bluuebunny/crossref_metadata_2025 huggingface dataset:
Methyl Bromide Emissions from a Covered Field: III. Correcting Chamber Flux for Temperature
Authors: Yates S. R. , Gan J. , Ernst F. F. , Wang D.
Published: July 2010

An experiment was conducted to investigate the environmental fate and transport of methyl bromide (MeBr) in agricultural systems. Part of this experiment involved the use of three flow‐through chambers to estimate the MeBr flux through a sheet of clear polyethylene plastic covering the field. Using the chamber data, the total mass lost to the atmosphere was estimated to be 96% of the applied mass, and the results were highly variable between chambers (i.e., standard deviation of 298 kg or 35%). The air temperature inside the chamber was found to be much higher than the air temperature outside and was highly correlated with the diurnal variation in incoming solar radiation. Since the diffusion through polyethylene film was found to be strongly dependent on the temperature, a method was developed to correct the chamber flux density data for enhanced diffusion caused by increases in the temperature inside the chamber. After correcting for temperature, the estimated total MeBr emission was reduced to approximately 59% (21% standard deviation) of the applied amount, which is about 5% less than was measured using other methods. When chambers are used to measure volatilization of MeBr or other fumigants from fields covered with a sheet of polyethylene plastic, the chambers should be designed to minimize internal heating or some method should be used to correct the volatilization rate for the effects of temperature.
A Tracer Test to Determine the Fate of Nitrate in Shallow Groundwater
Authors: Starr J. L. , Sadeghi A. M. , Parkin T. B. , Meisinger J. J.
Published: July 2010

The effectiveness of shallow groundwater areas to serve as a sink for NO3 is affected by many biological and physical properties. However, the direct impact of these properties on the fate of NO3 in shallow groundwater is not well understood, especially where the soils are intermittently saturated. This study was conducted to assess in situ reaction and transport of NO3‐N in an intermittent shallow groundwater system. Tracer experiments were conducted within an imposed constant flowing shallow groundwater. A constant‐head, single injection well technique was adapted for this study using multilevel soil water samplers placed at 14 locations around the center injection well. The use of Br as a tracer for NO3‐N in these constant‐flow experiments provided the means to assess in situ NO3‐N removal both with and without added C. In experiments without added C, an average NO3 removal rate of 0.33 g N m−2 d−1 was estimated. In a second experiment with dextrose added as an added C source, an average NO3 loss rate 1.06 g N m−2 d−1 was observed. The observed response to added dextrose indicates that the N removal processes were primarily microbial in origin, i.e., the NO3 was denitrifled or immobilized into microbial biomass.
Wood and Combination Wood‐Fired Boiler Ash Characterization
Authors: Someshwar Arun V.
Published: July 2010

Ashes resulting from the combustion of wood residues in industrial boilers are characterized relative to (i) macroelement compositions, (ii) trace and heavy metal microelement compositions, (iii) organics, and (iv) polychlorinated dibenzo‐dioxins and ‐furans (PCDD/Fs). Ash compositions, both macro‐ and microelements, are compared with coal ash and limestone. Microelements in wood ashes are also compared with other potential soil amendments such as pulp mill sludges. The impact of burning sludge and combinations of coal and wood residue on ash metal concentrations is presented. Levels of PCDD/Fs in ash resulting from combustion of 100% inland wood residue, salty wood, or bleached mill sludge with wood residue are reviewed, as are the levels of PCDD/Fs in ashes and soot resulting from residential wood combustion. The concentrations of metals in wood ash are comparable to other potential soil amendments. The concentration in wood ash of common organics of environmental concern appears to be negligible. The levels of PCDD/Fs in the ash appear to have a direct correlation with extraneous sources of chloride in the wood fuel.
Nitrogen Transport from Tallgrass Prairie Watersheds
Authors: Dodds W.K. , Blair J. M. , Henebry G. M. , Koelliker J. K. , Ramundo R. , Tate C. M.
Published: July 2010

Discharge and N content of surface water flowing from four Karst watersheds on Konza Prairie Research Natural Area, Kansas, managed with different burn frequencies, were monitored from 1986 to 1992. The goal was to establish the influence of natural processes (climate, fire, and bison grazing) on N transport and concentration in streams. Streams were characterized by variable flow, under conditions that included an extreme flood and a drought during which all channels were dry for over a year. The estimated groundwater/stream water discharge ratio varied between 0.15 to 6.41. Annual N transport by streams, averaged across all watersheds and years, was 0.16 kg N ha−1 yr−1. Annual N transport per unit area also increased as the watershed area increased and as precipitation increased. Total annual transport of N from the prairie via streams ranged from 0.01 to 6.0% of the N input from precipitation. Nitrate and total N concentrations in surface water decreased (P < 0.001, r values ranged from 0.14–0.26) as length of time since last fire increased. Increased watershed area was correlated negatively (P < 0.0001) to stream water concentrations of NO−3N and total N (r values = −0.43 and −0.20, respectively). Low N concentration is typical of these streams, with NH+4‐N concentrations below 1.0 µg L−1, NO−3‐N ranging from below 1.4 to 392 µg L−1, and total N from 3.0 to 714 µg L−1. These data provide an important baseline for evaluating N transport and stream water quality from unfertilized grasslands.
Zinc and Cadmium Toxicity to Alfalfa and Its Microsymbiont
Authors: Ibekwe A. M. , Angle J. S. , Chaney R. L. , van Berkum P.
Published: July 2010

