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941.
By studying landscape form and patterns, we can study processes at multiple scales and determine how collectively those processes inform us about function(s). Integrating landscape ecology from a biogeographical perspective with geographic information science (GIScience) practices offers new ways to study how landscapes change over time and space, including how they can be measured, analyzed, and modeled for management needs. This article presents methodologies and selected results of analyzing spatial patterns from field data across multiple scales by examining standing dead tree (snag) processes across wildfire‐disturbed landscapes in Arizona. Our primary motivation was to illustrate a particular type of work benefiting from the coalescing of landscape ecology and GIScience, functioning at the methodological and practical overlap of these two contributing fields. Our management goals were to (1) describe spatial patterns and characteristics of snags in pairs of burned and unburned ponderosa pine forests of Arizona in four recent (within the past ten years) wildfires, (2) document bird response to wildfires by combining landscape ecology and GIScience methods, and (3) link these patterns to snag monitoring plots and cavity‐nesting bird use to predict the probability of snag use by birds and cavity nesters based on snag characteristics (snag use model). The methods and results demonstrate how integration of landscape ecology with both GIS and GIScience improves the ways to study landscapes and land management issues, in this case offering guidelines for retention of snags that provide habitat for wildlife. 相似文献
942.
I. D. L. Foster T. M. Mighall H. Proffitt D. E. Walling P. N. Owens 《Journal of Paleolimnology》2006,35(4):881-895
We present 137Cs profiles for three low lying coastal lagoons in Southwest England that show a decline in activity with sediment depth.
137Cs inventories are lower than expected by comparison with local reference inventories despite the fact that sampling was undertaken
in the deep-water zone of each lake where sediment and 137Cs focusing would be expected. At all three locations, lake sediment 7Be and unsupported 210Pb (210Pbun) inventories are not significantly lower than the local reference inventory. 137Cs inventories in the study cores range from 38 to 95% of local reference inventories. The standing water level and mud: water
interface at two sites are below maximum tide level and, at all three sites, salinity increases significantly in the water
columns between low and high tide and in the pore waters of the underlying sediments. We suggest that the difference in hydrostatic
pressure between sea level and standing water levels in the lagoons forces salt water up through the sediment column and that
monovalent cations (especially Na+ and K+) replace 137Cs on exchange sites leading to the upward migration and loss of 137Cs. Rising sea levels may therefore contribute to remobilisation and release of 137Cs to the aquatic environment from the sediments of coastal lagoons. 相似文献
943.
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
944.
945.
Ground motion scaling in the Marmara region, Turkey 总被引:1,自引:0,他引:1
A. Akinci L. Malagnini R. B. Herrmann R. Gok M. B. Sørensen 《Geophysical Journal International》2006,166(2):635-651
946.
947.
J. Grabowski L. Krzemiski P. Nescieruk E. Starnawska 《Geophysical Journal International》2006,166(3):1077-1094
Results of palaeomagnetic investigations of the Lower Cretaceous teschenitic rocks in the Silesian unit of the Outer Western Carpathians in Poland bring evidence for pre-folding magnetization of these rocks. The mixed-polarity component reveals inclinations, between 56° and 69°, which might be either of Cretaceous or Tertiary age. Apparently positive results of fold and contact tests in some localities and presence of pyrhotite in the contact aureole suggest that magnetization is primary, although a Neogene or earlier remagnetization cannot be totally excluded since inclination-only test between localities gives 'syn-folding' results. Higher palaeoinclinations (66°–69°) correlate with a younger variety of teschenitic rocks dated for 122–120 Ma, while lower inclinations (56°–60°) with an older variety (138–133 Ma). This would support relatively high palaeolatitudes for the southern margin of the Eurasian plate in the late part of the Early Cretaceous and relatively quick northward drift of the plate in this epoch, together with the Silesian basin at its southern margin. Declinations are similar to the Cretaceous–Tertiary palaeodeclinations of stable Europe in the eastern part of the studied area but rotated ca. 14°–70° counter-clockwise in the western part. This indicates, together with older results from Czech and Slovakian sectors of the Silesian unit, a change in the rotation pattern from counter-clockwise to clockwise at the meridian of 19°E. The rotations took place before the final collision of the Outer Carpathians nappe stack with the European foreland. 相似文献
948.
