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921.
U. Altenberger R. Schmid R. Oberhänsli 《International Journal of Earth Sciences》2008,97(6):1301-1314
As part of the Yangtze plate, segments of the Dabie Shan terrane of Central China underwent ultra-high pressure metamorphism
during Triassic subduction. We studied the geochemistry of the abundant eclogites to evaluate the nature of the protoliths
and their geodynamic setting. Although some previous geochemical work exists, the analyses and interpretation herein are based
on a new subdivision of the ultra-high pressure sequence into basement and cover units (Changpu and Ganghe Unit), revealing
new and important results. In addition, eclogites of the so-called HP Unit south of the UHP units were studied. Whereas the
large ion lithophile elements indicate postmagmatic, metasomatic changes of some samples, the high-field strength elements
and the rare earth elements display original magmatic trends. The geochemical characteristics of the eclogites of the ultra-high
pressure areas display a strong dependence on their “structural” and geographic position. The eclogites of the basement and
the Changpu Unit indicate melt intrusion and extrusion in a continental rift system, i.e. during extensional tectonics. In
contrast, the Ganghe Unit is characterized by a pronounced chemical homogeneity. The composition of the eclogites indicates
generation from a mantle source highly influenced by slab-derived fluids. Those of the HP Unit show similar characteristics.
Magmatism of the Ganghe and HP Unit probably occurred in a continental arc setting. A similar age for both units, geographically
and/or tectonically separated, is possible. The geodynamic interpretation based on the geochemistry of the four units points
to a Neoproterozoic scenario in which the protoliths of the HP and the cover units could have been of similar age and deposited
in one evolving geological system. A rift-related larger-scale basin might have formed, e.g. a continental back-arc basin
behind a magmatic arc after or simultaneous to sedimentation and magmatism in the magmatic arc. Alternatively, magmatism occurred
in independent geodynamic settings, distinct in time and space. The units were juxtaposed during exhumation, after subduction
to varying depths. 相似文献
922.
923.
Nathan S. Hall R. Wayne Litaker Elizabeth Fensin Jason E. Adolf Holly A. Bowers Allen R. Place Hans W. Paerl 《Estuaries and Coasts》2008,31(2):402-418
A dense bloom of the ichthyotoxic dinoflagellate Karlodinium veneficum was discovered in the Neuse River Estuary, North Carolina, on 19 October 2006 and was associated with four subsequent fish
kills. Microscopic, photopigment, DNA, and toxicological techniques confirmed bloom identity and toxicity. High-resolution
spatio-temporal data from ship-board and fixed automated sampling stations provided a unique opportunity to investigate the
environmental conditions that initiated, maintained, and terminated the K. veneficum bloom. Bloom initiation and growth were favored by high nutrient availability and reduced dispersal during the period of
declining riverine discharge after Tropical Storm Ernesto. K. veneficum out-competed other co-occurring dinoflagellates, perhaps because of the production of karlotoxins that are known to act as
grazing deterrents and to facilitate mixotrophic feeding. Once the bloom was established, small-scale hydrodynamic processes,
coupled with vertical migration, concentrated cells along a frontal convergence to high densities (>200,000 cells per milliliter).
By 26 October 2006, wind mixing and possible nutrient stress disrupted the bloom. Release of cell-bound toxins during the
bloom collapse likely accounted for the associated fish kill events where fish were reported as exhibiting typical symptoms
of karlotoxin poisoning. The dynamics of this bloom underscore the tight control of harmful algal blooms by meteorological
forcing, hydrology, and sediment nutrient input in this shallow lagoonal estuary. 相似文献
924.
