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291.
Transparent exopolymer particle (TEP) distributions were examined in North Carolina’s Neuse River Estuary (NRE) over a 1-year
period, and experiments were conducted to examine controls upon TEP formation. TEP-carbon averaged 16% of the total organic
carbon pool in the NRE. From May to early August 2007, TEP ranged from 805 to 1,801 μg xanthan gum (XG) L−1. A large phytoplankton bloom peaked in early August and then subsequently declined. Within 2 weeks of the bloom’s peak, TEP
concentrations increased to >3,500 μg XG L−1 and remained elevated through mid-December. Decreasing water temperatures and enhanced retention due to drought conditions
in Fall 2007 likely aided in the persistence of TEP concentrations during this timeframe. Thereafter, TEP decreased coincident
with increased river flow and flushing of the estuary that began in January 2008, and TEP remained low (ranging from 991 to
1,712 μg XG L−1) until the end of April 2008. TEP was positively correlated with salinity, suggesting that cation availability (which co-varies
with salinity and stabilizes the structural integrity of TEP) may play a role in estuarine TEP formation. In two cation addition
experiments using water from the mesohaline region, TEP concentrations tended to be higher in treatments with vs. without
cations added. Statistically significant relationships were also found between in situ TEP concentrations and pH, mixing,
and temperature, suggesting that a complex suite of environmental parameters affect TEP formation and its distribution in
estuaries. 相似文献
292.
293.
陕西关中及周边地区近500a来初夏旱涝事件初步分析 总被引:4,自引:0,他引:4
基于华山树轮宽度差值年表重建的陕西关中及周边地区近500a来的初夏干燥指数序列,对该地区初夏极端旱涝事件及其连续旱涝变化特征进行了初步分析.区域干燥指数与Palmer指数在变化上极为相似,可用于反映该地区的旱涝变化.结果表明:该地区近500a来初夏共发生18次极端干旱事件和11次极端洪涝事件,除公元1521年与历史文献记录的旱涝事件相反,公元1513年、1574年、1675年和1945年未发现历史记录外,其余年份均能找到相应记录;近500a来初夏存在9个显著的连续偏旱期和10个显著的连续偏涝期,并以16和19世纪发生的连续旱涝事件最为频繁,而17和18世纪发生的旱涝事件相对较少,20世纪发生的干旱事件明显多于洪涝事件. 相似文献
294.
295.
Dr. Hans Krumm 《International Journal of Earth Sciences》1962,51(2):478-493
Zusammenfassung Der Tonmineralbestand fränkischer Keuper- und Lias-Tone wechselt in vertikaler Richtung deutlich zwischen Sedimenten unterschiedlicher Entstehungsbedingungen. In horizontaler Richtung bleibt er dagegen innerhalb dieser Einheiten ziemlich gleich. Bei den terrestrischen Sedimenten kann eine Wechselwirkung zwischen Verwitterung (Klima), Ablagerung und Tonmineralbestand verfolgt werden, bei den marinen Sedimenten ist dies infolge der Umbildungen im marinen Milieu schwierig.Eine ausführliche Veröffentlichung soll demnächst erscheinen in Beiträge zur Mineralogie und Petrographie. 相似文献
296.
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
297.
Soil erosion susceptibility assessment and validation using a geostatistical multivariate approach: a test in Southern Sicily 总被引:2,自引:0,他引:2
A certain number of studies have been carried out in recent years that aim at developing and applying a model capable of assessing
water erosion of soil. Some of these have tried to quantitatively evaluate the volumes of soil loss, while others have focused
their efforts on the recognition of the areas most prone to water erosion processes. This article presents the results of
a research whose objective was that of evaluating water erosion susceptibility in a Sicilian watershed: the Naro river basin.
A geomorphological study was carried out to recognize the water erosion landforms and define a set of parameters expressing
both the intensity of hydraulic forces and the resistance of rocks/soils. The landforms were mapped and classified according
to the dominant process in landsurfaces affected by diffuse or linear water erosion. A GIS layer was obtained by combining
six determining factors (bedrock lithology, land use, soil texture, plan curvature, stream power index and slope-length factor)
in unique conditions units. A geostatistical multivariate approach was applied by analysing the relationships between the
spatial distributions of the erosion landforms and the unique condition units. Particularly, the density of eroded area for
each combination of determining factors has been calculated: such function corresponds, in fact, to the conditional probability
of erosion landforms to develop, under the same geoenvironmental conditions. In light of the obtained results, a general geomorphologic
model for water erosion in the Naro river basin can be depicted: cultivated areas in clayey slopes, having fine-medium soil
texture, are the most prone to be eroded; linear or diffuse water erosion processes dominate where the topography is favourable
to a convergent or divergent runoff, respectively. For each of the two erosion process types, a susceptibility map was produced
and submitted to a validation procedure based on a spatial random partition strategy. Both the success of the validation procedure
of the susceptibility models and the geomorphological coherence of the relationships between factors and process that such
models suggest, confirm the reliability of the method and the goodness of the predictions. 相似文献
298.
Prof. Dr. Hans Ertel 《Pure and Applied Geophysics》1963,55(1):119-122
Resumen Como aplicación hidrodinámica de un problema más general, tratado al principio, demostraremos el siguiente teorema:El rotacional del campo de la variación unitaria del torbellino de las partículas que se mueven rotacionalmente en líquidos ideales y homogéneos puede representarse por medio de paréntesis deLagrange.
Zusammenfassung Als hydrodynamische Anwendung eines eingangs behandelten allgemeineren Problems wird folgender Satz bewiesen:Der Rotor des Feldes der individuellen Ableitung des Wirbelvektors der sich drehend bewegenden Partikel idealer und homogener inkompressibler Flüssigkeiten läßt sich mittels der Klammersymbole vonLagrange darstellen.相似文献
299.
Rudolf?BráZdilEmail author Christian?Pfister Heinz?Wanner Hans?Von?Storch JüRg?Luterbacher 《Climatic change》2005,70(3):363-430
This paper discusses the state of European research in historical climatology. This field of science and an overview of its development are described in detail. Special attention is given to the documentary evidence used for data sources, including its drawbacks and advantages. Further, methods and significant results of historical-climatological research, mainly achieved since 1990, are presented. The main focus concentrates on data, methods, definitions of the “Medieval Warm Period” and the “Little Ice Age”, synoptic interpretation of past climates, climatic anomalies and natural disasters, and the vulnerability of economies and societies to climate as well as images and social representations of past weather and climate. The potential of historical climatology for climate modelling research is discussed briefly. Research perspectives in historical climatology are formulated with reference to data, methods, interdisciplinarity and impacts. 相似文献
300.