bluuebunny/crossref_metadata_2025 huggingface dataset:
The Fate and Transport of Viruses through Surface Water Constructed Wetlands
Authors: Chendorain Michael , Yates Marylynn , Villegas Frank
Published: July 2010

Coliphage removal efficiency and the effects of wetland hydrology on virus transport were determined for constructed wetlands in San Jacinto, CA. Mathematical models were used to further characterize virus transport. MS2, an F‐specific RNA (FRNA) coliphage was used as a model for human enteric viral behavior. Two wetland types were studied, a one‐phase cell and three‐phase cell. These wetlands received unchlorinated secondary effluent at a constant rate. The mean residence time in the wetlands was 9 ± 3 d as determined using bromide as a conservative tracer. Assuming 100% porosity, a plug flow model predicts this mean residence time within the experimental standard deviation (8 d). This suggests that a negligible volume was occupied by vegetation and settled solids. The convection‐dispersion equation adequately simulated the residence time distribution of the conservative tracer. MS2 removal in the wetlands was experimentally determined to be 97 ± 3%. There was no distinction between the two wetland types in terms of removal efficiency. The average coliphage decay rate was calculated to be 0.44 per day. However, the error involved with using the first order decay rate was high, 83 ± 12%. Therefore, first order decay does not adequately describe removal processes within the wetland. Most virus removal occurred within the first 3 m (k = 4.0 ± 1.8 d−1) with a removal efficiency of 85.3 ± 0.6%. The remainder had a decay rate of 0.20 ± 0.17 d−1 with a removal efficiency of 56 ± 33%.
Electromagnetic Survey of Cornfield with Repeated Manure Applications
Authors: Eigenberg R. A. , Nienaber J. A.
Published: July 2010

Waste management sites are subject to nutrient buildup from storage, treatment, and repeated application of manure. Methods are needed to quickly assess a site or field location to survey nutrient levels and estimate risk potential. Electromagnetic (EM) conductivity methods have been shown to be sensitive to areas of high nutrient levels (Eigenberg et al., 1996) and offer promise to provide field assessments. In this report, high density electromagnetic field mapping is described as a method to isolate and detect areas of nutrient buildup in a cornfield receiving waste management research treatments. Various manure and compost rates have been applied to this research field for replacement of commercial fertilizer with the treatment assignments remaining identical over a 4‐yr period. Electromagnetic conductivity measurements were able to differentiate (P < 0.0001) the N check treatment (commercial application rate) vs. manure applied at the recommended P rate, compost applied at the P rate, and compost applied at the N rate. The N check treatment and the manure applied at the N rate treatment resulted in nearly identical mean values for EM readings and were not statistically distinguishable. Analysis of soil cores (NO3, Cl, P, K, SO4, NH4, Na, electrical conductivity, and soil moisture content) randomly located within each treatment were compared to EM readings at the same locations. The Pearson correlation coefficients revealed strong (P = 0.02 or better) correlations for all constituents except NH4 (P = 0.308). Treatment effects were significant (P < 0.05) for all soil constituents except NH4 and water content.
Responses of Soil Respiration to Clipping and Grazing in a Tallgrass Prairie
Authors: Bremer Dale J. , Ham Jay M. , Owensby Clenton E. , Knapp Alan K.
Published: July 2010

Soil‐surface CO2 flux (Fs) is an important component in prairie C budgets. Although grazing is common in grasslands, its effects on Fs have not been well documented. Three clipping treatments: (i) early‐season clipping (EC); (ii) full‐season clipping (FC); and (iii) no clipping (NC); which represented two grazing strategies and a control, were applied to plots in a tallgrass prairie in northeastern Kansas, USA. Measurements of Fs were made with a portable gas‐exchange system at weekly to monthly intervals for 1 yr. Concurrent measurements of soil temperature and volumetric soil water content at 0.1 m were obtained with dual‐probe heat‐capacity sensors. Measurements of Fs also were obtained in grazed pastures. Fs ranged annually from 8.8 × 10−3 mg m−2 S−1 during the winter to 0.51 mg m−2 s−1 during the summer, following the patterns of soil temperature and canopy growth and phenology. Clipping typically reduced Fs 21 to 49% by the second day after clipping despite higher soil temperatures in clipped plots. Cumulative annual Fs were 4.94, 4.04, and 4.11 kg m−2 yr−1 in NC, EC, and FC treatments, respectively; thus, dipping reduced annual Fs by 17.5%. Differences in Fs between EC and FC were minimal, suggesting that different grazing strategies had little additional impact on annual Fs. Daily Fs in grazed pastures was 20 to 37% less than Fs in ungrazed pastures. Results suggest that grazing moderates Fs during the growing season by reducing canopy photosynthesis and slowing translocation of carbon to the rhizosphere.
Incorporating Temperature Effects on Pesticide Degradation into a Management Model
Authors: Wu Jinquan , Nofziger D. L.
Published: July 2010

