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161.
162.
163.
A climatic driver for abrupt mid-Holocene vegetation dynamics and the hemlock decline in New England 总被引:1,自引:0,他引:1
The mid-Holocene decline of eastern hemlock is widely viewed as the sole prehistorical example of an insect- or pathogen-mediated collapse of a North American tree species and has been extensively studied for insights into pest-host dynamics and the consequences to terrestrial and aquatic ecosystems of dominant-species removal. We report paleoecological evidence implicating climate as a major driver of this episode. Data drawn from sites across a gradient in hemlock abundance from dominant to absent demonstrate: a synchronous, dramatic decline in a contrasting taxon (oak); changes in lake sediments and aquatic taxa indicating low water levels; and one or more intervals of intense drought at regional to continental scales. These results, which accord well with emerging climate reconstructions, challenge the interpretation of a biotically driven hemlock decline and highlight the potential for climate change to generate major, abrupt dynamics in forest ecosystems. 相似文献
164.
We ask whether vole herbivory in experimental grassland plots is sufficient to create an unpalatable community. In a six-year experiment, meadow voles (Microtus pennsylvanicus) reduced plant standing crop between 30% and 72%, well within the range of ungulate effects. Moreover, meadow voles reduced their available forage species by changing the plant community composition: four grass species and a legume upon which they foraged declined sharply in cover and/or number of individuals, five forbs avoided by voles increased, and two forbs neither declined nor increased with either measure. Reductions of diversity occurred when voles first defoliated the plots in 2000 but disappeared as plant species avoided by voles replaced vulnerable plants. Within six years, meadow voles created plant communities dominated by species that they did not eat. 相似文献
165.
Olchawa E Bzowska M Stürzenbaum SR Morgan AJ Plytycz B 《Environmental pollution (Barking, Essex : 1987)》2006,142(2):373-381
Three-day dermal exposure of Dendrobaena veneta to metal ions differentially disrupts the immunocompetence/pathogen balance. Zn does not accumulate in the earthworm body, Cu accumulation is temperature-independent while Cd accumulation is stronger at 22 degrees C than at 10 degrees C. During in vitro incubation with metal ions at 22 degrees C, growth of coelom-derived bacteria is enhanced by Zn, but significantly or almost completely inhibited by Cu or Cd. In contrast, under in vivo conditions at 22 degrees C, bacterial load is decreased only after Cd exposure, but increased after Zn and Cu exposures. At 10 degrees C bacteria growth is almost completely inhibited in all groups except Cu-treated animals. Coelomocyte number is unaffected in animals exposed to Zn, but significantly decreased after exposure to Cd (at 22 degrees C) and Cu (at 22 degrees C and 10 degrees C) with concomitant changes of amoebocyte-to-eleocyte ratio in favour of amoebocytes. Metal exposure up-regulates expression of metallothioneins in coelomocytes, mainly amoebocytes. 相似文献
166.
The John Heinz National Wildlife Refuge is subject to pollution from multiple sources. We studied development of snapping turtle (Chelydra serpentina) and painted turtle (Chrysemys picta) embryos from the refuge from 2000 through 2003. Mean annual deformity rate of pooled painted turtle clutches over four years ranged from 45 to 71%, while that of snapping turtle clutches ranged from 13 to 19%. Lethal deformities were more common than minor or moderate deformities in embryos of both species. Adult painted turtles had a higher deformity rate than adult snapping turtles. Snapping turtles at JHNWR had high levels of PAH contamination in their fat. This suggests that PAHs are involved in the high level of deformities. Other contaminants may also play a role. Although the refuge offers many advantages to resident turtle populations, pollution appears to place a developmental burden on the life history of these turtles. 相似文献
167.
