bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acute toxicity of copper and silver toCeriodaphnia dubiain the presence of food
Authors: Kolts Jason M. , Boese Connie J. , Meyer Joseph S. 
Published: July 2006

AbstractFood is added to exposure solutions in cladoceran chronic toxicity tests and sometimes in acute toxicity tests, but its effects on the bioavailability of toxicants have not been studied extensively. We compared the toxicity of waterborne Ag and Cu to Ceriodaphnia dubia in the presence or absence of food (a mixture of a yeast–Cerophyll®–trout chow slurry and a green alga) in two series of acute toxicity tests. In the first series, we added food to Ag or Cu exposure solutions 0, 30, 60, or 120 min before transferring C. dubia into the solutions. In the second series, we exposed C. dubia to waterborne Ag or Cu for 30, 60, and 120 min in the absence of food. Adding food before transferring C. dubia into the exposure solutions greatly decreased the toxicity of Ag, but had less effect on the toxicity of Cu. In contrast, adding food after transferring C. dubia into the exposure solutions did not alter the toxicity of Ag considerably and did not alter the toxicity of Cu as much as the reverse sequence. Median effects concentrations (EC50s) for 30-, 60-, and 120-min unfed Ag tests were within the range of EC50s for 48-h unfed Ag tests, suggesting most uptake that contributes to acute Ag toxicity to C. dubia occurs within the first 30 to 60 min. However, uptake that contributes to acute Cu toxicity to C. dubia appears to occur over more than 2 h. Therefore, standard food decreases the toxicity of waterborne Ag and Cu to C. dubia, and the timing of adding food to exposure solutions is especially important in Ag tests.
Genotoxicity of polar fractions from a herbicide-contaminated soil does not correspond to parent contaminants
Authors: Kubátová Alena , Dronen Laura C. , Hawthorne Steven B. 
Published: July 2006

Abstract
Fractionation with biological and chemical analysis has been proposed to characterize the risk associated with complex samples. Thus, we have employed hot pressurized water for fractionating a herbicide-contaminated soil. Genotoxicity was found in polar and midpolarity fractions extracted from a historically herbicide-contaminated soil. However, the parent herbicides as well as organic solvent extracts (consisting of herbicides) were not genotoxic. Thus, polar organics formed by natural degradation of herbicides may be responsible for the genotoxic response. For correct assessment of the toxicity of complex matrices such as soils, both contaminated and uncontaminated samples need to be studied for their toxicological impact.
A comparison of the effects of single and repeated exposure to an organophosphate insecticide on acetylcholinesterase activity in mammals
Authors: Long Sara M. , Dawson Alistair , Shore Richard F. 
Published: July 2006

AbstractExposure to organophosphate (OP) pesticides can occur in free-living mammals in treated areas. Risk to nontarget animals from OPs usually is assessed with acute exposure data, but exposure of wild animals is likely to be intermittent and chronic. We compared the effects of single or repeated (hourly and daily) exposure to dimethoate on acetylcholinesterase (AChE) activity in laboratory mice to assess the suitability of standard laboratory tests for assessing risk. Mice were exposed either to a single dose (10 or 30 mg/kg) or to short-term repeated (three hourly doses of 10 mg/kg) intraperitoneal doses of dimethoate, and brain and serum AChE activity were measured. No significant difference was found in the degree of inhibition of AChE activity following acute and short-term repeated exposure. In a second experiment, mice were given three daily doses of 10 or 20 mg/kg of dimethoate, and both AChE activity and hepatic cytochrome P450 enzyme activity were measured. Daily exposure resulted in a dose-dependent decline in brain and serum AChE activity, and inhibition increased progressively with successively repeated exposures. However, this effect was relatively small compared to the effect of dose. Cytochrome P450 enzyme activity (CYP2B) was inhibited in the dimethoate-dosed mice. Our results indicate that acute dose–response toxicity studies are suitable models for predicting the likely occurrence of adverse effects from either short- or longer-term exposure of wild mammals to anticholinesterase compounds. Likely differences in exposure pattern between the laboratory and the natural environment are unlikely to bias the predictive power of these studies significantly.
Comparison of selenium bioaccumulation in the clams Corbicula fluminea and Potamocorbula amurensis: A bioenergetic modeling approach
Authors: Lee Byeong-Gweon , Lee Jung-Suk , Luoma Samuel N. 
Published: July 2006