The impact of agrochemicals on groundwater quality has been the subject of considerable research and public debate. Mathematical models often are used to predict the fate of these chemicals and to develop regulations. In this research, we modified the pesticide degradation component of a management model to estimate soil temperature with depth and time and to incorporate the effect of temperature variation on the pesticide degradation rate. Estimated pesticide mass leaching beyond a depth of 1 m was two or more orders of magnitude greater when the temperature effect was incorporated into the model. Predicted soil temperatures at four different depths using measured surface soil temperatures followed the seasonal temperature variation of observed data with an average deviation <0.3°C. Among the input parameters analyzed, the amount of pesticide leached was most sensitive to uncertainties in activation energy of a degradation reaction, reference half‐life, and annual mean soil temperature. Uncertainty in annual change in surface soil temperature had a moderate impact on the simulated amount of pesticide leached. Uncertainties in damping depth and time lag of annual minimum temperature had little effect. Uncertainties in model parameters can result in differences on the order of one‐ to fourfold in simulation output. Although these are large, they are clearly much less than the differences of 2 to 8 orders of magnitude, which can occur if temperature effect is ignored. We conclude that models used for pesticide risk assessment should incorporate temperature effects on degradation. The algorithm presented here can be incorporated readily into many leaching models.
Charge Properties and Nitrate Adsorption of Some Acid Southeastern Soils
Authors: Eick Matthew J. , Brady Warren D. , Lynch Colleen K.
Published: July 2010

Numerous studies have been conducted examining nitrate (NO3) leaching losses from agricultural land. Simulation models have been developed that allow one to predict the potential of NO3 to leach to groundwater. However, many of these models treat NO3 as a conservative tracer and do not evaluate surface chemistry. This study evaluated the surface charge properties and NO3 adsorption capacity of four acid southeastern subsoils. Significant anion exchange capacity and NO3 retention was found for two of the soils. Point of zero net charge (PZNC) was determined using an ion exchange method. Values of 3.1 and 3.6 were determined for two of the soils while PZNC values were not quantifiable for the other two soils in the pH range of 3 to 7. Nitrate adsorption isotherms were measured on untreated and chloride‐saturated soils. Nitrate adsorption maxima determined from the linearized form of the Langmuir equation ranged from 1.40 to 2.13 cmolc kg−1. Coefficients of determination (R2) and adsorption maxima increased after chloride saturation. This was attributed to competition from anions such as sulfate, fluoride, and phosphate. Net positive charge and NO3 retention were found to depend on the type and quantity of both variable and permanent charged minerals present in the soil and the composition of the exchange complex. These results demonstrated that acid subsoils high in variable charge minerals may have the potential to retard NO3 movement to groundwater. Therefore, simulation models may need to account for NO3 adsorption when modeling NO3 movement in acid soils dominated by variable charge minerals.
Effects of Precipitation and Air Temperature on Phosphorus Fluxes from Rhode River Watersheds
Authors: Correll David L. , Jordan Thomas E. , Weller Donald E.
Published: July 2010

We studied fluxes of total P, total phosphate, and total organic P from seven contiguous small watersheds on the Atlantic Coastal Plain in Maryland for up to 25 yr. These watersheds have perched aquifers so all groundwater discharges as well as surface runoff were measured at V‐notch weirs equipped with volume‐integrating, flow‐proportional samplers. Interannual variations in annual and seasonal precipitation during this study spanned approximately the range of 160‐yr weather records in the region. Annual total‐P area yields from the overall watershed varied 28‐fold, correlations of all P‐species fluxes with precipitation were highly significant, and power function regressions of precipitation vs. P‐flux explained from 42 to 55% of the variance in the latter. Phosphorus fluxes from a cropland watershed were much higher and more variable with volume of precipitation, while fluxes from a forested watershed were much lower and primarily composed of organic P. Correlations of P fluxes with precipitation were higher in the spring. Annual and seasonal P concentrations also often increased significantly with precipitation. Variations in seasonal mean air temperature sometimes explained significant amounts of variance in P fluxes, especially phosphate from cropland. A regression model was used to construct graphical and tabular summaries.
Efficiency of a Subsurface Constructed Wetland System Using Native Southwestern U.S. Plants
Authors: Maschinski Joyce , Southam Gordon , Hines Jeff , Strohmeyer Scott
Published: July 2010

A small‐scale three‐cell (in series) subsurface (SSF) constructed wetland that used 16 previously untested native Arizona plants was found to be effective in the treatment of secondary waste at high elevation (2350 m) in northern Arizona. Fifteen of the 16 plant species survived in at least one of the cells in the system. Plant survival depended on their position in the cells, with increased survival rates downstream from the effluent input to cell 1, on water depth, and on individual species selection. The wetland was effective in removing both chemical pollutants (total Kjeldahl nitrogen [TKN], ammonia, nitrate, total kjeldahl phosphorus [TP], and phosphate) and bacteriological indicator organisms of human pathogens (total coliforms and fecal coliforms). The fecal coliform counts of the effluent exiting the third cell were below the recreational full‐body contact (swimming) standard (200 cfu/100 mL) in 14 out of the 15 mo of operation. The TKN and TP concentrations were reduced by 84 and 73%, respectively compared to nutrients entering the system. The loss of N suggests that a combined nitrification/denitrification process is active in the wetland. However, after 9 mo of operation, nitrate levels began to increase beyond the target of 1 mg/L indicating that nitrification rates are exceeding denitrification rates and that the wetland cells are aerobic. The constructed wetland system effectively conserves water. Because it is used to irrigate plantings near the constructed wetland, the nutrient concentrations in the effluent aid plant growth.
Denitrification as a Sink for Dissolved Nitrous Oxide in a Freshwater Riparian Fen
Authors: Blicher‐Mathiesen Gitte , Hoffmann Carl Chr.
Published: July 2010