The availability of heavy metals in soil depends on their speciation in solution and chemical activities of free metals. To examine the sensitivity of alfalfa (Glycine max L.), its microsymbiont, and the process of N2 fixation to Zn2+ and Cd2+ activities, a growth chamber study was conducted. Nutrient solution was used with the chelator, EGTA, to buffer Zn2+ and Cd2+ activities. The activities of Zn2+ and Cd2+ ranged from pZn2+ = 8.0 to 5.0 and pCd2+ = 10.5 to 8.0 mol L−1. Plants grown in pZn2+ = 5.25 and 5.0; and pCd2+ = 8.75 and 8.65 were stunted and chlorotic with interveinal necrosis. In these treatments, shoot concentrations of Zn and Cd averaged about 300 and 50 mg kg−1, respectively. This resulted in a 20 and 90% yield reduction for plants grown in pZn2+ = 5.25 and 5.0, respectively. Yield reduction was 50 and 75% for pCd2+ = 8.75 and 8.65, respectively. Plants supplied with mineral N had about 40% greater shoot yield than plants inoculated with rhizobia. No nodulation occurred at pZn2+ = 5.0, but at pZn2+ = 5.25 and pCd2+ = 8.75 and 8.65, there was a delay in nodulation. All nodules formed were mostly effective in N2 fixation. Enumeration of viable cells showed a significant decline of total cell counts from 105.5 cell mL−1 in the control to 105.1 and 104.8 at the highest Zn2+ and Cd2+ activities, respectively. At the activities studied, Cd was more toxic to rhizobia than Zn. However, at the highest activities, toxicity of metals were so severe that root development was inhibited and in some cases resulted in plant death. These results suggest that toxicity of Zn and Cd was greater to plants than to rhizobia.
Persistence of Metribuzin and Metabolites in Two Subarctic Soils
Authors: Conn J. S. , Koskinen W. C. , Werdin N. R. , Graham J. S.
Published: July 2010

Persistence and leaching of 14C‐metribuzin [4‐amino‐6‐(1,1‐dimethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4H)‐one] and metabolites were determined in Tanana (loamy, mixed, nonacid Pergelic Cryaquept) and Beales (sandy, mixed Typic Cryochrept) silt loam soils under irrigated potato (Solanum tuberosum L.) and dryland barley (Hordeum vulgare L.) conditions in the subarctic. Overall, dissipation of total 14C (metribuzin and metabolites) was significantly slower (P > 0.05) in Tanana than Beales soil over the first 105 d, but by 468 d, the 14C remaining (51% of applied) did not differ (0.05 < P) between soils. Initial degradation of metribuzin was rapid in both soils but was not significantly different between soils (0.05 < P). At 35 after application 24% of applied metribuzin remained. At the end of the study (468 d), 5.0% of the applied metribuzin was still present. Unextractable residues accounted for the greatest amount of 14C remaining in the soils. Of the extractable metabolites, greater amounts of desaminometribuzin were found in both soils than diketometribuzin or desaminodiketometribuzin. More water moved through the irrigated than nonirrigated soil as evidenced by bromide movement. Also, more 14C moved to 15 to 22.5 cm depth in the irrigated than in the nonirrigated soil, but <1% of applied 14C was detected below 22.5 cm for both soils and irrigation treatments. Rapid metribuzin degradation in combination with sorption processes minimized leaching of total metribuzin residues through these subarctic surface soils.
Transient Diffusion, Adsorption, and Emission of Volatile Organic Vapors in Soils with Fluctuating Low Water Contents
Authors: Petersen L. W. , El‐Farhan Y. H. , Moldrup P. , Rolston D. E. , Yamaguchi T.
Published: July 2010

Laboratory experiments were conducted on large packed soil columns (15 cm diam., 40 cm length) under unsaturated conditions. Trichloroethene (TCE) was introduced at the bottom of the columns. The emissions of TCE from the soil surface were monitored. The soil‐water content at the soil surface was changed by alternating dry and water‐saturated air sweeping over the column surface, thus changing the vapor sorption capacity of the soil. The retardation of VOC gas transport, due to the change in adsorption capacity with change in soil‐water content, was determined by sampling the soil‐air and the sweep air flushing the column headspace. Soil‐water content was monitored by the time‐domain reflectometry (TDR) technique. The transport of VOC gases from experiment initiation until steady‐state was simulated using a numerical simulation model, in which diffusion and equilibrium partition theory were incorporated. Measured and simulated concentration profiles as well as volatilization fluxes agreed very well. The decrease in soil‐water content, caused by sweeping dry air over the column surface, resulted in an increase in the soil adsorption capacity up to several orders of magnitude (mainly in the top few centimeters of soil). Both increase and decrease in soil‐water content affected the volatilization flux manifested in large rapid peaks of TCE volatilizing from the surface. This behavior was likewise simulated using a numerical model with changing diffusion coefficients and retardation factors as function of soil‐air content, and good agreement was obtained between model simulations and measured data.
Transport of Anthropogenic Uranium from Sediments to Surface Waters During Episodic Storm Events
Authors: Batson Vicky L. , Bertsch P. M. , Herbert B. E.
Published: July 2010

