Fluvial Geochemistry through a Short-Duration, Tropical-Cyclone Induced Discharge event in the Burdekin River and Hann Creek, North Queensland, Australia     

Jan Alexander  Chris R. Fielding  Simon J. Wakefield  Mark T. George  Clare F. Cottnam 《Aquatic Geochemistry》2001,7(4):275-293

The chemical composition of river water integrates a number of factors such as weathering, land use, climate, vegetation cover and human activity that individually affect its chemistry. Short term variations may also be significant. The Burdekin River, NE Australia, is an example of a class of tropical streams which experiences two to four orders of magnitude variation in discharge in response to seasonal but erratic monsoonal and cyclonic rainfall. In these systems individual discharge events last for days to weeks. Given the inherent difficulty sampling these events published data on water chemistry (and thus calculated fluxes and global budgets) may tend to be biased to low flow conditions. One such discharge event in February 1996 has been investigated for its impact on the chemistry of the water. Major cations (Na, Mg, K, Ca) all decreased in concentration as the water level rose, as did the minor elements Sr, Ba and U. Some other trace elements, notably Rb, Cr, Pb and REE were enriched in the peak flow waters. The flux of all measured elements increased substantially during the seven days of the discharge event. Such short term but significant events will have a major impact on the annual fluxes of elements delivered to the oceans from the land and global discharge budgets may need to take them into account when refining databases in the future.  相似文献   

Source identification of PM_2.5 in an arid Northwest U.S. City by positive matrix factorization   总被引：1，自引：0，他引：1  

Eugene Kim  Timothy V. Larson  Philip K. Hopke  Chris Slaughter  Lianne E. Sheppard  Candis Claiborn 《Atmospheric Research》2003,66(4):291-305

Spokane, WA is prone to frequent particulate pollution episodes due to dust storms, biomass burning, and periods of stagnant meteorological conditions. Spokane is the location of a long-term study examining the association between health effects and chemical or physical constituents of particulate pollution. Positive matrix factorization (PMF) was used to deduce the sources of PM_2.5 (particulate matter ≤2.5 μm in aerodynamic diameter) at a residential site in Spokane from 1995 through 1997. A total of 16 elements in 945 daily PM_2.5 samples were measured. The PMF results indicated that seven sources independently contribute to the observed PM_2.5 mass: vegetative burning (44%), sulfate aerosol (19%), motor vehicle (11%), nitrate aerosol (9%), airborne soil (9%), chlorine-rich source (6%) and metal processing (3%). Conditional probability functions were computed using surface wind data and the PMF deduced mass contributions from each source and were used to identify local point sources. Concurrently measured carbon monoxide and nitrogen oxides were correlated with the PM_2.5 from both motor vehicles and vegetative burning.  相似文献   

Symbols, not data: rare trees and vegetation history in Mali   总被引：1，自引：0，他引：1  

Chris S Duvall 《The Geographical journal》2003,169(4):295-312

Historical analysis of botanical literature concerning the trees Gilletiodendron glandulosum and Guibourtia copallifera in Mali's Manding Plateau reveals that the dominant representation of these plants has helped to perpetuate colonial-era theories of vegetation history, African land management, and natural resource politics in West Africa. The French botanist Aubréville described these plants as proof of the theory of vegetation history that blamed poor land management by rural Africans for a steady and continuing destruction of vegetation from its presumed original forest climax. Although Aubréville's representation of these trees was justified within the 1930s scientific context he worked, subsequent researchers uncritically maintained his conclusions even though the changed scientific context in which they worked did not justify such representation. Subsequent ecological research also failed to substantiate Aubréville's representation of these trees, yet several influential modern botanical works have uncritically accepted colonial-era botanical literature founded on his ideas. Thus, modern botanical works have perpetuated a simplistic and inaccurate narrative of resource use under an appearance of objectivity. As a result, policy recommendations based on the modern botanical sources remain almost identical to colonial-era policies. Based on the similarity of colonial-era and modern portrayals of these trees, this paper argues that a regional discursive formation recently described by other authors may be expanded to include southern Mali, which carries negative implications for decentralization reform in Mali.  相似文献   

