Journal of Environmental Quality 31:1-5 (2002)
© 2002 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
EXECUTIVE SUMMARIES
This Issue in Journal of Environmental Quality
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Ag Phosphorus and Water Quality Are Interconnected (LEASEQ)
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Soluble reactive phosphorus (SRP) in northwestern Ohio river water has declined during the past 20 years in response to decreased applications of fertilizer P. Calhoun now compares current levels of soluble P in the soil surface horizons with historical soil survey samples of original soluble P concentrations. Results show that soluble P in the soil is controlled by a combination of fertilizer and tillage management, soil properties, and landscape factors interacting over time. The change in soluble P in the soil is not as responsive to fertilizer P sales as is SRP in river water. The close relationship between fertilizer P sales and river SRP suggests that a persistent, but declining, percentage of added P annually moves into the drainage system.
F.G. Calhoun (calhoun.2{at}osu.edu)
Relationships among Plant Available Phosphorus, Fertilizer Sales, and Water Quality in Northwestern Ohio. J. Environ. Qual. 31:38–46.
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Hot Blueberries from Radioactive Soils
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The natural uptake of radionuclides by plants can introduce contaminants into the human food chain. Morton et al. report that native blueberries concentrated the radionuclides differentially within the plants. Thorium (Th) concentrations were higher in leaves than in stems, while uranium (U) concentrations were nearly equal in both tissues. Uranium uptake was more related to soil properties than Th uptake, even though plants absorbed more Th than U. Thus, soil manipulations may be more effective in increasing plant uptake of U, as in phytoremediation. Thorium uptake seems to be more independent of soil properties, but may be more strongly affected by internal plant thresholds.
C.V. Evans (evansc{at}uwp.edu)
Natural Uranium and Thorium Distributions in Podzolized Soils and Native Blueberry. J. Environ. Qual. 31:155–162.
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Sulfur Linked to Toxic Methylmercury in Everglades
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The process of sulfate reduction to sulfide in oxygen-depleted wetland sediments is linked to the production of toxic methylmercury. In the Florida Everglades, moderate sulfate concentrations stimulate methylmercury production, but high sulfide buildup inhibits the process. Bates et al. describe spatial patterns in sulfate concentrations and sulfur isotopic ratios in surface water, ground water, and rainwater, and report that the excess sulfur originates from the Everglades Agricultural Area and enters the wetlands by way of the canals. Methylmercury hot spots in the wetlands coincide with the downgrade edge of the sulfate plume. These findings suggest that sulfur, generally considered to be environmentally innocuous, could be a problem when used as a soil amendment near oxygen-depleted wetlands.
A.L. Bates (abates{at}usgs.gov)
Tracing Sources of Sulfur in the Florida Everglades. J. Environ. Qual. 31:287–299.
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Twenty Years of Change: Agriculture and Water Quality (LEASEQ)
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Four related articles, written by the same group of authors, are from "The Lake Erie Agricultural Systems for Environmental Quality" (LEASEQ) project and are summarized below.
1. Nonpoint-source pollution is increasingly recognized as a primary cause of water quality decline, and agricultural land use is often identified as the main contributor to this problem in rural areas. Is such impairment irreversible? In the first of a series of papers in this issue, Richards et al. introduce a 20-year retrospective study of the relationships among agricultural land use, management, economics, soil and water quality, climate, and related factors in the Lake Erie watershed in northwest Ohio: the LEASEQ project.
2. They report that agricultural land use dominates the LEASEQ study area in northwestern Ohio and is one of the most important influences on water quality. Major crops are corn, soybean, and wheat. In the 20 years of this study, the number of farms decreased, but average farm size increased correspondingly. Acreage in soybean increased while that in wheat decreased; land area yields of all three crops increased. Nutrient applications increased until the early 1980s and then decreased again.
3. Major improvements in water quality in the LEASEQ study area were documented over the 20 years of the project. Phosphorus, the target of management efforts to rehabilitate Lake Erie, showed the largest decreases. Soluble phosphorus concentrations declined by more than 75%, and total phosphorus declined by about 40%. Total Kjeldahl nitrogen (organic nitrogen + ammonia) decreased by about 25%. Nitrate nitrogen was unchanged or increased slightly. These changes are due mostly to changes in agricultural practices.