Remobilization of sediment‐associated uranium (U) from contaminated floodplain sediments to a stream adjacent to a nuclear weapons processing facility during episodic rain events was investigated. In addition, U solid phase associations in suspended sediments were assessed by a sequential chemical extraction procedure to gauge U chemical lability. Mass flux estimates determined from base flow measurements potentially underestimate the amount of U transported from contaminated terrestrial sources to surface water systems. Erosional processes can effectively mobilize sediment‐associated contaminants during storms or flooding. During the various storm events measured, approximately 1500 to 2800% more U was exported to Upper Three Runs Creek (UTRC) relative to base flow measurements. Sequential extraction results suggest the suspended sediment load transports the bulk of U in labile forms predominantly as acid soluble (specifically adsorbed), MnO2 occluded and organically bound phases. This implies that U may be available to the ecosystem under a range of environmental conditions likely to be encountered within depositional environments (e.g., Eh and pH) or as a result of industrial processes. This study demonstrates the need to evaluate contaminant transport during storm events from exposed contaminated sediments, or from industrial waste stockpiles subject to erosion.
Cadmium Uptake for Swiss Chard Grown on Composted Sewage Sludge Treated Field Plots: Plateau or Time Bomb?
Authors: Chang A. C. , Page A. L. , Hyun Hae‐nam
Published: July 2010

Two hypotheses have been proposed to describe the phytoavailability of potentially toxic metals in sewage sludge treated soils. The plateau theory argues that the metal adsorption capacity added with sludge will persist as long as the metals of concern persist in the soil and the metals would remain in chemical forms not readily available for plant uptake. Therefore, the metal concentrations of plant tissue will reach a plateau as sewage sludge mass loading increases and remain at this plateau after termination of sludge application. The sludge time bomb hypothesis postulates that a soil's metal adsorption capacity is augmented by soil organic matter added as sewage sludge. This capacity, however, will revert back to its original background level with time following termination of sewage sludge application as mineralization of organic matter releases metals into more soluble forms, thus a time bomb. We employed a set of experimental data obtained from a 10‐yr field‐based sewage sludge land application experiment to evaluate the hypotheses of the plateau and the time bomb. The evaluation involved analysis of Cd concentration of Swiss chard grown on soils that either received sewage sludge application continuously or no longer received sewage sludge application. The results indicate that necessary conditions for plateau and time bomb to take place may be found. But an actual plateau or time bomb was not evident from 10 yr of experimental data in which the sewage sludge application reached 2880 Mg ha−1.
Transport of Bromide under Intermittent and Continuous Ponding Conditions
Authors: Ashraf M. S. , Izadi B. , King B.
Published: July 2010

An understanding of water and chemical transport through the soil is crucial for the development of proper irrigation and nutrient management practices. Because of natural heterogeneity and variability of soils, results often cannot be extrapolated between sites and from laboratory to field. In this study, transport of bromide (Br−) was investigated in a silt loam soil under intermittent and continuous ponding conditions using 10 pairs of stations in a 0.40‐ha field. Each station consisted of a double ring infiltrometer and three solution samplers installed at 30, 60, and 100 cm depths. A 3‐cm pulse of KBr− with an average Br− concentration of 500 ppm was applied to each station. Upon depletion of the pulse, 8 cm of water was ponded in each infiltrometer. For the continuous ponding stations, water was added daily and infiltrated volume was recorded. For each intermittent treatment, the time between subsequent irrigations was equal to the time for complete 8 cm infiltration plus 7 d of redistribution time. Solution samples were collected from all samplers on a daily basis for 3 mo, and analyzed for bromide concentration in the lab. At 30‐cm depth, the mean tracer velocities for intermittent and continuous ponding treatments were larger than piston flow velocities by factors of 2.05 and 1.57, respectively. Solute velocities decreased with depth for both treatments. Nutrient management models based on piston flow velocities may overestimate the mass of available nutrients to plants in the root zone.
Long‐Term Study of Volatile Organic Compound Recovery from Ampulated, Dry, Fortified Soils
Authors: Minnich Marti M. , Zimmerman John H. , Schumacher Brian A.
Published: July 2010

Our objective was to evaluate the stability and extractability of volatile organic compounds (VOCs) when fortified on dry soils and stored in sealed ampules. Two desiccator‐dried soils were fortified with eight neat VOCs, benzene, toluene, ethylbenzene, o‐xylene, 1,1,1‐trichloroethane (TCA), trichloroethene (TCE), tetrachloroethene (PCB), and 1,1,2,2‐tetrachloroethane (TTCA) at 800 ng each VOC/g soil. The fortified soil was portioned into ampules, sealed, and stored in the dark at 25°C for up to 56 wk. Replicate ampules were analyzed after 2 d and 2, 4, 8, 13, 34, and 56 wk by two extraction procedures modified from the U.S. Environmental Protection Agency's (USEPA's) low‐ and high‐level purge‐and‐trap procedures (SW‐846 Methods 5030/8021).The modified high‐level procedure (1‐h methanol extraction at 25°C prior to purge‐and‐trap analysis) yielded significantly higher recoveries of all compounds on both soils as compared with the low‐level procedure, with the exception of benzene on the Charleston soil. Moreover, when measured by the high‐level procedure, concentrations of benzene, toluene, ethylbenzene, and o‐xylene (BTEX) remained relatively unchanged during the 56‐wk study. The results indicate that the 1‐h, 25°C methanol extraction was sufficient for extraction of the BTEX compounds from these soils. For the chlorinated compounds, regression analysis demonstrated significant trends of changing concentrations over time. Recoveries of TCA decreased at a rate of 3 and 4 ng/g/week and recoveries of TTCA decreased at rates of 8 and 17 ng/g/week on the Hayesville and Charleston soils, respectively. PCE concentrations did not show any significant concentration changes, while TCE concentrations increased at 6 and 7 ng/g/week for the Hayesville and Charleston soils, respectively. We submit that the 1‐h, 25°C methanol extraction was inadequate for removal of the chlorinated compounds. Additionally, we postulate that dehydrochlorination of TTCA to form TCE occurred in desiccator‐dried soil.
Herbicide Persistence and Mobility in Recharge Lake Watershed in York, Nebraska
Authors: Ma L. , Spalding R. F.
Published: July 2010