Critical loads of acidity for Irish lakes     

Julian Aherne  Chris J. Curtis 《Aquatic Sciences - Research Across Boundaries》2003,65(1):21-35

Critical loads of acidity have been estimated for Irish lakes (277) using survey data from the Republic of Ireland and Northern Ireland, and compatible inputs and methods across both regions. This is the first trans-region application of the Steady-State Water Chemistry model for the island of Ireland. Results indicate that a small percentage of lakes (10.8%, 30 lakes) have low critical loads of acidity (<50.0 mmol_c m^-2 yr^-1). Based on bulk sulphate deposition, exceedance of critical load was observed in 6.9% of the sampled lakes (19 lakes). Inferences relating to the whole lake population cannot be made, as statistical lake surveys were not carried out. However, as the surveys were weighted towards acid-sensitive lakes, the current study suggests that Irish lakes are not under a significant threat from anthropogenic acidification. The acidifying impact of nitrogen was incorporated into the exceedance calcula tion by superimposing the present leaching of nitrogen onto sulphate deposition. This increased exceedance by ഌ% (i.e., from 11 to 19 lakes). Despite the potential uncertainties associated with using default values and relationships in the Steady-State Water Chemistry model, uncertainty analysis indicated that the critical loads were relatively stable. The critical acid neutralising capacity limit (specified water quality criterion) had the greatest effect on the critical load. In the current study, a catchment dependent limit was employed (ranged: 0-50 7mol_c L^-1; mean: 35 7mol_c L^-1) rather than a single fixed value.  相似文献   

Snow Avalanche Hazard in Canada – a Review     

Chris Stethem  Bruce Jamieson  Peter Schaerer  David Liverman  Daniel Germain  Simon Walker 《Natural Hazards》2003,28(2-3):487-515

Snow avalanches affect recreation, transportation, resource industries and property. During the 1990s an average of 12.5 persons per year were killed in avalanches in Canada. The snow avalanche hazard has affected people and facilities in B.C, Alberta, Yukon, NWT, Nunavut, Ontario, Quebec and Newfoundland. Avalanche risk may be voluntary, for example skiing and snowmobiling, or involuntary, for example public transportation corridors. A worst-case avalanche scenario is most likely to occur in the Western Cordillera, resulting from a single large-scale weather pattern, where a cold period resulting in the development of a weak layer in the snowpack is followed by a series of major mid-winter storms. Emergency preparedness for avalanches is most advanced in western Canada. New education and information initiatives in Quebec and Newfoundland are aimed at improving preparedness there. Current research is focused on avalanche forecasting, weather forecasting for avalanche prediction, avalanche failure characteristics, forestry and avalanches and geomorphology and avalanches. An important area of future research is the impact of climate change on avalanches, particularly in northern Canada.  相似文献   

Report of the Editors   总被引：1，自引：0，他引：1  

Jim Best  Chris Fielding  Ian Jarvis  Peter Mozley 《Sedimentology》2003,50(3):619-622

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Estuarine production of juvenile dungeness crab (cancer magister) and contribution to the Oregon-Washington coastal fishery     

David A. Armstrong  Chris Rooper  Donald Gunderson 《Estuaries and Coasts》2003,26(4):1174-1188

