bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Transport of Solutes to Groundwater Using Transfer Functions
Authors: Roth Kurt , Jury William A.
Published: July 2010

Transport of chemicals through the unsaturated zone into groundwater is in general a highly nonlinear process with a pronounced spatial structure of which only a very limited number of measurements is economically and technically feasible. In most applications, it is thus not practicable to model these processes with high spatial and temporal resolutions. However, in an agricultural environment chemicals are usually applied to large areas, and we are generally interested in their long‐term effects on groundwater quality. With these restrictions, the transport processes may be averaged in space and time over sufficiently large regions such that it may be permissible to use a stationary, linear approximation. An efficient way to study such systems exploits that a stationary, linear system is completely determined by its transfer function, that is, by its response to a narrow pulse input. We use a general formalism to represent the transport processes implicitly by the relation between the flux and the resident concentration of a conservative chemical. To model the transport of nonconservative chemicals, this description is coupled, as it was done by (Villermaux, 1981), with a model of the local interactions. We obtain an expression for the transfer function of a linearly adsorbing chemical with linear adsorption kinetics and first‐order decay in the water and in the adsorbed phase which is based on the measured transfer function of a conservative tracer. This procedure has the major advantage that parameter estimation and model validation tests can be applied to the chemical reaction processes alone.
Sorption of Para‐Xylene Vapors on Salt‐Treated Soils Measured by Flow‐Equilibration and Gas Chromatography Methods
Authors: Rhue R.D. , Pennell K.D. , Reve W. H. , Hornsby A. G.
Published: July 2010

The impact of soil properties other than organic C content and surface area on vapor‐phase sorption has rarely been considered. This study was conducted to determine the effect of salt, namely CaCl2, on the sorption of p‐xylene vapor under anhydrous and hydrated conditions. Sorption on Webster soil (Typic Haploquolls) before and after removal of organic C was measured using a flow‐equilibration method. In addition, the utility of an eluted pulse gas chromatography method was evaluated using the sand fraction of Oldsmar soil (Alfic Arenic Haplaquods) as a column‐packing material. The CaCl2 significantly decreased p‐xylene sorption at both 0 and 90% RH for both adsorbents. Under anhydrous conditions, reduced sorption by Oldsmar sand was evidenced at low p‐xylene vapor pressures by a constant net retention volume and symmetrical peaks, indicating linear sorption and ideal behavior at these vapor pressures (i.e., the Henry's region). In the absence of salt, the net retention volume continued to increase at p‐xylene vapor pressures as low as 0.33 Pa, indicating isotherm nonlinearity, even at this low vapor pressure. This difference in retention behavior suggests that salt modified the nature of the surface of the sorbents. Under hydrated conditions, the reduction in sorption may be related to the salting‐out effect of CaCl2 on gas solubility in adsorbed water films. These data suggest that the distribution and migration of organic vapors may be substantially greater in salt‐affected soils due to reduced sorption on both the dry and water‐coated solid phases that are present.
Toxicity of Tributyltin Chloride to Anaerobic Nitrogen Transformations in Sediment and Porewater
Authors: Bergeron Virginie , Blais Jean Simon , Wharf Ivor , Marshall William D.
Published: July 2010

The influence of tributyltin chloride (TBTCl) on N transformations in anoxic sediment cultures, during approximately 14‐d incubations, was studied using acetylene inhibition and acetylene reduction techniques as measures of microbially mediated denitrification and dinitrogen fixation, respectively. The accumulation of N2O, CO2 and C2H4 with time was modeled with a best‐fit polynomial to detect statistically significant differences between treatments and with a three‐segment continuous line model to assess lag times, rates of accumulation and rates of subsequent loss of these gases from the headspace. In sediment cultures, the presence of up to 100 mg L−1 of TBT had a barely detectable influence on these transformations. However, the analogous processes in porewater, prepared by centrifuging sediment slurry at 3 000 × g for 30 min, were appreciably modified by the presence of > 1 mg L−1 of this toxicant. Although the two media were different in terms of their denitrifying potential and their fermenting capacity, dose‐related responses in the porewater were evident for both processes. Apparently the presence of particulate matter in the sediment slurry appreciably attenuated the inhibitory effects of the toxicant. Moreover, a portion of the denitrifiers in cultures of porewater developed a resistance to 100 mg L−1 of TBT in the medium and reduced added nitrate stoichiometrically. When transferred to autoclaved medium containing the same level of toxicant, aliquots of the resistant culture stoichiometrically reduced the added nitrate after a shorter lag time. The resistance was not the result of metabolic detoxification as indicated by the recovery of 74% of toxicant in an unchanged form, after 15 d incubation, using analytical methods which would have detected a 1% conversion of TBT to either Bu2Sn2+ or to BuSn3+. When added, at 10 mg L−1, to autoclaved porewater, an appreciable portion of the toxicant became associated with residual particulate matter (the fraction removed by centrifugation at 10 000 × g but not by 3 000 × g) with only approximately 9% remaining in the supernatant fluid. When 0.5 mL of TBT‐resistant culture was added to the identical matrix and incubated, the TBT in the supernatant phase was reduced below the limit of detection and only 40% was recovered in the particulate/microbial cell fraction. Thus, both particulate materials and microbial growth immobilized TBT serving to limit its concentration in the surrounding water.
Hydrologic Controls in Nitrate, Sulfate, and Chloride Concentrations
Authors: Schnabel R. R. , Urban J. B. , Gburek W. J.
Published: July 2010