Langenbach T Maciel SJ Neves BC Hagler AN Mano DM Vugman NV 《Journal of environmental science and health. Part. B》2006,41(4):415-425
Microbial displacement in the soil is an important process for bioremediation and dispersal of wastewater pathogens. We evaluated cell movement in surface and subsurface red-yellow podzolic soil driven by advection and microbial motility and also survival of a microbial population at high pressure as is prevalent in deep soil layers. Pseudomonas fluorescens Br 12, resistant to rifampycin and kanamycin, was used as a model organism traceable in non-sterile soil. Our results showed that more than 40% of the P. fluorescens population survived under high pressure, and that microbial motility was not a major factor for its displacement in the soil. Cells were adsorbed in similar amounts to surface and subsurface soils, but more viable cells were present in the leachate of surface than in subsurface soils. The nature of this unexpected cell binding to the subsurface soil was studied by EPR, Mossbauer, NMR, and infrared techniques, suggesting iron had a weak interaction with microbes in soil. P. fluorescens movement in soil resulted mainly from convection forces rather than microbial motility. The transport of this bacterium along the transept toward groundwater encountered restricted viability, although it survived under high pressure conditions simulating those in deep soil layers. 相似文献
168.
Hansen DA Edgerton E Hartsell B Jansen J Burge H Koutrakis P Rogers C Suh H Chow J Zielinska B McMurry P Mulholland J Russell A Rasmussen R 《Journal of the Air & Waste Management Association (1995)》2006,56(10):1445-1458
Measurements of pollutant gases, airborne particulate matter mass and composition, and meteorology have been made at a core site near downtown Atlanta, GA, since August 1998 in support of the Aerosol Research and Inhalation Epidemiology Study (ARIES). This site is one of eight in the Southeastern Aerosol Research and Characterization network. The measurement objective is to provide a long-term, multivariate dataset suitable for investigating statistical associations of respiratory and cardiovascular disease with airborne particulate matter composition, meteorology, and copollutant gases through epidemiologic modeling. Measurements are expected to continue through 2010. Ancillary multiyear measurements at additional sites in the Atlanta metropolitan area and in short-term exposure assessments have been used to estimate the exposure/measurement error associated with using data from a central site to approximate human exposures for the entire area. To date, 13-, 25-, and 53-month air quality datasets have been used in epidemiologic analyses. 相似文献
169.
Radon concentration measurements in atmosphere were taken in years from 1997 to 1999 in Milan and at pre-alpine sites located north of Lombardy. In this paper the results of measuring campaigns and a comparison of radon levels observed in the hilly area north of the town and on the pre-Alps are reported. The general criteria of the measurements and the interpretative models of radon concentration are presented. The Lake Maggiore area shows evidence of a great nocturnal stability and frequent formation of Nocturnal Stable Layer. The peculiar findings in the high altitude stations confirm the use of radon as an indicator of atmospheric dispersion of pollutants in an area with complex orography. The afternoon minimum values are concordant for the different stations: this implies a remixing in afternoon hours over the whole area investigated. 相似文献
170.
As complex social phenomena, public involvement processes are influenced by contextual factors. This study examined agency
goals for public involvement and assessed the importance of local context in remedial action planning, a community-based water
resources program aimed at the cleanup of the 42 most polluted locations in the Great Lakes Basin. Agency goals for public
involvement in remedial action plans (RAPs) were agency-oriented and focused on public acceptance of the plan, support for
implementation, and positive agency-public relations. Corresponding to these goals, citizen advisory committees were created
in 75% of the RAP sites as a primary means for public input into the planning process. Factors that influenced the implementation
of public involvement programs in remedial action planning included public orientation toward the remediation issue, local
economic conditions, the interaction of diverse interests in the process, agency and process credibility, experience of local
leadership, and jurisdictional complexity. A formative assessment of “community readiness” appeared critical to appropriate
public involvement program design. Careful program design may also include citizen education and training components, thoughtful
management of ongoing agency-public relations and conflict among disparate interests in the process, overcoming logistical
difficulties that threaten program continuity, using local expertise and communication channels, and circumventing interjurisdictional
complexities. 相似文献