4. Between 1975 and 1995, annual phosphorus inputs decreased due to reductions in fertilizer and manure inputs. Annual outputs increased due to increasing crop yields. Net phosphorus accumulation rates decreased substantially, but remained positive throughout the period. This budget analysis suggests that riverine phosphorus export should have increased throughout the study period, with smaller increases in more recent years. Substantial decreases in phosphorus export reflect the adoption of practices that minimize losses of recently applied phosphorus fertilizer in surface runoff, coupled with changes in winter weather conditions.
R.P. Richards
(prichard{at}heidelberg.edu)
1. The Lake Erie Agricultural Systems for Environmental Quality Project: An Introduction. J. Environ. Qual. 31: 6–16.
2. Trends in Agriculture in the LEASEQ Watersheds, 1975–1995. J. Environ. Qual. 31:17–24.
3. Trends in Water Quality in LEASEQ Rivers and Streams (Northwestern Ohio), 1975–1995. J. Environ. Qual. 31:90–96.
4. Phosphorus Budgets and Riverine Phosphorus Export in Northwestern Ohio Watersheds. J. Environ. Qual. 31: 96–108.
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Evaluating Lake Erie Pollution Abatement Programs (LEASEQ)
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Over the past 25 years, state and federal government agencies have made a sustained commitment to improving water quality in Lake Erie and its tributaries. Forster and Rausch report that although these programs provided the impetus for many farmers to become better stewards of soil and water resources, questions remain about how efficiently funds were allocated. Their report is based on an examination of government agricultural pollution abatement programs in the watersheds of two prominent Lake Erie tributaries, the Maumee and Sandusky Rivers. They summarized total project expenditures and evaluated the cost effectiveness of these actions (i.e., cost per tonne of soil saved).
D.L. Forster
(dforster{at}postbox.acs.ohio-state.edu)
Evaluating Agricultural Nonpoint-Source Pollution Programs in Two Lake Erie Tributaries. J. Environ. Qual. 31: 24–31.
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Conservation Tillage Evaluated for Lake Erie Basin Farms (LEASEQ)
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Rapid voluntary adoption of conservation tillage practices has occurred in the Lake Erie Basin. Forster describes two approaches to examine the effects of conservation tillage practices on farms' economic performance. First, a statistical approach is used to investigate the effects of rotation and tillage system on farm economic performance, using data from a sample of representative farms in the Lake Erie Basin. Second, a bioeconomic simulation model is developed that links alternative farming practices with production, profits, pollutants, and farm size. Conclusions from these two approaches, statistical analyses and simulation modeling, differ, and an explanation for these differing conclusions is presented.
D.L. Forster
(dforster{at}postbox.acs.ohio-state.edu)
Effects of Conservation Tillage on the Performance of Lake Erie Basin Farms. J. Environ. Qual. 31:32–37.
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Pollutant Export Picture Muddied by Soil Type (LEASEQ)
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Soil variability in watersheds accounts for much of the confusion in evaluating downstream water quality data and determining sources of nonpoint pollution. In a review of upstream water quality studies in northwestern Ohio, Calhoun finds that the soil series explains variation in pollutant export from rural landscapes. Clayey, lake plain soils that are not tile-drained are greater sources of suspended solids than are the loamy soils found on moraines. Tile-drained lake plain soils export more nutrients such as nitrates and phosphates, in solution, than do the better drained, sloping moraine soils. However, the tile-drained soils of the lake plains export substantially less sediment than do the non-tile-drained soils. He suggests that greater attention be given to the lake plains of the Maumee and Sandusky River basins as pollutant sources and as targets for improved agricultural management practices. The assumption that sloping moraine areas are the primary source of pollutants should be reexamined based on this review.
F.G. Calhoun (calhoun.2{at}osu.edu)
Soils, Water Quality, and Watershed Size: Interactions in the Maumee and Sandusky River Basins of Northwestern Ohio. J. Environ. Qual. 31:47–53.
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Soil Erosion and Sediment Sources in an Ohio Watershed (LEASEQ)
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Reducing sediment loads to improve water quality requires a better understanding of how different agricultural practices influence erosion and sediment transport. Matisoff et al. show that the fallout radionuclides 7Be, 210Pb, and 137Cs exhibit unique soil distributions resulting not only from their respective fallout histories and half-lives, but also in accordance with agricultural practices. They used the stream flux of each radionuclide and their soil distributions to calculate a uniform depth of soil erosion. Results from one Lake Erie tributary watershed show that the average erosion depth from a single storm event was 11.4 ± 5.1 µm for a traditionally tilled sub-basin compared with 4.0 ± 3.4 µm for a comparably sized nontilled sub-basin.