The monthly variations of below- and aboveground biomass of Spartina alterniflora were documented for a south Louisiana salt marsh from March 2004 to March 2005, and in March 2006 and 2007. The annual production rate above- and belowground was 1821 and 11,676 g m?2, respectively (Smalley method), and the annual production rate per biomass belowground was 10.7 g dry weight?1, which are highs along the latitudinal distributions of the plant’s range. The average root + rhizome/shoot ratio (R&R/S) was 2.6:1, which is lower than the R&R/S ratios of 4 to 5.1 reported for Spartina sp. marshes in the northeastern US. The belowground biomass increased from July to September and fluctuated between October and November, after which it declined until February when the growing season began. The belowground biomass was dominated by rhizomes, which declined precipitously in spring and then rose to a seasonal high in the month before declining again as the late summer rise in inflorescence began. Over half of the root biomass in a 30-cm soil profile was in the upper 10 cm, and in the 10- to 20-cm profile for rhizomes. The maximum March biomass above- and belowground was four to five times that of the minimum biomass over the four sampling years. The net standing stock (NSS) of N and P in live biomass aboveground compared to that in the belowground biomass was about 1.7 times higher and equal, respectively, but the NSS of N and P for the live + dead biomass was about six times higher belowground. The average nitrogen/phosphorous molar ratios of 16:1 aboveground is in agreement with the often tested N limitation of biomass accumulation aboveground, whereas the 37:1 belowground ratio suggests that there is an influence of P on R&R foraging for P belowground. Some implications for management and restoration are, in part, that salt marshes should be evaluated and examined using information on the plant’s physiology and production both below- and aboveground. 相似文献
925.
Tamás Mikes Dominik Christ Rüdiger Petri István Dunkl Dirk Frei Mária Báldi-Beke Joachim Reitner Klaus Wemmer Hazim Hrvatović Hilmar von Eynatten 《Swiss Journal of Geoscience》2008,101(1):31-54
Sandwiched between the Adriatic Carbonate Platform and the Dinaride Ophiolite Zone, the Bosnian Flysch forms a c. 3000 m thick, intensely folded stack of Upper Jurassic to Cretaceous mixed carbonate and siliciclastic sediments in the Dinarides. New petrographic, heavy mineral, zircon U/Pb and fission-track data as well as biostratigraphic evidence allow us to reconstruct the palaeogeology of the source areas of the Bosnian Flysch basin in late Mesozoic times. Middle Jurassic intraoceanic subduction of the Neotethys was shortly followed by exhumation of the overriding oceanic plate. Trench sedimentation was controlled by a dual sediment supply from the sub-ophiolitic high-grade metamorphic soles and from the distal continental margin of the Adriatic plate. Following obduction onto Adria, from the Jurassic–Cretaceous transition onwards a vast clastic wedge (Vranduk Formation) was developed in front of the leading edge, fed by continental basement units of Adria that experienced Early Cretaceous synsedimentary cooling, by the overlying ophiolitic thrust sheets and by redeposited elements of coeval Urgonian facies reefs grown on the thrust wedge complex. Following mid-Cretaceous deformation and thermal overprint of the Vranduk Formation, the depozone migrated further towards SW and received increasing amounts of redeposited carbonate detritus released from the Adriatic Carbonate Platform margin (Ugar Formation). Subordinate siliciclastic source components indicate changing source rocks on the upper plate, with ophiolites becoming subordinate. The zone of the continental basement previously affected by the Late Jurassic–Early Cretaceous thermal imprint has been removed; instead, the basement mostly supplied detritus with a wide range of pre-Jurassic cooling ages. However, a c. 80 Ma, largely synsedimentary cooling event is also recorded by the Ugar Formation, that contrasts the predominantly Early Cretaceous cooling of the Adriatic basement and suggests, at least locally, a fast exhumation. 相似文献
926.
Jeremy M. Testa W. Michael Kemp Walter R. Boynton James D. Hagy III 《Estuaries and Coasts》2008,31(6):1021-1037
We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage
treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We
analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions
and also computed monthly rates of net production of dissolved O2 and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt- and water-balance model.
Point-source loading of DIN and DIP to the estuary declined by 40–60% following upgrades to sewage treatment plants and correlated
with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration
resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottom-layer O2 consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower
estuary, chl-a, turbidity, and surface-layer net O2 production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary
appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average
river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chl-a and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value
of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems,
and (3) the potential water quality impacts of altered coastal food webs. 相似文献
927.