Denitrification as a sink of dissolved nitrous oxide (N2O) was investigated in a freshwater riparian fen. In a 15‐m transect extending from the hillslope and into the fen the groundwater concentrations of nitrate (NO−3) declined from 1.8 mM NO−3 (25 mg L−1) to less than 0.01 mM NO−3, dissolved oxygen (O2) and nitrous oxide (N2O) declined from approximately 110 µM O2 (3.5 mg O2 L−1) and 4.0 µM N2O‐N (56 µg N L−1), respectively, to zero and the dissolved N2 concentration increased by 589 µM N2‐N (8.2 mg N L−1). The NO−3 reduction was 0.42 µM cm−3 d−1 or 7.71 µM cm−2 d−1 in sediment columns with continuous upward groundwater flow through the sediment. Concomitant with NO−3 reduction, N2O was produced at a rate of 54.4 nM N2O‐N cm−2 d−1 in this same 18‐cm narrow sediment zone. However, the N2O produced was subsequently reduced at the same rate closer to the sediment surface. In 15NO−3 experiments on chloramphenicol‐treated anaerobic sediment slurries, the denitrifying enzyme activity (DEA) was estimated to be 118 ± 16.7 nmol N (N2‐N + N2O‐N) g fresh weight 1−1 d−1, of which 36% accumulated as N2O. Thus, in this permanently water‐covered riparian fen, denitrification served as a sink for both the dissolved N2O in groundwater recharging the fen and the N2O produced within the riparian sediment.
Local Climate Influences on Precipitation, Cloud Water, and Dry Deposition to an Adirondack Subalpine Forest: Insights from Observations 1986–1996
Authors: Miller Eric K. , Friedland Andrew J.
Published: July 2010

Few studies of total atmospheric deposition (dry deposition, cloud droplet capture, rainfall, and snowfall) of major elements (S, N, Ca, Mg, and K) have been conducted in high‐elevation forests. This paper presents the results of the first long‐term observations (1986–1996) of total atmospheric deposition (wet + dry + cloud water) to a subalpine forest in the northeastern USA. Total atmospheric deposition of N to a forest at 1050 m elevation on Whiteface Mountain, NY, averaged 17.2 kg ha−1 yr−1, with 6.5 kg ha−1 yr−1 deposited as NH4 and 10.8 kg ha−1 yr−1 as NO3. Total S deposition averaged 18.3 kg ha−1 yr−1. Orographic effects both enhanced rainfall and increased interannual variance of ion concentrations and wet deposition compared to nearby low‐elevation monitoring stations. Cloud droplet capture by the forest canopy varied substantially from year‐to‐year in response to changing meteorological conditions, contributing between 6 and 31% of total annual water inputs, which averaged 156.1 cm yr−1. Cloud water deposition was responsible for approximately 50%, and dry deposition approximately 10% of total annual N and S deposition. The signal from known decadal trends in atmospheric concentrations and fluxes of S in the northeastern USA was partially masked by high‐frequency (intra‐ and inter‐annual) variance associated with local climatic effects on precipitation and cloud water fluxes at this high‐elevation site. These observations suggest that atmospheric deposition rates to high‐elevation forests may be more responsive to climatic fluctuations and less responsive to recent and expected changes in atmospheric chemical burdens than in surrounding low‐elevation ecosystems.
Evaluation of Dissipation Mechanisms for Benzo[a]pyrene in the Rhizosphere of Tall Fescue
Authors: Banks M. K. , Lee E. , Schwab A. P.
Published: July 2010

Although polycyclic aromatic hydrocarbons are common contaminants in soil and are potentially carcinogenic and mutagenic, little is known about their fate in the soil/root environment. The impact of tall fescue (Festuca arundinacea Schreber) on chemical and biological transformations of benzo[a]pyrene in soil was investigated in a greenhouse experiment in which 14C‐benzo[a]pyrene was added to soil and placed in sealed chambers with and without plants. The distribution of 14C in soil, plant tissue, and CO2 was quantified. Dissipation due to mineralization and volatilization accounted for <2% of the total 14C added in both planted and unplanted chambers and was greater in the presence of plants. Plant uptake of 14C was <0.12%. Residual benzo[a]pyrene was lower in soil with plants (44%) than in the absence of plants (53%). The majority of the 14C label was associated with the soil matrix. The presence of plants enhance the degradation of highly adsorbed, recalcitrant benzo[a]pyrene in soil.
Biological Selenium Volatilization: Method of Measurement under Field Conditions
Authors: Lin Z.‐Q. , Hansen D. , Zayed A. , Terry N.
Published: July 2010

An open‐flow chamber sampling system was developed for measurements of selenium (Se) volatilization from soil and vegetated areas under field conditions. This paper provides detailed information on the design, construction, and calibration of the chamber sampling system. Volatile Se was collected using a Plexiglas collection chamber, 0.71 m long, 0.71 m wide, and 0.76 in high; the chamber provided an internal volume of 0.38 m3 and enclosed a ground area of 0.5 m2. Volatile Se produced inside the collection chamber was trapped by activated carbon filters from the air leaving the chamber. The trapped Se was extracted from the charcoal filters in alkaline‐peroxide solution. The system has a maximum measurement capacity of 10 mg Se m−2 over a sampling period of 24 h at an air flow rate of 0.43 m3 h−1. Measurements of Se volatilization from the soil‐halophyte system in central California were carried out to demonstrate the efficiency of this sampling system under field conditions.
Role of Groundwater Flow in Tile Drain Discharge
Authors: Vaughan Peter J. , Suarez Donald L. , Simunek Jirka , Corwin Dennis L. , Rhoades James D.
Published: July 2010

