bluuebunny/crossref_metadata_2025 huggingface dataset:
Riparian Afforestation Effects on Water Yields and Water Quality in Pasture Catchments
Authors: Smith Christine M.
Published: July 2010

The flow records for two pasture headwater catchments for 9 yr before, and 9 yr after riparian afforestation in one catchment were compared. Average rainfall was 1021 mm yr−1. Riparian afforestation reduced water yields by 68 to 104 mm (21–55%) when the Pinus radiata stand was 8 to 10 yr old. Delayed runoff declined by 52 to 93 mm yr−1 (27–63%). Afforestation reduced the quickflow yield in 1 yr (22 mm or 40%). Peak flows declined in small events, were not affected in medium‐sized events, and may have increased in large events. The large reductions in yield indicate that the riparian zone had a disproportionately important influence on catchment hydrology. They are attributed to high transpiration losses from the riparian pine in seasons with water deficits, and higher than usual forest interception losses because of the small‐scale planting. Streamwater sediment, total and dissolved N and P concentrations in these two catchments and another riparian afforested catchment were monitored for 2 yr. Concentrations were generally lower in the completely pastured catchment. Estimated annual sediment, total P, Kjeldahl N, and nitrate exports from the pasture catchment were 31 to 60%, 70%, 61 to 64% and 58 to 74% of those from the riparian afforested catchments in spite of a higher water yield. Possible explanations for the poor water quality in riparian afforested catchments are described including the lack of riparian wetlands, in‐stream vegetation, and close riparian ground cover. The consequences of riparian afforestation in pasture catchments may not readily be predicted from the impacts of complete catchment afforestation.
Selenium in Kesterson Reservoir Ephemeral Pools Formed by Groundwater Rise: I. A Field Study
Authors: Tokunaga Tetsu K. , Benson Sally M.
Published: July 2010

One of the principal initial plans for managing Se contamination at Kesterson Reservoir (Merced County, California) entailed excavation to a depth of at least 0.15 m in order to remove soils with Se concentrations higher than 4 mg kg−1. Prior to implementing this plan, surface waters were collected from numerous shallow ephemeral pools that formed during the winters of 1986 to 1988. Elevated concentrations of Se were measured in all of these pools. Pools formed during this period from a combination of overland flow from adjacent nonseleniferous pond waters, rainfall ponding, and emergence of the fluctuating shallow water table above the soil surface. Selenium in these ephemeral pool waters originated primarily from dissolution of surface salt crusts and from displacement of seleniferous soil solutions up to the surface. Through the monitoring of a test plot where 0.30 m of the surface soil had been removed, the potential was demonstrated for shallow water table rise to displace seleniferous soil solutions to the surface, resulting in highly seleniferous ephemeral pools. In the test plot, ephemeral pool Se concentrations often exceeded 103µg L−1. This study clearly demonstrated (i) that pools formed over soils with total Se concentrations in the range of 0.5 to 1.7 mg kg−1 could still provide a highly seleniferous aquatic environment, (ii) that the total Se concentration in a soil can be a misleading parameter to use in determining target goals for remediation, and (iii) that the excavation strategy was inappropriate for the Kesterson Reservoir setting.
Sampling Unsaturated‐Zone Water for Trichloroethene at Picatinny Arsenal, New Jersey
Authors: Smith James A. , Cho H. Jean , Jaffé Peter R. , MacLeod Cecilia L. , Koehnlein Susan A.
Published: July 2010

A new method of collecting samples of unsaturated‐zone water for quantitative analysis for a volatile organic compound, trichloroethene (TCE), was compared to three other, previously described sampling methodologies in the laboratory and in the field. In the laboratory, prepared water samples containing TCE in a known concentration (20 µg/L) were sampled repeatedly by using each of the four methods to quantify method precision and accuracy. To compare the four methods in the field, unsaturated‐zone water above a TCE‐contaminated water‐table aquifer was transferred from a depth of 2 m to land surface with 0.15‐m‐long suction lysimeters attached to 1.85‐m lengths of stainless‐steel tubing. Statistical analyses of the laboratory and field data indicate that the new method, which involves collecting the water samples in gas‐tight glass syringes, is superior to the other three methods for the quantitative sampling and analysis of TCE on the basis of its high precision and accuracy and ease of use. This method was used to collect additional samples from the field site to quantify the spatial variability of TCE concentrations in the unsaturated‐zone water. Results of analysis of variance of the data indicate that the spatial concentration variability is important, and that differences in TCE concentration are statistically significant for horizontal distances less than 3.6 m.
Sludge‐Borne Salt Effects on Survival of Bradyrhizobium japonicum
Authors: Madariaga G. M. , Angle J. S.
Published: July 2010