G. Matisoff (gxm4{at}po.cwru.edu)
Soil Erosion and Sediment Sources in an Ohio Watershed using Beryllium-7, Cesium-137, and Lead-210. J. Environ. Qual. 31:54–61.
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Sediment Transport Monitored in Lake Erie Watersheds (LEASEQ)
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The travel length and time of sediment particles eroded from the landscape have enormous implications for the evaluation of programs to reduce sediment-borne pollution. If the travel time is long, benefits from the adoption of prevention or remediation efforts cannot be expected to occur rapidly, and failure to observe benefits may reflect sediment lag time rather than program inadequacy. Matisoff et al. report that suspended sediment transport distances were longer in streams draining areas of no-till (19–26 km) than in the streams draining areas of conventional tillage (6–15 km). The transport distances are long relative to the lengths of the stream channel and indicate erosion control methods implemented in the watershed should be reflected quickly in downstream waters. They used kinematic wave analysis and fallout radionuclide tracers to determine particle transport distances in thunderstorm runoff in two agricultural watersheds.
G. Matisoff (gxm4{at}po.cwru.edu)
Radionuclides as Indicators of Sediment Transport in Agricultural Watersheds that Drain to Lake Erie. J. Environ. Qual. 31:62–72.
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Teflon Soil Solution Sampler Adsorbs Heavy Metals
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Monitoring heavy metals in the soil involves many considerations regarding the sampling technique and changes in the soil solution composition caused by the soil solution sampler. Adsorption and desorption reactions between the sampler material and the soil solution is very important. Andersen et al. describe the adsorption of Cd, Cu, Ni, and Zn to a poly(tetrafluorethene) soil solution sampler at low concentrations for different pH levels and ionic strengths. Adsorption of Cd, Ni, and Zn is generally low, being lowest at low solution pH and high ionic strength. In contrast, adsorption of Cu to the sampler material is substantial for all solution pH and ionic strength levels tested, with almost all Cu passing through the sampler being adsorbed.
M.K. Andersen (man{at}kvl.dk)
Adsorption of Cadmium, Copper, Nickel, and Zinc to a Poly(tetrafluorethene) Porous Soil Solution Sampler. J. Environ. Qual. 31:168–175.
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Reducing Uncertainty of Heavy Metal Accumulation Estimates
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Present agricultural land-use and atmospheric deposition can lead to heavy metal accumulation rates in soils that might violate soil quality standards in the future. To provide meaningful information for suitable preventive measures, Keller et al. take into account uncertainties of input parameter in modeling cadmium and zinc balances for a region of about 100 km2 in Switzerland. They used the stochastical balance model PROTERRA-S to reveal large uncertainties of the heavy metal balances, i.e., standard deviation of the net metal fluxes were of the same order of magnitude as their average values. The study gave valuable insights for strategies to reduce heavy metal enrichment in soils, and for reducing uncertainty in balances by further investigations to determine highly sensitive parameters more accurately.
A. Keller
(armin.keller{at}ito.umnw.ethz.ch)
Assessment of Uncertainty and Risk in Modeling Regional Heavy-Metal Accumulation in Agricultural Soils. J. Environ. Qual. 31:175–187.
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Forage Regrowth Reduces Phosphorus Runoff
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Runoff during intense rainstorms on sloping agricultural landscapes frequently contains dissolved or soil-attached phosphorus that can promote the growth of aquatic weeds or algae. Grasses, or other forages, are normally used to reduce phosphorus in runoff by maintaining vegetative cover, filtering soil out from rainwater runoff, or by facilitating water infiltration into the soil profile. The use of annual broadcast phosphorus fertilization on such perennial forages, coupled with intense defoliation through machinery or livestock, suggests that management practices could greatly affect phosphorus losses. Using simulated rainfall, Zemenchik et al. report that under such fertilization regimes, species selection was not nearly as effective in reducing runoff phosphorous loss as was avoiding excessive defoliation by maintaining at least 1.5 Mg ha-1 of forage biomass on landscape.
R.A. Zemenchik
(rob.zemenchik{at}cnh.com)
Bioavailable Phosphorus in Runoff from Alfalfa, Smooth Bromegrass, and Alfalfa–Smooth Bromegrass. J. Environ. Qual. 31:280–286.