Nitrate‐nitrogen, SO4, and Cl concentrations and discharge rates from a small, upland watershed in east central Pennsylvania were analyzed in the context of a layered aquifer. A pattern of greater NO3‐N concentrations during periods of greater discharge was generally followed by declining concentrations during hydrograph recession. The coincident temporal pattern of NO3‐N and discharge appears hydrologically controlled because both NO3‐N and SO4 exhibited similar patterns even though there are important differences in their behavior and reactivity in biologically controlled systems. Chemical concentration patterns in stream flow arose from flow through a two‐layer geologic system in which NO3‐N and SO4 concentrations were different between layers. The substantially lower concentrations observed in the deeper water were attributed to recharge from areas with forest and mixed land uses. Discharge from this deeper layer supported the lowest flows and the lowest chemical concentrations observed in stream flow. Increases in stream flow resulted from greater discharge from the shallower groundwater layer. Adding discharge from the shallower groundwater resulted in higher chemical concentrations in stream flow. Nitrate‐nitrogen concentration estimated with a mixing cell model, in which concentration changes result from dilution only, closely matched measured concentration.
An Innovative Approach to Estimate Bioavailable Phosphorus in Agricultural Runoff Using Iron Oxide‐Impregnated Paper
Authors: Sharpley Andrew N.
Published: July 2010

The transport of bioavailable phosphorus (BAP) in agricultural runoff can accelerate the eutrophication of receiving water bodies. Bioavailable P is comprised of dissolved P (DP) and bioavailable particulate phosphorus (BPP). Although several algal assays and chemical extractions have been proposed to estimate BAP, procedural and theoretical limitations have restricted their widespread use. This study evaluates the use of Fe oxide‐impregnated paper strips (Fe‐oxide strips) to estimate the potential BAP content of runoff from 20 agricultural watersheds in the Southern Plains during 1988 to 1990. In the proposed method, BAP and DP are determined by shaking 50 mL of unfiltered or filtered runoff, respectively, with one Fe‐oxide strip for 16 h. Phosphorus is removed from the strip by 0.1 M H2SO4 and measured, with BPP calculated as the difference between BAP and liP. Growth of Selenastrum capricornutum was related (r2 = 0.63–0.96) to the BPP content of runoff sediment in 2‐ to 29‐d incubations. Bioavailable PP estimated by the proposed strip method and more widely used NaOH extraction, closely followed a 1:1 relationship. Averaged for all runoff events, strip DP was 90 and 75% of DP determined by standard direct methods, for watersheds with and without tillage, respectively. The lower estimates of strip DP may be partially attributed to a greater transport of acid‐hydrolyzable organic and condensed DP in runoff from no‐till compared to tilled watersheds. Acting as a P sink, the strip method may have a stronger theoretical basis than chemical extraction in estimating algal‐available P in agricultural runoff. In addition, the simplicity of the proposed Fe‐oxide strip method will allow BAP estimation with limited resources and may facilitate evaluation of the impact of agricultural runoff on the biological productivity of receiving waters.
Sewage Sludge Proteins: I. Extraction Methodology
Authors: Lerch R. N. , Barbarick K. A. , Azari P. , Sommers L. E. , Westfall D. G.
Published: July 2010

The extraction and quantitation of sewage sludge proteins is a pre‐requisite to evaluating their role as labile C and N sources in sludge‐amended soil. The objective of this study was to develop extraction methodology for the routine quantitation of sewage sludge proteins. Seven sewage sludges were obtained and prepared by oven drying at 55 °C followed by extensive grinding and mixing to produce homogenous samples. Proteins were extracted using H2O, 10% (v/v) Triton X‐100 (a non‐ionic detergent), and 1 M NaOH, and they were analyzed using the Lowry protein assay with bovine serum albumin standards. Protein contents of extracts ranged from (in g kg−1, dry wt. basis): (i) H2O, 1.3 to 24; (ii) 10% Triton X‐100, 3.6 to 59; and (iii) 1 M NaOH, 53 to 280. Water and detergent‐extractable proteins were less than, and base‐extractable proteins were within, literature values reported for total sludge proteins. The coefficients of variation (CV) for each extractant and all sludges were, with one exception, below 6%. The three methodologies provided precise and reproducible data for the extraction of sewage sludge proteins. The detergent extraction procedure is recommended for routine use because of its shorter extraction time.
A Mechanical Stage‐Height Stormflow Sampler
Authors: Riekerk Hans
Published: July 2010

A vacuum‐powered sequential stormflow sampler with intake valves controlled by floats during both rising and falling water levels was developed and tested. The rising float assembly of each subunit triggered a mouse‐trap valve that opened two vacuum lines, one of which directly collected a water sample. Simultaneously, a needle valve in the float pipe closed and kept the second intake line primed. The weight of the float assembly in the falling water level opened the second intake line to collect a water sample. Differences in time‐series data from field trials of the stage‐height sampler with six subunits ascending at 15‐cm intervals as compared with a time‐controlled sampler varied an average of 21 %.
Slope Effects on Cadmium Load of Eroded Sediments and Runoff Water
Authors: Korentajer L. , Stern R. , Aggasi M.
Published: July 2010