The soil population of Bradyrhizobium japonicum, the microsymbiont of soybean [Glycine max (L.) Merr.], is reduced following land application of sewage sludge. Previous research on the ability of B. japonicum to survive in soil recently amended with sewage sludge has been conflicting as to whether sludge‐borne salts or heavy metals inhibit survival. To examine this question, sewage sludge compost was added to a rhizobia‐free, Sassafras sandy loam soil (Typic Hapludult, fine loamy mixed mesic) amended with various rates of sludge compost, inoculated with B. japonicum USDA 110 ARS and the mixture was incubated for 42 d. The population of B. japonicum was reduced to nearly undetectable levels when inoculated into soil amended with sludge compost at a rate of 25%. The sludge compost was subsequently leached with 3‐, 6‐, 9‐ and 12‐column void volumes of distilled water resulting in sludge compost samples with equal concentrations of heavy metals but decreasing concentrations of soluble salts. Leached and unleached compost samples were added to soil at a rate of 25% and the mixture inoculated with B. japonicum. Soil amended with sludge compost leached with six void volumes water exhibited the highest rhizobial population, while soil amended with unleached sludge compost contained the lowest rhizobial population. In soil amended with sludge compost leached with 3‐, 9‐, and 12‐void volumes water, populations were not significantly different. Results demonstrate that sludge‐borne soluble salts, and not heavy metals, are primarily responsible for short‐term reductions in bradyrhizobial populations following the application of very high rates of sludge to soil.
Aluminum in Soil Solutions from a Subalpine Spruce‐Fir Forest at Whiteface Mountain, New York
Authors: Miller E.K. , Huntington T.G. , Johnson A.H. , Friedland A.J.
Published: July 2010

Direct or indirect Al toxicity has been suggested as a principal factor in forest tree declines. We monitored ambient soil solutions in undisturbed and experimentally manipulated soils from a fir [Abies balsamea (L.) Mill.]‐spruce forest on Whiteface Mountain, NY, in order to characterize soil solution Al concentrations over a range of acid anion loadings. Under both natural and experimental conditions total Al and labile Al concentrations rarely exceeded values (180–250 µmol L−1) associated with reduced root growth in red spruce (Picea rubens Sarg.). Over a 2‐yr period ambient soil solutions averaged 76 and 46 µmol L−1 total Al in the organic and mineral horizons, respectively. The highest monthly mean concentrations occurred in winter. Disturbance‐induced NO3 accumulation and simulated acid rain applications produced higher peak Al values in experimental plots than were observed in undisturbed and untreated plots. Although soils of the fir‐spruce zone exhibited the potential to yield solutions with phytotoxic Al concentrations, it appears that such concentrations are both spatially and temporally limited and infrequently present a direct stress to root growth in red spruce.
Dissolved Organic Matter and Adsorption‐Desorption of Dimefuron, Atrazine, and Carbetamide by Soils
Authors: Barriuso E. , Baer U. , Calvet R.
Published: July 2010

Dissolved organic matter (DOM) from several sources influenced the adsorption and the desorption by soil of three herbicides: dimefuron {4‐[2‐chloro‐4‐(3,3‐dimethylureido) phenyl]‐2‐t‐butyl‐1,3,4‐oxadiazolin‐5‐one},atrazine (2‐chloro‐4‐ethylamino‐6‐isopropyl‐amino‐striazine), and carbetamide [D‐N‐ethyl‐2‐(phenyl‐carbamoyloxy)propioamide)]. The DOM was endogenous (water soluble and humic compounds directly extracted from soil) or exogenous (water soluble organic matter from compounds applied to soils through agricultural practices: sewage sludge, fermented straw, and farmyard slurry; and two model compounds—tannic acid and an anionic surface active agent). Experiments were conducted to quantify the importance of herbicide sorption in three separate systems: DOM‐soil, DOM‐herbicide in solution, and DOM‐adsorbed herbicide. Herbicide adsorption strongly increased in the presence of water soluble materials from fermented straw, which explained the lowest desorption obtained with this DOM. On the other hand, the water soluble extracts of liquid or solid sludge favored herbicide desorption. Generally, adsorption of the less soluble herbicides (dimefuron and atrazine) was favored when soil was pretreated with DOM, and their adsorption generally decreased when DOM was preincubated with herbicides before soil contact. Opposite effects were generally noted for the most soluble herbicide (carbetamide). A new empirical, two‐compartment model provided a good description of desorption isotherms. The first compartment (a linear desorption) was similar for most DOM types. The differences in desorption isotherms were mainly related to the different behavior of the second compartment (an exponential desorption), in which the molecules were more strongly adsorbed.
Dependence of Aldicarb Residue Degradation Rates on Groundwater Chemistry in the Wisconsin Central Sands
Authors: Kraft George J. , Helmke Philip A.
Published: July 2010

Aldicarb sulfoxide (ASO) (2‐methyl‐2‐(methylsulfinyl)propanal O‐[(methylamino)carbonyl]oxime) and aldicarb sulfone (ASO2) (2‐methyl‐2‐(methylsulfonyl)propanal O‐[(methylamino)carbonyl]oxime) degradation rates were measured in incubations simulating three depths (0.5, 5, and 10 m) of Wisconsin central sand plain (WCSP) aquifer. The incubations differed mainly in pH (5.8, 6.5, and 7.2, respectively, for the three depths) and pO2 (20 kPa [0.2 atm] for the 0.5‐ and 5‐m depths, 1.5 kPa [0.015 atm] for the 10‐m depth). Degradation rates corresponded to half‐lives ranging from years to less than a month. Aldicarb sulfone (ASO2) degraded faster than ASO at the same depth. No ASO degradation was measured under aerobic, pH 5.8 conditions; no ASO oxidation was observed in any incubation. The shortest half‐lives, 19 and 32 d for ASO and ASO2, respectively, were obtained under the low pO2 conditions. The results of this and a previous experiment provide degradation rates for a cross‐section of WCSP groundwater chemistries. Thus, with knowledge of the groundwater chemistry at a given WCSP location, degradation rates can be estimated. Degradation rates of common groundwater contaminants as functions of chemical and physical controlling factors could prove valuable to groundwater managers for endeavors such as wellhead protection.
Washoff of Ultra‐Low‐Volume‐Oil‐Applied Insecticides from Cotton Plants as a Function of Time between Application and Rainfall
Authors: Willis G.H. , McDowell L.L. , Southwick L.M. , Smith S.
Published: July 2010