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Gas Permeability of Films
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Plastic films are used in a wide variety of applications for the exclusion or containment of water vapor and other gases. The permeability of plastic films to gases is of particular concern in food packaging and in agricultural fumigation. Papiernik et al. present a method to determine the permeability of plastic films, which is independent of the concentration gradient, using a sealed static chamber to monitor gas diffusion across a film. They provide a detailed description of an apparatus suitable for the measurement of mass transfer coefficients. Previous methods to measure film permeability produced a parameter that was dependent on the concentration gradient maintained across the film.
S.K. Papiernik
(spapiernik{at}ussl.ars.usda.gov)
An Apparatus for Measuring the Gas Permeability of Films. J. Environ. Qual. 31:358–361.
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Molybdenum Immobilized under Reducing Conditions
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Constructed wetlands have recently been investigated as a remediation method for trace element contaminated water. However, the fate of some trace elements under such conditions is unknown. Using an in-situ method, Fox and Doner show that iron-coated sand in wetland sediments is an important sink for arsenic, molybdenum, and vanadium. For molybdenum, significant levels of accumulation occur in bulk sediments, with water depth and redox status strongly influencing the solubility of molybdenum. These results indicate the importance of oxidation–reduction status on the mobility and accumulation of molybdenum in wetland systems and underscore the importance of iron minerals for trace element retention, even in reducing environments.
H.E. Doner
(doner{at}nature.berkeley.edu)
Trace Element Retention and Release on Minerals and Soil in a Constructed Wetland. J. Environ. Qual. 31: 331–338.
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Pesticide Leaching Predictions Are Uncertain
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Pesticide leaching models are used to guide important decisions such as the placement of crop protection products on the market. Dubus and Brown report that modeled predictions of pesticide losses by leaching are influenced most by parameters related to sorption and degradation and, that under specific circumstances, losses can also be greatly affected by changes in hydrological properties of the soil. They investigated the sensitivity of the preferential flow MACRO using two methods (one-at-a-time and Monte Carlo sensitivity analyses) and four base-case scenarios (two pesticides, two soils). Taking the uncertainty of the most sensitive parameters into account in the modeling is a priority to enable robust decision-making in pesticide registration.
I.G. Dubus (i.dubus{at}cranfield.ac.uk)
Sensitivity and First-Step Uncertainty Analyses for the Preferential Flow Model MACRO. J. Environ. Qual. 31: 227–240.
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Aggregation State Alters Atrazine Residue Release
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The persistence of atrazine residues in soils has been attributed to the incorporation of the pesticide into the natural carbon pool. Consequently, the remobilization and fate of atrazine residues are related to the turnover of soil organic matter. Munier-Lamy et al. show that the mineralizations of soil organic matter and atrazine residues have similar decomposition patterns. Results suggest that the aggregation state of the sample is important in the release of atrazine, and also in the formation of bound residues.
C. Munier-Lamy
(munier{at}cpb.cnrs-nancy.fr)
Degradation of 14C-Atrazine Bound Residues in Brown Soil and Rendzina Fractions. J. Environ. Qual. 31:241–247.
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Copper and Zinc Speciation in Soil–Sludge Mixes
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Vulkan et al. have characterized the chemical species of zinc (Zn) and copper (Cu) in the soluble fractions of soil–sludge mixtures with respect to their charge, molecular weight, and stoichiometry using ion exchange resin and gel chromatography procedures. Copper in the water extracts of the sludge–sand mixtures was found almost exclusively in low molecular weight (below 1000 Da) complexes and mainly as negatively charged species throughout an incubation period of 100 days. Zinc tended to form zwitter ions (chemical forms). Complexation capacity of the DOC in the sludge water extract, extrapolated to infinite dilution, was 8.75 M Cu kg-1 DOC.
R. Vulkan (rayav{at}bgumail.bgu.ac.il)
Copper and Zinc Speciation in the Solution of a Soil–Sludge Mixture. J. Environ. Qual. 31:193–203.
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Water Table Control Alters Herbicide Loss
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The movement of herbicides from points of application to waterways is affected by cultural practices and environmental factors. Tile drainage may reduce the amount of herbicide in runoff but resulting losses are still unacceptable. Controlled drainage may function to preserve rain in the soil profile where it can best benefit the growing crop. Gaynor et al. found no differences in herbicide loss when tile drainage was controlled at a depth of 30 cm from the soil surface compared to free drainage in tile at a 60-cm depth. Controlled drainage using subsurface irrigation at a 30-cm depth promoted surface runoff and increased herbicide loss as a result of the reduced soil water storage capacity. Controlled drainage with subsurface irrigation increased soil dissipation of metribuzin and loss of des-ethyl atrazine. Water table control had no effect on residues of atrazine or metolachlor in soil.