Re-evaluation of focal depths and source mechanisms of selected earthquakes in the Afar depression 总被引:1,自引:0,他引:1
We present a stepwise inversion procedure to assess the focal depth and model earthquake source complexity of seven moderate-sized earthquakes (6.2 > M w > 5.1) that occurred in the Afar depression and the surrounding region. The Afar depression is a region of highly extended and intruded lithosphere, and zones of incipient seafloor spreading. A time-domain inversion of full moment tensor was performed to model direct P and SH waves of teleseismic data. Waveform inversion of the selected events estimated focal depths in the range of 17–22 km, deeper than previously published results. This suggests that the brittle–ductile transition zone beneath parts of the Afar depression extends more than 22 km. The effect of near-source velocity structure on the moment tensor elements was also investigated and was found to respond little to the models considered. Synthetic tests indicate that the size of the estimated, non-physical, non-isotropic source component is rather sensitive to incorrect depth estimation. The dominant double couple part of the moment tensor solutions for most of the events indicates that their occurrence is mainly due to shearing. Parameters associated with source directivity (rupture velocity and azimuth) were also investigated. Re-evaluation of the analysed events shows predominantly normal faulting consistent with the relative plate motions in the region. 相似文献
949.
Sam L. VanLandingham 《Journal of Paleolimnology》2006,36(1):101-116
Fossil diatoms in the Valsequillo area are important in supplying adequate paleoecological evidence for the in situ deposition (in the absence of strong water currents necessary for the displacement and redeposition) of artifacts as large
as those at the Hueyatlaco Archaeological Site. The paleoecology of lacustrine diatom-bearing samples from four nearby localities
in the Valsequillo region all correlated with numerous diatomaceous samples from the Hueyatlaco Site (Puebla, Mexico) and
indicate an autochthonous deposition of the artifacts at that site. This correlative evidence is consistent with a deposition
in Sangamonian to Illinoian time and is based on the relationships of percentages of taxa in categories of the current, pH,
and halobian spectra in six lines of correlation of samples between the Hueyatlaco Site and the four localities. 相似文献
950.
Environmental Changes at the Desert Margin: An Assessment of Recent Paleolimnological Records in Lake Qarun, Middle Egypt 总被引:1,自引:0,他引:1
R. J. Flower C Stickley N. L. Rose S Peglar A. A. Fathi P. G. Appleby 《Journal of Paleolimnology》2006,35(1):1-24
Lake Qarun has been profoundly affected by a combination of human activities and climatic changes during the past 5000 years.
Instrumental records available for the 20th century show that during most of this period both lake water level and salinity increased and that by the late 1980s lake water salinity was approximately that of seawater.
Sediment cores (c. 1 m long) were collected from this shallow (Zmax 8.4 m) saline lake in 1998 and the master core (QARU1) was used to examine the potential of paleolimnology for reconstructing
the recent environmental history of the site. According to 137Cs and 210Pb radio-assay, the recent sediment accumulation rate in QARU1 was around 5 mm year−1 during the latter half of the 20th century but radionuclide levels were low. Spheroidal carbonaceous particles (SCPs) were
present in the upper c. 30 cm of QARU1 and indicates contamination by low level particulate pollution, probably beginning
around 1950. The record of exotic pollen (Casuarina) indicated that sediment at 51–52 cm depth dated to around 1930. Otherwise the pollen spectra indicated a strongly disturbed
landscape with high ruderals and increased tree planting particularly since c. 1950. Diatom records were strongly affected
by taphonomic processes including reworking and differential preservation but typical marine diatoms increased after the 1920s.
Instrumental records show that the lake became more saline at this time. Freshwater taxa were present at approximately similar
abundances throughout the core. This distribution probably reflected a combination of processes. Reworking of ancient freshwater
diatomites is one likely source for freshwater diatoms in QARU1 but some taxa must also be contributed via the freshwater
inflows. Overall, the diatom stratigraphy indicated increasingly salinity since the 1920s but provided no firm evidence of
lake eutrophication. Diatom inferred salinity reconstructions were in only partial agreement with instrumental records but
inferred for the lower section of the core (pre 20th century to the 1960s) accord with measured water salinity values. Surficial
sediments of Lake Qarun contain environmental change records for the 20th century period but high sediment accumulation rate
and pollen reflect the high degree of human disturbance in the region. Because of poor preservation and evidence of reworking,
the relationships between diatom records and past water quality changes require careful interpretation, especially in the
upper section of the core. Nevertheless, early to mid 20th century measurements of increasing lake water salinity are well
supported by sediment records, a change that is probably linked to ingress of saline ground water 相似文献