Estuaries provide nursery habitat for juvenile stages of several commercial decapod crustaceans worldwide, and those in the Northeastern Pacific are viewed as providing this function for Dungeness crab,Cancer magister. It is difficult to ascertain the degree to which such estuarine production of juveniles eventually contributes to coastal adult populations and fisheries since there are no direct surveys of adult abundance. As other authors have done, we used fishery landings data to compute the long-term average contribution of 1 + juvenile crab populations reared in estuaries to future coastal fisheries. We focused on Oregon and Washington states, but grouped landings in two large geographic zones by combining fishery ports as adjacent to Large Estuarine Zones (LEZ; Grays Harbor and Willapa Bay, Washington, and both sides of the Columbia River) and Small Estuarine Zones (SEZ; all other ports in Oregon). Mortality estimates were used to reduce 1 + crab abundance to surviving legal males, and portrayed as percent of the fisheries. Trends in the SEZ indicate that an average of only about 5–7% of estuarine production adds to the coastal adult population and contributes about $0.7 million to the fishery. The contribution is 25–30% in the LEZ (but may be higher since interannual density varies up to 5 times) and is worth about $3.9 million based on present ex-vessel value. Analyses of crab distribution and density indicate that the majority of an estuarine population (50–80%) is located in lower side channels (LSC) in spring and summer where temperature is higher and prey within and on adjacent intertidal flats is high. The potential average dollar value of equivalent legal male crab produced from the juvenile population is about $180 ha^?1 in LSC (but $280 ha^?1 in Grays Harbor where long-term density is highest), and lower in other estuarine habitats ($50–100 ha^?1). Estuarine juvenile production provides a relatively stable source of recruits to coastal adult populations, and large systems in the LEZ are important nurseries. Since direct coastal settlement of larvae does occur but is highly variable, the estuarine contribution may be especially important when physical forcing or unusual events lead to low survival of the coastal 0+ cohort. An unusually long period of very low landings in the LEZ from 1981–1987 is interpreted in light of the Mount St. Helens eruption (1980) and subsequent transport and deposition of very fine silt fractions over much of the LEZ nearshore shelf that may have adversely affected several year classes of small, early benthic phase juveniles at that time.  相似文献   

Real-Time GPS Data Transmission Using VSAT Technology     

Michael E. Jackson  Chuck Meertens  Oivind Ruud  Spencer Reeder  Warren Gallaher  Chris Rocken 《GPS Solutions》2002,5(4):10-19

The University NAVSTAR Consortium (UNAVCO) Boulder Facility is assessing Very Small Aperture Terminal (VSAT) technology for near real-time transmission of GPS data from a remote receiver to a central processing facility. The study is motivated by the need for a robust, cost-effective data communications solutions to transfer GPS data from remote sites where no other communication alternatives exist. Future large-scale plate boundary deformation initiatives using spatially dense networks of GPS will require receivers to be located where the science dictates, and not the power or communications infrastructure. For other applications, such as determining rapid GPS orbits and time transfer, there is a push toward reducing the latency in GPS data used to produce GPS data products and differential corrections (Talaya & Bosch, 1999; Jackson, Meertens, & Rocken, 2000; Muellerschoen, Bar-Sever, Bertiger, & Stowers, 2001), and to support upcoming Low Earth Orbiting (LEO) missions requiring low latency, 1-s GPS data. In this paper we evaluate two Ku-band systems, the Nanometrics Libra VSAT and the StarBand 2-way satellite Internet VSAT. The Nanometrics system test results show that continuous, 1-s GPS data can be streamed from multiple remote stations within the VSAT footprint, quality checked, and delivered for processing with a <2.5-s latency (mean 1.2 s) and a 99.8% reliability. Benefits of the Nanometrics system include global coverage, control of bandwidth allocation and data hub, and the low power draw of the system. Negatives include the cost of hub and remote infrastructure and the need to negotiate landing rights issues on a country-by-country basis. The UNAVCO Facility currently operates a Nanometrics hub and three remote VSAT systems. The StarBand system showed 98.9% reliability with a maximum latency of 10.2 s (mean latency 1.7 s) for 1-Hz GPS data and an average uplink speed of 31.7 kbps. Benefits of the StarBand system include the cost and small profile of the remote antenna. Negatives include coverage limited to coterminous United States and the high power draw of remote systems. ? 2002 Wiley Periodicals, Inc.  相似文献   

Climatic Implications of the Kyoto Protocol: The Contribution of International Spillover   总被引：6，自引：0，他引：6  