Tile systems drain water applied to agricultural fields as irrigation and precipitation but also may intercept regional groundwater flow. Identification and characterization of the potential sources of tile water is essential for informed management of salinity and contaminants. Factors influencing tile discharge including depth of water applied, evapotranspiration, water storage, drain blockage, and interception of regional groundwater flow were evaluated to determine which may be related to a fivefold variation in cumulative tile discharge among six sumps located 100 km west of Fresno, CA. Cumulative depths drained were calculated for 5 yr of weekly irrigation, precipitation, and discharge data. Evapotranspiration and water storage were estimated using the UnsatchemGeo variably‐saturated water flow model. Well water levels measured on 19 dates were spatially‐averaged providing spatial variation of depth‐to‐water among the drained areas. Variability in depth of water drained (0.18–0.95 m) was large and was not correlated with either water applied (3.26–4.58 m, r2 = 0.03) or with computed water flux from the bottom of the soil column (0.05–0.31 m, r2 = 0.00). Groundwater interception by tile drains was a factor because depth‐to‐water was negatively correlated with discharge (r2 = 0.42) and drawdown of groundwater levels by drains was relatively larger for those drained areas encountered first during regional groundwater flow. For all six sumps, drained water is likely derived from locally applied water and interception of regional groundwater flow implying that standard two‐dimensional models of flow to drains, representing only water applied locally, would not be applicable to modeling of drain flows or drain‐water solute concentrations.
Predicting Land Use Impacts on Regional Scale Groundwater Recharge and Discharge
Authors: Salama Ramsis , Hatton Tom , Dawes Warrick
Published: July 2010

The paper presents the development and evaluation of methods that estimate recharge and discharge, water flow, and salt fluxes in rivers. The methods in combination provide an inferential framework to predict dryland salinity and the selection of the appropriate management scenarios. Hydrogeomorphic Analysis of Regional Spatial Data (HARSD) was used for delineating hydrogeologically homogenous units, and to translate limited hydrological data into hydraulic head surfaces and ultimately a steady state flow net representing recharge‐discharge relationships. A complex, physically based water, energy, and carbon model (WAVES) was developed and tested to provide recharge estimates required for the flow net simulations. Remote sensing imagery and analysis techniques involving airborne, advanced very high resolution reflectance (A VHRR) and LANDSAT‐Thematic Mapper (TM) data were used to infer the temporal and spatial patterns of leaf area index (LA1) and land‐cover type. The techniques were applied in 22 subcatchments in the Loddon and Campaspe and for the two major catchments. Modeled recharge was consistent with local estimates based on inverse methods and with subcatchment‐scale estimates based on stream salt loads under a steady‐state assumption. The calibrated flow nets for each of the subcatchment have been used to test the sensitivity of this system to changes in recharge resulting from land use change. It is shown, for example, that the Upper Campaspe subcatchment would require the reforestation of key recharge areas totaling 45% of the subcatchment to reduce salt loads from approximately 25 000 Mg yr−1 down to 18 000 Mg yr−1 under steady state assumption.
Efficient Calculation of Solute Transport in Heterogeneous Soils Exhibiting Non‐Richards‐Type Unsaturated Flow
Authors: de Rooij Gerrit H. , de Vries Peter
Published: July 2010

Soil heterogeneity hampers our ability to calculate field‐scale solute leaching. Many of the existing field‐scale modeling attempts are laborious, time consuming, and computationally demanding. Non‐Richards‐type flows (e.g., fingering) cannot be handled by methods based solely on the heterogeneity of the soil hydraulic properties. We developed a time‐ and cost‐effective approach that starts with a plot‐scale solute transport model that must incorporate any special flow features in the field of interest. The field was modeled as an ensemble of plotscale columns with random properties. The computational demand was reduced by: (i) simplifying the plot‐scale model; (ii) keeping the most influential parameters stochastic; (iii) replacing a full Monte Carlo simulation by systematic parameter sampling; and (iv) transforming the model output for one column to that of another where possible. The method was demonstrated for a field exhibiting fingered flow in the topsoil. A recently developed model to calculate solute leaching from a single finger served as the column‐scale model. Three parameters appeared to be key for solute leaching to the groundwater. For two of them, the breakthrough curve for one value of the parameter could be transformed to approximate the curve for all other values. Consequently, field‐scale solute leaching could be computed with <20 model runs.
A Groundwater Exposure Assessment. for Cloransulam‐Methyl in the U.S. Soybean Market
Authors: van Wesenbeeck Ian J. , Havens Patrick L.
Published: July 2010

