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61.
62.
A large number of pitchstone fragments and artefacts have recently been discovered at a Neolithic settlement site in Ballygalley, Co. Antrim, Northern Ireland. They consist predominantly of flakes and un‐reworked lumps and cores, with only one complete tool being found. Since no sources of workable pitchstone exist in Ireland, the source must have been the abundant pitchstone volcanic rocks found on the Hebridean Islands of northwest Scotland. The composition of the glass from a number of artefacts is highly siliceous, indicating that they were derived from pitchstones on the Island of Arran; pitchstones from all other Scottish locations are less silica‐rich. In addition, analysis of pyroxene and amphibole microcrystallites within the pitchstone suggests that the Corriegills area of Arran is the most likely source of the Ballygalley artefacts, although the precise outcrop has proved elusive. These finds, and others across Ireland, show that raw materials were being transported and probably traded over considerable distances despite there being suitable alternative sources of material for making tools (flint, etc.) available in the local area. This suggests that the pitchstone had a very specialist use. © 2002 Wiley Periodicals, Inc. 相似文献
63.
G Minton JR Kema Kema A Todd L Korte PB Maganga JR Migoungui Mouelet 《African Journal of Marine Science》2017,39(4):423-433
Private industry, the Government of Gabon and two international NGOs collaborated to conduct marine surveys off the coast of Gabon, Central Africa. Surveys addressed multiple objectives of surveillance and monitoring, the documentation of the distribution of and threats to the marine megafauna, and capacity-building among government agents and local early-career scientists. During 22 days of survey effort over a two-year period, observers documented humpback whales Megaptera novaeangliae, bottlenose dolphins Tursiops truncatus, Atlantic humpback dolphins Sousa teuszii and common dolphins Delphinus delphis. Humpback whale presence was limited to the months of July to November. Bottlenose dolphins were present year-round and photo-identification of individuals indicated a closed, resident population, with an abundance estimate of 118 (CV = 21.6%, 95% CI 78–180). Small open-decked fishing vessels with gillnets were observed concentrated around river mouths within 2 km of shore, while commercial trawlers were at least 10 km offshore; all were confirmed to be registered and legal. Observations of marine turtles, flocks of marine birds, and floating logs and other debris were sparse. This multi-stakeholder collaboration to conduct a marine survey can serve as an effective model by which funding and logistic support from private industry paired with technical expertise from NGOs and academic institutions can benefit marine and coastal conservation. 相似文献
64.
Katherine C. Filippino Todd A. Egerton William S. Hunley Margaret R. Mulholland 《Estuaries and Coasts》2017,40(1):80-94
Due to the unpredictable nature of intense storms and logistical constraints of sampling during storms, little is known about their immediate and long-term impacts on water quality in adjacent aquatic ecosystems. By combining targeted experiments with routine monitoring, we evaluated immediate impacts of two successive storm events on water quality and phytoplankton community response in the tidal James River and compared these findings to a non-storm year. The James River is a subestuary of the Chesapeake Bay and sampling was conducted before, during, and after Hurricane Irene and Tropical Storm (TS) Lee in 2011 and during the same time period (late summer/early fall) in 2012 when there were no storms. We collected and compiled data on nutrient and chlorophyll a concentrations, phytoplankton abundance, nitrogen uptake, primary productivity rates, and surface salinity, temperature, and turbidity in the meso- and polyhaline segments of the James River. Hurricane Irene introduced significant amounts of freshwater over the entire James River and Chesapeake Bay watersheds, while rainfall from TS Lee fell primarily on the tidal fresh region of the James River and headwaters of the Chesapeake Bay. Dinoflagellates dominated the algal community in the meso- and polyhaline segments prior to the storms in 2011, and a mixed diatom community emerged after the storms. In the mesohaline river segment, cyanobacteria abundance increased after TS Lee when salinities were depressed, likely due to washout from the oligohaline and tidal fresh regions of the river. In 2012, dinoflagellates dominated the community in both segments of the river during late summer but diatoms were also abundant and their biomass fluctuated throughout the summer and fall. Cyanobacteria were not present in either segment. Overall, we observed that the high-intensity rainfall from Hurricane Irene combined with high flushing in the headwaters as a result of TS Lee likely reduced primary productivity and altered community composition in the mesohaline segment but not the more estuarine-influenced polyhaline segment. Understanding the influence of high freshwater flow with a short residence time associated with storms is key to the planning and management of estuarine restoration as such disturbances are projected to increase as a result of climate change. 相似文献
65.