Model development for predicting the movement of foliar‐applied pesticides depends on being able to characterize the dynamics of pesticide disappearance from plants, including washoff by rainfall. This study was conducted to determine the effect of elapsed time between spray application and initial rainfall on pesticide washoff from foliage. Methyl parathion [0, 0‐dimethyl,0‐(p‐nitrophenyl) phosphorothioate] and fenvalerate [(RS)‐α‐cyano‐3‐phenoxybenzyl (RS)‐2‐(4‐chlorophenyl)‐3‐methylbutyrate] were applied in oil by rotary‐atomizer controlled‐droplet applicators to mature cotton (Gossypium hirsutum L.) plants. Simulated rainfall (51 mm in 1 h) was applied to the plants at different times after insecticide application to determine washoff characteristics for both compounds. Residues of both insecticides became increasingly resistant to washoff with increasing time interval between pesticide application and initial rainfall. The mean amounts of both insecticides washed from the plants (i) were related to the square of the mean insecticide loads on the plants and (ii) decreased exponentially with time.
Bare Soil Evaporation and Solute Movement in Selenium‐Contaminated Soils of Kesterson Reservoir
Authors: Zawislanski Peter T. , Tokunaga Tetsu K. , Benson Sally M. , Oldfather Joan M. , Narasimhan T.N.
Published: July 2010

Two approaches were taken to estimate evaporation of water from the surface of a salt‐encrusted and Se contaminated soil in a playalike environment at Kesterson Reservoir, California. Direct evaporation flux measurements were made using a lysimetric (gravimetric) approach and revealed a seasonal dependence of bare soil evaporation rates, which ranged from 0.1 to 1.5 mm d−1. The low range is suggestive of a vapor‐flux control of bare soil evaporation due to the presence of a salt crust. Temporal changes in chloride concentrations and soil moisture content were used in a quantitative assessment of a mean seasonal evaporative flux. Bare soil evaporation rates measured by these two methods compared favorably. Although concentrations of salts and Se in near‐surface soil fluctuated seasonally during a drier than average year, a slight net decline in salt concentrations was observed over 12 mo due to rainfall infiltration and the associated solute transport. Increases in Se near the soil surface due to an evaporatively driven flux appear unlikely in this setting, due to low rates of bare soil evaporation as compared with downward fluxes due to rainfall infiltration.
Bromide Movement at Selected Sites in a Dissected Piedmont Landscape
Authors: Bathke G. R. , Cassel D. K. , McDaniel P. A.
Published: July 2010

Soil hydraulic properties vary across landscape positions due to changes in soil profile characteristics. Water and solute transport in soils are intimately related to soil property and water balance relationships. The objectives of this study were to identify the interdependency of solute transport on hydrologic, pedologic, and geomorphic properties of a dissected Piedmont landscape and to determine soil features conducive to lateral water movement within the soil profile. Crystalline KBr was applied at a rate of 1 kg/m2 in 15 m long by 15 cm deep trenches on 11 Aug. 1987 to one linear slope (LS1) and two headslope (HS1 and HS2) positions in a clayey, kaolinitic, thermic Typic Kanhapludult soil under pasture in the Piedmont of North Carolina. Soil cores were taken on 8 Mar. 1988, 20 July 1988, and 3 Nov. 1988 in a grid of sample positions along the trench (PAT) and downslope from the trench (DFT). The highest Br− levels on 8 March were found at LS1, followed by HS2, in the B horizons at the 0.25 m DFT. Solute concentrations declined with DFT and time at every site. Differences in Br− distribution with PAT indicated that preferential movement occurred at LS1, but only to a minor extent at HS1 and HS2. The centers of mass of the Br− profiles at LS1 and HS2 were found in the upper B horizons. Bromide moved deeper at HS1, where the soil profile was formed entirely in hillslope alluvium and had the lowest clay and dithionite‐extractable iron (Fed) contents throughout the solum. The alluvial‐residual parent material discontinuity between the Bt1 and Bt2 horizon of HS2 contributed to greater lateral Br− transport compared with site LS1, where bulk density and macroporosity changed minimally and/or gradually with depth. Water and Br− transport was dominantly vertical through the soil profile at LS1.
A Field Chamber for Testing Air Pollution Effects on Mature Trees
Authors: Albaugh Timothy J. , Mowry Fred L. , Kress Lance W.
Published: July 2010

