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931.
Spatial heteroscedasticity may arise jointly with spatial autocorrelation in lattice data collected from agricultural trials
and environmental studies. This leads to spatial clustering not only in the level but also in the variation of the data, the
latter of which may be very important, for example, in constructing prediction intervals. This article introduces a spatial
stochastic volatility (SSV) component into the widely used conditional autoregressive (CAR) model to capture the spatial clustering
in heteroscedasticity. The SSV component is a mean zero, conditionally independent Gaussian process given a latent spatial
process of the variances. The logarithm of the latent variance process is specified by an intrinsic Gaussian Markov random
field. The SSV model relaxes the traditional homoscedasticity assumption for spatial heterogeneity and brings greater flexibility
to the popular spatial statistical models. The Bayesian method is used for inference. The full conditional distribution of
the heteroscedasticity components can be shown to be log-concave, which facilitates an adaptive rejection sampling algorithm.
Application to the well-known wheat yield data illustrates that incorporating spatial stochastic volatility may reveal the
spatial heteroscedasticity hidden from existing analyses. 相似文献
932.
Patricia E. Linton Laura Shotbolt Andrew D. Thomas 《Water, air, and soil pollution》2007,186(1-4):97-113
High concentrations of heavy metals are known to be toxic to many soil organisms. The effects of long-term exposure to lower levels of metals on the soil microbial community are, however, less well understood. The southern Pennines of the U.K. are characterised by expanses of ombrotrophic peat soils that have experienced deposition of high levels of heavy metals since the mid to late 1800s. Concentrations of metals in the peat remain high but the effect of the contamination on the in-situ microbial communities is unknown. Geochemical and molecular polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing techniques were used to derive new information on the metal chemistry and microbial populations in peat soils from six locations in the southern Pennines. All sites were highly acidic (pH 3.00–3.14) with high concentrations of potentially toxic heavy metals, particularly porewater Zn and particulate-associated Pb. The results also reveal a split in site characteristics between the most polluted sites with the highest levels of bioavailable metals (Bleaklow, FeatherBed Moss and White Hill) and those with much lower bioavailable metals (Cowms Moor, Holme Moss and Round Hill). There was no difference in the number of dominant bacterial species between the sites but there were significant differences in the species composition. At the three sites with the highest levels of bioavailable metals, bacterial species with a high similarity to acidophilic sulphur- and iron-oxidizing bacteria and those from high metal environments were detected. The transformations carried out by these metal mobilising and acid producing bacteria may make heavy metals more bioavailable and therefore more toxic to higher organisms. Bacteria with similarity to those typically found in forest and grassland soils were documented at the three sites with the lowest levels of bioavailable metals. The data highlight the need for further studies to elucidate the species diversity and functionality of bacteria in heavy metal contaminated peats in order to assess implications for moorland restoration. 相似文献
933.
Carla M. Koretsky Johnson R. Haas Noah T. Ndenga Doug Miller 《Water, air, and soil pollution》2006,173(1-4):373-403
Seasonal variations in pore water and solid phase geochemistry were investigated in urbanized minerotrophic peat sediments located in southwestern Michigan, USA. Sediment pore waters were collected anaerobically, using pore water equilibrators with dialysis membranes (“peepers”) and analyzed for pH, alkalinity, dissolved ΣPO4 ?3, ΣNH4 +, ΣS?2, SO4 ?2, Fe+3, Fe+2, and Mn+2 at 1-2 cm intervals to a depth of 50 cm. Cores collected adjacent to the peepers during all four seasons were analyzed for reactive solid phase Fe according to extraction methods proposed by Kostka and Luther (1994). The association of Fe and trace metals (Mn, Pb, Zn, Cu, Cr, Co, Cd, U) with operationally defined solid phase fractions (carbonates, iron and manganese oxides, sulfides/organics and residual) was assessed for cores extracted during winter and spring using extraction methods proposed by Tessier et al. (1979, 1982). Pore water Fe and S data demonstrate a clear seasonal variation in redox stratification of these sediments. The redox stratification becomes more compressed in spring and summer, with relatively more reducing conditions closer to the sediment water interface (SWI), and less reducing conditions near the SWI in fall and winter. In the upper 10–15 cm of sediment, the pool of ascorbate extractable Fe, thought to be indicative of reactive Fe(III) oxides, diminishes during spring and summer, in agreement with seasonal changes in redox stratification indicated by the pore water data. Tessier extractions indicate that the total extractable quantity of all metals analyzed in this study decrease with depth, and that the majority of the non-residual Fe, Pb, Zn, Cu, Cr, Co, Cd, and U is typically associated with the sulfide/organic fraction of the sediments at all depths. Non-residual Mn, in contrast, is significantly associated with carbonates in the upper 15–25 cm of the sediment, and predominantly associated with the sulfide/organic fraction only in deeper sediments. 相似文献
934.