J.D. Gaynor (gaynorj{at}em.agr.ca)
Runoff and Drainage Losses of Atrazine, Metribuzin, and Metolachlor in Three Water Management Systems. J. Environ. Qual. 31:300–308.
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Methylene Chloride as a Carrier Solvent
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Methylene chloride is used as a carrier solvent to add phenanthrene to soil. Schwartz and colleagues have described the effect of methylene chloride quantity on mineralization kinetics, soil phospholipid fatty acid profiles, and phenanthrene. Methylene chloride dosages of 25 L/kg soil or more resulted in an enrichment of unsaturated phospholipid fatty acids, suggesting that soil microorganisms had adjusted their cell membranes in response to the solvent. The amount of methylene chloride used to spike phenanthrene in soil also affected the mineralization kinetics and spatial distribution of phenanthrene.
E. Schwartz (eschwart{at}du.edu)
Impact of Methylene Chloride on Microorganisms and Phenanthrene Mineralization in Soil. J. Environ. Qual. 31: 144–149.
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Plants Remove Metals from Polluted Soils
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It has been long known that certain plants, called hyperaccumulators, can absorb high levels of metals. Lasat reviews recent attempts to use these species in the removal of toxic metals from contaminated soil. The potential for metal phytoextraction depends upon complex metal–plant interactions that occur in the rhizosphere. A better understanding of chemical and biochemical mechanisms that govern metal availability for uptake and storage in plants can lead to improved agronomic practices and can enhance the effectiveness of phytoremediation for environmental cleanup. The review examines biological mechanisms relevant to metal phytoextraction, and suggests future research needs.
M. Lasat (lasat.mitch{at}epa.gov)
Phytoextraction of Toxic Metals: A Review of Biological Mechanisms. J. Environ. Qual. 31:109–120.
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Field Study on Pesticide Fate in Tropical Soils
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Although pesticide use is increasing in tropical agriculture, few comprehensive studies on soil pesticide dynamics under field conditions exist from these climates. Laabs et al. observed a fast dissipation of 10 pesticides in clayey and sandy tropical soils of Brazil. The leaching of pesticides was lower than expected based on temperate studies, with preferential flow transport as the dominant translocation process in the clayey soil, whereas matrix flow contributed significantly to pesticide transport in the sandy soils. Nevertheless, progressive leaching of some pesticides in the soil profile, and their occurrence in lysimeter water beyond the root zone, indicate that nonpoint ground water contamination may occur under tropical conditions despite the rapid disappearance of pesticides from the topsoil layer.
V. Laabs
(volker.laabs{at}uni-bayreuth.de)
Fate of Pesticides in Tropical Soils of Brazil under Field Conditions. J. Environ. Qual. 31:256–268.
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Toxicity of Acifluorfen Herbicide Is Photoinduced
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Sunlight plays an important role in the degradation of many pesticides. Scrano et al. describe photodegradation products in the degradation of the herbicide acifluorfen. They determined the role of free radicals in the photodegradation of acifluorfen, and proposed a radical mechanism. Although acifluorfen was not toxic to Daphnia magna S at a concentration of 0.1 mM, photoproducts derived from the herbicide after 36 h of UV-exposure were particularly harmful to the test organism. These results strengthen the hypothesis that derivative substances can sometimes be more toxic than the parent molecule.
S.A. Bufo (bufo{at}unibas.it)
Photochemistry and Photoinduced Toxicity of Acifluorfen, a Diphenyl-Ether Herbicide. J. Environ. Qual. 31: 268–274.
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Rainfall Determines Nutrient Loss
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Low precipitation rates will cause N to be temporarily immobilized in litter and soil base cations to be enriched, according to a report by Johnson et al. Alternatively, increased precipitation will cause a long-term depletion of soil base cations. Results are based on a study where soil leaching was examined after experimentally manipulating throughfall (+33%, -33%, and ambient) in a deciduous forest. Reduced throughfall resulted in reduced N leaching from and greater N immobilization in the O horizon. Additionally, greater concentrations of most ions in soil solutions obtained from the mineral soil horizons were observed. Although increased throughfall lead to greater N leaching, N content in the O horizon and mineral soil horizon soil solutions were not significantly affected.
D.W. Johnson (dwj{at}unr.edu)
The Effects of Throughfall Manipulation on Soil Leaching in a Deciduous Forest. J. Environ. Qual. 31:204–216.