Little information is available on the effects of slope on Cd load of runoff water emanating from the Cd‐contaminated soils. A laboratory rainfall simulator study was conducted to assess the effects of slope on runoff, sediment yield, and Cd load of runoff water and eroded soil sediments. The experiment was conducted with three Cd‐amended soils (20 mg kg−1) of varying degrees of erodibility, i.e., Msinga clay loam (Paleudalf, low erodibility), Jozini sandy loam (Haploustalf, moderate erodibility), and Mngazi clay (Pelloxerert, high erodibility), using four slopes (10, 20, 30, and 40%) and three replicates. A Cd‐adsorption experiment and sequential extraction techniques were employed to characterize Cd soil affinity and Cd partitioning in soil. Cadmium runoff losses varied from 4.6 to 58.5% of the applied Cd. Sediment Cd accounted for over 93% of the total Cd load of the runoff slurry. The Cd load of runoff increased with an increasing degree of soil erodibility, reflecting the effects of increased removal of a Cd‐contaminated surface soil layer. With increasing slope, sediment yield and sediment‐associated Cd increased. Slope did not have a significant effect on the soluble Cd load of runoff water. In the Jozini soil, an increase in slope resulted in a sharp decrease in the clay and Cd enrichment ratios (the ratios between clay and Cd contents of the sediment and their respective contents in the soil of origin). In the other two soils enrichment ratios were unaffected by slope. Soluble Cd load of runoff water was less than 28% of the mobile (extractable with 1 M NH4NO3) Cd content of the soils. Differences in soluble Cd load could not be accounted for by the differences in the soils' Cd sorption characteristics or their mobile Cd content, suggesting that these parameters are inappropriate for estimating the extent of soluble Cd losses from the soils.
Estimating Phosphorus in Agricultural Runoff Available to Several Algae Using Iron‐Oxide Paper Strips
Authors: Sharpley A. N.
Published: July 2010

The transport of bioavailable P (BAP) in agricultural runoff can stimulate freshwater eutrophication. Previous research has shown that the amount of P removed by Fe‐oxide impregnated paper strips (Fe‐oxide strips) is related to the growth of Selenastrum capricornutum in laboratory incubations. As only one algal type was used, additional assays were conducted to determine if Fe‐oxide strips can estimate the potential bioavailability of P in runoff to Anabaena, Ankistrodesmus, and Euglena, which are common in eutrophic waters of the Southern Plains. Algal growth was related (P > 0.001) to the amount of P extracted from runoff sediment by Fe‐oxide strips. For a given strip P content of runoff sediment, algal cell count increased in the order Anabaena, Euglena, Selenastrum, and Ankistrodesmus. Thus, the amount of P removed from runoff by Fe‐oxide strips, estimates the BAP content of runoff that may be potentially available for uptake by several common freshwater algae.
Boron and Selenium Removal in Boron‐Laden Soils by Four Sprinkler Irrigated Plant Species
Authors: Bañuelos G. S. , Cardon G. , Mackey B. , Ben‐Asher J. , Wu L. , Beuselinck P. , Akohoue S. , Zambrzuski S.
Published: July 2010

High concentrations of B and Se found in some arid environments are detrimental to sustainable agriculture. Vegetation management may be a remediation strategy designed to reduce soil B and Se concentrations to nontoxic levels. Two separate field experiments were conducted to study B and Se uptake in four different plant species grown in soil containing high concentrations of B (water‐extractable B ranging from 1–10 mg kg−1 soil) and Se (total soil Se ranging from 0.1–1.2 mg kg−1 soil). The four species were Brassica juncea L. Czern and Coss (Indian mustard), Festuca arundinacea Schreb cv. Fawn (tall fescue), Lotus corniculatus L. (birdsfoot trefoil), and Hibiscus cannibinus L. (kenaf). In the 1990 experiment, there were no differences in either tissue B or Se concentrations among the species. The mean tissue concentration was 105 mg B kg−1 dry matter (DM) and 0.75 mg Se kg−1 DM, respectively. In the 1991 experiment, mean shoot tissue concentrations of B ranged from a low of 96 mg kg−1 DM in tall fescue to a high of 684 mg B kg−1 DM in leaves from kenaf. Indian mustard accumulated the greatest amount of Se (>1 mg Se kg−1 DM), while the mean tissue concentration among the other three species was 0.36 mg Se kg−1 DM. For both experiments, soil samples were taken prior to planting and after harvest for each species to a depth of 0 to 30 and 30 to 60 cm, and analyzed for water‐extractable B and total Se. Summary data from all species indicated that extractable soil B and total Se concentrations were reduced between 0‐ to 60‐cm soil depth by 52 and 48% in 1990, and by 24 and 13% in 1991, respectively. Planting any of the four species tested in B‐laden soils may lead to a reduction in both B and Se concentrations in the soil.
Vegetative Uptake of Technetium‐99 from Buried, Solidified, Low‐Level Radioactive Waste
Authors: Murphy Charles E. , Johnson Trudy L.
Published: July 2010