A study was conducted to examine the leaching potential for cloransulam‐methyl, a new soybean herbicide, in the U.S. soybean market. Expected environmental concentrations (EECs) of cloransulam‐methyl in groundwater were simulated in 60 soils in the use area using the PRZM2 model executed within the PATRIOT shell using conservative soil, weather, and chemical inputs. Modeling results suggested that cloransulam‐methyl is potentially mobile in coarse‐textured soils with <1.5% organic matter (OM) and not mobile in finer‐textured soils. The maximum predicted EEC in groundwater for the most vulnerable soil modeled was 2.7 µg L−1 (ppb), more than two orders of magnitude below the USEPA defined health level of 1000 µg L−1, based on toxicological data. Comparison of EEC distributions in groundwater and EC25 distributions for nontarget terrestrial plants obtained from conservative Tier 2 phytotoxicity studies suggest adequate safety, if shallow groundwater was used as a source of irrigation water on nontarget terrestrial plants. A GIS assessment of coarse textured soils with OM <1.5% and GW <1.83 m deep showed that <2, 3, and 1% of the soils in any given state in the Midwest, Eastern, or Southern soybean markets, respectively, contained soils meeting those criteria for vulnerability (based on modeling). Results of this modeling and exposure assessment are consistent with the rapid dissipation and low mobility of cloransulam‐methyl observed in four terrestrial field dissipation studies conducted in the U.S. soybean market, and suggest that potential mobility of cloransulam‐methyl should have no significant environmental impact.
Nitrogen Mineralization and Nitrification in Suburban and Undeveloped Atlantic White Cedar Wetlands
Authors: Zhu Wei‐Xing , Ehrenfeld Joan G.
Published: July 2010

The presence of urban and suburban lands adjacent to wetlands may cause changes in nutrient‐cycling processes, due to changes in the quality of the ground‐ and surface waters that drain from the developed uplands into the wetland. We studied N‐cycling processes in Atlantic white cedar [Chamaecyparis thyoides (L.)] swamps in the New Jersey Pinelands to determine their sensitivity to the development of adjoining uplands. We conducted a 19‐wk aerobic incubation to measure N mineralization and nitrification potentials in wetland soils from both developed and undeveloped watersheds. The cumulative inorganic N mineralized during the incubation was two to three times higher in soils from developed sites than from the undeveloped sites. There was virtually no nitrification in undeveloped wetlands, while in developed wetlands, most N mineralized was further nitrified. In developed sites, there was also more nitrification in hollow soils than in hummock soils. Both nitrification and the fraction of soil organic matter mineralized were highly correlated with pH and with soil ash content. These results suggest that increases in ash content of peats attributable to sediment transported and deposited in urban runoff, causes increases in pH, which in turn allows large populations of nitrifiers to develop. Excess mineral N generated within the wetlands through changes in microbial function thus may be as important as N inputs in drainage water in affecting plant community composition, and may cause wetlands to become sources of N to downstream ecosystems rather than serving as regional sinks.
Mangrove Soils in Removing Pollutants from Municipal Wastewater of Different Salinities
Authors: Tam N. F. Y. , Wong Y. S.
Published: July 2010

Soil leaching experiments were conducted to assess the capacity of mangrove soils in purifying synthetic wastewater containing pollutant concentrations four times of that found in local municipal sewage and of two salinities (fresh vs. saline water). Results on leachate nutrient and heavy metal concentrations reveal that the mangrove soils were capable of removing certain amount of pollutants from wastewater, and the removal efficiency varied between pollutants. The soils were most effective in retaining heavy metals such as Cu but were less effective for Mn and Zn. Similarly, the wastewater‐borne NH+4 was more easily leached than P. The soil data show that most pollutants were accumulated in the top layer (0–1.5 cm) of the soil tray, with little downward migration. Differences between treated and control soil nutrient and heavy metal concentrations were not found in the soil masses below the surface 1.5 cm. In the surface layer, the mangrove soils treated with wastewater had significantly higher concentrations of NH+4‐N, total and extractable P, total and extractable Cu, Cd, Zn and Mn. On the other hand, there was no significant elevation in total nitrogen content in mangrove softs treated with wastewater when compared with the control. Soils receiving wastewater prepared in deionized water (fresh) had slightly higher pollutant concentrations, and larger enrichment factors than that treated with saline wastewater (containing 1.5% salinity). These results suggest that mangrove soils could retain pollutants from wastewater but its efficiency would slightly be affected by salinity.
A Study of Suspended and Colloidal Matter in the Leachate from Lysimeters and its Role in Pesticide Transport
Authors: Worrall F. , Parker A. , Rae J. E. , Johnson A. C.
Published: July 2010

The relative importance of suspended (>0.45 µm) and organic colloidal (<0.45 µm) matter in the transport of pesticide through and across a soil was studied by monitoring suspended and colloidal matter from lysimeters over a winter (1994–1995) and relating it to the leaching of pesticides. The major results were: (i) The organic colloidal matter and suspended sediment appeared at different times in the leachate. (ii) The suspended sediment was enriched in total organic carbon (TOC). (iii) The leaching of pesticide occurred largely in first few samples following rainfall, coinciding with the occurrence of the colloidal matter. (iv) Modelling the distribution of pesticide between the colloids, suspended matter, and pure solution suggests that negligible amounts of isoproturon are carried on suspended sediment and the organic colloids are more important. The importance of organic colloids may be even more significant for compounds more hydrophobic than those studied here: this has implications for the management of soils and pesticides in relation to the release of organic colloids into solution.
Amelioration of Subsoil Acidity through Surface Application of Organic Manures
Authors: Hue N. V. , Licudine D. L.
Published: July 2010