Elevated levels of herbicides in surface and groundwater are a concern in the Cornbelt in the USA. This study was conducted to interpret the herbicide behavior in a watershed system using data collected from runoff, Recharge Lake, and groundwater influenced by agriculture and lake seepage. The York Ground Water Recharge Project was constructed on a tributary of Beaver Creek, which drains a 3327‐ha watershed of primarily row‐cropped heavily irrigated farmland. The estimated average runoff is 1.48 × 106 m3 yr−1 under a precipitation norm of 635 mm yr−1. Maximum atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) inputs to Recharge Lake occurred in May and June runoff events and resulted in average lake concentrations of 36 and 17 µg L−1 in 1993 and 1994, respectively. Only about 0.28 and 0.19% of total applied atrazine was lost to runoff in 1993 and 1994, respectively. The deethylatrazine (DEA) to atrazine molar ratio (DAR) decreased rapidly over a period of several hours in runoff samples, which is consistent with inputs from recently atrazine‐treated soil. After the spring runoff, herbicide levels in Recharge Lake rose rapidly in response to the runoff event, then diminished gradually over a period of months. Atrazine concentrations in Recharge Lake decreased exponentially with time. Degradation half‐lives were 237 d (r = 0.93) in 1993 and 209 d (r = 0.91) in 1994. Adjusted DEA concentrations in Recharge Lake remained relatively constant, indicating little evidence for biotic degradation and suggesting that abiotic degradation of atrazine to hydroxyatrazine (2‐hydroxy‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) was the most likely major degradative pathway in Recharge Lake.
The Sorption of Nonionic Organic Solutes to Humic Acid‐Mineral Complexes: Effect of Cosolutes
Authors: Onken B. M. , Traina S. J.
Published: July 2010

In binary isotherms, pyrene and naphthalene sorption were enhanced by the presence of anthracene as a cosorbate. Sorption enhancement was observed at low fractional organic carbon content (foc) (<3 × 10−5) and diminished foc increased. The addition of cosolutes to low foc systems (<3 × 10−5) appeared to aid the transition from adsorption/condensation type surface interactions to an interaction more like partitioning. It is postulated that observed sorption enhancement in higher foc systems (= 3 × 10−5) was due to an increase in effective foc resulting from cosolute sorption. The presence of a cosolute did not affect systems where partitioning was already the primary process. If partitioning was not occurring, the addition of a cosolute reduced the surface excess of the solute by competing for adsorption sites. This competition occurred until surface organic C increased to a sufficient concentration to promote partitioning. This research indicates that the use of Koc values derived from Kow data in low foc systems significantly underestimate the interactions of nonionic organic solutes with low organic C surfaces.
Efficiency of Grass Buffer Strips and Vegetation Height on Sediment Filtration in Laboratory Rainfall Simulations
Authors: Pearce Robert A. , Trlica M. J. , Leininger Wayne C. , Smith James L. , Frasier Gary W.
Published: July 2010

A laboratory rainfall simulation was conducted to compare the influence of three lengths of vegetation buffer strips and two vegetation heights on sediment filtration. The purpose of the experiment was to help evaluate stubble height grazing guidelines. Rainfall (50 mm h−1) was sprayed simultaneously over six trays (0.3 × 1.0 m). Concurrently, sediment laden (150 g tray−1) overland flow (50 mm h−1) was introduced to the upslope end of the trays. Two trays contained 12.5 cm, two trays contained 25.0 cm, and two trays contained 50.0 cm of Kentucky bluegrass (Poa pratensis L.) buffer strips during each simulation run. Paired buffer length trays either were clipped to the soil surface or grass was 10 cm tall. A significant interaction existed between vegetation buffer length and vegetation height. The clipped to the soil surface vegetation height was more effective as a sediment filter with the 12.5 cm buffer length than was the 10.0 cm height. Conversely, the 10.0 cm vegetation height was more efficient as a sediment filter with a 50 cm buffer length than was the clipped to the soil surface vegetation. No differences in sediment filtration efficiency existed between vegetation heights at the 25 cm buffer length. Additionally, 50 mm h−1 of rainfall was applied and 50 mm h−1 overland flow was added to six trays containing bare soil (no vegetation). Three the bare soil trays received sediment laden (150 g tray−1) overland flow and three trays received sediment free overland flow. All trays with the three vegetation buffer lengths had less sediment yield than did the bare soil trays. Results from this study suggest that vegetation height alone is not a suitable guideline for estimating sediment filtration and that length of vegetation buffer was more important than vegetation height in filtering sediment.
Simulating Atrazine Transport Using Root Zone Water Quality Model for Iowa Soil Profiles
Authors: Azevedo A. S. , Kanwar R. S. , Singh P. , Ahuja L. , Pereira L. S.
Published: July 2010

The pesticide component of the Root Zone Water Quality Model (RZWQM) was calibrated and evaluated for two tillage systems: no‐till (NT) and moldboard plow (MB). The RZWQM is a process‐based model that simulates the water and chemical transport processes in the soil‐crop‐atmosphere system. Observed data on atrazine concentrations in the soil profile, for model calibration and testing, were obtained from a field study in Iowa.