At the Savannah River Site, it is planned to dispose of liquid, lowlevel nuclear waste by incorporating the waste into a solid, concrete waste form called saltstone. Saltstone monoliths will be buried in claycapped, subterranean vaults. Although the vault/cap burial system is designed to severely limit the access of vegetative roots to the saltstone, a study was begun in 1984 to determine the potential for root uptake of radionuclides, in case an unforeseen accident should cause exposure of the buried saltstone. Thirty‐two lysimeters were designed, constructed, and filled with soil. Saltstone samples, containing the liquid, low‐level supernate from a waste disposal demonstration program, were buried in some of the lysimeters. The blocks were placed at varying depths to investigate the relationship between source depth and plant uptake. Other lysimeters, not containing saltstone, were used as controls. Crops, grass, and trees were planted in the lysimeters and sampled periodically to determine radionuclide concentrations. Water samples also were collected from the lysimeter sumps and analyzed for radionuclide content. In the 5 yr following establishment of the lysimeters, only technetium‐99 (Tc‐99) and cesium‐137 (Cs‐137) could be detected at elevated concentrations in the vegetation. The Cs‐137 concentration difference between the plants grown in control and saltstone lysimeters was so small that the difference was only barely detectible against background. The Tc‐99 concentration was significantly higher in the vegetation and the sump water of the lysimeters containing saltstone, when compared to the control lysimeters. The Tc‐99 uptake by the vegetation appears to be related to release of the Tc‐99 from the saltstone into the soil water. The Tc‐99 concentration in vegetation and sump waters shows a similar pattern, including an initial period of very low concentrations followed by a coincident build‐up period and a period of relatively uniform concentration. Vegetative uptake factors were calculated for uptake of Tc‐99 from soil water. The results were very similar for the vegetative parts of all the species grown, 111 to 376 (nBq/kgvegetation)/(nBq/kgwater). The uptake factor calculated for the seeds of crops was less by a factor of 100 than the uptake factor for vegetative parts.
A Greenhouse System for Determining Pesticide Movement from Golf Course Greens
Authors: Smith A. E. , Weldon O. , Slaughter W. , Peeler H. , Mantripragada N.
Published: July 2010

There is an increasing concern for the potential movement of chemicals from the treated sites following the use of certain management strategies for turfgrass maintenance. In some areas, these concerns are being translated into proposed government regulations for turfgrass management that could reduce amounts of chemicals available for the management strategies. The objective of this study was to develop a lysimeter system with a controlled environment for measuring the potential movement of pesticides through golf course greens designed to simulate United States Golf Association specifications. A track irrigation system was mounted above 36 lysimeters to simulate irrigation and rainfall common to the golf courses in the Piedmont region of Georgia. The system was tested for a 52‐wk period using ‘Tifdwarf’ bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy]. An excellent turfgrass sod was maintained during the trial period. The coefficient of variation (CV) in water delivery within the growth boxes was 5.6% and the average Cv of water delivery between the 36 growth boxes was 6.2%. The two rows of lysimeters contained either a 80:20 or 85:15 (sand/sphagnum peat moss) mixture. The average Cv for differences in volume of effluent exiting the lysimeter bases was 22%. Data for determining the potential movement of applied chemicals from golf course greens can be obtained from this system.
A Mimicked In‐Situ Remediation Study of Metal‐Contaminated Soils with Emphasis on Cadmium and Lead
Authors: Mench Michel J. , Didier Valérie L. , Löffler Monika , Gomez Alain , Masson Pierre
Published: July 2010

The capacity of several additives, i.e., lime, Thomas phosphate basic slag (TBS), hydrous iron oxides (HFO), hydrous manganese oxides (HMO), and Beringite, added to soil to fix Cd or Pb, was evaluated using two pot experiments in tandem with soil extractions. Three soils from France with metal contents ranging from 0.17 to 108 mg Cd kg−1 soil dry weight (DW) and 47 to 1112 mg Pb kg−1 soil DW were studied. Metal sources were: sludge‐borne metals (Soil A), fallout from a smelter (Soil B), and emission from a tetraethyl Pb production facility (Soil C). Ryegrass (Lolium spp.) or tobacco (Nicotiana tabacum L.) shoots were harvested. The addition of HMO decreased to a maximum extent Cd in ryegrass and tobacco for Soils A and B, but did not suppress the differences in Cd uptake between the two plant species. Use of HMO reduced Pb concentrations only in ryegrass shoots. Thomas phosphate basic slag lowered Pb bioavailability in Soils B and C. The addition of HMO into Soils A and B reduced Cd concentrations in water, 0.1 M Ca(NO3)2, or 0.43 M acetic acid (HOAc) extracts, but not in 0.05 M EDTA pH 7 extracts. Water and sequential extractions were employed on Soil C: HMO caused the most reduction in Pb water‐soluble and HOAc‐extractable fractions, and rendered Pb less extractable with H2O2 and more with HONH3Cl. The decrease of Cd‐ and Pb‐soluble fractions was reflected in their suppressed bioavailability. Among the screened additives, HMO exhibited a most promising potential to reduce either Cd or Pb transfer from soil to soil solution or their entry into the food chain via plant uptake. This material would be promising for in‐situ remediation technologies geared to restore Cd‐ and Pb‐contaminated soils. However, little is known about the kinetics and persistence of this chemical under field conditions.
Role of Genotype in the Response of Loblolly Pine to Tropospheric Ozone: Effects at the Whole‐Tree, Stand, and Regional Level
Authors: Taylor George E.
Published: July 2010

