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901.
Steve Cherry Gary C. White Kim A. Keating Mark A. Haroldson Charles C. Schwartz 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(2):195-215
Current management of the grizzly bear (Ursus arctos) population in Yellowstone National Park and surrounding areas requires annual estimation of the number of adult female bears
with cubs-of-the-year. We examined the performance of nine estimators of population size via simulation. Data were simulated
using two methods for different combinations of population size, sample size, and coefficient of variation of individual sighting
probabilities. We show that the coefficient of variation does not, by itself, adequately describe the effects of capture heterogeneity,
because two different distributions of capture probabilities can have the same coefficient of variation. All estimators produced
biased estimates of population size with bias decreasing as effort in creased. Based on the simulation results we recommend
the Chao estimator for model M
h
be used to estimate the number of the female bears with cubs of the year; however, the estimator of Chao and Shen may also
be useful depending on the goals of the research. 相似文献
902.
The simultaneous analysis of mixed discrete and continuous outcomes using nonlinear threshold models
Todd Coffey Chris Gennings 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(1):55-77
Mixed discrete and continuous outcomes are commonly measured on each experimental unit in dose-response studies in toxicology.
The dose-response relationships for these outcomes often have dose thresholds and nonlinear patterns. In addition, the endpoints
are typically correlated, and a statistical analysis that incorporates the association may result in improved precision. We
propose an extension of the generalized estimating equation (GEE) methodology to simultaneously analyze binary, count, and
continuous outcomes with nonlinear threshold models that incorporates the intra-subject correlation. The methodology uses
a quasi-likelihood framework and a working correlation matrix, and is appropriate when the marginal expectation of each outcome
is of primary interest and the correlation between endpoints is a nuisance parameter. Because the derivatives of threshold
models are not continuous at each point of the parameter space, we describe the necessary modifications that result in asymptotically
normal and consistent estimators. Using dose-response data from a neurotoxicity experiment, the methodology is illustrated
by analyzing five outcomes of mixed type with nonlinear threshold models. In this example, the incorporation of the intra-subject
correlation resulted in decreased standard errors for the threshold parameters. 相似文献
903.
Background and Objectives
Soil nitrate nitrogen (NO3 −-N) accumulation is related closely to NO3 − leaching, which is an important issue in groundwater pollution, especially in intensive agricultural areas with saline soils where volumes of water are used in irrigation to avoid salt accumulation in the root zone. However, in the saline environment in Hai River Basin, China, the importance of detailed research into NO3 −-N distribution in the root zone has not been adequately recognized. Considering the impacts of eco-environmental system N and crop production, the present study aimed at contributing to an understanding of the effects of N application rate on soil NO3 −-N distribution, NO3 −-N residue, N loss, and maize (Zea mays L.) yield in this region. 相似文献904.
Joshua M. Tebbs Melinda H. McCann 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):534-551
Insect-vectored plant diseases impact the agricultural community each year by affecting the economic value, the quantity,
and the quality of crops. Controlling the spread of disease is an important area in risk assessment, and understanding the
dynamics of vector populations helps researchers to develop effective treatments. In this article, we consider an experimental
design commonly used by researchers who study plant disease and examine large-sample, likelihood-based hypothesis tests that
can be used to characterize disease-transmission behavior in a stratified population. Small-sample size and power results
along with design considerations are provided. We illustrate our testing procedures using two real data examples and provide
recommendations for plant-disease researchers in the field. 相似文献
905.