A 3.6 m tall by 3 m diam. open‐top chamber system built on 12‐m towers for the dispensing and exclusion of air pollutants in the foliage of mature loblolly pine (Pinus taeda L.) trees was tested. Statistically significant position and height differences in O3 concentration inside the chamber were found for different wind speed categories. Calculation of a relative O3 concentration (ROC) showed remarkably similar relative O3 profiles for charcoal filtered (CF) and 2x ambient (2x) chambers. Large reductions in ROC are found above the 2.4‐m level in both chambers. Ambient air intrusion was reduced in the modified chamber because it was protected by the canopy and contained a tree crown lessening air movement in the chamber. The mean temperature increase in the chamber from 1200 to 1259 h EST was 2.2°C, whereas the maximum temperature increase was 4.8°C. Statistically significant positional temperature differences were found within the chamber. The chamber system design was found useful in testing the effects of gaseous air pollutants on the crown of mature trees and is recommended for designed experiments.
A Methodology for Establishing Phytotoxicity Criteria for Chromium, Copper, Nickel, and Zinc in Agricultural Land Application of Municipal Sewage Sludges
Authors: Chang A. C. , Granato T. C. , Page A. L.
Published: July 2010

This study illustrates a methodology of evaluating phytotoxicity criteria for metals, when sewage sludges are applied on cropland. The analyses are based on data available in technical literature and fundamental principles of soil fertility and plant nutrition. First, data from laboratory experiments, where plants were grown in media treated with only one metal element, were used to develop an empirical cause‐and‐effect relationship between metal concentration in plant tissue and growth retardation of plants. This relationship is used to select the phytotoxicity threshold (metal concentration of plant tissue corresponding to a given level of plant injury). Then, data from land application of sewage sludge experiments were used and soil metal loading rates were plotted against the corresponding plant tissue metal concentrations. The probability of plants, grown on soils with a given range of metal loadings, exceeding the phytotoxicity threshold may be calculated. Finally, an appropriate loading range is selected based on the risk of exceeding the phytotoxicity threshold that is considered acceptable. In this exercise, the data were extracted without imposing any bias and represent a wide range of conditions where land application of municipal sewage sludge has been practiced nationwide. The reliability of the results, however, remain dependent on the quality of the data. A great deal of information already exists in the published literature. Through this exercise, gaps in the technical data base may be identified.
An Information Management Technology Program for ex ante Nutrient Loss Reduction from Farms
Authors: Lemberg Beth , McSweeney William T. , Lanyon Les E.
Published: July 2010

Reducing nutrient losses from farms to the environment can be done before or after the nutrients have been applied to the fields. If effective best management practices can be implemented before nutrients are applied (ex ante), difficult and uncertain remedial management practices can be avoided. The relative environmental and economic consequences of an information management technology program were compared under two contrasting water resource protection perspectives by linear programming simulation of a dairy farm. The information program was based on measuring the amount of materials transferred to and from the fields as crops and manure, and the sampling and analyses of those materials. Potential N losses to the environment were reduced substantially and costs of the information management program were generally more than offset by the savings in fertilizer expenditures compared to the outcome when no credit was given to manure nutrients in the fertilization of farm crops. Exacting requirements for nutrient utilization under a restrictive water resource protection perspective resulted in only a fraction of the total manure produced being spread on the farm fields, however. The negative economic impact of this limitation was potentially much greater than the costs to implement the information management technology program. Standards for both the extent of the information required to adequately meet the environmental expectations and the acceptable range of the expectations must be established if the management practice is to be feasible and successful.
Sediment and Nutrient Loss from Clay Soils as Affected by Tillage
Authors: Chichester F. W. , Richardson C. W.
Published: July 2010

Agricultural source pollution of water resources has been a source of concern in recent years. Research is needed to define mechanisms of chemical and sediment loss in runoff from agricultural land, and to develop management practices that minimize transport of these pollutants. This study was designed to compare the effect of no‐till (NT) and conventional chisel‐till (CT) soil management on runoff water volumes, sediment loss, and N and P loss from small watersheds on a clay soil. Three NT and three CT watersheds located on Houston Black clay vertisol soil (fine, montmorillonitic, thermic, Udic Pellusterts) in east central Texas were used for the study. Wheat (Triticum aestivum L.), corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench] were grown rotationally on the watersheds from 1984 to 1989. Runoff amounts, sediment loss, and N and P losses were measured for each rainfall event that produced runoff. Runoff volume was not changed by tillage system and sediment loss and N and P losses in runoff were less, on average, from NT than from CT. Runoff averaged 1.3 ML ha−1 annually for both CT and NT. Average annual quantities for sediment and nutrient losses were: 160 kg ha−1 and 1575 kg ha−1 for sediment, 3.8 kg ha−1 and 8.1 kg ha−1 for N, and 0.8 kg ha−1 and 1.5 kg ha−1 for P for NT and CT, respectively. These results indicate that the loss of sediment and nutrients from agricultural lands could be minimized by using NT on clay soils.
Evaluation of Phosphate Materials for Control of Acid Production in Pyritic Mine Overburden
Authors: Spotts Edward , Dollhopf Douglas J.
Published: July 2010