Elizabeth A. McHuron James T. Harvey J. Margaret Castellini Craig A. Stricker Todd M. O’Hara 《Marine pollution bulletin》2014
We measured total selenium and total mercury concentrations ([TSe] and [THg]) in hair (n = 138) and blood (n = 73) of harbor seals (Phoca vitulina) from California to assess variation by geography and sex, and inferred feeding relationships based on carbon, nitrogen, and sulfur stable isotopes. Harbor seals from Hg-contaminated sites had significantly greater [THg], and lesser [TSe] and TSe:THg molar ratios than seals from a relatively uncontaminated site. Males had significantly greater [THg] than females at all locations. Sulfur stable isotope values explained approximately 25% of the variability in [THg], indicating increased Hg exposure for seals with a greater use of estuarine prey species. Decreased [TSe] in harbor seals from Hg-contaminated regions may indicate a relative Se deficiency to mitigate the toxic effects of Hg. Further investigation into the Se status and the potential negative impact of Hg on harbor seals from Hg-contaminated sites is warranted. 相似文献
66.
Using the Climate Forecast System Reanalysis as weather input data for watershed models 总被引:4,自引:0,他引:4
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Daniel R. Fuka M. Todd Walter Charlotte MacAlister Arthur T. Degaetano Tammo S. Steenhuis Zachary M. Easton 《水文研究》2014,28(22):5613-5623
Obtaining representative meteorological data for watershed‐scale hydrological modelling can be difficult and time consuming. Land‐based weather stations do not always adequately represent the weather occurring over a watershed, because they can be far from the watershed of interest and can have gaps in their data series, or recent data are not available. This study presents a method for using the Climate Forecast System Reanalysis (CFSR) global meteorological dataset to obtain historical weather data and demonstrates the application to modelling five watersheds representing different hydroclimate regimes. CFSR data are available globally for each hour since 1979 at a 38‐km resolution. Results show that utilizing the CFSR precipitation and temperature data to force a watershed model provides stream discharge simulations that are as good as or better than models forced using traditional weather gauging stations, especially when stations are more than 10 km from the watershed. These results further demonstrate that adding CFSR data to the suite of watershed modelling tools provides new opportunities for meeting the challenges of modelling un‐gauged watersheds and advancing real‐time hydrological modelling. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
67.
Environmental impacts of dredging and other sediment disturbances on corals: A review 总被引:2,自引:0,他引:2
A review of published literature on the sensitivity of corals to turbidity and sedimentation is presented, with an emphasis on the effects of dredging. The risks and severity of impact from dredging (and other sediment disturbances) on corals are primarily related to the intensity, duration and frequency of exposure to increased turbidity and sedimentation. The sensitivity of a coral reef to dredging impacts and its ability to recover depend on the antecedent ecological conditions of the reef, its resilience and the ambient conditions normally experienced. Effects of sediment stress have so far been investigated in 89 coral species (~10% of all known reef-building corals). Results of these investigations have provided a generic understanding of tolerance levels, response mechanisms, adaptations and threshold levels of corals to the effects of natural and anthropogenic sediment disturbances. Coral polyps undergo stress from high suspended-sediment concentrations and the subsequent effects on light attenuation which affect their algal symbionts. Minimum light requirements of corals range from <1% to as much as 60% of surface irradiance. Reported tolerance limits of coral reef systems for chronic suspended-sediment concentrations range from <10mgL(-1) in pristine offshore reef areas to >100mgL(-1) in marginal nearshore reefs. Some individual coral species can tolerate short-term exposure (days) to suspended-sediment concentrations as high as 1000mgL(-1) while others show mortality after exposure (weeks) to concentrations as low as 30mgL(-1). The duration that corals can survive high turbidities ranges from several days (sensitive species) to at least 5-6weeks (tolerant species). Increased sedimentation can cause smothering and burial of coral polyps, shading, tissue necrosis and population explosions of bacteria in coral mucus. Fine sediments tend to have greater effects on corals than coarse sediments. Turbidity and sedimentation also reduce the recruitment, survival and settlement of coral larvae. Maximum sedimentation rates that can be tolerated by different corals range from <10mgcm(-2)d(-1) to >400mgcm(-2)d(-1). The durations that corals can survive high sedimentation rates range from <24h for sensitive species to a few weeks (>4weeks of high sedimentation or >14days complete burial) for very tolerant species. Hypotheses to explain