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261.
A method based on SPME is described for assessing the gaseous dichlorvos concentration in confined atmospheres like a greenhouse after a pesticide application. Sampling was made by using SPME with PDMS fibres immersed into a 250 mL sampling flask into which air samples were dynamically pumped from the analysed atmosphere. Sampling duration was 40 min and samples were then analysed by GC-MS. Calibration was performed from a vapour saturated air sample and gas phase diluted samples, and this procedure afforded a curve with a regression coefficient (R2) higher than 0.98. The repeatability of these measurements was observed with an RSD of 2.5%. This analysis procedure was then applied for the determination of gaseous dichlorvos concentrations versus time, in the atmosphere of an experimental 8 m2 and 20 m3 greenhouse. The pesticide was sprayed according to real cultivation conditions and measurements were made from 2 up to 74 h after application affording observed concentrations in the range of decades and hundreds of microg m(-3) (corresponding limits of detection and quantification were found at the level of a few microg m(-3)). 相似文献
262.
A mass balance model was applied to simulate the long-term fate of PAHs in San Francisco Bay. The model treats the Bay as a single box with interacting water and sediment compartments, and includes loading, volatilization, outflow to the ocean, degradation, and burial in deep sediment. The estimated time required for loss of one-half of the mass in the Bay in the absence of loading ranged from 20 d for naphthalene to 5 yr for benzo(b)fluoranthene. Uncertainty analysis using Monte Carlo simulation indicated a high degree of influence and uncertainty for degradation rates, suggesting that improved estimates of degradation would significantly improve the predictive ability of the model. A comparison of model calculations to literature values suggested that external PAH loading to San Francisco Bay was at or above previous estimates of 3600 kgyr(-1), and that degradation in the Bay was within the range of commonly published estimates for high molecular weight PAHs (4.0 x 10(-5) to 4.0 x 10(-4)d(-1)). 相似文献
263.
264.
Jui-Der Liou Chih-Ping Chen W. Roy Breg John C. Hobbins Maurice J. Mahoney Teresa L. Yang-Feng 《黑龙江环境通报》1993,13(1):1-8
From September 1984 to April 1991, we performed cytogenetic analysis on fetal blood samples from 214 second-and third-trimester pregnancies. One hundred and thirty-four cases were referred to consider the possibility of chromosomal mosaicism following amniocyte studies. The confirmation rate of mosaicism is at 0 per cent (0/9), 1·4 per cent (1/70), and 40 per cent (22/55) for cases of level I, level II, and level III mosaicism, respectively. Four out of 17 cases were positive for the diagnosis of fragile X syndrome. Of 63 cases with abnormal ultrasound findings, blood disorders, or other genetically related clinical conditions, 11 were found to have a chromosome abnormality. Fetal blood sampling is a valuable adjunct to other methods in the prenatal diagnosis of chromosomal mosaicism or pseudomosaicism. It is also useful when rapid cytogenetic diagnosis is desired because of malformations detected in pregnancies at a late gestational age. 相似文献
265.
An EPA program for monitoring ecological status and trends 总被引:1,自引:0,他引:1
Jay J. Messer Rick A. Linthurst W. Scott Overton 《Environmental monitoring and assessment》1991,17(1):67-78
Despite hundreds of millions of dollars spent annually in the United States on environmental monitoring, policy and decision makers seldom have ready access to monitoring data to aid in prioritizing reasearch and assessment efforts or to assess the extent to which current policies are meeting the desired objectives. EPA is currently conducting research to evaluate options for establishing an integrated, cooperative monitoring program, with participation by federal, state, and private entities, that could result in annual statistical reports and interpretive summaries on the status and trends in indicators of adverse disturbance and corresponding health of the nation's ecosystem on the regional and national scale.The research described in this article has not been subjected to U.S. Environmental Protection Agency review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. 相似文献
266.
Restoration of a Canadian Prairie Wetland with Agricultural and Municipal Wastewater 总被引:1,自引:0,他引:1
3 /day (800,000 US gallons) of municipal wastewater and beef processing wastewater. A large nongovernmental organization hastened
restoration with a development process that outlined restoration goals and management objectives to satisfy a dual mandate
of wastewater treatment and wildlife habitat creation. In 1995, after five years of wastewater additions, the basins had been
refilled and the surrounding uplands had been acquired and restored. The Frank Lake Conservation Area currently provides high-quality
habitat for a variety of wildlife in a region where many of the native plants and animals species have been lost due to habitat
loss and fragmentation. The success of upland and water management strategies is reflected in the increase of target species'
abundance and richness: 50 shorebird species, 44 waterfowl species, 15 raptor species, and 28 other new bird species have
returned to the marsh since restoration. As well, significant N and P reduction occurs as waters flow through the first basin
of the marsh. The management strategies of this project that satisfied a dual mandate serve as a model to guide managers of
other large-scale wetland restoration projects. 相似文献
267.