Acid mine drainage is a serious and pervasive threat to surface and groundwater quality in the USA. Recent research has indicated that phosphate can be effective at immobilizing Fe and inhibiting the production of acid associated with the oxidation of pyritic mine wastes. Four phosphate materials were replicate tested for their ability to inhibit acid production from pyritic coal overburden using a soxhlet humidity cell leaching technique. These materials included two apatite ores (Comineo ore and Texas Gulf ore) at an application rate of 30 g kg−1 by weight apatite [Ca5(PO4)3OH] and two byproducts of the phosphate industry (Cominco waste and Stauffer sludge) at rates of 10, 30, and 50 g kg−1 apatite by weight. Results of leachate analyses indicate that all phosphate sources at all rates of application resulted in significant (P ≤ 0.05) decreases in titratable acidity vs. a control Acidity reductions ranged from a low of 7% for samples treated with Cominco waste (10 g kg−1) to a high of 67% for Texas Gulf ore‐treated samples. Texas Gulf ore, Stauffer sludge (10, 30, and 50 g kg−1) and Cominco waste (10, 30, and 50 g kg−1) significantly reduced dissolved total Fe concentrations in leachate, with Stauffer sludge (50 g kg−1) and Texas Gulf ore producing the most notable diminutions (62 and 63%, respectively). Maximum decreases in sulfate (SO2−4) concentrations of 26, 20, and 25% were achieved by applications of Texas Gulf ore and Stauffer sludge (30 and 50 g kg−1), respectively. The more effective overall performance of the Stauffer sludge and Texas Gulf ore was attributed to the considerably greater relative surface area and P solubility of these amendments. Results of a scanning electron microscope examination of amendments corroborate these findings.
Retention of Dissolved Organic Carbon and Sulfate in Aggregated Acid Forest Soils
Authors: Guggenberger Georg , Zech Wolfgang
Published: July 2010

Adsorption of dissolved organic carbon (DOC) and sulfate was examined in mineral A and B horizons of aggregated acid forest soils from declining (Oberwarmensteinach) and healthy (Wülfersreuth) Norway spruce [Picae abies (L.) Karst.] stands in northeastern Bavaria, Germany. Adsorption studies were conducted in the laboratory on undisturbed, aggregated soil samples under nonequilibrium conditions using a miscible displacement method. Initial mass relationships suggest a net release of DOC in the A horizons of both stands at all DOC concentration levels added. In contrast, the B horizons retained DOC from solutions containing more than 4 to 5 g C m−3 in the Oberwarmensteinach B horizon, and 2 to 3 g m−3 in the Wülfersreuth B horizon, respectively. These concentrations correspond to mean annual DOC concentrations in the B horizon solutions of both sites. Addition of sulfate (1.60 molc SO4 m−3) significantly reduced DOC retention, suggesting competition between SO4 and parts of DOC for adsorption sites. Retention of sulfate from solution occurred concentrations with more than 0.38 to 0.42 molc SO4 m−3 in Oberwarmensteinach, and 0.25 to 0.31 molc SO4 m−3 in Wülfersreuth, respectively. Compared with batch experiments, the miscible displacement method resulted in lower affinities of the soils for DOC. Reduction of DOC and sulfate retention by the use of the flow‐generated technique is due to the consideration of sorption kinetics, which are influenced by soil structure and texture. Although this method underestimates the affinity of a soil for DOC to a certain extent, we suggest that it reflects the situation in the field quite well. Flow‐generated experiments showed that the decline phenomena of spruce in Oberwarmensteinach correspond with a reduced potential for DOC retention in the upper B horizon, as well as with lower sulfate retention throughout the profile.
Degradation and Transport of Dicamba in a Clay Soil
Authors: Comfort S.D. , Inskeep W.P. , Macur R.E.
Published: July 2010

Dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) has been identified as one of five pesticides present in Montana groundwaters. We determined the effects of degradation and time of water application on the transport of dicamba in a Lohmiller clay soil (fine, montmorillonitic, mesic Ustic Torrifluvent). Carbon 14‐labeled dicamba was surface applied (0.35 kg ha−1) to disturbed soil columns (5.0 cm diam; 29 cm length) previously conditioned with 3 mM CaCl2. The columns were allowed to incubate (23.5 °C) in triplicate for 0, 14, 21, 28, and 42 d. Following incubation, the columns were attached to a vacuum chamber containing a fraction collector and leached with 3 mM CaCl2 under unsaturated conditions. Dicamba breakthrough curves were determined for each incubation period. The percentage of dicamba recovered in the column effluent decreased from 85% (of total applied) after no incubation to 9.5% after 42 d of incubation. The decline of dicamba in the effluent coincided with an accumulation of dichlorosalicyclic acid at the soil surface. Dicamba half‐lives determined under batch conditions were 23.5 d at 28 °C, 38 d at 20 °C, and 151 d at 12 °C, and were all higher than the half‐life estimated from the decrease in column effluent concentrations over time (13.5 d). The simulation model, LEACHM, was used to predict transport of dicamba after the different incubation periods. LEACHM adequately estimated the mass of dicamba leached, but underestimated the maximum dicamba concentrations observed in the effluent. Both simulated and observed results indicated that the transport of dicamba can be greatly reduced if sufficient degradation of dicamba is allowed to occur before irrigation or precipitation.
Tests of the Pesticide Root Zone Model and the Aggregate Model for Transport and Transformation of Aldicarb, Metolachlor, and Bromide
Authors: Parrish Rudolph S. , Smith Charles N. , Fong Fred K.
Published: July 2010