Abstract
Selenium uptake from food (assimilation efficiency) and dissolved phase (influx rate) as well as loss kinetics (efflux rate) were compared between two bivalves, Corbicula fluminea and Potamocorbula amurensis. The effects of salinity and temperature on these kinetic parameters for both clam species also were evaluated. The Asiatic clam, C. fluminea, more efficiently assimilated Se associated with algae (66–87%) than Se associated with oxic sediments (20–37%). However, no consistent difference was found between Se assimilation efficiencies from both food types (19–60%) for P. amurensis. The temperature and salinity had a minor influence on the Se assimilation from ingested food. However, the effects of temperature and salinity were more evident in the uptake from dissolved sources. The influx rate of Se(IV) increased by threefold with the increase of temperature from 5 to 21°C for C. fluminea. The increase of salinity from 4 to 20 psu decreased the uptake rate constant (ku) of Se in P. amurensis from 0.011 to 0.005 L/g/h, whereas salinity change (0–8 psu) had a negligible effect on the Se influx rate of C. fluminea. The Se influx rate of P. amurensis decreased by half with the 3.5-fold increase in tissue dry weight. The rate constant of loss was greater for P. amurensis (0.029/d at 8 psu) than for C. fluminea (0.014/d at 0 psu and 0.01/d at 8 psu). A bioenergetic model suggests that dietary uptake is the dominant pathway for Se bioaccumulation in the two clams in San Francisco Bay and that interspecies differences in Se bioaccumulation can be explained by differences in food ingestion rates.
Isolation and partial characterization of proteins involved in maternal transfer of selenium in the western fence lizard (Sceloporus occidentalis)
Authors: Unrine Jason M. , Jackson Brian P. , Hopkins William A. , Romanek Christopher 
Published: July 2006

Abstract
Selenium from dietary exposure is efficiently transferred from mother to offspring in oviparous vertebrates, where it can cause severe teratogenic effects. We isolated and partially characterized proteins involved in maternal transfer of selenium in the oviparous lizard Sceloporus occidentalis using size-exclusion chromatography, inductively coupled plasma–mass spectrometry, and polyacrylamide gel electrophoresis. Selenium from dietary selenomethionine exposure was incorporated into at least three egg proteins. One of these proteins was lipovitellin. The other two proteins may be part of a previously unknown mechanism of maternal transfer of Se that is independent of vitellogenesis or albumin secretion. Our results suggest at least three pathways for maternal transfer of Se in vertebrates that may vary in importance depending on the species.
Inhibition of aquatic toxicity of pyrethroid insecticides by suspended sediment
Authors: Yang Weichun , Spurlock Frank , Liu Weiping , Gan Jianying 
Published: July 2006

Abstract
The use of pyrethroid insecticides is increasing in both agricultural and urban environments. Although pyrethroids display very high acute toxicities to water column organisms in laboratory tests, environmental water samples typically contain suspended sediment (SS) that can reduce the freely dissolved concentration of pyrethroids, hence their bioavailability. Consequently, phase distribution could play an important role in pyrethroid aquatic toxicology. In this study, we evaluated the effect of SS on the acute toxicity of four widely used pyrethroid insecticides to Ceriodaphnia dubia. In all assays, median lethal concentrations (LC50s) consistently increased with increasing SS, demonstrating the pronounced inhibitory effects of SS on pyrethroid toxicity. The LC50s in the 200 mg/L SS solutions were 2.5 to 13 times greater than those measured in sediment-free controls. Solid-phase microextraction (SPME) was used to determine the apparent distribution coefficient Kd for the pyrethroids in the water samples. Under the assumption that only the freely dissolved fraction is bioavailable, the measured Kd was used to predict C. dubia LC50s in the water samples. The predicted LC50s were within a factor of two of the measured values for 95% of the treatments. Results from this study suggest that the inhibitory effect of SS can be highly significant and must be considered in estimating exposures to pyrethroids in aquatic systems. The SPME methodology could be used effectively to measure bioavailable concentration and to predict the actual ecotoxicologic effects of pyrethroids.
Land Use Change Effects on Forest Carbon Cycling Throughout the Southern United States
Authors: Woodbury Peter B. , Heath Linda S. , Smith James E. 
Published: July 2006