Gemechu Keneni Mussa Jarso Tezera Wolabu Getnet Dino 《Genetic Resources and Crop Evolution》2005,52(5):539-549
An experiment was conducted in 2001 at Holetta and Kulumsa, Ethiopia, to study the extent and pattern of genetic diversity
in Ethiopian field pea (Pisum sativum L.) landraces. One hundred forty-eight germplasm accessions were grown in an alpha lattice design with 2 replications. Data
on 12 traits were collected and analyzed. Differences among the accessions were significant for most of the traits (except
number of seeds/ pod) at each location even though differences pooled over location were mostly non-significant. The accessions
were grouped into five clusters of different sizes. Accessions from the southern part of the country (Arsi) distributed overall
clusters while those from the northern half (North and South Wello, North Gonder and North Shewa) fell into clusters C1 to C3. Cumulative effects of a number of characters dictated differentiation of the accessions into clusters. There was no definite
relationship between geographic diversity and genetic diversity as overlapping was encountered in clustering pattern among
accessions from different parts of the country. Accessions from different regions might have similar genetic background and
those from the same origin might also have different genetic background. Therefore, geographic diversity should not necessarily
be used as an index of genetic diversity and parental selection should be based on a systematic study of genetic diversity
in a specific population. Genetic distances among most of the clusters were significant that crosses between parents selected
out of them are expected to generate desirable genetic recombination. Selection should also consider the special advantages
of each cluster and each accession within a cluster. Future germplasm collection, conservation and breeding efforts should
focus not only on inter-regional diversity but also on intra-regional diversity. 相似文献
935.
Gemechu Keneni Mussa Jarso Tezera Wolabu Getnet Dino 《Genetic Resources and Crop Evolution》2005,52(5):551-561
A field experiment was conducted in 2001 at Holetta and Kulumsa, Ethiopia, to study genetic diversity in Ethiopian faba bean
(Vicia faba L.) landraces. One hundred sixty random germplasm accessions were grown in an alpha lattice design with two replications. Data
on 12 traits were collected and analyzed. Significant differences were observed among the accessions for most of the traits
(except number of pods/podding nodes) at each location even though differences pooled over location were mostly non-significant.
Cluster analysis distinguished seven diversity classes of different sizes. Accessions from the northern half of the country
(North and South Wello, North Gonder and North Shewa) were closely related while those from the southern part of the country
(Arsi) were highly diverse. Cumulative effects of a number of characters dictated differentiation of the accessions into clusters.
Some overlapping were encountered between accessions from the northern and those from the southern parts of the country. The
study revealed that accessions from different regions might have similar genetic background and those from the same origin
might also have different genetic background. Therefore, geographic diversity should not necessarily be used as an index of
genetic diversity and parental selection should be based on a systematic study of genetic diversity in a specific population.
Genetic distances between most of the clusters were significant that crosses between parents selected out of them are expected
to generate desirable progenies. Future germplasm collection, conservation and utilization strategies should put more focus
not only on inter-regional diversity in the country as a whole but also on intra-regional diversity in Arsi. 相似文献
936.
Hongjie Li Robert L. Conner Qin Chen Robert J. Graf André Laroche F. Ahmad A. D. Kuzyk 《Genetic Resources and Crop Evolution》2005,51(8):827-835
Wheat streak mosaic virus (WSMV), vectored by the wheat curl mite (WCM),Aceria tosichella Keifer, is one of the most destructive viral diseases of wheat found in many wheat producing areas of the world. Host resistance is the most effective method for controlling this disease and its vector. Symptomatological analysis and enzyme-linked immunosorbent assay (ELISA) were used to characterize WSMV-resistance in wheat-alien partial amphiploid lines and their derivatives. The results showed that most of partial amphiploids derived fromThinopyrum ponticum andTh. intermedium were free of systemic symptoms with very low ELISA readings that were similar to that of the non-inoculated Chinese Spring control. While the partial amphiploid lines 693 and PWM706 were identified as new genetic resources of resistance to WSMV. The present study demonstrated that both symptomatological and ELISA methods efficiently assessed WSMV-resistance in the wheat-alien hybrids and systemic symptom incidence and ELISA absorbance readings were highly correlated (r
2 = 0.8658–0.9323) over time following inoculation. The ELISA results also indicated that the virus did not buildup in the plant tissues of these virus-resistant partial amphiploids. Similar results were observed in chromosome translocation and substitution lines that have the geneWsm1 conferring WSMV resistance. However, the lines containing the geneWsm1 and all the partial amphiploid lines, except Agrotana, were susceptible to the WCM. One line derived from a cross of wheat and Agrotana, was effective in controlling the spread of WSMV and was highly resistant to the WCM. Another line and an accession ofTriticum dicoccoides (Koern.) Schweinf. were highly susceptible to WSMV and WCM. Early disease development was delayed in a new hard red winter cultivar McClintock. The partial WSMV-resistance of McClintock was demonstrated by initially low ELISA readings, and a lower percentage of infected plants than other WSMV-susceptible wheat. The use of the identified promising sources of resistance to WSMV and the WCM in wheat breeding is discussed.LRC Contribution No. 387-01061. 相似文献
937.