Two statistical parameters, maximum error (ME) and coefficient of determination (CD), were used to evaluate the ability of the RZWQM to predict atrazine concentrations in the soil profile. The ME, CD, and other statistical tests indicated that there was a significant difference between predicted and observed atrazine concentrations. Comparison of simulated vs. observed atrazine concentrations with 1:1 line showed that atrazine concentrations were overpredicted, especially in the later part of the growing season. However, the model correctly predicted depth of atrazine penetration in the soil profile. Also, the range of predicted atrazine concentrations was within the same order of magnitude as observed concentrations. Although observed atrazine concentrations were usually higher in surface layers under MB than in NT treatment, the model did not show any consistent tillage effects on atrazine distribution in the soil profile. The results from this simulation study indicated that the following factors may be critical and should be considered when simulating pesticide transport in the subsurface environment: (i) macropore flow, (ii) variation in Koc and pesticide half‐life with depth, and (iii) interception of pesticide by surface residue during application.
Atrazine Mineralization in Laboratory‐Aged Soil Microcosms Inoculated with s‐Triazine‐Degrading Bacteria
Authors: Radosevich Mark , Traina Samuel J. , Tuovinen Olli H.
Published: July 2010

An atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine)‐mineralizing bacterial isolate was used as a biological probe to investigate the effects of atrazine residence time on subsequent bioavailability and biodegradatlon. [U‐14C‐ring]‐atrazine was reacted with sterile soils collected from long‐term, experimental, no‐till and conventional‐tillage plots. After aging for 1 d to 3 mo, the atrazine‐treated soils were inoculated with the bacterium (7 × 107 cells g−1) and 14CO2 evolution was measured with time. Mineralization of [U‐14C‐ring]‐atrazine could be described with a first‐order rate equation in soils from both tillage systems. Atrazine was rapidly mineralized in no‐till soil aged for 1 d, with 50% of the initial radioactivity recovered as 14CO2 within 2 d after inoculation. Both the mineralization rate constants (k) and the extent of mineralization (Pmax) decreased with soil residence time. conventional‐till soil, no significant aging effect was observed for soil reacted for 7 d; however, both the k and Pmax, values decreased with extended aging. Measurements of soil solution‐phase atrazine were determined by high‐pressure liquid chromatography analysis after solutions were retrieved by centrifugation. In no‐till soil, the observed degradation rates were 38 to 227 times slower than those predicted on the basis of solution‐phase experiments. The respective rates were 25 to 63 times slower in the conventional‐till soil. The results suggest that a significant fraction of the solution‐phase atrazine was sequestered from microbial attack and that the unavailable fraction increased with soil residence time.
The Aqueous Geochemistry of the Abandoned Spenceville Copper Pit, Nevada County, California
Authors: Levy D. B. , Custis K. H. , Casey W. H. , Rock P. A.
Published: July 2010

The Spenceviile Pit in Nevada County, CA, has been filled with acidic mine drainage for approximately 75 yr and is an active source of acidity and trace metals to an adjacent stream. This study was conducted to characterize the aqueous chemistry of the Spenceville Pit to better understand pit lake geochemistry. Filtered samples were collected at regular depth intervals and analyzed for Ca, Mg, Na, K, Fe, Al, Mn, Cu, Zn, Ba, Si, Ph, and P. The geochemical speciation model MINTEQA2 was used to calculate the activity ratios of Fe2+ (aq) to Fe3+ (aq) based on measurement of oxidation‐reduction potential using a combination Pt/Ag‐AgCl electrode, and to calculate saturation indices for various mineral phases. Sampling of the Spenceville Pit in summer (August) and in winter (December) shows that the deeper waters exhibit considerably higher concentrations of metals compared with the shallow waters, and that the water column may be permanently stratified. Neither the scavenging of trace metals (Cu, Ni, and Zn) by particulate iron‐hydroxide minerals nor their precipitation as metal sulfides exerts significant control on the distribution of metals in the pit water. Instead, elemental distributions appear to be controlled by the process of cyclic filling and evaporation. Analysis of mineral saturation states in the pit water and x‐ray diffraction analysis of the bottom sediments indicate that gypsum (CaSO4·2H2O), goethite (α‐FeOOH), jarosite [KFe3(SO4)2(OH)6], jurbanite (AlOHSO4·5H2O), and strengite (FePO4·2H2O) are solids that may potentially control elemental concentrations in the water colunm.
Carbon Dioxide‐Enriched Agroecosystems: Influence of Tillage on Short‐Term Soil Carbon Dioxide Efflux
Authors: Prior S. A. , Rogers H. H. , Runion G. B. , Torbert H. A. , Reicosky D. C.
Published: July 2010

Increasing atmospheric carbon dioxide (CO2) concentration can increase biomass production that may influence carbon (C) dynamics in terrestrial ecosystems. Soil CO2 efflux as affected by crop residues from high CO2 environments managed under different tillage systems has not been explored. This study examined the effects of tillage systems in a legume [soybean [Glycine max (L.) Merr.]] and nonlegume [grain sorghum [Sorghum bicolor] (L.) Moench.] CO2‐enriched agroecosystem on the rates of short‐term CO2 evolution from a Blanton loamy sand (loamy siliceous, thermic Grossarenic Paleudults). In the spring of 1994, CO2 efflux observations initiated within 5 s after a tillage event were compared to no‐tillage conditions for 8 d in plots where both crop species had been grown in open top field chambers under two CO2 conditions (ambient and twice ambient) for two seasons (1992 and 1993). Added CO2 increased yields, residue, and root biomass; higher percent ground cover was also observed in CO2‐enriched plots prior to the tillage treatment. Differences in C/N ratio of the residue may have influenced CO2 efflux rates; C/N ratio was highest for sorghum and was increased by elevated CO2. Efflux patterns were characterized by flushes of CO2 following initial tillage and rainfall events. Species × tillage and CO2 × species interactions were noted on several days and for total CO2 efflux values. Our results suggest that short‐term CO2 fluxes may be greater for tilled soybean and for soybean grown under elevated CO2; however, short‐term flux rates in the sorghum crop were affected by tillage, but not by CO2 level. These short‐term results should be viewed with caution when predicting long‐term C turnover in agroecosystems.
Chemical Fractionation of Cadmium, Copper, Nickel, and Zinc in Contaminated Soils
Authors: Ma Lena Q. , Rao Gade N.
Published: July 2010