ABSTRACTWe modeled the effects of afforestation and deforestation on carbon cycling in forest floor and soil from 1900 to 2050 throughout 13 states in the southern United States. The model uses historical data on gross (two‐way) transitions between forest, pasture, plowed agriculture, and urban lands along with equations describing changes in carbon over many decades for each type of land use change. Use of gross rather than net land use transition data is important because afforestation causes a gradual gain in carbon stocks for many decades, while deforestation causes a much more rapid loss in carbon stocks. In the South‐Central region (Texas to Kentucky) land use changes caused a net emission of carbon before the 1980s, followed by a net sequestration of carbon subsequently. In the Southeast region (Florida to Virginia), there was net emission of carbon until the 1940s, again followed by net sequestration of carbon. These results could improve greenhouse gas inventories produced to meet reporting requirements under the United Nations Framework Convention on Climate Change. Specifically, from 1990 to 2004 for the entire 13‐state study area, afforestation caused sequestration of 88 Tg C, and deforestation caused emission of 49 Tg C. However, the net effect of land use change on carbon stocks in soil and forest floor from 1990 to 2004 was about sixfold smaller than the net change in carbon stocks in trees on all forestland. Thus land use change effects and forest carbon cycling during this period are dominated by changes in tree carbon stocks.
Soil Organic Carbon Sequestration in Cotton Production Systems of the Southeastern United States
Authors: Causarano H. J. , Franzluebbers A. J. , Reeves D. W. , Shaw J. N. 
Published: July 2006

ABSTRACTPast agricultural management practices have contributed to the loss of soil organic carbon (SOC) and emission of greenhouse gases (e.g., carbon dioxide and nitrous oxide). Fortunately, however, conservation‐oriented agricultural management systems can be, and have been, developed to sequester SOC, improve soil quality, and increase crop productivity. Our objectives were to (i) review literature related to SOC sequestration in cotton (Gossypium hirsutum L.) production systems, (ii) recommend best management practices to sequester SOC, and (iii) outline the current political scenario and future probabilities for cotton producers to benefit from SOC sequestration. From a review of 20 studies in the region, SOC increased with no tillage compared with conventional tillage by 0.48 ± 0.56 Mg C ha−1 yr−1 (H0: no change, p < 0.001). More diverse rotations of cotton with high‐residue‐producing crops such as corn (Zea mays L.) and small grains would sequester greater quantities of SOC than continuous cotton. No‐tillage cropping with a cover crop sequestered 0.67 ± 0.63 Mg C ha−1 yr−1, while that of no‐tillage cropping without a cover crop sequestered 0.34 ± 47 Mg C ha−1 yr−1 (mean comparison, p = 0.04). Current government incentive programs recommend agricultural practices that would contribute to SOC sequestration. Participation in the Conservation Security Program could lead to government payments of up to $20 ha−1 Current open‐market trading of C credits would appear to yield less than $3 ha−1, although prices would greatly increase should a government policy to limit greenhouse gas emissions be mandated.
Effects of Land Use on Soil Inorganic Carbon Stocks in the Russian Chernozem
Authors: Mikhailova Elena A. , Post Christopher J. 
Published: July 2006

ABSTRACTLittle is known about changes in soil inorganic carbon (SIC) stocks with depth and with land use in grassland ecosystems. This study was conducted to determine SIC stocks under different management regimes in the Mollisol, one of the typical soils in grasslands. Four sites were sampled: a native grassland field (not cultivated for at least 300 yr), an adjacent 50‐yr continuous fallow field, a yearly cut hay field in the V.V. Alekhin Central‐Chernozem Biosphere State Reserve in the Kursk region of Russia, and a continuously cropped field in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as fine‐silty, mixed, frigid Pachic Hapludolls. Significant differences occurred in SIC stocks between cultivated and grassland soil. The inorganic carbon stocks in the top 2 m were 107 Mg ha−1for the native grassland, 91 Mg ha−1for the yearly cut hay field, 242 Mg ha−1for the continuously cropped field, and 196 Mg ha−1for the 50‐yr continuous fallow. The SIC was in the form of calcium carbonate and was mostly stored below the 1‐m depth. The largest difference between inorganic carbon stocks was observed between the continuously cropped field and native grassland. The increase in inorganic carbon in the continuously cropped field and continuous fallow was attributed to initial cultivation and fertilization. Soil inorganic carbon in Mollisols is not accounted for in the current global carbon estimates.
Effects of Land Use on Soil Respiration
Authors: Carlisle Eli A. , Steenwerth Kerri L. , Smart David R. 
Published: July 2006