The interaction between tropospheric ozone (O3) and genotype in loblolly pine (Pinus taeda L.) is explored, focusing on the consequences of different genotypes in a range of basic and applied issues. General conclusions for loblolly pine are: (i) a genetic component underlying phenotypic variation in ozone response is documented at the biochemical, physiological, and whole‐plant level; (ii) ozone resistance determined from needle injury is not associated with resistance determined from growth or gas exchange; (iii) mode of inheritance of resistance based on growth is not documented, although evidences point to a multilocus model; (iv) resistance involves avoidance and tolerance mechanisms, and evidence for pleiotropy indicates that resistance carries costs that are important in terms of physiologic ecology and breeding strategies; and (v) breadth of genetically determined variation has consequences for experimental designs, ecological risk assessment, genetic diversity and air quality standards. The threshold for growth effects on average seedlings approaches a 12‐h mean concentration of 45 nL L−1, which is below extant air quality in many Southeastern forests. The threshold for sensitive cohorts approaches 25 nL L−1, near the projected concentration a century ago (19 nL L−1). Extant ozone levels are affecting the average loblolly pine intermittently and sensitive cohorts frequently or continuously. The responsiveness of sensitive cohorts is important in understanding how regional stresses will impact ecological resources. Air pollution research in the last decade emphasized the development of exposure‐response relationships, centering on selection of statistical indicators of atmospheric ozone. The conclusion that genetic variation is a major source of variation indicates that further improvement in exposure‐response relationships will emerge from efforts addressing variability driven by biospheric rather than atmospheric processes.
Hexavalent Chromium Solubility and Reduction in Alkaline Soils Enriched with Chromite Ore Processing Residue
Authors: James Bruce R.
Published: July 2010

Health‐based regulatory limits and remediation strategies for chromate [Cr(VI)] in alkaline soils enriched with chromite ore processing residue (COPR) should be based on oxidation‐reduction and solubility interactions of Cr. A laboratory study characterized the solubility of Cr(VI) by sequential batch equilibrations and teachings from two COPR‐enriched soils using dilute salt and acid solutions. Batch equilibrations quantified reduction of soluble and insoluble Cr(VI) in the whole soils and extracted solutions. The soils, termed Low Hex and High Hex, contained 105 and 460 mg Cr(VI) kg−1, 1.8 and 10.4 g total Cr kg−1, and had pH values of 8.5 and 10.4, respectively. Total cumulative Cr(VI) removed by the extractions was 49 and 386 mg kg−1 by both the batch equilibrations and leaching methods in the Low and High Hex soils, respectively, and no differences were found among the extractants. Addition of Mn2+ resulted in 50 to 100% reduction of soluble Cr(VI) in both soils without pH adjustment, a new finding that is thermodynamically predictable at pH > 7.2, and it is in sharp contrast to the ability of Mn(III,IV) oxides to oxidize Cr(III) to Cr(VI) in more acidic soils and Mn oxide suspensions. Additions of Fe2+, steel wool (Fe), leaf litter, and lactic acid (a component of human sweat) also reduced various quantities of soluble and insoluble Cr(VI) in the soils, depending on pH, reducing agent, and soil. Soluble Cr(VI) in these COPR‐enriched soils appeared to be controlled by dissolution of a moderately soluble chromate salt, such as CaCrO4, and not by sorption or oxidation‐reduction equilibria.
Considerations for Evaluating Controlled Exposure Studies of Tree Seedlings
Authors: Peterson Charles E. , Mickler Robert A.
Published: July 2010

Tree seedling exposure studies, covering a wide range of experimental conditions in pollutant treatments, species, facilities, and exposure regimes, have been conducted during the past several years to determine acute effects and relative sensitivity of tree species in response to simulated acid precipitation and gaseous pollutants. Because of the difficulties inherent in conducting controlled exposures with mature trees (e.g., size, variability among experimental units, and costs associated with replication of treatments), seedling exposure studies have been initiated as the quickest way to address these issues. However, sufficient consideration has not been given to either the comparability of seedling studies or to their appropriate inference. The statistical power of any given analysis is rarely discussed when the outcomes are published. Appropriate and documented statistics of experimenter bias are often not reported, and variability in the exposure regime (i.e., treatment target levels) and the measurement of experimental variables is assumed to be zero, rather than quantified. Finally, the populations of seedlings for which seedling experiments have inference, the extent to which seedling responses are applicable to mature trees and forest condition, and the limitations in national or regional generalizations are crucial issues often left to an individual reader's interpretation without the benefit of adequate quantitative information presented by the authors.
Nitrate Leaching from Nitrogen‐Fertilized and Manured Corn Measured with Zero‐Tension Pan Lysimeters
Authors: Jemison John M. , Fox Richard H.
Published: July 2010