Heavy metals are potentially toxic to human life and the environment. Metal toxicity depends on chemical associations in soils. For this reason, determining the chemical form of a metal in soils is important to evaluate its mobility and bioavailability. Sequential extraction was used to fractionate four heavy metals (Cd, Cu, Ni, and Zn) from nine contaminated soils into six operationally defined groups: water soluble, exchangeable, carbonate, Fe‐Mn oxide, organic, and residual. The residual fraction was the most abundant pool for all four metals examined. A significant amount (2.4–44%) of Zn was present in the potentially available fraction: nonresidual fraction. A major portion (40–74%) of Cu was associated with the organic, Fe‐Mn oxide, and carbonate fractions in most of the soils. Contamination of Cd and Ni in these soils was not as severe as Zn and Cu. Assuming that mobility and bioavailability of these metals are related to their solubility and geochemical forms, and that they decrease in the order of extraction sequence, the apparent mobility and potential bioavailability for these four metals in the soils were: Zn > Cu > Cd > Ni. Metal distributions in different chemical fractions in these soils depended on respective total metal concentrations, except for Zn.
Wheat Grain Cadmium as Affected by Long‐Term Fertilization and Soil Acidity
Authors: Gavi F. , Basta N. T. , Raun W. R.
Published: July 2010

Several studies have reported increases in grain Cd from long‐term continuous wheat (Triticum aestivum L.) systems. Increases in grain Cd have been associated with commercial fertilizer use, but information on long‐term use of N and P fertilizers on wheat grain Cd is limited. The objective of this study was to evaluate the impact of fertilization on wheat grain Cd from eight long‐term experiments that received 15 to 63 yr of N, P, and K fertilizer. Total Cd and Zn in soil and grain and soil properties including pH were determined. In general, long‐term N or P fertilization did not increase grain Cd, grain Zn, or soil Cd. In part, N and P fertilizer did not increase grain Cd because fertilizer did not increase soil Cd or Zn. Nitrogen fertilizer decreased soil pH in two experiments but these decreases were small (≤0.5) and did not affect grain Cd or Zn. Grain Cd and Zn were inversely related to soil pH, but not related to N or P fertilization. The relationship between soil pH (3.8 to 6.8) and grain Cd (9.7 to 45.2 µg kg−1) was described by a plateau‐linear‐plateau model with a negative slope from soil pH 5.0 to 6.4. The largest soil Cd and Zn contents were associated with high pH values, but grain Cd and Zn were inversely related to soil Cd and Zn. The maximum grain Cd content (45 µg kg−1) determined in this study was less than maximum limits of 50 to 100 µg Cd kg−1 in wheat grain established in other countries.
Biogeochemical Cycling in Coniferous Ecosystems on Different Aged Marine Terraces in Coastal Oregon
Authors: Bockheim J. G. , Langley‐Turnbaugh S.
Published: July 2010

Biogeochemical cycling was studied in Sitka spruce [Picea sitchensis (Bong.) Carr.] and western hemlock‐Douglas‐fir [Tsuga heterophylla (Raf.) Sarg.‐Pseudotsuga menziesii (Mirbel) Franco] ecosystems on chronosequence of five uplifted marine terraces in coastal Oregon. The terraces occur 0.25 to 8.6 km from the Pacific Ocean and range from 80 to ∼500 kyr in age. The soils are highly weathered and include Inceptisols on the youngest terrace and Spodosols with clay‐enriched horizons and Ultisols on the older terraces. Bulk precipitation, throughfall, and soil solutions (four depths) were collected monthly from November 1992 through April 1993. The solutions were analyzed for pH, dissolved cations (Na, Mg, Ca, K, Fe, Al, and Si), anions (Cl, SO4, HCO3, NO3, and PO4), and organic C. Cations (µmolc L−1) in all solutions were ranked: Na > Mg > Ca ≥ K > H; anions were ranked: Cl > SO4 > NO3 >> HCO3. The Na/Cl ratio in all solutions was comparable to that of seawater. The mean sums of cations and anions in all solutions declined sharply with distance from the coast. Throughfall enrichment of all ions suggests that aerosol impaction of sea salts is a dominant process within the coastal fogbelt of Oregon. In that the soils have low inherent fertility, the trees appear to obtain Ca, Mg, K, and S primarily from atmospheric sources. These nutrients are utilized by abundant fine roots in the forest floor and upper 5 to 20 cm of mineral soil. Net cation loss is less than in other areas of the Pacific Northwest and is controlled by organic anions rather than the bicarbonate anion.
Nitrogen Cycling in Piedmont Vegetated Filter Zones: I. Surface Soil Processes
Authors: Verchot Louis V. , Franklin E. Carlyle , Gilliam J. Wendell
Published: July 2010