Subsoil acidity is a serious constraint to crop production, and is difficult to correct by conventional liming practices. Thus, different approaches to ameliorating acid subsoils are needed. A column leaching study was conducted to compare the effects of chicken manure and sewage sludge amendments, each at 20 g kg−1, with CaSO4 and CaCO3, each at 5.56 cmol (½Ca2+) kg−1, on Al and Ca concentrations in the subsoil of an Ultisol having pH 4.4, 80% Al saturation and 2.78 cmolc kg−1 exchangeable Al. Treatments were incubated moist for 14 d with the top 5 cm soil of 50 cm long soil columns, then leached with 37.8 cm of water in 5 d. The soil columns were then cut into four equal segments for chemical analysis. Results showed that the manures were effective in increasing soil‐solution pH and Ca, and decreasing soil‐solution Al and percentage of Al saturation in the subsoil, particularly below the 15 cm depth. Soil‐solution C, nearly constant through the soil profile, averaged 2.8 mM in the CaSO4 treatment and 7.6 mM in the chicken manure treatment. A subsequent solution experiment on the competitive complexation of Al and Ca with model organic ligands supported the contention that (i) manure‐derived organic molecules facilitated the downward movement of Ca as Ca complexes, and (ii) along their downward path, these Ca complexes reacted with Al, releasing Ca that would become plant‐available, and forming complexed Al that may be nonphytotoxic.
Microbial Responses to Coal Fly Ash under Field Conditions
Authors: Schutter Mary E. , Fuhrmann Jeffry J.
Published: July 2010

Coal fly ash may be a valuable soil amendment because it contains plant nutrients and liming agents and has a silty texture that can improve the water‐holding capacities of sandy, drought‐prone soils. Short‐term laboratory studies have indicated that addition of unweathered fly ash to soil can stress microbial populations and their activities, but effects of fly ash addition at the field scale are not known. In this study, field plots received 0 or 505 Mg fly ash ha−1 (incorporated by conventional tillage to a depth of 40 cm) and were subsequently cropped to a fallow‐corn (Zea mays L.)‐wheat (Triticum aestivum L.) rotation or continuous fescue (Festuca arundinacea Schreb.). Twenty months later, during the wheat phase of the rotation, the plots were sampled (0–15 cm) and assayed for activity of soil enzymes (dehydrogenase, alkaline phosphatase, arylsulfatase, and denitrifying enzymes); numbers of aerobic heterotrophs, ammonium oxidizers, denitrifiers, and bradyrhizobia; and N mineralization, nitrification, and denitrification potentials. Nitrification potentials doubled in fly ash‐amended soils, and numbers of denitrifiers were 200‐fold higher in fescue‐cropped, fly ash‐amended soils relative to fescue‐cropped, non‐amended soils. No other large differences in microbial populations or activities were found. The lack of detrimental effects on microorganisms in the field was possibly due to reductions in fly ash's soluble salt and trace element concentrations with time, the mild alkalinity of the fly ash used in this study, and the positive responses of crops to fly ash amendment.
Influence of Daily Carbon Dioxide Exposure Duration and Root Environment on Soybean Response to Elevated Carbon Dioxide
Authors: Heagle A. S. , Booker F. L. , Miller J. E. , Pursley W. A. , Stefanski L. A.
Published: July 2010

Little is known about effects of daily CO2 enrichment duration and root environment on plant response to elevated CO2. Two experiments were performed with Essex soybean (Glycine max L. Merr.) in open‐top field chambers to address these questions. In one experiment, effects of 12 and 24 h d−1 exposures to double‐ambient CO2 were compared for plants grown in 14 L pots that were either insulated to moderate soil temperature or not insulated. Although never significant statistically, trends at some growth stages suggested that nighttime CO2 enrichment contributed to growth and yield. Plants grew and yielded more in insulated than noninsulated pots, but there were no significant CO2 enrichment × insulation interactions. In the second experiment, response to approximately 1.3, 1.6, and 1.9 times ambient CO2 was compared for plants grown in the ground or 14 L pots. Enhancement of photosynthesis, growth, and yield by CO2 enrichment was similar in pots and in the ground. Linear responses to different CO2 concentrations were significant for all yield components in both root environments, whereas quadratic responses were significant for plants in pots but not for plants in the ground. Tests of proportionality of response for yield components showed no evidence of significant differences between plants in pots and in the ground except weight per 100 seeds. Seed yield enhancement at 1.9 times ambient CO2 was 36% for plants in pots and 33% for plants in the ground. Overall, proportional response of soybean to CO2 enrichment was relatively uniform in spite of large differences in baseline growth and yield.
Microcosm Studies on the Volatility of Pesticides from Soil Surfaces
Authors: Lembrich D. , Beese F. , Scheunert I.
Published: July 2010

A laboratory model was developed to investigate pesticide volatilization from soil surfaces under various boundary conditions. Carbon‐14‐1abeled terbutylazine (2‐chloro‐4‐ethylamino‐6‐t‐butylamino‐1,3,5‐triazine) was applied to the surface of different soils in doses commonly used in agriculture. The experimental setup was designed to study the dynamics of the volatilization process. Short sampling intervals give information about temporal changes in loss rates, which allows to quantify the influence of the application mode. Drop application, for example, leads to volatilization kinetics different from those by spraying, especially in the initial phase. Another aim of the experiments is to describe soil matrix effects on pesticide volatility. After a test period of 10 d the cumulative vapor loss ranged from minimum 6.9% (loamy sand) to maximum 23.1% (weakly loamy sand) of the applied 14C‐terbutylazine. In the case of a silty loam it was shown that soil moisture had a strong effect on terbutylazine volatilization. Rising the soil water suction resulted in a drastic decline in volatility.
Pesticide‐Contaminated Soil Sample Stability during Frozen Storage
Authors: Puchalski Michele , Horvath Gareth , Loughran Michael , Elsner Gary , Koskinen William
Published: July 2010