Excessive N fertilization increases the potential for nitrate (NO−3) leaching, but no research has evaluated NO−3 leaching from corn (Zea mays L.) receiving economic optimum N rates (EON). This study assessed (i) flow‐weighted average concentration and mass of nitrate‐N (NO3‐N) leached from nonmanured and manured corn treated with five fertilizer N levels and at EON, and (ii) the relationship between NO3‐N mass in the 1.2‐m soil profile following harvest and the flow‐weighted average leachate concentrations. Following application of liquid dairy manure each April, the field was chiseled and disked prior to planting. Ammonium nitrate was broadcast at planting (0–200 kg N ha−1 in 50‐kg increments and 0–100 kg N ha−1 in 25‐kg increments) in the nonmanured and manured corn. Eighteen (0.465 m2) pan lysimeters were placed 1.2 m below the soil surface in zero, intermediate, and high N treatments. Zero‐N plots had 3‐yr average flow‐weighted leachate concentrations less than 10 mg NO3‐N L−1. At EON, the 3‐yr averages were 18.8 and 19.3 mg NO3‐N L−1 for nonmanured and manured corn. Nitrogen rate influenced mass of NO3‐N leached only when collection efficiency estimates were used to account for pan bypass flow. In the nonmanured corn, the 3‐yr average amount of NO3‐N leached was 107 kg ha−1 or 36% of the N applied at EON. Total mass of NO3‐N in the 1.2‐m soil profile following harvest was useful to predict annual flow‐weighted average leachate NO3‐N concentrations, but this is not practical in most soils of the Northeast.
Denitrification Loss from Two Pennsylvania Floodplain Soils
Authors: Schnabel R. R. , Stout W. L.
Published: July 2010

Denitrification losses and dissolved nitrous oxide concentration within a well‐ and poorly‐drained soil under ryegrass (Lolium perenne L.) were measured for ≈12 mo. The soils received up to 252 kg N/ha as potassium nitrate in two equal amounts. Denitrification increased in March as the soil warmed to 5 to 7 °C with the highest rates occurring soon after N was applied. Approximately 30% of annual loss occurred within 2 wk of fertilization. Dissolved nitrous oxide concentration peaks corresponded to periods with elevated denitrification. On average, the poorly‐drained soil denitrified the equivalent of 40% of applied N (up to 110 kg N/ha). Less than 2.5 kg/ha was denitrified from the well‐drained soil. The degree of anoxia in the measurement apparatus substantially effected measured denitrification rates. Consequently, it is important to know the relationship between redox in‐situ and in the measurement apparatus.
Phosphorus Retention by Wetland Soils used for Treated Wastewater Disposal
Authors: Gale P. M. , Reddy K. R. , Graetz D. A.
Published: July 2010

Wetlands function as buffers for nutrients loaded from terrestrial ecosystems through drainage and surface discharges. The objectives of our study were to (i) determine the P retention capacity of representative wetland soils being used for disposal of treated wastewater and (ii) relate P retention characteristics to selected physicochemical properties to evaluate likely mechanisms of P removal in the soils. Intact soil cores (0–40 cm) and bulk soil samples (0–15 cm) were collected from a system of natural and constructed wetlands currently being used for disposal of treated wastewater. Floodwater P concentrations of the intact soil cores were monitored over time to determine the rate of P removal. Batch experiments were conducted to determine maximum P retention capacity of the soils. Soil samples were analyzed for inorganic P pool sizes, and selected physicochemical properties. During a 21 d hydraulic retention time, the constructed wetlands (sandy, low organic matter soils) retained 52 to 66% of added P, as compared with 46 to 47% retained by the natural wetlands (high organic matter soils). The P retention maximum, as estimated using the Langmuir model, ranged from 196 to 1821 mg P kg−1 (aerobic incubations) and from 32 to 1415 mg P kg−1 (anaerobic incubations). The P sorption maximum for these soils could be predicted by batch equilibration with a single high P solution. Anaerobic conditions increased P solubility. Organic P pools and the Fe‐Al‐bound fraction seemed to control P chemistry in these natural and constructed wetlands.
An Improved Zero‐Tension Lysimeter to Monitor Colloid Transport in Soils
Authors: Thompson Michael L. , Scharf Richard L.
Published: July 2010

Mobile colloids may facilitate the long‐distance transport of actinides, organic contaminants, and heavy metals in soil, surface water, and groundwater. Detection of colloid‐facilitated contaminant transport in soils requires adequate monitoring before, during, and after in‐situ remediation treatments. Zero‐tension lysimeters (ZTLs) are devices designed to collect water that moves through the soil under the influence of gravity; they can also be used to collect mobile colloids. A ZTL that is suitable for monitoring colloid‐facilitated contaminant migration consists of a specially designed collection cup placed below an undisturbed core of soil that has been initially withdrawn with a hydraulically powered tube. Field tests of the lysimeter were conducted at a site near Ames, IA, where three levels of municipal sewage sludge were applied to the soil in 1992. Each ZTL required about 45 min for a two‐person crew to install at 50‐cm depth. Turbidity measurements of leachate following summer storms revealed considerable spatial variability in colloid migration, supporting the use of ZTLs that can be installed quickly and cheaply in large numbers at a study site. The ZTL described has significant advantages over conventional designs with respect to simplicity and speed of installation. Therefore, it allows colloid transport to be monitored at more locations at a given site. In addition, because of the improved spatial resolution in sampling and monitoring, if contaminants are mobilized, their source can be more easily identified than with piezometer‐based monitoring methods.
Response of Plants to Interacting Stresses (ROPIS): Program Rationale, Design, and Implications
Authors: Goldstein Robert , Ferson Scott
Published: July 2010