substantial differences in sensitivity between different coral species include the growth form of coral colonies and the size of the coral polyp or calyx. The validity of these hypotheses was tested on the basis of 77 published studies on the effects of turbidity and sedimentation on 89 coral species. The results of this analysis reveal a significant relationship of coral sensitivity to turbidity and sedimentation with growth form, but not with calyx size. Some of the variation in sensitivities reported in the literature may have been caused by differences in the type and particle size of sediments applied in experiments. The ability of many corals (in varying degrees) to actively reject sediment through polyp inflation, mucus production, ciliary and tentacular action (at considerable energetic cost), as well as intraspecific morphological variation and the mobility of free-living mushroom corals, further contribute to the observed differences. Given the wide range of sensitivity levels among coral species and in baseline water quality conditions among reefs, meaningful criteria to limit the extent and turbidity of dredging plumes and their effects on corals will always require site-specific evaluations, taking into account the species assemblage present at the site and the natural variability of local background turbidity and sedimentation. 相似文献
68.
Todd A. McAlary Paul J. Nicholson Lee K. Yik David M. Bertrand Gordon Thrupp 《Ground Water Monitoring & Remediation》2010,30(2):73-85
Subslab soil gas sampling and analysis is a common line of evidence for assessing human health risks associated with subsurface vapor intrusion to indoor air for volatile organic compounds; however, conventional subslab sampling methods have generated data that show substantial spatial and temporal variability, which often makes the interpretation difficult. A new method of monitoring has been developed and tested that is based on a concept of integrating samples over a large volume of soil gas extracted from beneath the floor slab of a building to provide a spatially averaged subslab concentration. Regular field screening is also conducted to assess the trend of concentration as a function of the volume removed to provide insight into the spatial distribution of vapors at progressive distances away from the point of extraction. This approach minimizes the risk of failing to identify the areas of elevated soil vapor concentrations that may exist between discrete sample locations, and can provide information covering large buildings with fewer holes drilled through the floor. The new method also involves monitoring the extraction flow rate and transient vacuum response for mathematical analysis to help interpret the vapor concentration data and to support an optimal design for any subslab venting system that may be needed. 相似文献
69.
Large concentrations of employment have developed outside traditional central business districts. Our research focuses on analyzing the changing distribution of employment in metropolitan areas by using tract-to-tract commuting data from Census 2000 to identify high-employment nodes within large metropolitan areas. We propose a new way to delineate clusters of contiguous high-employment tracts based on the job density in these areas. We then compare outlying employment clusters with traditional central business districts and contrast employment clusters of varying job densities. Our method has several advantages over existing methods of identifying employment clusters: it is conceptually simple, can use publicly available data, relies on a standardized geographic unit applicable across the entire United States, and offers the ability to examine data from multiple census years. 相似文献
70.
The nature of energy-flux transitions during the onset of midlatitude spring has not been widely examined, despite their critical implications for global-scale biospheric measures and climate change. Further conventional assessment of these phenomena across multiple locations is restricted by satellite-derived data limitations, and the paucity of surface measurement sites. In this paper, we explore a new phenology-based strategy for evaluating the spring surface energy-balance shift that can address these concerns. Our technique can reflect native-species responses and atmospheric surface layer change at a variety of sites, using synoptic-scale first leaf and first bloom phenology models. We test the approach at three locations with diverse climates, and within a group of stations in the state of Oklahoma, which has moderate climate variations across an east-to-west gradient. The results show that the onset of spring in midlatitudes is a modally abrupt (rather than gradual) seasonal transition in terms of energy balance (sensible and latent heat levels) and carbon-flux change that can be linked directly to vegetation phenology. The consistent temporal pattern and magnitude of flux variations across diverse sites suggest that this technique has potential as a proxy for spring energy-balance change at many locations. [Key words: phenology, spring, energy balance, North America.] 相似文献