Surface runoff is a major transport mechanism for particulate‐bound and dissolved N species from agricultural fields. One means of reducing nutrient loading in surface waters is the use of vegetative filter zones. The objective of this study was to evaluate the effectiveness of two forested filter zones (FFZ) for removing N from runoff in the Piedmont region of North Carolina. We used a spreading device to ensure dispersed flow in the FFZ. In addition to measuring inputs and outputs from each FFZ, we characterized the N cycle in the surface 30 cm of the soil profile to determine the fate of different N species retained in the FFZ. N loading increased as water passed through FFZ1: NO3‐N increased by 1.6 kg ha−1 yr−1, organic‐N increased by 13.4 kg ha−1 yr−1 and NH4‐N decreased by 0.2 kg ha−1 yr−1. The second FFZ was more effective with net retention of 0.2 kg ha−1 yr−1 for NO3‐N, 0.5 kg ha−1 yr−1 for organic‐N and 0.2 kg ha−1 yr−1 for NH4‐N. The FFZ were ineffective during the winter and spring when water filled pore space exceeded 35% in FFZ1 and 25% in FFZ2, and infiltration was low. Infiltration was the key factor controlling N pollutant removal from surface runoff. Therefore, the clayey soils of the Piedmont may not be as effective as the sandy coastal plain soils studied by other authors. Results from the analysis of the N cycle suggest that both uptake by the vegetation and leaching to deeper soil layers were the dominant fates of inorganic‐N.
Potential for Localized Compaction to Reduce Leaching of Injected Anions
Authors: Baker J. L. , Laflen J. M. , Schreiber M. M.
Published: July 2010

Nitrate‐nitrogen (NO3‐N) frequently is found in subsurface drainage waters from N‐fertilized cropland at concentrations exceeding 10 mg L−1, the drinking water standard. In this laboratory study, localized compaction during bromide (Br) application was studied as a potential method to reduce concentrations of anions such as Br− and NO−3 in water percolating from the top 30 cm of soil. Rainfall simulation was used to apply water under controlled conditions to undisturbed 76 by 76 by 30 cm deep soil columns taken from chisel‐plowed and no‐till fields in the fall after soybean [Glycine max (L.) Merr.] harvest. Potassium bromide at 149 kg ha−1 was broadcast or point injected with, or without, compaction around the point of injection. There were no significant differences in water volumes percolating through the columns, but concentrations and losses of Br in drainage water for the compacted point injection treatment were significantly less than those in drainage water from soil columns for point injection without compaction or broadcast application. The average Br concentration for no‐till compacted point injection was about 11% of the broadcast and 7% of the uncompacted point injection. For the chisel plow, the concentration for the compacted point injection was about 15% of both the broadcast and uncompacted point injection. Losses were also of about the same percentages. Localized compaction around the point of injection significantly reduced anion leaching in these undisturbed soil columns. This concept could be implemented in the field through design of applicators that compact the soil in a zone around either point‐injected or knifed‐in fertilizer.
Transport and Photolysis of Pentachlorophenol in Soils Subject to Evaporating Water
Authors: Donaldson Susan G. , Miller Glenn C.
Published: July 2010

Pentachlorophenol (PCP) was applied to loamy sand and sandy clay loam soils to determine the effect of upward evaporative flux on the rates of photolytic loss. Subirrigated soil columns were irradiated by ultraviolet lamps or sunlight to measure relative rates of photolytic loss under differing soil moisture regimes. Photolysis was initially rapid in loamy sand soil under near‐saturated flow conditions, with up to 55% more lost in light‐exposed treatments in 14 d as compared to dark controls. Rates of transport were slower in sandy clay loam soil, reflecting a soil sorption distribution coefficient of 10 mL/g, as compared to 0.4 mL/g in the loamy sand. Despite slower upward movement, similar amounts of photodegradation of PCP had occurred in the sandy clay loam soil after 14 d. Dropping the water table to the 15 or 25 cm depth resulted in unsaturated flow and increased losses to volatilization, with a much lower relative contribution of photodegradation over the course of the experiments. Up to 77% was lost from the loamy sand soil dark treatments during the 14‐day period, due to volatilization and irreversible sorption. Processes that translocate PCP into the sunlit surface zone under near‐saturated soil moisture conditions can be expected to enhance rates of photolytic loss while minimizing volatilization.
Determination of Total Dissolved Phosphorus in Soil Solutions
Authors: Rowland A. P. , Haygarth P. M.
Published: July 2010

Soils are increasingly acknowledged as a source of P discharges in surface water. In order to monitor the transfer processes from soil to streams and rivers, a simple, sensitive, accurate, and robust method is required to determine trace concentrations of total dissolved P (TDP) in soil solution. This matrix provides a unique challenge to the analyst because it often contains trace concentrations of P in the presence of higher concentrations of organic and colloidal fractions that can interfere. Leachate waters were collected from lysimeter experiments covering 10 different soil types from the UK, ranging from sandy lowland agricultural grassland soil to an upland natural peaty gley soil, to critically evaluate the performance of different methods of analysis. Solutions of model compounds also provided measures of performance. Three methods involving digestion and colorimetric determination and one direct instrumental method were assessed. Methods evaluated were a mild digestion (persulfate), two rigorous oxidation procedures (peroxide‐Kjeldahl and nitric acid‐sulfuric acid) and inductively coupled plasma‐optical emission spectrometry (ICP‐OES). The ICP‐OES lacked the sensitivity to determine P concentrations below 100 µg L−1. Nitric acid‐sulfuric acid, a multi‐staged procedure, gave erratic recovery and was vulnerable to contamination. The best method for the analysis of soil solution or leachates was the acidified persulfate digestion because it produced reliable and accurate data. Thus we recommend that acid persulfate digestion is used to determine TDP in soil solution.
Sterile and Nonsterile Degradation of Carbon‐14‐Primisulfuron in Soil from Four Depths
Authors: Miller J. L. , Wollum A. G. , Weber J. B.
Published: July 2010