The Response of Plants to Interacting Stresses (ROPIS) program was designed to provide a mechanistic framework for analysis and prediction of the effects of air pollution (i.e., tropospheric ozone, acidic precipitation) and other environmental stresses on plants. Focusing on regionally important tree species, the program used experimental studies in the field and laboratory in combination with modeling efforts to evaluate how stresses affect material flow and transformation within the plant and material flow across the plant's boundaries with the soil and the atmosphere. Based on the wealth of results from the program, the stresses directly or indirectly altered flows and transformations that control a plant's carbon, nutrient, and water balances; in turn, these stress‐induced effects altered material uptake, biomass production, partitioning of dry matter at the whole‐plant level, and the plant's ability to compete for limited resources in the environment. It is proposed that process‐level models of material flow within a plant and between a plant and the surrounding environment can be used to integrate and predict plant response to interacting stresses of natural and anthropogenic origin.
Integrating the Effects of Simultaneous Multiple Stresses on Plants Using the Simulation Model TREGRO
Authors: Weinstein David A. , Yanai Ruth D.
Published: July 2010

TREGRO, a model of tree physiological response to environmental stress, was developed to examine the details of tree response to the interaction between ozone stress and nutrient deficiency. TREGRO was used to test the hypothesis that the nutrient deficiency would exacerbate growth reductions caused by ozone. When TREGRO was applied to a range of multiple‐stress scenarios involving these two stresses, the simulated effects of the combined stresses in reducing red spruce (Picea rubens Sarg.) tree growth were less than the sum of the effects simulated when each stress was acting alone. Red spruce, a species with a growth strategy involving low maximum potential growth rates and storage in C reserves, showed simulated patterns of allocation that minimized the added effect of ozone when Mg nutrient availability was low. In contrast, ponderosa pine (Pinus ponderosa Dougl.), a species that allocated C to the construction of new tissue preferentially, showed little ability to ameliorate ozone stress under low nutrient conditions. In neither case were the effects of ozone increased by nutrient deficiency. It is speculated that a species which maintains maximum C demand rates considerably below rates of C supply may be better able to adjust to conditions of multiple stresses.
Managing Agricultural Phosphorus for Protection of Surface Waters: Issues and Options
Authors: Sharpley Andrew N. , Chapra S. C. , Wedepohl R. , Sims J. T. , Daniel T. C. , Reddy K. R.
Published: July 2010

The accelerated eutrophication of most freshwaters is limited by P inputs. Nonpoint sources of P in agricultural runoff now contribute a greater portion of freshwater inputs, due to easier identification and recent control of point sources. Although P management is an integral part of profitable agrisystems, continued inputs of fertilizer and manure P in excess of crop requirements have led to a build‐up of soil P levels, which are of environmental rather than agronomic concern, particularly in areas of intensive crop and livestock production. Thus, the main issues facing the establishment of economically and environmentally sound P management systems are the identification of soil P levels that are of environmental concern; targeting specific controls for different water quality objectives within watersheds; and balancing economic with environmental values. In developing effective options, we have brought together agricultural and limnological expertise to prioritize watershed management practices and remedial strategies to mitigate nonpoint‐source impacts of agricultural P. Options include runoff and erosion control and P‐source management, based on eutrophic rather than agronomic considerations. Current soil test P methods may screen soils on which the aquatic bioavailability of P should be estimated. Landowner options to more efficiently utilize manure P include basing application rates on soil vulnerability to P loss in runoff, manure analysis, and programs encouraging manure movement to a greater hectareage. Targeting source areas may be achieved by use of indices to rank soil vulnerability to P loss in runoff and lake sensitivity to P inputs.
Nitric and Nitrous Oxide Emissions and Soil Nitrate Distribution in a Center‐Pivot‐Irrigated Cornfield
Authors: Guenzi W. D. , Hutchinson G. L. , Beard W. E.
Published: July 2010

Research on soil N loss mechanisms remains a high priority not only because of the need to increase agricultural N use efficiency, but also because of environmental concernsuch as NO−3 contamination of groundwater and increasing N oxide concentrations in the atmosphere. We measured NO and N2O emissions and downward movement of NO−3 in an eastern Colorado corn (Zea mays L.) field irrigated with a modified center‐pivot system that applied water to alternate furrows. One hour after infiltration of the irrigation water, emission rates measured by an enclosure method ranged from 0 to 6 g N ha−1 d−1 for NO and 0 to 26 g N ha−1 d−1 for N2O. The emission rates were largest after the first irrigation and much smaller following subsequent irrigations. Greater N oxide evolution from nonirrigated furrows than adjacent irrigated furrows probably resulted from lateral transport of gases produced in the wet soil. Analyses of soil cores taken after planting and after harvest provided no evidence that NO−3 moved below the root zone during the growing season, despite the presence of substantially more inorganic N than required for maximum corn yield. These data suggest that when the size and frequency of irrigations are efficiently managed, use of a low energy precision application (LEPA) irrigation system results in no N loss to groundwater and no economically significant gaseous N oxide loss to the atmosphere.
Factors Controlling Seasonal Nutrient Profiles in a Subtropical Peatland of the Florida Everglades
Authors: Koch‐Rose M. S. , Reddy K. R. , Chanton J. P.
Published: July 2010