Aro TL Larmo PS Bäckman CH Kallio HP Tahvonen RL 《Journal of agricultural and food chemistry》2005,53(5):1482-1488
The fatty acid composition and contents of fat and fat-soluble vitamins of three salted products prepared from Icelandic herring were analyzed. The effects of storage on the products over their shelf life, 6 or 12 months, were investigated. The average oil content of salted, gutted herring and salted fillets in vacuum remained constant, 17 and 12% of wet weight, respectively. In the pickled product the oil content decreased during the 12 months of storage from 13 to 12%. The composition of the products was typical for herring, the most abundant fatty acids being oleic (18:1n-9), palmitic (16:0), cetoleic (22:1n-11), and gadoleic (20:1n-9) acids. Monounsaturated acids constituted clearly the main group with a proportion of >50% of all fatty acids. Eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) comprised together >12% of all fatty acids. During storage, some hydrolysis of triacylglycerol (TAG) occurred, causing a slight reduction in practically all esterified fatty acids. In none of the three products was the loss of polyunsaturated fatty acids from TAG greater than the loss of saturated ones, indicating that the loss of EPA and DHA was not due to oxidation. After packing, the average content of vitamins A, D, and E in the products varied between 27 and 87 microg/100 g (wet weight), between 17-28 microg/100 g (wet weight), and between 77-120 microg/100 g (wet weight), respectively. During storage, the level of vitamin A decreased significantly, whereas no loss of vitamin D was observed. The content of vitamin E was low in all products and showed wide variation. When compared to the recommended daily intake, it could be concluded that the products investigated were good and stable sources of long-chain n-3 fatty acids (EPA, DHA) and vitamin D. 相似文献
906.
D. Wallschläger H. Hintelmann R. D. Evans R. -D. Wilken 《Water, air, and soil pollution》1995,80(1-4):1325-1329
It has been shown that an untreated mercury-polluted floodplain soil (containing 10 μg/g per dry weight (d.w.) total Hg and 12 ng/g (d.w.) monomethylmercury compounds (MMM)) of the river Elbe in Northern Germany contains both dimethylmercury (DMM) and elemental mercury (Hg°). This is the first time ever that DMM has been detected in unmodified soils. A novel purge- and-trap-technique involving a sequential thermodesorption-separation of the two species after trapping on a carbon molecular sieve (CMS) has been developed that allows the determination of the two species DMM and Hg° from aqueous solutions or soil samples by GC-CVAFS. The compounds' identities as Hg-species were confirmed by GC-ICP/MS. A DMM-concentration of 740 pg/g (d.w.) was determined in the soil; the Hg°-concentration was found to be at least four times larger, but could not yet be quantified. Since no precautions against losses via evapoartion were taken during sampling and storage, the original concentrations were probably much higher. Both DMM and Hg° are easily purged with N2 from soils as well as from soil suspensions, indicating that the two species may readily evaporate from those soils under natural conditions. The amount of DMM determined in the soil suspension was significantly lower (80 pg/g (d.w.)) compared to that in the original soil sample, suggesting that DMM might not be stable under these conditions. Also, it was shown that in natural samples, MMM can be converted into DMM in the presence of sulfide, at S2?-levels as low as 100 μg/g. 相似文献
907.
Abrie J. van der Merwe Albertus L. Pretorius 《Journal of Agricultural, Biological & Environmental Statistics》2003,8(3):328-343
This article applies Bayesian nonparametric techniques of analysis to the mixed linear model. The distribution of the random
effects is specific as a nonparametric prior. A Dirichlet process prior is specified on the space of prior distributions.
A modified Dirichlet process is described and applied using a Gibbs sampler. The approach is demonstrated in an investigation
of the changes over time of packed cell volume in two breeds of cattle. 相似文献
908.