ABSTRACTWe examined constraints on soil CO2 respiration in natural oak woodlands, and adjacent vineyards that were converted approximately 30 yr ago from oak woodlands, in the Oakville Region of Napa Valley, California. All sites were located on the same soil type, a Bale (variant) gravelly loam (fine‐loamy, mixed, superactive, thermic Cumulic Ultic Haploxeroll) and dominated by C3 vegetation. Seasonal soil CO2 efflux was greatest at the oak woodland sites, although during the summer drought the rates of soil CO2 efflux measured from oak sites were generally similar to those measured from the vineyards. Soil profile CO2 concentrations at the oak woodland sites were lower below 15 cm despite higher CO2 efflux rates. Soil gas diffusion coefficients for oak sites were larger than for vineyard sites, and this indicated that the apparent discrepancy in soil profile carbon dioxide concentration ([CO2]) may be caused by a diffusion limitation. Soil profile [CO2] and δ13C values showed substantial temporal changes over the course of a year. Vineyard soil CO2 was more depleted in 13CO2 below 25 cm in the soil profile during the active growing season as indicated by more negative δ13C ratios. This result indicated that different C sources were being oxidized in vineyard soils. Annual C losses were less from vineyard soils (7.02 ± 0.58 Mg C ha−1 yr−1) as compared to oak soils (15.67 ± 1.44 Mg C ha−1 yr−1), and both were comparable to losses reported in previous investigations.
DAYCENT National‐Scale Simulations of Nitrous Oxide Emissions from Cropped Soils in the United States
Authors: Del Grosso S. J. , Parton W. J. , Mosier A. R. , Walsh M. K. , Ojima D. S. , Thornton P. E. 
Published: July 2006

ABSTRACTUntil recently, Intergovernmental Panel on Climate Change (IPCC) emission factor methodology, based on simple empirical relationships, has been used to estimate carbon (C) and nitrogen (N) fluxes for regional and national inventories. However, the 2005 USEPA greenhouse gas inventory includes estimates of N2O emissions from cultivated soils derived from simulations using DAYCENT, a process‐based biogeochemical model. DAYCENT simulated major U.S. crops at county‐level resolution and IPCC emission factor methodology was used to estimate emissions for the approximately 14% of cropped land not simulated by DAYCENT. The methodology used to combine DAYCENT simulations and IPCC methodology to estimate direct and indirect N2O emissions is described in detail. Nitrous oxide emissions from simulations of presettlement native vegetation were subtracted from cropped soil N2O to isolate anthropogenic emissions. Meteorological data required to drive DAYCENT were acquired from DAYMET, an algorithm that uses weather station data and accounts for topography to predict daily temperature and precipitation at 1‐km2 resolution. Soils data were acquired from the State Soil Geographic Database (STATSGO). Weather data and dominant soil texture class that lie closest to the geographical center of the largest cluster of cropped land in each county were used to drive DAYCENT. Land management information was implemented at the agricultural–economic region level, as defined by the Agricultural Sector Model. Maps of model‐simulated county‐level crop yields were compared with yields estimated by the USDA for quality control. Combining results from DAYCENT simulations of major crops and IPCC methodology for remaining cropland yielded estimates of approximately 109 and approximately 70 Tg CO2 equivalents for direct and indirect, respectively, mean annual anthropogenic N2O emissions for 1990–2003.
Carbon Banks
Authors: Esuola Adeyemi G. , Weersink Alfons 
Published: July 2006

ABSTRACTCarbon sequestration is one of the options that can be used to reduce atmospheric carbon, but its use in an offset market is complicated by the temporary nature of sequestered carbon and the risks associated with carbon release and price. In this paper a carbon bank is proposed to handle these problems. The bank is both an aggregator and a risk bearer. Sink generators deposit their credits with the bank and are paid for maintaining their “savings” with the bank. The carbon bank is also the source where large‐scale emitters can come and buy either a temporary or permanent credit and pay the bank in return for the credit and services provided. The advantages of the bank over alternative institutional designs include lower transaction costs, flexible carbon credits and price, and lower risk to risk‐averse parties. The carbon bank could be an effective means to deal with many of the unresolved issues within the forthcoming Canadian offset system.
Long‐Term Cropping System Effects on Carbon Sequestration in Eastern Oregon
Authors: Machado Stephen , Rhinhart Karl , Petrie Steve 
Published: July 2006