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Phosphorus Leaching Losses from Two Grassland Soils
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Many sorbing substances such as phosphate (P) can be transported through soils very quickly by preferential flow. Sinaj et al. investigate P leaching induced by flood irrigation in a lysimeter study. The authors show that P is very mobile in the topsoil, but is restricted in subsoil due the subsoil's higher P-fixing capacity. As a result, the occurrence of preferential flow per se in the studied soils is not sufficient to cause large net losses of P, even with high exchangeability of P in topsoil. This study demonstrates the risks associated with assessing potential P losses on the basis of P mobility in the topsoil alone.
S. Sinaj (sokrat.sinaj@ipw.agrl.ethz.c)
Phosphorus Exchangeability and Leaching Losses from Two Grassland Soils. J. Environ. Qual. 31:319–330.
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Oxygen, Nitrate, and Sulfate Affect Emissions from Lake Sediments
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In many fresh waters, concentrations of oxygen and sulfate are decreasing, while nitrate concentrations are increasing. These shifts can affect the emissions of greenhouse gases from sediments. Liikanen et al. show that even small changes in the availability of electron acceptors in freshwater systems can alter the release rate of greenhouse gases and their global warming potentials (GWP). Reductions in oxygen and sulfate availability increase methane fluxes and GWP. However, decreased sulfate content in fresh waters also decrease carbon dioxide production. Nitrate loading reduces methane release but increases nitrous oxide production in sediments, causing a net decrease in GWP with low nitrate load but a net increase in GWP with high nitrate load.
A. Liikanen (Anu.Liikanen{at}uku.fi)
Gas Dynamics in Eutrophic Lake Sediments Affected by Oxygen, Nitrate, and Sulfate. J. Environ. Qual. 31:338–349.
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Organic Matter and Surfactants Determine Hydrocarbon Fate
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Natural and synthetic organic compounds are known to increase the apparent solubility of hydrophobic organic compounds, and they co-exist in natural water systems. Cho et al. report that the solubility of three polycyclic aromatic hydrocarbons in natural organic matter and anionic surfactant solution was lower than their solubility in natural organic matter solution alone. This is likely due to the fact that the cations that are released when the anionic surfactant dissociates may form ion pairs with acidic or phenolic groups associated with the natural organic matter. This underlies importance of the understanding of the characteristics of natural organic matter and surfactants in water.
J.-W. Park (jaepark{at}ewha.ac.kr)
Combined Effect of Natural Organic Matter and Surfactants on the Apparent Solubility of Polycyclic Aromatic Hydrocarbons. J. Environ. Qual. 31:275–280.
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Wetland Services Are a Bargain
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The role of wetlands in ameliorating surface water quality is well known, but the "cost" of this ecosystem service to the receiving wetland is unclear. Gustafson and Wang describe a linkage between the degraded surface waters coming from agricultural watersheds and an altered species composition in a priority conservation wetland in northern Vermont. The vegetation of the peripheral hardwood swamp forest, which forms a buffer for an ombrotrophic (rainfed, low nutrient) bog, had a greater proportion of the flora characterized by weedy species, and fewer characteristic bog species, than reference areas affected only by forested watersheds. These results suggest that stewardship of natural ecosystems requires a landscape-level perspective to protect long-term conservation values.
D. Wang (Deane.Wang{at}uvm.edu)
Effects of Agricultural Runoff on Vegetation Composition of a Priority Conservation Wetland, Vermont, USA. J. Environ. Qual. 31:350–357.
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Slope Length, Soil Type Determine Manure Phosphorus Loss
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Phosphorus (P) loss in overland flow varies with spatial distribution of soil P, land management, and hydrologic pathways. McDowell and Sharpley now describe the effects of upslope applications of manure on P losses in overland flow at varying distances down slope. Dissolved P concentrations in overland flow were related to the amount of clay transported in flow before, rather than after, manure application, due to the transport of larger, low-density particles. The P concentration in overland flow decreased with distance down slope, due to dilution rather than sorption of P by surface soil during flow. Ultimately, total P losses reflected the initial soil P concentration, even after manure application. Therefore, when applying manure to the landscape, the source position relative to slope length and initial soil P concentrations should both be considered when looking at areas of potential P loss within a watershed.
R. McDowell
(richard.mcdowell{at}agresearch.co.nz)
Phosphorus Transport in Overland Flow in Response to Position of Manure Application. J. Environ. Qual. 31:217–227.
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