Motivated by the problem of detecting spatial autocorrelation in increment- averaged data from soil core samples, we use the
Cholesky decomposition of the inverse of an autocovariance matrix to derive a parametric linear regression model for autocovariances.
In the absence of autocorrelation, the off-diagonal terms in the lower triangular matrix from the Cholesky decomposition should
be identically zero, and so the regression coefficients should be identically zero. The standard F-test of this hypothesis and two bootstrapped versions of the test are evaluated as autocorrelation diagnostics via simulation.
Size is assessed for a variety of heteroskedastic null hypotheses. Power is evaluated against autocorrelated alternatives,
including increment-averaged Ornstein-Uhlenbeck and Matérn processes. The bootstrapped tests maintain approximately the correct
size and have good power against moderately autocorrelated alternatives. The methods are applied to data from a study of carbon
sequestration in agricultural soils. 相似文献
268.
A universal law of animal group size distribution correlates well to observed fish school size distribution from fisheries catch data. I applied the law to fisheries independent aerial survey data of southern bluefin tuna (Thunnus maccoyii) collected over a 10-year period in the Great Australian Bight. The law does not correlate to the observed school size distribution. A computer model originally demonstrated the formation of the universal law from simple rules. I redesigned this model as an individual-based simulation model calibrated from acoustic tag observations and state a mathematical formula for a resultant new family of transient group size distributions. The new formula correlates accurately to the simulation and to the aerial survey data. I use the mathematical model to estimate area of aggregation and total abundance. This approach is new as it does not seek stationary states of group size distribution and because it demonstrates a quantitative relationship between individual behaviour and group size distribution. This work elevates the pattern of group size distribution from a curiosity to a useful tool, and introduces a new family of transient distributions that may have a general application to other grouping phenomena. 相似文献
269.
Kelly M. Proffitt Robert A. Garrott Jay J. Rotella 《Behavioral ecology and sociobiology》2008,62(10):1679-1687
The Trivers–Willard model predicts that in polygynous species, superior-quality females will maximize their fitness by producing
male offspring. Using a sample of 1,780 Weddell seal (Leptonychotes weddellii) pups recorded over 31 years, we investigated relationships between offspring sex ratio and maternal age, reproductive experience,
an index of maternal lifetime reproductive output, and annual environmental variations. We found evidence that females with
higher index of lifetime reproductive output were more likely to produce male than female offspring but found only weak evidence
that large-scale environmental variations influenced sex ratios. Our results suggest that mothers manipulate offspring sex
to maximize their own fitness, and inherent maternal quality may influence offspring sex. These findings support the Trivers–Willard
sex-allocation model.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
270.
The influence of intraguild predation on prey suppression and prey release: a meta-analysis 总被引:4,自引:0,他引:4
Intraguild predation (IGP) occurs when one predator species consumes another predator species with whom it also competes for shared prey. One question of interest to ecologists is whether multiple predator species suppress prey populations more than a single predator species, and whether this result varies with the presence of IGP. We conducted a meta-analysis to examine this question, and others, regarding the effects of IGP on prey suppression. When predators can potentially consume one another (mutual IGP), prey suppression is greater in the presence of one predator species than in the presence of multiple predator species; however, this result was not found for assemblages with unidirectional or no IGP. With unidirectional IGP, intermediate predators were generally more effective than the top predator at suppressing the shared prey, in agreement with IGP theory. Adding a top predator to an assemblage generally caused prey to be released from predation, while adding an intermediate predator caused prey populations to be suppressed. However, the effects of adding a top or intermediate predator depended on the effectiveness of these predators when they were alone. Effects of IGP varied across different ecosystems (e.g., lentic, lotic, marine, terrestrial invertebrate, and terrestrial vertebrate), with the strongest patterns being driven by terrestrial invertebrates. Finally, although IGP theory is based on equilibrium conditions, data from short-term experiments can inform us about systems that are dominated by transient dynamics. Moreover, short-term experiments may be connected in some way to equilibrium models if the predator and prey densities used in experiments approximate the equilibrium densities in nature. 相似文献