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排序方式: 共有396条查询结果,搜索用时 156 毫秒
391.
392.
Scott A. Rush Jill A. Olin Aaron T. Fisk Mark S. Woodrey Robert J. Cooper 《Estuaries and Coasts》2010,33(4):963-970
Much of North America’s tidal marsh habitat has been significantly altered by both natural and man-made processes. Thus, there
is a need to understand the trophic ecology of organisms endemic to these ecosystems. We applied carbon (δ
13C) and nitrogen (δ
15N) stable isotope analysis, along with isotope mixing models, to egg yolk, liver, and muscle tissues of clapper rails (Rallus longirostris) and their likely prey items. This analysis enabled us to explore variation in trophic niche and diet composition in this
important marsh bird in two northern Gulf of Mexico tidal marshes that are river and ocean-dominated. For the river-associated
estuary, δ
13C and δ
15N of egg yolks, liver, and pectoral muscle tissue samples provided evidence that clapper rails maintained a similar diet during
both the winter and the breeding season. A trophic link between C3 primary productivity and the clapper rail’s diet was also indicated as the δ
13C of clapper rail egg yolks related negatively with the aerial cover of C3 macrophytes. Clapper rails from the ocean-dominated estuary had a narrower trophic niche and appeared to be utilizing marine
resources, particularly, based on modeling of liver stable isotope values. Variation in stable isotope values between egg
yolk and liver/muscle in both systems suggests that endogenous resources are important for egg production in clapper rails.
These results demonstrate that diet composition, prey source, and niche width of clapper rails can vary significantly across
different estuaries and appear to be influenced by hydrological conditions. 相似文献
393.
Michael J. Durako Piotr Kowalczuk Michael A. Mallin William J. Cooper Jason J. Souza David H. Wells 《Estuaries and Coasts》2010,33(6):1430-1441
Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m3s−1) was only 25% of the wet year discharge (429 ± 337 m3s−1). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter
(CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to
PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied
little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher
nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a
CDOM
(412)] ranged from 0.05 to 8.25 m−1 with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater
river inputs, CDOM may exert a major limiting influence over near-shore primary production. 相似文献
394.
M. Latif K. Sperber J. Arblaster P. Braconnot D. Chen A. Colman U. Cubasch C. Cooper P. Delecluse D. Dewitt L. Fairhead G. Flato T. Hogan M. Ji M. Kimoto A. Kitoh T. Knutson H. Le Treut T. Li S. Manabe O. Marti C. Mechoso G. Meehl S. Power E. Roeckner J. Sirven L. Terray A. Vintzileos R. Voß B. Wang W. Washington I. Yoshikawa J. Yu S. Zebiak 《Climate Dynamics》2001,18(3-4):255-276
An ensemble of twenty four coupled ocean-atmosphere models has been compared with respect to their performance in the tropical Pacific. The coupled models span a large portion of the parameter space and differ in many respects. The intercomparison includes TOGA (Tropical Ocean Global Atmosphere)-type models consisting of high-resolution tropical ocean models and coarse-resolution global atmosphere models, coarse-resolution global coupled models, and a few global coupled models with high resolution in the equatorial region in their ocean components. The performance of the annual mean state, the seasonal cycle and the interannual variability are investigated. The primary quantity analysed is sea surface temperature (SST). Additionally, the evolution of interannual heat content variations in the tropical Pacific and the relationship between the interannual SST variations in the equatorial Pacific to fluctuations in the strength of the Indian summer monsoon are investigated. The results can be summarised as follows: almost all models (even those employing flux corrections) still have problems in simulating the SST climatology, although some improvements are found relative to earlier intercomparison studies. Only a few of the coupled models simulate the El Niño/Southern Oscillation (ENSO) in terms of gross equatorial SST anomalies realistically. In particular, many models overestimate the variability in the western equatorial Pacific and underestimate the SST variability in the east. The evolution of interannual heat content variations is similar to that observed in almost all models. Finally, the majority of the models show a strong connection between ENSO and the strength of the Indian summer monsoon. 相似文献
395.
Christopher M. Free Olaf P. Jensen Sherri A. Mason Marcus Eriksen Nicholas J. Williamson Bazartseren Boldgiv 《Marine pollution bulletin》2014
Despite the large and growing literature on microplastics in the ocean, little information exists on microplastics in freshwater systems. This study is the first to evaluate the abundance, distribution, and composition of pelagic microplastic pollution in a large, remote, mountain lake. We quantified pelagic microplastics and shoreline anthropogenic debris in Lake Hovsgol, Mongolia. With an average microplastic density of 20,264 particles km−2, Lake Hovsgol is more heavily polluted with microplastics than the more developed Lakes Huron and Superior in the Laurentian Great Lakes. Fragments and films were the most abundant microplastic types; no plastic microbeads and few pellets were observed. Household plastics dominated the shoreline debris and were comprised largely of plastic bottles, fishing gear, and bags. Microplastic density decreased with distance from the southwestern shore, the most populated and accessible section of the park, and was distributed by the prevailing winds. These results demonstrate that without proper waste management, low-density populations can heavily pollute freshwater systems with consumer plastics. 相似文献
396.
An unusual nodular form of monazite has been found to account for abnormally high levels of cerium in panned heavy mineral concentrates from stream sediments in several areas in Wales and pan of Exmoor. Textural features indicate a pre-metamorphic, diagenetic origin within Lower Palaeozoic shale or siltstone host-rocks but REE patterns show only minor variation, including relative enrichment in europium, from ‘average’ granitic monazite. The similarities between these occurrences, described for the first time from the British Isles, and those previously described from Brittany and elsewhere are discussed. 相似文献