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51.
It is becoming more apparent that commonly used statistical methods (e.g. analysis of variance and regression) are not the
best methods for estimating limiting relationships or stressor effects. A major challenge of estimating the effects associated
with a measured subset of limiting factors is to account for the effects of unmeasured factors in an ecologically realistic
matter. We used quantile regression to elucidate multiple stressor effects on end-of-season biomass data from two salt marsh
sites in coastal Louisiana collected for 18 yr. Stressor effects evaluated based on available data were flooding, salinity
air temperature, cloud cover, precipitation deficit, grazing by muskrat, and surface water nitrogen and phosphorus. Precipitation
deficit combined with surface water nitrogen provided the best two-parameter model to explain variation in the peak biomass
with different slopes and intercepts for the two study sites. Precipitation deficit, cloud cover, and temperature were significantly
correlated with each other. Surface water nitrogen was significantly correlated with surface water phosphorus and muskrat
density. The site with the larger duration of flooding showed reduced peak biomass, when cloud cover and surface water nitrogen
were optimal. Variation in the relatively low salinity occurring in our study area did not explain any of the variation inSpartina alterniflora biomass. 相似文献
52.
Quantitative analyses of variations in morphological features of charcoal were undertaken in a 210Pb-dated sediment core from Prosser Lake (British Columbia, Canada). Seven morphological types of charcoal were defined by particle shape, major-minor axis ratio, apparent porosity and progradation to unburned material. The distribution of morphotypes and total charcoal abundances were assessed as a proxy for fire events recorded between 1919 and 2000 and to subsequent mechanisms of transportation-sedimentation to lake sediments. Charcoal morphotypes showed distinct relationships to recorded area burned by fires. Fragile charcoal fragments with highly irregular porosity (termed Type M) displayed the strongest correlation to burned area (r2 = 0.51; P = 0.0001) and did not produce any false-positive signal for fires recorded within a radius of 20 km around the lake. We infer that high porosity and low density Type M fragments are aerially transported and directly deposited on the lake, and that the fragility of Type M charcoal prevents significant quantities from being secondarily transported and incorporated into the sedimentary record. We propose that charcoal morphology is an important but underutilized technique that can yield important insights into fire type, proximity and transportation-sedimentation processes. 相似文献
53.
Dire financial constraints and the threats of forced structural reform have had the unforeseen effect of forcing municipal councils across Australia to reconsider their operational activities and organisational arrangements. With considerable ingenuity, numerous municipalities have proposed and sometimes adopted new structural formations that embody various forms of co-operative service provision. This remarkable development has unfortunately been largely ignored in the scholarly literature on Australian local government. In a modest effort aimed at remedying this neglect, the present paper seeks to outline the small, rural New South Wales Gilgandra Shire Council's (2004) ‘Co-operative/Local Government Service Company’ model, place it in the broader context of alternative models of local governance suitable for Australian conditions, and evaluate its characteristics. 相似文献
54.
M. Catherine Eimers Andrew M. Paterson Peter J. Dillon Sherry L. Schiff Brian F. Cumming Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109
Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in
the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~
20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ 34S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment
were relatively low (1.9–5 mg S g−1 dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in
δ 34S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally
reciprocal depth pattern between total S concentration and δ 34S ratios. While initial shifts in total S and δ 34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both the magnitude and pattern of up-core S enrichment and shifts in δ 34S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and
δ 34S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake
characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S
deposition in this region, likely due to redox-related mobility of S in upper sediment. 相似文献
55.
K. W. Helen Lau Keith E. Louden Sharon Deemer Jeremy Hall John R. Hopper Brian E. Tucholke W. Steven Holbrook Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170
New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins. 相似文献
56.
Brian Emmerson James Jackson Dan McKenzie Keith Priestley 《Geophysical Journal International》2006,167(3):1233-1272
57.