Michael J. Grubb  Chris Hope  Roger Fouquet 《Climatic change》2002,54(1-2):11-28

We explore the long-run impact of the Kyoto Protocol commitments to limit greenhouse gas emissions under various assumptions about the international spillover arising from actions led by the industrialised countries. International spillover comprises many complex processes including substitution due to price effects, diffusion of technology innovations, and policy and political spillovers. We represent these in terms of their aggregate impact on emission intensities over the next century. Limiting industrialised country emissions alone has limited environmental benefit if there is no international spillover; in our base case atmospheric concentrations by the end of the century rise to 730 ppm. However, this implies a large divergence of emission intensities, contrary to both empirical long term aggregate trends, and to identifiable influences towards convergence associated with economic globalisation. In contrast, if spillover leads to convergence of emission intensities by 2100, atmospheric concentrations are kept to below 560 ppm and are close to stabilising. Weargue that zero or negative international spillover, as assumed in manyanalyses, is not credible; we estimate the most likely range for the international spillover parameter in our model to be 0.5–1.0. For our base scenario this would imply a mean global average temperature change from pre-industrial levels by 2100 of 2.7–3.4 °C instead of 4.2 °C,and rising at only 0.15–0.29 °C/decade instead of 0.45 °C/decade.Long-run sea-level rise is greatly curtailed. The regional benefits to the industrialised countries are also magnified because of the spillover to developing county emissions. Although the aggregate degree of spillover is uncertain, the available evidence suggests that it will be important and environmentally beneficial in aggregate. Spillover will help to spread the global effectiveness of the Kyoto first period and subsequent commitments, and deserves much further scrutiny.  相似文献   

Ar/Ar illite dating of Late Caledonian (Acadian) metamorphism and cooling of K-bentonites and slates from the Welsh Basin, U.K.     

Hailiang Dong  Chris M. Hall  Alex N. Halliday  Donald R. Peacor  Richard J. Merriman  Brin Roberts 《Earth and Planetary Science Letters》1997,150(3-4):337-351

The vacuum-encapsulation laser ⁴⁰Ar³⁹Ar technique allows extremely small (10⁻⁶ g) samples of fine-grained materials such as diagenetic clays to be dated. Here we show that the method can be extended to higher-grade clay minerals. The integration of transmission electron microscopic (TEM) characterization with ⁴⁰Ar³⁹Ar dating of vacuum encapsulated samples permits the resolution of the timing of metamorphic growth/cooling from the time of diagenesis. We have applied this technique to well characterized Lower Paleozoic slates and K-bentonites from the Welsh Basin, which span the transition from anchizonal to epizonal grade, which had been previously studied using RbSr and SmNd dating.

TEM observations of epizonal K-bentonites and slate showed that illite in these samples is of 2M₁ polytype, of muscovite-like composition, and oriented parallel to cleavage, suggesting that they are of metamorphic origin. Total gas ages (equivalent to conventional KAr ages) for encapsulated epizonal K-bentonites and slate (340–408 Ma) are considerably variable. The Ar retention ages (calculated from ³⁹Ar and ⁴⁰Ar atoms retained in the sample after irradiation) are more consistent (383–411 Ma). The ³⁹Ar recoil losses are minor for illites from whole rock samples of epizonal K-bentonites but very significant for clay separates of epizonal slate. Plateaus in age spectra were observed in epizonal K-bentonites and slate. The plateau ages (414–421 Ma) and retention ages (383–411 Ma) can be correlated with the onset of Acadian metamorphism and culmination of uplift and inversion of the Welsh Basin, respectively. These ages are significantly younger than the 450 Ma ages previously reported for diagenetic clays using the same method, suggesting that diagenetic history has been lost in these epizonal K-bentonites and slate.

TEM observations of anchizonal slates showed that there are two modes of illite. The first mode is similar to that observed in epizonal samples, suggesting a metamorphic origin. The second mode consists of the 1M_d polytype, has typical diagenetic illite composition, and is oriented parallel to bedding, suggesting a diagenetic origin. Total gas ages for encapsulated anchizonal slates vary considerably (361–422 Ma). The retention ages are more consistent (413–432 Ma) than the total gas ages. The ³⁹Ar recoil losses are more significant than those for epizonal K-bentonites and slate. Plateaus in age spectra are generally not observed. However, the consistent retention ages for the anchizonal slates correspond to the plateau ages for the epizonal samples, and are inferred to represent the onset of Acadian metamorphism.

These data, when combined with our previously published results for diagenetic shales, suggest that thermal conditions near the boundary of anchizonal and epizonal grades are necessary to completely reset Ar systems in shales and slates.  相似文献