ABSTRACTSoil organic carbon (SOC) has beneficial effects on soil quality and productivity. Cropping systems that maintain and/or improve levels of SOC may lead to sustainable crop production. This study evaluated the effects of long‐term cropping systems on C sequestration. Soil samples were taken at 0‐ to 10‐, 10‐ to 20‐, 20‐ to 30‐, and 30‐ to 40‐cm soil depth profiles from grass pasture (GP), conventional tillage (CT) winter wheat (Triticum aestivumL.)–fallow (CTWF), and fertilized and unfertilized plots of continuous winter wheat (WW), spring wheat (SW), and spring barley (Hordeum vulgareL.) (SB) monocultures under CT and no‐till (NT). The samples were analyzed for soil organic matter (SOM) and SOC was derived. Ages of experiments ranged from 6 to 73 yr. Compared to 1931 SOC levels (initial year), CTWF reduced SOC by 9 to 12 Mg ha−1in the 0‐ to 30‐cm zone. Grass pasture increased SOC by 6 Mg ha−1in the 0‐ to 10‐cm zone but decreased SOC by 3 Mg ha−1in the 20‐ to 30‐cm zone. Continuous CT monocultures depleted SOC in the top 0‐ to 10‐cm zone and the bottom 20‐ to 40‐cm zone but maintained SOC levels close to 1931 SOC levels in the 10‐ to 20‐cm layer. Continuous NT monocultures accumulated more SOC in the 0‐ to 10‐cm zone than in deeper zones. Total SOC (0‐ to 40‐cm zone) was highest under GP and continuous cropping and lowest under CTWF. Fertilizer increased total SOC only under CTWW and CTSB by 13 and 7 Mg ha−1in 13 yr, respectively. Practicing NT for only 6 yr had started to reverse the effect of 73 yr of CTWF. Compared to CTWF, NTWW and NTSW sequestered C at rates of 2.6 and 1.7 Mg ha−1yr−1, respectively, in the 0‐ to 40‐cm zone. This study showed that the potential to sequester C can be enhanced by increasing cropping frequency and eliminating tillage.
Carbon Storage by Urban Soils in the United States
Authors: Pouyat Richard V. , Yesilonis Ian D. , Nowak David J. 
Published: July 2006

ABSTRACTWe used data available from the literature and measurements from Baltimore, Maryland, to (i) assess inter‐city variability of soil organic carbon (SOC) pools (1‐m depth) of six cities (Atlanta, Baltimore, Boston, Chicago, Oakland, and Syracuse); (ii) calculate the net effect of urban land‐use conversion on SOC pools for the same cities; (iii) use the National Land Cover Database to extrapolate total SOC pools for each of the lower 48 U.S. states; and (iv) compare these totals with aboveground totals of carbon storage by trees. Residential soils in Baltimore had SOC densities that were approximately 20 to 34% less than Moscow or Chicago. By contrast, park soils in Baltimore had more than double the SOC density of Hong Kong. Of the six cities, Atlanta and Chicago had the highest and lowest SOC densities per total area, respectively (7.83 and 5.49 kg m−2). On a pervious area basis, the SOC densities increased between 8.32 (Oakland) and 10.82 (Atlanta) kg m−2 In the northeastern United States, Boston and Syracuse had 1.6‐fold less SOC post‐ than in pre‐urban development stage. By contrast, cities located in warmer and/or drier climates had slightly higher SOC pools post‐ than in pre‐urban development stage (4 and 6% for Oakland and Chicago, respectively). For the state analysis, aboveground estimates of C density varied from a low of 0.3 (WY) to a high of 5.1 (GA) kg m−2, while belowground estimates varied from 4.6 (NV) to 12.7 (NH) kg m−2 The ratio of aboveground to belowground estimates of C storage varied widely with an overall ratio of 2.8. Our results suggest that urban soils have the potential to sequester large amounts of SOC, especially in residential areas where management inputs and the lack of annual soil disturbances create conditions for net increases in SOC. In addition, our analysis suggests the importance of regional variations of land‐use and land‐cover distributions, especially wetlands, in estimating urban SOC pools.