Brian Murton 《New Zealand geographer》2006,62(1):25-38
Abstract: This paper examines how the cultural politics of resource management were played out on the North Kaipara beach between about 1900 and 1971 between Māori and the representative of the Crown, the Marine Department. Particular attention is devoted to how, after regulations were introduced to protect toheroa, the giant surf clam, Māori struggled to assert their rights through a range of transgressions. The paper argues that this illustrates how cultural politics works both from the top down (the Marine Department's implementation of policy) and the bottom up (Māori resistance). It concludes that through an examination of this particular 'culture war', the foreshore emerges as a contested domain where politics, culture and epistemology are inseparable. 相似文献
58.
The aim of this work is the joint application and integration of non-invasive geoelectrical methods for studying the landfill of Savoia di Lucania (Southern Italy). This landfill for its engineering features and small dimensions (70 m × 30 m × 6 m) represents an optimal test site to assess a geophysical survey protocol for municipal solid waste landfills investigation and monitoring. The landfill of Savoia di Lucania has been built with a reinforced concrete material and coated with a high-density polyethylene (HDPE) liner. Three electrical resistivity tomographies (ERT), two self-potential (SP) map surveys and one induced polarization (IP) section have been performed, both in the surrounding area and inside the waste landfill. The geophysical investigations have well defined some buried boundaries of the landfill basin and localized the leachate accumulation zones inside the dumpsite. Comparison of our results with other engineering and geological investigations could be the key for evaluating the integrity of the HDPE liner. Finally, the joint use of the ERT, IP and SP methods seems to be a promising tool for studying and designing new monitoring systems able to perform a time-lapse analysis of waste landfill geometry and integrity. 相似文献
59.
Implications of the relationship between catchment vegetation type and the variability of annual runoff 总被引:1,自引:0,他引:1
The impact of changing catchment vegetation type on mean annual runoff has been known for some time, however, the impact on the variability of annual runoff has been established only recently. Differences in annual actual evapotranspiration between vegetation types and the potential effect of changing vegetation type on mean annual runoff and the variability of annual runoff are briefly reviewed. The magnitude of any change in the variability of annual runoff owing to a change in catchment vegetation type is related to the pre‐ and post‐change vegetation types and the seasonality of precipitation, assuming that the variability of annual precipitation remains constant throughout. Significant implications of the relationship between vegetation type and the variability of annual runoff are presented and discussed for water resource management, stream ecology and fluvial geomorphology. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
60.
Joseph J. Luczkovich Garcy P. Ward Jeffrey C. Johnson Robert R. Christian Daniel Baird Hilary Neckles William M. Rizzo 《Estuaries and Coasts》2002,25(6):1143-1163
We established trophic guilds of macroinvertebrate and fish taxa using correspondence analysis and a hierarchical clustering strategy for a seagrass food web in winter in the northeastern Gulf of Mexico. To create the diet matrix, we characterized the trophic linkages of macroinvertebrate and fish taxa present inHalodule wrightii seagrass habitat areas within the St. Marks National Wildlife Refuge (Florida) using binary data, combining dietary links obtained from relevant literature for macroinvertebrates with stomach analysis of common fishes collected during January and February of 1994. Heirarchical average-linkage cluster analysis of the 73 taxa of fishes and macroinvertebrates in the diet matrix yielded 14 clusters with diet similarity ≥ 0.60. We then used correspondence analysis with three factors to jointly plot the coordinates of the consumers (identified by cluster membership) and of the 33 food sources. Correspondence analysis served as a visualization tool for assigning each taxon to one of eight trophic guilds: herbivores, detritivores, suspension feeders, omnivores, molluscivores, meiobenthos consumers, macrobenthos consumers and piscivores. These trophic groups, corss-classified with major taxonomic groups, were further used to develop consumer compartments in a network analysis model of carbon flow in this seagrass ecosystem. The method presented here should greatly improve the development of future network models of food webs by providing an objective procedure for aggregating trophic groups. 相似文献