Mathematical models are widely used to predict leaching of pesticides and nutrients in agricultural systems. This work was conducted to investigate the predictive capability of the Pesticide Root Zone Model (PRZM) and the Aggregate model (AGGR) for the pesticides aldicarb [2‐methyl‐2‐(methylthio)propionaldehyde O‐(methylcarbamoyl)oxime], metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl)acetamide], and for a bromide tracer. Model predictions were compared with data collected during 1984 to 1987 in the Dougherty Plain area of southwestern Georgia. Field data were used to estimate mean concentrations of pesticide and bromide residues in the soil profile on various dates after application in each of four growing seasons. Both models tended to predict rates of movement of bromide tracer compounds in excess of that observed. For metolachlor, a pesticide with a sorption‐partition coefficient that is higher than for other compounds in the study, both models provided reasonably accurate predictions within the upper 30‐cm zone. For the pesticide aldicarb, results were more variable. The results suggest that the hydrologic components of both models are more accurate for the upper zones, but they are imprecise in deeper zones, underpredicting vertical dispersion and overpredicting transport velocity.
Soil, Climate, and Atmospheric Deposition Relationships with Elemental Concentrations in Annual Rings of Tuliptree
Authors: McClenahen J. R. , Vimmerstedt J. P.
Published: July 2010

The objectives of this study were to investigate the relationships of contrasting soil properties, climate and atmospheric pollutant (especially S) deposition to elemental concentrations in tree rings. Concentrations of 12 elements were determined in annual rings of tuliptree (Liriodendron tulipifera L.) by proton‐induced x‐ray emission for the 50 even years from 1880 to 1980 within an urbanized‐industrial region in northeastern Ohio. Xylem concentrations of nine elements were consistently and significantly greater on Site 1 where soils were coarse textured and base status was low, than on Site 2 where soils were medium textured and base status was greater. Time series analysis detected high frequencies of elemental pulse interventions during periods of rising S emissions in the 1920s and mid‐1940s. Additionally, step changes in xylem S during these periods, and recently declining xylem S may also reflect changing S emissions. Significant climatic regressions [seasonal mean temperatures and total precipitation, plus annual basal area increment (BAI)] were obtained for 11 elements. Prior fall precipitation was the most consistent and important climate variable associated with xylem chemistry. A significant negative association of BAI with xylem Ca on Site 1, where soil Ca was low, suggested a growth dilution effect and the possibility that soil Ca may be near a critical limit. Soil properties influenced both the absolute concentrations of nearly all elements in xylem and relationships between xylem chemistry and climate. Variations in climate, in addition to soil, are therefore important considerations in spatial and temporal comparisons of xylem chemistry.
Effects of Climatic Variations over 11 Years on Nitrate‐Nitrogen Concentrations in the Raccoon River, Iowa
Authors: Lucey K. J. , Goolsby D. A.
Published: July 2010

Nitrate‐nitrogen (NO3‐N) concentrations at public water‐supply intakes on the Des Moines and Raccoon Rivers in Iowa exceeded the maximum contaminant level (MCL) of 10 mg L−1 for public water supplies established by the USEPA for extended periods of time from March through early August 1990. The excessive NO3‐N levels followed 2 yr of less than normal precipitation in 1988 and 1989. The largest daily NO3‐N load (771 t) transported during the last 17 yr in the Raccoon River occurred in June 1990. The streamflow hydrograph for the Raccoon River for March 1990 prior to seasonal fertilizer application indicates that high NO3‐N concentrations characterize the recession side of the hydrograph. High NO3‐N concentrations in streamflow persisted as streamflow decreased to baseflow conditions. This implies that substantial quantities of NO3‐N were being leached from the soil and transported by subsurface flow during early 1990. A multiple linear‐regression model was developed to predict NO3‐N concentrations in the Raccoon River from readily‐obtainable streamflow and climatic data. The four‐variable model explained about 70% of the variability in the concentration of NO3‐N. The mean streamflow for the previous 7‐d period accounted for about 50% of the total variability.
Designing Septic Tank Filter Fields Based on Effluent Storage during Climatic Stress
Authors: Rutledge E. M. , Teppen B. J. , Mote C. R. , Wolf D. C.
Published: July 2010

Septic tank filter fields (FFs) in many soils undergo seasonal hydraulic failure due to climatic stress. We investigated the hydraulic behavior of an experimental FT with a 61 cm wide, 9.0 m long, and 76 cm deep bed constructed in a loamy‐skeletal, siliceous, mesic, Typic Fragiudult with a perched seasonal water table. The true water table was estimated to be deeper than 30 m. The FF was loaded with 15 L m−2 d−1 of septic tank effluent and monitored for 5 yr. At times each year, in response to rainfall, effluent rose within the bed to near the soil surface and spread laterally into the adjoining soil. This effluent was “stored” until climatic stress ceased. The experimental FF stored an estimated 20 d of effluent input; 220 L (14%) could be stored in the bed and 1410 L (86%) in the soil adjacent to the bed. Hydraulic stress events were the design‐limiting periods for FF loading. The experimental FF operated without detection of surfaced effluent for 5 yr, so 20 d of storage was chosen as the design goal for evaluating FF designs in this soil. The loading rate for noninteracting beds was inversely proportional to bed width, so the most efficient FFs should consist of narrow beds. When 61 cm wide beds were placed closer together than 5.9 m center‐to‐center, their storage volumes began to interact and loading rates had to be reduced accordingly. This approach to FF design for soils with perched seasonal water tables suggests that loading rates be determined either by effluent storage or by the rate of effluent movement out of the beds, whichever is most limiting.
Mobility of Agrochemicals through Soil from Two Tillage Systems
Authors: Levanon D. , Codling E. E. , Meisinger J. J. , Starr J. L.
Published: July 2010