Stephanie L. Meadows-Shropshire Chris Gennings W. Hans Carter 《Journal of Agricultural, Biological & Environmental Statistics》2005,10(1):104-117
In the analysis of mixtures of drugs/chemicals it is often of interest to test for the presence of interaction. If the hypothesis
of no interaction (additivity) is not rejected, then the analyst may reasonably claim additivity if and only if the study
is powered to a desired (e.g., biologically meaningful) level. The objective of this article is to address the sample size
and power issues related to testing the hypothesis of additivity at specified mixture points. The study of disinfectant by-products
(DBPs) found in drinking water, described in earlier literature, is used to illustrate the procedures for estimating power
and sample sizes for detecting interactions at specified mixtures. The four trihalomethanes used in the study are bromodichloromethane
(BDCM), chlorodibromomethane (CDBM), chloroform (CHCl3), and bromoform (CHBr3) 相似文献
938.
Purpose
Soil macropores play a principal role in water infiltration but they are highly variable. The objectives of this study were (1) to investigate the temporal change in macropores of an Ultisol as affected by land use and slope position and (2) to analyze contribution of macropores to water infiltration.Materials and methods
Water infiltration was measured at upper and lower slopes in citrus orchard and watermelon field once every 2 months for 1 year using tension infiltrometers at a successive pressure head from ?12, ?6, ?3, to 0 hPa.Results and discussion
Hydraulic conductivity (K) was significantly affected by land use and slope position except at 0 hPa pressure head, showing a significant temporal variation. Effective macroporosity, derived from the increment of hydraulic conductivity between ?3 and 0 hPa, showed a significant temporal variation. Such temporal variation was land use (P?<?0.05) and slope position (P?<?0.001) dependent. Despite of low proportion in total soil volume (averaged 3.5 cm3 m?3), the macropores contributed 47 % of water flux on average. The macroporosity was more stable and higher in the citrus orchard (2.43 cm3 m?3, coefficient of variance (CV)?=?75 %) than in the watermelon field (1.72 cm3 m?3, CV?=?117 %) and contributed more to infiltration in the citrus orchard (60 %, CV?=?16 %) than in the watermelon field (33 %, CV?=?43 %) as well, because tillage was operated only in the watermelon field.Conclusions
No-tillage increased water conducting macropores but did not increase hydraulic conductivity irrespective of slope position.939.
Hongbiao Cui Yuchao Fan Lei Xu Jing Zhou Dongmei Zhou Jingdong Mao Guodong Fang Long Cang Zhenqiu Zhu 《Journal of Soils and Sediments》2016,16(5):1498-1508
Purpose
In situ immobilization of heavy metal-contaminated soils with the repeated incorporation of amendments can effectively reduce the bioavailability of soil heavy metals. However, the long-term application of amendments would lead to the destruction of soil structure and accumulation of soil toxic elements, ultimately affecting food security and quality. Thus, the sustainability of the amendments in a heavy metal-contaminated soil was evaluated from 2010 to 2012.Materials and methods
Batch field experiments were conducted in the soils, which were amended with apatite (22.3 t ha?1), lime (4.45 t ha?1), and charcoal (66.8 t ha?1), respectively. The amendments were applied only one time in 2009, and ryegrass was sown each year. Ryegrass and setaria glauca (a kind of weed) were harvested each year. Concentrations of copper (Cu) and cadmium (Cd) were determined by batch experiments. Five fractions of Cu and Cd were evaluated by a sequential extraction procedure.Results and discussion
Ryegrass grew well in the amended soils in the first year, but it failed to grow in all the soils in the third year. However, setaria glauca could grow with higher biomass in all the amended soils. The treatment of apatite combined with plants was more effective than lime and charcoal treatments in removing Cu and Cd from the contaminated soils by taking biomass into account. Apatite had the best sustainable effect on alleviating soil acidification. The Cu and Cd concentrations of CaCl2-extractable and exchangeable fractions decreased with the application of amendments. Moreover, apatite and lime could effectively maintain the bioavailability of Cu and Cd low.Conclusions
Apatite had a better sustainable effect on the remediation of heavy metal-contaminated soils than lime and charcoal. Although all the amendment treated soils did not reduce soil total concentrations of Cu and Cd, they could effectively reduce the environmental risk of the contaminated soils. The findings could be effectively used for in situ remediation of heavy metal-contaminated soils.940.
Mairead Shore Phil Jordan Per-Erik Mellander Mary Kelly-Quinn Karen Daly James Tom Sims David P. Wall Alice Rowena Melland 《Journal of Soils and Sediments》2016,16(5):1643-1654