relationship. Although the thermal unit approach has its limitations, its ease of calculation and demonstrated predictive capability suggest it may be a valuable tool for improving N utilization efficiency.
Nitrogen Retention in Forest Soils
Authors: Johnson Dale W.
Published: July 2010

Factors affecting N retention in both fertilized and natural forest ecosystems are reviewed. Collectively, the literature suggests that current conceptual models describing N competition among heterotrophs, plants, and nitrifiers in the soil may need some modification. Nitrifiers seem to be better competitors for N than previously recognized, especially in situations where N inputs are continuously elevated (such as in polluted sites or with repeated fertilization). The assumption that heterotrophs are the most effective competitors for N may be valid for the short term with relatively low N inputs, but may not hold true over the long term or with high N inputs. The apparent “mining” of N from soils by trees in N‐poor sites suggests that they, rather than heterotrophs, are the most effective long‐term competitors for N in such cases. Nonbiological reactions of N with soil organic matter are known to be a major cause of N immobilization following fertilization and may represent significant competition for N during decomposition in unfertilized sites as well.
A Supplemental Ultraviolet‐B Radiation System for Open‐Top Field Chambers
Authors: Booker F.L. , Fiscus E.L. , Philbeck R.B. , Heagle A.S. , Miller J.E. , Heck W.W.
Published: July 2010

Studies suggest that increased ultraviolet‐B (UV‐B) radiation at the earth's surface due to stratospheric ozone (O3) depletion may affect crop production. Current levels of tropospheric O3 are known to decrease crop yields. To assess the combined effects on plants of increased UV‐B radiation and chronic exposure to O3, a commonly used constant‐addition supplemental UV‐B radiation system was modified for use in open‐top field chambers. Lamp banks containing 14 filtered UV‐B‐313 fluorescent lamps were suspended in 33 chambers to which either charcoal‐filtered, nonfiltered, or nonfiltered air plus O3 was added. Lamp banks provided ample levels and distribution of biologically effective UV‐B (UV‐BBE) radiation for stimulating up to a 29% loss of column O3, according to a radiative transfer model. However, ground‐based measurements of solar UV‐BBE radiation provided a more realistic base than the model for simulations of column O3 loss using supplemental UV‐B radiation. Shading by the lamp bank and chamber assembly reduced the daily solar UV‐BBE, UV‐A, and visible irradiances inside the chamber on average by 24% ± 5% compared with ambient levels. Biweekly adjustments of the supplemental UV‐BBE irradiance level and exposure period provided treatments that were proportional to the seasonal trend in solar UV‐BBE radiation. Control of supplemental UV‐BBE irradiance in proportion to solar UV‐BBE irradiance during the day would better simulate the effects of stratospheric O3 depletion. However, the constant‐addition system was a simpler and less expensive method than the proportional‐addition system for examining the relative sensitivity of plants to the combined effects of increased UV‐B radiation and O3 under field conditions.
Simultaneous Determination of Arsenite, Arsenate, Selenite, and Selenate by Suppressed Ion Chromatography
Authors: McGeehan S.L. , Naylor D.V.
Published: July 2010

Studies of chemical processes involving As and Se in soil solution require accurate determination of arsenite, arsenate, selenite, and selenate. Many of the currently used speciation techniques rely on indirect measurement of one or more species. Direct, simultaneous measurement of these As and Se ionic species was achieved using a commercially available suppressed ion chromatography system and a Na2CO3‐NaHCO3 eluant. Electrochemical and conductivity detectors were used in series with a dual‐channel integrator to quantify arsenite, arsenate, selenite, and selenate. Resolution of the As and Se ionic species from the other ions depended on the nature of the eluant. An eluant containing 2 mM Na2CO3 and 1.7 mM NaHCO3 provided a good compromise between analyte resolution and time of analysis. Concentrations of 1 mg L−1 each of arsenite, arsenate, selenite, and selenate were measured in the presence of 50 mg L−1 each of F, Cl, NO3‐N, SO4‐S, and PO4‐P. Detection limits ranged from 0.016 mg L−1 for selenite to 0.120 mg L−1 for arsenate. The detection limits for arsenate and selenite obtained using this suppressed ion chromatographic technique were lower than values reported in the literature using nonsuppressed ion chromatography. Precision of analysis decreased with decreasing analyte concentration. The ion chromatographic method was compared to spectroscopic methods using analyses of soil solution, receiving As and Se spikes, and analyses of adsorption equilibrium solutions. The results of this study show that suppressed ion chromatography is a reliable method for determination of the As and Se oxyanions in soil solution.
Remediation of Solvent‐Contaminated Soils by Aeration
Authors: Kempton Houston , Davis Andy , Olsen Roger
Published: July 2010

A bench‐scale box test was performed to evaluate the feasibility of rototilling to remediate excavated soils contaminated with tetrachloroethylene (PCE), trichloroethylene (TCE), and 1,1,1‐trichlorocthane (1,1,1‐TCA). Two clay‐rich soils (A and B) containing 0.15% organic C and different concentrations of the target analytes were placed in 15‐cm thick layers under a 10 km h−1 wind, tilled daily, and samples collected and analyzed periodically. Soil A (25 000 µg kg−1 PCE) lost 80% after 24 h and 97% after 407 h. Soil B (8881 µg kg−1 PCE) lost 29% after 24 h and 92% after 407 h. Initial TCE and 1,1,1‐TCA concentrations ranged from 793 to 1570 µg kg−1. Relative volatilization loss rates were similar to that of PCE. The average volatilization half‐lives of the solvents were 1.2 d for PCE, 0.58 d for TCE, and 0.64 d for 1,1,1‐TCA. Removal of the analytes slowed considerably after 200 h, with a small (up to 10%) amount of each analyte retained in refractory sites. Residual solvent concentrations in soils A and B after 407 h were 835 and 719 µg kg−1 PCE, 38 and 95 µg kg−1 TCE, and 21 and 31 µg kg−1 1,1,1‐TCA. Simulations of volatilization using the pesticide root zone model (PRZM) accurately predicted the loss of PCE, TCE, and 1,1,1‐TCA over the first 24 h when most of the solvent volatilized, but the model over predicted contaminat losses at longer durations when remnant soil concentrations were less than six times the concentration bound to refractory sites.