The fate of agrochemicais is often greatly affected by the surface‐soil conditions in the field. This study was conducted to characterize the impact of two contrasting tillage systems on the movement of agrochemicals in soil. The two tillage systems were plow‐tillage (PT) and no‐tillage (NT) for corn (Zea mays L.) production. The study included incubation and leaching of undisturbed soil columns and disturbed soil samples from 16‐yr plots subject to the two tillage regimes. The agrochemicals used in the study were NH4NO3, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine‐2,4 diamine), carbofuran (2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranyl methylcarbamate), diazinon (0,0‐ diethyl‐O‐(6‐methyl‐ 2(1‐methethyl)‐4‐pryamidinyl phosphor‐ othioate), and metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐metoxy‐1‐methylethyl) acetamide). The results of this study show greater ponded flow movement of all agrochemicais in soils under PT vs. NT conditions. Strong evidence was found for preferential flow through the soil, with the chemicals by‐passing much of the soil‐matrix under recently plowed soils as well as NT soils. Nitrate leaching was significantly greater under PT than NT, apparently due to greater mineralizing activity of the PT soil compared with the NT soil. The pesticide movement also tended to be greater under PT than NT. Caution should be exercised in generalizing to field conditions, but these data suggest that there can be greater leaching losses of surface‐applied agrochemicals to groundwater under PT than under NT.
A Zero‐Tension Sampler for the Collection of Soil Water in Macropore Systems
Authors: Simmons K. E. , Baker D. E.
Published: July 2010

A zero‐tension sampler was designed for the collection of soil leachate at 1.2 m in the soil profile to determine the effects of dairy manure and NH3NO3 applications on water quality in soils possessing a macropore structure. Nitrate‐N concentrations in soil water collected from these samplers were compared with concentrations in soil water collected from conventional ceramic porous‐cup samplers. The zero‐tension samplers were constructed from 5‐cm polyvinyl chloride (PVC) pipe and installed at a 45° angle in the soil profile. This design minimized the amount of field excavation and the interruption of routine cultivation. On average, approximately 50% of the samplers contained solution after rainfall and the data were effective at demonstrating the effect of macropore flow on NO3‐N concentrations in the leachate. Nitrate‐N concentrations in soil water collected from porous‐cup samplers were consistently higher than those collected from zero‐tension samplers. Mean NO3‐N concentrations in soil water from porous‐cup and zero‐tension samplers ranged from approximately 5 to 60 mg L−1 and 0 to 20 mg L−1, respectively.
Sensitivity of Critical Load Estimates for Surface Waters to Model Selection and Regionalization Schemes
Authors: Holdren George R. , Strickland Timothy C. , Shaffer Paul W. , Ryan Patrick F. , Ringold Paul L. , Turner Robert S.
Published: July 2010

A critical load is the amount of atmospheric pollutant that can be deposited on a sensitive ecosystem without causing measurable, longterm degradation in ecosystem form or function. We compare several methods for making critical load estimates of SO4 deposition to lakes; these methods are among those identified by participants in the United Nations‐Economic Commission for Europe (UNECE) Convention on Long‐Range Transboundary Air Pollution. The models were originally developed to address surface water acidification issues. Critical loads are computed here as the levels of deposition required to reduce surface water acid neutralizing capacities (ANC) from present values to either 25 µeq L−1 or 0 µeq L−1. These end points were selected to provide a common basis for comparing critical load values obtained from the various models, and are not intended to provide definitive critical load estimates. Using the amount of deposition required to decrease steady‐state surface water ANC values from 25 to 0 µeq L−1, about 9 ± 2 kgSO4 ha−1 yr−1 in the northeastern USA as a basis for comparison, we find that models make significantly different projections regarding ecosystem sensitivites to deposition. For lakes with critical load values in the range of current deposition in the Northeast (i.e., 18–56 kg SO4 ha−1 yr−1), model results differ by as much as 82 kg SO4 ha−1 yr−1. Differences in results are observed not only between models, but within models when slightly different approaches are used for estimating certain parameters. The interpretation of model results depends strongly on how systems are grouped regionally. While the results suggest that reductions in deposition from current levels would reduce adverse effects in sensitive lakes, the magnitude and timing of the reductions necessary and the determination of appropriate population end points are decisions that will ultimately be made by risk managers rather than risk assessors.
Characterization of Wind Erosion Sediments in the Red River Valley of North Dakota
Authors: Cihacek L.J. , Sweeney M.D. , Deibert E.J.
Published: July 2010

Wind erosion is a serious problem in the Red River Valley of North Dakota. Wind erosion sediments were characterized to evaluate their potential as nonpoint source pollutants for surface water and shallow groundwater. Thirty‐four sites from the South Dakota border to the Canadian border were sampled to measure physical and chemical characteristics of displaced sediment and field soils. Collected sediments originated from fields with soils having silt loam, silty clay loam or silty clay textures. Sediments had >98% water‐stable aggregates and average NO−3‐N levels of 105 mg kg−1. Calcareous sediments (22 samples) were significantly higher in pH, NO−3‐N and electrical conductivity (EC), while noncalcareous sediments (12 samples) were higher in P and K. Soils from sugar beet (Beta vulgaris L.) and small grain fields tended to have higher NO−3‐N levels than fields with other crops or cropping practices. Agricultural chemical residues were detected and identified at two sample sites. A comparison of displaced sediments with field soils showed significant increases in NO−3‐N, P, K and EC in the sediments and a significant reduction in pH. Nearly 96% of the NO−3‐N could be leached out of the sediments in an initial leaching. Wind erosion sediments have the potential to be nonpoint sources of NO−3‐N and salinity for surface and groundwater.
Binding Mechanism of 2,4‐Dichlorophenoxyacetic Acid by Organo‐Clays
Authors: Hermosin M. C. , Cornejo J.
Published: July 2010