Little information is available in the literature on pesticide‐contaminated soil sample stability during frozen storage. This research was conducted to evaluate the effects of sample holding times on frozen clay loam, clay, and loamy sand soils spiked with eight different herbicides: EPTC (S‐ethyl dipropylthiocarbamate); trifluralin (α, α, α‐trifluoro‐2,6‐dinitor‐N,N‐dipropyl‐p‐toluidine); atrazine (6‐chloro‐N2‐ethyl‐N4‐isopropyl‐1.3.5‐triazine‐2,4‐diamine); alachlor (2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl)acetanilide); dicamba (3,6‐dichloro‐2‐methoxybenzoic acid); 2,4‐D (2,4‐dichlorophenoxyacetic acid); silvex ((±)‐2‐(2,4,5‐trichlorophenoxy)propionic acid); and 2,4,5‐TB (4‐(2,4,5‐trichlorophenoxy)butanoic acid). Each soil was spiked with eight herbicides (1 mg kg−1 each herbicide) and stored at −15°C for up to 450 d. The pesticides tested could generally be stored up to 450 d without affecting pesticide recovery on all soil types with the exception of trifluralin. Trifluralin decreased by 50% in the loamy sand, 40% in the clay loam, and 66% in the clay soil over the length of the study. In the loamy sand, clay loam, and clay soils a significant decrease in trifluralin concentration occurred at Day 180, 360, and 270, respectively. This study shows that long‐term frozen storage can affect the sample integrity of some pesticide‐contaminated soils. In addition, soil type can be a factor in sample integrity during frozen storage. Spiked controls should be a part of quality assurance and quality control during long‐term frozen storage.
Mercury and Organic Carbon Relationships in Streams Draining Forested Upland/Peatland Watersheds
Authors: Kolka R. K. , Grigal D. F. , Verry E. S. , Nater E. A.
Published: July 2010

We determined the fluxes of total mercury (HgT), total organic carbon (TOC), and dissolved organic carbon (DOC) from five upland/peatland watersheds at the watershed outlet. The difference between TOC and DOC was defined as particulate OC (POC). Concentrations of HgT showed moderate to strong relationships with POC (R2 = 0.77) when all watersheds were grouped. Although POC only accounts for 10 to 20% of the OC transported, we estimate that it is associated with 52 to 80% of the HgT transported from the five watersheds. Total transport of HgT from the watersheds ranged from 0.70 to 2.82 µg m−2 yr−1. Watershed geometry and hydrology play important roles in determining the influence of OC on HgT transport in forested watersheds. Watershed properties such as peatland area have considerable promise as predictors for estimating HgT transport in streams draining forested watersheds in the Great Lakes States.
Copper Solution Geochemistry in Arable Soils: Field Observations and Model Application
Authors: Römkens Paul , Hoenderboom Guido , Dolfing Jan
Published: July 2010

The solubility and vertical displacement of Cu in near neutral arable soils largely depends on the presence of dissolved organic carbon (DOC) in solution. In this paper the solubility of Cu in sandy soils is predicted by a previously calibrated model that describes Cu binding to both low and high molecular weight components of DOC. Soil solution samples were obtained by centrifugation of field moist soil. Dissolved Cu concentrations increased with DOC and total soil Cu content, but decreased with organic matter and pH; after lime application, both DOC and Cu solubility were strongly reduced in the CuSO4‐treated soils. No single multiple linear regression equation could be obtained, however, that was able to describe the dissolved Cu concentrations in the various treatments. In contrast to this, a two‐species Langmuir model enabled us to describe the dissolved Cu concentrations in soil solution samples quite well in the pH range from 4.2 to 6 in both contaminated and noncontaminated soils (R2 = 0.5–0.9 for various treatments). Measured Cu concentrations were generally underpredicted by the model below pH 4.2. In the manured soil, the predictive capacity of the model decreased with depth (R2 = 0.6 in the topsoil to 0.3 in the deeper soil horizons), which is most likely related to changes in the nature of DOC. The use of a relatively simple model that requires only a few input parameters may prove useful for the prediction of the solubility of Cu under field conditions.
Ammonia Volatilization from Freshwater Fish Ponds
Authors: Gross A. , Boyd C. E. , Wood C. W.
Published: July 2010