Approximately 75% of soil nutrients in the Everglades are stored in the organic form; thus, factors affecting seasonal organic matter and associated nutrient mineralization will influence nutrient availability to marsh vegetation. To assess the factors controlling mineralization in the field, pore water nutrients including NH+4, NO−3 and, soluble reactive P (SRP) were determined along with soil Eh, pH, temperature, and water levels at eutrophic, mesotrophic, and oligotrophic sites through a dry and rainy season. Indicators of anaerobic microbial activity, SO2−4, methane (CH4), CH4‐stable isotope signatures, and dissolved inorganic carbon (DIC) were sampled at all three sites. At the enriched site, SRP and NH+4 levels were 95 and 706 µM during summer months and 11 and 26 µM spring concurrent with N/P ratios of three and maximum macrophyte growth. Low seasonal variability in SRP was found at oligotrophic sites where pore water N/P ratios ranged from 39 to 551 throughout the year. During the spring dry season, Eh exceeded 300 mV at all three sites. In all other seasons, soils remained flooded and Eh averaged −100 to −200 mV. Methane and DIC, and isotopic 13C ratios in the eutrophic sites, relative to those found under oligotrophic conditions, suggest greater microbial production rates at enriched sites. Oligotrophic Everglades soils appear to have limited microbial activity and consequently, dampened seasonal pore water nutrient levels in response to fluctuating Eh, pH, water level, and temperature regimes.
In‐Situ Dissipation of Benomyl, Carbofuran, Thiobencarb, and Triclopyr at Three Soil Depths
Authors: Johnson W. G. , Lavy T. L.
Published: July 2010

Data are lacking concerning the persistence of pesticides used in Arkansas rice production. Studies were conducted to examine the dissipation characteristics in field studies of four commonly used pesticides. Crowley silt loam soil (fine, montmorillonitic thermic Typic Albaqualfs) from 2, 20, or 60 cm was treated with benomyl (methyl‐1‐(butylcarbamoyl)‐2‐benzimidazole‐2‐yl carbamate), carbofuran (2,3‐dihydro‐2,2‐dimethylbenzofuran‐7‐yl methylcarbamate), thiobencarb (S‐[(4‐chlorophenyl)methyl]diethylcarbamothioate), or triclopyr ([(3,5,6‐trichloro‐2‐pyridinyl)oxy]acetic acid), and buried in leaching or degradation containers for 0, 34, 104, 184, 280, 371, 736, or 1066 d at Stuttgart, AR. Degradation of carbofuran, thiobencarb, and triclopyr was more rapid than the benomyl metabolite MBC (methyl‐2‐benzimidazole carbamate) with the time for 50% of the initial dose to dissipate (DT50) being 94 d or less. The carbofuran metabolite 3‐keto carbofuran (2,3‐dihydro‐2,2‐dimethyl‐3‐keto‐benzofuranyl‐N‐methyl carbamate) was not detected during this time period. Trace levels of 3‐hydroxy carbofuran (2,3‐dihydro‐2,2‐dimethyl‐3‐hydroxy‐benzofuranyl‐N‐methyl carbamate) were detected periodically. The benomyl metabolite MBC was the most persistent pesticide in this study with DT50 values of 179 to 1020 d. The rates of dissipation decreased with increasing soil depth for all pesticides.
The Distribution of Uranium and Thorium Decay‐Series Radionuclides in the Environment—A Review
Authors: Cowart J. B. , Burnett W. C.
Published: July 2010

Natural radioactivity has played an indispensable role in the development of the earth to the form and shape that we now observe. Energy from radioactivity powers the large‐scale processes that move the continents and cycle the elements. Most of the energy due to radioactivity comes from members of the three decay‐series, two of which are parented by isotopes of uranium, 238U and 235U, and one by 232Th. These decay‐series cascade to produce radioactive offspring such as Ra, Rn, and Po, but the ultimate fate of all members of these series is to end as a stable isotope of Pb. Rocks or minerals that provide sites for the long‐lived decay‐series parents, U and Th, are destined to be associated with the other members of the decay‐series. The rocks that tend to host U and Th include some crystalline rocks such as granite and quartz‐conglomerate metamorphics, and certain sedimentary rocks such as organic shales, sandstones, carbonates, and phosphorites. All materials at the earth's surface eventually are broken down to their constituent parts and then, usually by the agency of water, transported to environments where they again may be geochemically sorted. The sorting processes at or near the surface of the earth operate on radioelements just as they do on other elements. The result is that the various radioelements are not simply dispersed but rather tend to accumulate in certain environments or rock types. Thus, the behavior of the radioelements found in the natural environment is based on their geochemistry, half‐life, and the nature of their surroundings.
Papermill Sludge, Phosphorus, Potassium, and Lime Effect on Clover Grown on a Mine Soil
Authors: Feagley S. E. , Valdez M. S. , Hudnall W. H.
Published: July 2010

Pots containing mine soil treated with lime, fertilizer, and bleached, primary papermiil sludge (at the rate of 56, 112, and 224 Mg/ha added alone or in combination with fertilizer [P and K]) were planted to subterranean clover (Trifolium subterranean L.) in the first phase of a two‐phase study. Fertilizer was found necessary to revegetate the mine soil, and the addition of sludge and fertilizer significantly (α<0.05) increased yield over the fertilizer only. This favorable effect of sludge was observed during the second harvest, with 112 Mg/ha giving the maximum yield. Biological N2 fixation and native N did not raise the N concentration in clover within the normal range (2.9–3.8%). Fertilizer application improved N uptake by the forage. The N concentration in clover declined with successive harvests. However, sludge application minimized this decline. Phosphorus was found to be at normal range (0.1–0.2%) in all cases, except at the sludge rate of 112 and 224 Mg/ha without fertilizer. Excessive tissue concentrations of K, Ca, S, Fe, Cu, Zn, and Al were observed in the unfertilized mine soil and K, Ca, Zn, and Al were excessive in all treatments.