The use of wood ash in forestry has been questioned because of the potential risk associated with its cadmium (Cd) content (1–30 mg kg–1). In agriculture, wood ash is only allowed for use as a fertilizer when its Cd content is below 3 mg kg–1. This restriction has not been applied to forest soils and there is a lack of knowledge about the potentially harmful effects of the Cd in wood ash on forest ecosystems. This paper summarizes our recent studies on the microbial communities of boreal coniferous forest humus exposed to Cd-containing wood ash treatment. The main objectives of our studies were to test if the Cd in wood ash has the potential to affect the humus layer microflora of coniferous upland forests and if it has the potential to enter the human food chain. These objectives were tested both in laboratory and field experiments with ash and ash spiked with Cd (in laboratory 400 or 1,000 mg Cd kg–1 as CdO or CdCl2; in field 400 mg Cd kg–1 as CdO). In one study the dissolution of ash was accelerated by irrigating it with simulated acid rain (SAR). Wood ash increased humus layer pH and microbial activities (respiration or thymidine incorporation rates) and changed its microfloral community structure (Biolog, PLFA, 16S or 18S rDNA PCR-DGGE) in both laboratory and field experiments. Spiking ash with Cd induced no further changes in the above-mentioned variables compared to ash alone. The Cd added with wood ash did not become bioavailable as detected with a bacterial biosensor Bacillus subtilis BR151(pTOO24). The form and level of Cd added in the ash had no further effect on the microbiological variables studied. Irrigation of ash with SAR did not increase the amount of bioavailable Cd, although the dissolution rate of the ash was increased. The concentration of Cd in soil water and in the berries of Vaccinium uliginosum and V. vitis-idaea, and the amount of humus bioavailable Cd did not increase with applied ash or ash spiked with Cd although the ash spiked with Cd increased the amount of humus total and extractable Cd in the 4-year field study. Only the ash spiked with Cd and not the unspiked normal wood ash resulted in significantly higher Cd concentrations in the mushroom Lactarius rufus and a slight increase in the berries of Empetrum nigrum (first year only). In conclusion, the Cd in wood ash did not become bioavailable and harmful to forest soil microbes, or leach into the humus layer even when treated with simulated acid rain. It is thus safe to use wood ash as a fertilizer in forests. However, since wood ash adds Cd to the environment, it is recommended that the same sites should not be fertilized with wood ash more than once. The effects of wood ash (3 t ha–1) on forest soil humus layer microbes are long-term, lasting at least 20 years, and probably longer if higher application dose and/or hardened ash is used. 相似文献
909.
Cyanobacteria are important for global nitrogen cycle and often form complex associations referred to as cyanobacterial mats
or periphyton that are common in tropical, limestone-based wetlands. The objective of this study was to monitor the nitrogen
fixation rate using the acetylene reduction assay of these cyanobacterial mats in a tropical, unfertilized, and protected
wetland. To account for temporal and spatial variation of nitrogenase activity, we were interested in seasons in a hydrological
cycle (dry, rains, and end of rains), sites with different vascular vegetation, and rates of nitrogenase activity in a 24-h
cycle. The annual average of nitrogenase activity was 22 nmol C2H4 cm−2 h−1, with a range of <6 to 35 nmol C2H4 cm−2 h−1, and the annual nitrogen fixation rate of our study site (9.0 g N m−2 year−1) is higher than similar estimates from other freshwater wetlands. There was a clear temporal pattern in nitrogenase activity
with a maximum rate occurring during the rainy season (August) and a maximum nitrogenase activity occurring between 0600 and
1200 hours. We found spatial differences in nitrogenase activity among the four sites that could be attributed to variations
in species composition within the periphyton. 相似文献
910.
Anthropogenic N-deposition represents a significant input of N into semi-arid chaparral and coastal sage scrub (CSS) shrublands
of southern California. High levels of atmospheric N deposition have the potential to increase soil C and N mineralization,
and we hypothesize that semi-arid shrubland soil exposed to long-term (decades) high N deposition will have significantly
higher C and N mineralization potentials. This hypothesis was tested in a laboratory incubation where the inorganic N (NH4+NO3) and CO2 production of soils maintained at a constant temperature of 25°C and a soil moisture of 0.25 g H2O/g (65% water-filled pore space) were sampled sequentially over a 50-week period. The temporal trend in cumulative C and
N mineralization was well described by a first- and zero-order model, respectively. Long-term atmospheric N deposition significantly
increased potential N mineralization but not C mineralization, and both the rate and total N mineralization were significantly
positively correlated with the surface (0–10 cm) soil δ
15N natural abundance and negatively correlated with the surface soil C:N ratio. While the incubation techniques used here do
not provide realistic estimates of in situ C or N mineralization, these assays indicate that atmospheric N deposition has
significantly altered ecosystem N storage and cycling. 相似文献