This study evaluated ammonia (NH3) emissions to the atmosphere from fishpond waters and uneaten, floating feed. Channel catfish (Ictalurus punctatus) were stocked at 550 pond−1 in four, 400‐m2 ponds at the Auburn University Fisheries Research (AUFRU), Auburn, AL, on 30 May 1997. Feed (28% crude protein), prepared as floating pellets was applied daily. Ponds were harvested between 7 and 9 Oct. 1997. Ammonia traps were placed in ponds on a weather vane sampler. Ammonia emissions were measured from June through September 1997. In addition, NH3 volatilization from wetted catfish feed was measured in a laboratory experiment. Average NH3 volatilization from ponds ranged between 8.8 to 71.0 mg NH3‐N m2 d−1, and averaged 3.75% of total NH3 nitrogen (TAN) concentration in water. Positive linear correlations were found between the amount of feed applied and TAN concentration in the water and between TAN and NH3 volatilization. Volatilization from wetted feed was not a major NH3 loss to the atmosphere. The study suggested that 24 kg ha−1 of N were lost to the atmosphere between 23 June 1997 and 30 Sept. 1997 from ponds into which 158 kg ha−1 N were applied. In the USA, there are about 66 000 ha of catfish ponds. Extrapolation from this study suggests that 1584 t of NH3 could volatilize from catfish ponds each summer.
Effectiveness of Switchgrass Filter Strips in Removing Dissolved Atrazine and Metolachlor from Runoff
Authors: Mersie W. , Seybold C. A. , McNamee C. , Huang J.
Published: July 2010

The effectiveness of switchgrass (Panicum virgatum L.) filter strips in removing dissolved atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine) and metolachlor (2‐chloro‐N‐2‐ethyl‐6‐methylphenyl‐N‐2‐methoxy‐1‐methylethyl acetamide) in runoff was investigated using aluminum‐tilted beds set at 1% slope, filled with Emporia sandy loam soil (fine‐loamy, siliceous, thermic Typic Hapludults) and planted to switchgrass. Solution containing herbicides, followed by water alone after 2 and 4 wk were applied on the up slope of beds with and without switchgrass. Water samples from surface flow, lateral, and vertical leachates as well as soil samples were analyzed for the two herbicides using a gas chromatograph. Switchgrass filter strips reduced the mass of dissolved atrazine and metolachlor by 52 and 59% from the applied runon, respectively. The bare soil strips removed 41% of atrazine and 44% of metolachlor. Less than 0.5% of the applied herbicide was released by the two water runons 2 and 4 wk after herbicide‐solution application. The average concentrations of both herbicides in surface runoff were greater than in leachate samples. Herbicides were removed by the soil as runon moved through the soil profile. The concentration of either herbicide on the top surface (0–2.5 cm) was greater than in the soil immediately below (2.5–5 cm). Degradation of both herbicides was faster in beds with switchgrass than without. Greater amounts of both herbicides were retained in the first 67‐cm section of beds with the grass than without. Switchgrass helped to remove the herbicides by slowing runoff velocity and increasing their retention by soil.
Relating Agricultural Land Uses to In‐Stream Stormwater Quality
Authors: McFarland Anne M. S. , Hauck Larry M.
Published: July 2010

Sixteen largely agricultural watersheds in the upper portion of the North Bosque River of central Texas were instrumented to collect storm event samples for nutrient analysis. Flow‐weighted storm‐event mean concentrations were averaged across storm events to characterize the water quality at each site for storms sampled between November 1992 and August 1995. Nutrient concentrations were related to land uses above sampling sites using correlation and regression analysis to indicate major sources of nutrient nonpoint source pollution to the upper North Bosque River. Consistently, N and P concentrations increased as the proportion of land area used for dairy waste application fields (or milking cow densities) increased in the drainage basins above sampling sites. The proportion of total P (TP) in runoff represented by soluble reactive P (SRP) also increased as the percent of dairy waste application fields above a sampling site increased; likely as a response to the common practice of surface application of manure to permanent pasture. This increase in SRP is of particular importance because SRP is readily bioavailable in aquatic systems, thus increasing the potential for accelerated eutrophication in receiving waterbodies. The results of these analyses indicate a strong association between in‐stream nutrient concentrations during storm events and the percent of dairy waste application fields comprising a drainage area. This indicates a need to manage the movement of nutrients, particularly soluble P, from manure application fields in areas where in‐stream nutrient levels are considered a nonpoint source pollution problem.
Modeling Nitrogen Oxide Emissions from Current and Alternative Pastures in Costa Rica
Authors: Plant Roel A. J. , Bouman Bas A. M.
Published: July 2010

Emissions of nitrogen (N) oxide were simulated for one current, unsustainable pasture management system (Natural) and two alternative, sustainable systems (Grass‐Legume and Fertilized Improved) relevant to the Northern Atlantic Zone (NAZ) of Costa Rica. To produce frequency distributions of N oxide emissions, an expert system for generating technical coefficients of pastures was linked with a process‐based simulation model. The expert model generated parameter sets representing different options for the three management systems. The simulation model was rerun for each parameter set. Simulated nitrous oxide (N2O)‐N losses 25 yr after pasture establishment were 3 to 5 kg ha−1 yr−1 for natural pastures, 12 to 15 for grass‐legume mixtures, and 7 to 28 for fertilized grasses. Losses of nitric oxide (NO)‐N were 1 to 2 kg ha−1 yr−1 for natural pastures, 7 to 8 for grass‐legume mixtures, and 3 to 16 for fertilized grasses. Stepwise multiple regression showed that N2O‐N losses were explained by annual C input to the soil (R2 = 0.997), and NO‐N losses by attainable dry matter production (R2 = 0.972). Carbon input and dry matter production were controlled by stocking rate and fertilizer level. Soilatmosphere N oxide emissions from pastures may increase by a factor 3 to 5 when natural pastures are converted to improved pastures. Such conversion may increase the sustainability of the pasture by stopping the decline of soil N. However, the change is not necessarily sustainable from a global perspective because it increases the emission of N oxide greenhouse gases.