The interaction of the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) with decylammonium‐montmorillonite (C10M) and decylammonium‐vermiculite (C10V) was studied by measuring 2,4‐D adsorption at different pH levels, and by preparing herbicide‐organic clay complexes which were characterized by x‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT‐IR). The adsorption of 2,4‐D at different pH values indicated that the undissociated form was preferentially adsorbed on C10M, whereas the anionic form was adsorbed by C10V. The adsorption of 2,4‐D was much greater for C10V than for C10M. X‐ray diffraction diffractograms and FT‐IR spectra of C10M did not show any changes after exposure to 2,4‐D, indicating adsorption on external surfaces by weak lyopbilic, aromatic ring‐alkylchain(tail), bond. The d001 values of the two C10V samples expanded after 2,4‐D exposure from 2.1 to 2.9 nm and from 2.4 to 3.3 nm, indicating interlayer adsorption of the herbicide. The FT‐IR spectrum of herbicide‐C10V complex showed the presence of a small amount of the molecular form of 2,4‐D weakly adsorbed on external surfaces by lyophilic (ring‐tail) bonding, but most of the herbicide molecules were adsorbed at the interlayer spaces by hydrogen bonds between carbonyl group (vc=0 at 1634 cm−1) of 2,4‐D and ammonium group of the interlayer organic cations. Some 2,4‐D molecules in C10V complex appeared to be dissociated as suggested by two bands at 1590 and 1330 cm−1, which corresponded to the unsymmetrical and symmetrical vibrations, respectively, of the COO− groups.
Starch‐Encapsulated Atrazine: Efficacy and Transport
Authors: Schreiber M. M. , Hickman M. V. , Vail G. D.
Published: July 2010

Current data indicate that pesticides are a contributor to the groundwater contamination problem, with the herbicide atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] one of the most commonly found contaminates. Reports indicate that the highest levels of atrazine found appear to be associated with the heavy spring rains following application of presently used commercial formulations (CF) of atrazine. This work reports the role of new starch encapsulated (SE) granular formulations of atrazine that significantly reduce the initial mobility of atrazine without appreciable loss of weed control efficacy. Leaching studies in the laboratory indicate that SE formulations reduced movement of atrazine by 70% compared to CF in both silty clay loam and sandy soils following a 75 mm h−1 simulated rainfall. Results from leaching of intact soil blocks with simulated rainfall of 40 mm h−1 for 2 h showed CF leached 80 and 60% more atrazine than the SE formulation from chisel and no‐till systems, respectively. Granular size of SE formulations can affect the rate of release. Starch‐encapsulated formulations gave good to excellent control of most weeds at 10 sites in six Midwest states during the 1990 and 1991 growing seasons and resulted in corn (Zea mays L.) yields equal to or better than with CF. Control of some large seeded weeds such as velvetleaf (Abutilon theophrasti Medic.) and cocklebur (Xanthium strumarium L.) was variable from site to site with both SE and CF. Starch‐encapsulated formulations offer an excellent potential technology advancement for significant reduction of atrazine and other pesticide contaminates of groundwater with minimal loss of efficacy.
Pesticides in Shallow Groundwater in the Delmarva Peninsula
Authors: Koterba M. T. , Banks W. S. L. , Shedlock R. J.
Published: July 2010

A regional study of the areal and depth distribution of pesticides in shallow groundwater in the Delmarva Peninsula of Delaware, Maryland, and Virginia was done to (i) relate the pesticides detected to landscape and shallow subsurface features, and (ii) evaluate aquifer vulnerability and the potential contamination of drinking‐water supplies. Water samples collected at 100 wells from 1988 to 1990 were analyzed for concentrations of 36 pesticides, four metabolites, and other constituents. The most commonly detected residues were atrazine, cyanazine, simazine, alachlor, metolachlor, and dicamba. Concentrations were low; few exceeded 3 µg L−1. Most detections correlate with the intensive use of these herbicides in three widely distributed and commonly rotated crops—corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and small grain—particularly if grown in well‐drained soils. Most detections occurred in samples collected from shallow wells screened within 10 m of the overlying water table. The shallow depth distribution of most residues is consistent with their suspected history of use (ca. 20 yr), and patterns in shallow groundwater flow in the surficial aquifer in the study area. The areal and depth distributions of detectable residues in groundwater did not correlate with a vulnerability index, nor any of the component scores developed to estimate that index using the DRASTIC method. The shallow depth of most detections also indicates why few samples from water‐supply wells in this study had measurable concentrations of pesticides; most supply wells are deeper than 10 m below the water table. The low number of contaminated samples from supply wells implies that deep groundwater currently (1992) used for drinking generally does not contain detectable pesticide residues.