The degradation of 14C‐primisulfuron (2‐[[[[[4,6‐bis(difluoromethoxy)‐2‐pyrimidinyl]amino]carbonyl]amino]sulfonyl] benzoic acid) was monitored for 2 mo using soil microcosms under sterile and nonsterile conditions. Both chemical and biological degradation was detected. The half‐life was 2.1 wk for nonsterile samples from 0 to 5 cm, and 3.4 wk for nonsterile samples from 20 to 25 cm. After 7 wk, bound residues accounted for 48 and 27% of the recovered radioactivity in these samples, respectively. For sterile samples from the same depths, the half‐life was >7 wk and bound residues accounted for 7% of the recovered radiolabel. Disappearance and bound residue formation of primisulfuron were similar for both sterile and nonsterile samples from deeper in the profile (45–75 cm) indicating little biological degradation occurred in these subsurface samples. Chemical and microbial degradation of primisulfuron appeared to differ; the same metabolites were produced but at different times and in different amounts. Very little 14CO2 (<3%) was produced from any sample. These results indicate that initial hydrolyzation of the sulfonylurea bridge occurs both chemically and biologically, but does not occur readily in the subsoil. This may have implications for the prevention of groundwater contamination and for the bioremediation of contaminated soils.
Sorption of Thiazafluron by Iron‐ and Humic Acid‐Coated Montmorillonite
Authors: Celis R. , Cox L. , Hermosin M. C. , Cornejo J.
Published: July 2010

The intimate association between the different soil constituents may determine the sorptive behavior of soil aggregates. This study was conducted to study the influence of interassociation on the sorption capacity of montmorillonite for the polar uncharged herbicide thiazafluron (1,3‐dimethyl‐1‐(5‐trifluormethyl‐1,3,4‐thiadiazol‐2‐yl)urea). Calcium Wyoming montmorillonite was coated with iron species and humic macromolecules and sorption of thiazafluron determined and compared with that for the uncoated clay. The presence of precipitated Fe(III)‐OH‐species on montmorillonite gave rise to an increase in the specific surface area measured by N adsorption (from 18–45 m2 g−1) and to a decrease in the sorption of thiazafluron by the clay (from 156.9‐110.8 mmol kg−1). Both commercial and soil humic acid also decreased the sorption of thiazafluron by montmorillonite, but the decrease was higher in the case of soil humic acid (from 100.3‐77.0 mmol kg−1), which was more associated with the clay. Iron and organic matter removal from the clay surface increased again the sorption of the herbicide thiazafluron by montmorillonite. The results of this work show that mineral and organic coatings on clays alter the nature of the surface exposed for sorption of organics, thus affecting the sorption behavior of colloidal soil particles.
The Clean Water Act and Animal Agriculture
Authors: Martin John H.
Published: July 2010

Historically, impacts of agricultural activities on water quality, including animal production, generally were considered to be natural and uncontrollable. In the 1960s, this view began to change in response to public concern about highly visible incidents such as massive fish kills in the Midwest and shellfish bed closures on Long Island, NY, caused respectively by beef cattle feedlot runoff and the duck industry. Ultimately, these incidents led to the designation in the Federal Water Pollution Control Act Amendments of 1972 of feedlots as a point source category of water pollutants subject to regulation under the National Pollutant Discharge Elimination System permit program. The regulatory program that evolved is complex and confusing and is not well understood by many livestock and poultry producers. The transition from a narrow focus on pollutant discharges from confinement facilities to a broader scope has contributed to the confusing nature of this program. Included now are pollutant discharges traditionally viewed as nonpoint in character. An example of the broadening in scope of this program is a recent appellate decision holding that runoff from cropland used for disposal of manure from a facility designated as a point source also was a point source discharge of pollutants. Although this decision is consistent with the USEPA's claim of regulatory authority, it is not clear that it is consistent with the original intent of Congress. The decision, along with the general complexity and confusing nature of this regulatory program, suggests that revision is needed.
Boron Contents and Isotopic Compositions of Hog Manure, Selected Fertilizers, and Water in Minnesota
Authors: Komor S. C.
Published: July 2010

Boron‐isotope (δ11B) values may be useful as surrogate tracers of contaminants and indicators of water mixing in agricultural settings. This paper characterizes the B contents and isotopic compositions of hog manure and selected fertilizers, and presents δ11B data for ground and surface water from two agricultural areas. Boron concentrations in dry hog manure averaged 61 mg/kg and in commercial fertilizers ranged from below detection limits in some brands of ammonium nitrate and urea to 382 mg/kg in magnesium sulfate. Values of δ11B of untreated hog manure ranged from 7.2 to 11.2‰ and of N fertilizers were −2.0 to 0.7‰. In 22 groundwater samples from a sand‐plain aquifer in east‐central Minnesota, B concentrations averaged 0.04 mg/L and δ11B values ranged from 2.3 to 41.5‰. Groundwater beneath a hog feedlot and a cultivated field where hog manure was applied had B‐isotope compositions consistent with the water containing hog‐manure leachate. In a 775‐km2 watershed with silty‐loam soils in southcentral Minnesota: 18 samples of subsurface drainage from corn (Zea mays L.) and soybean (Glycine max L. Merr.) fields had average B concentrations of 0.06 mg/L and δ11B values of 5.3 to 15.1‰; 27 stream samples had average B concentrations of 0.05 mg/L and δ11B values of 1.0 to 19.0‰; and eight groundwater samples had average B concentrations of 0.09 mg/L and δ11B values of −0.3 to 23.0‰. Values of δ11B and B concentrations, when plotted against one another, define a curved mixing trend that suggests subsurface drainage and stream water contain mixtures of B from shallow and deep groundwater.