Coastal Habitat Use and Residency of Juvenile Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)
John K. Carlson Michelle R. Heupel Dana M. Bethea Lisa D. Hollensead 《Estuaries and Coasts》2008,31(5):931-940
Coastal habitat use and residency of a coastal bay by juvenile Atlantic sharpnose sharks, Rhizoprionodon terraenovae, were examined by acoustic monitoring, gillnet sampling, and conventional tag–recapture. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Crooked Island Sound, Florida. Over 3 years, sharks were monitored for periods of 1–37 days, with individuals regularly moving in and out of the study site. Individual sharks were continuously present within the study site for periods of 1–35 days. Patterns of movement could not be correlated with time of day. Home range sizes were typically small (average?=?1.29 km2) and did not vary on a yearly basis. Gillnet sampling revealed that juvenile Atlantic sharpnose sharks were present in all habitat types found within Crooked Island Sound, and peaks in abundance varied depending on month within a year. Although telemetry data showed that most individuals remained within the study site for short periods of time before emigrating, conventional tag–recapture data indicates some individuals return to Crooked Island Sound after extended absences (maximum length?=?1,352 days). Although conventional shark nursery theory suggests small sharks remain in shallow coastal waters to avoid predation, juvenile Atlantic sharpnose sharks frequently exited from protected areas and appear to move through deeper waters to adjacent coastal bays and estuaries. Given the high productivity exhibited by this species, the benefit gained through a nursery that reduces predation may be limited for this species. 相似文献
928.
This paper deals with groundwater hydrology at a prominent fracture zone landslide slope (Nuta–Yone landslides) in Japan with
an objective to explore an efficient method for the application of landslide stability enhancement measures. The correlation
analyses between the hydrological parameters and ground surface movement data at this landslide resulted in low correlation
values indicating that the geological formation of the area is extremely complex. For the purpose of understanding the groundwater
flow behavior in the landslide area, a three-dimensional transient groundwater flow model was prepared for a part of the landslide
slope, where the levels of effectiveness of applied landslide stability enhancement measures (in the form of multilayered
deep horizontal drains) are different, and was calibrated against the measured water surface elevations at different piezometer
locations. The parameter distributions in the calibrated model and the general directions of the groundwater flow in terms
of flow vectors and the results of particle tracking at the model site were interpreted to understand the reasons for variations
in effectiveness of existing landslide stability enhancement measures and to find potentially better locations for the implementation
of future landslide stability enhancement measures. From the modeling results, it was also understood that groundwater flow
model can be effectively used in better planning and locating the landslide stability enhancement measures. 相似文献
929.
印度板块和亚洲大陆在何时何地碰撞 总被引:1,自引:0,他引:1
印度板块和亚洲大陆的初始碰撞时间是所有相关的喜马拉雅-西藏造山体系演化模式的主控条件,并严重影响到对众多与青藏高原隆升和东亚大陆挤出相关的地质过程速率的解释,以及对新生代全球气候变化的理解。尽管印度板块和亚洲大陆汇聚的速率在55Ma突然减缓被广泛地认为是初始碰撞的标志,但这次碰撞所造成的主要构造效应直到20多个百万年以后才显现出来。对印度板块和亚洲大陆相对位置的重新估算,表明它们在55Ma时并没有达到可以彼此发生碰撞的距离。基于来自西藏新的野外证据和对已有数据的重新评估,认为初始碰撞发生在始新世—渐新世之交(约34Ma),并对55Ma时发生的地质事件提出了另一种解释 相似文献
930.
Bioaccumulation of heavy metals in organs of fresh water fish Cyprinus carpio (Common carp) 总被引:3,自引:2,他引:1
R. Vinodhini M.Sc. M.Phil. M. Narayanan M.Sc. Ph.D. 《International Journal of Environmental Science and Technology》2008,5(2):179-182
The objective of the present study is to determine the bioaccumulation of heavy metals in various organs of the fresh water fish exposed to heavy metal contaminated water system. The experimental fish was exposed to Cr, Ni, Cd and Pb at sublethal concentrations for periods of 32 days. The elements Cd, Pb, Ni and Cr were assayed using Shimadzu AA 6200 atomic absorption spectrophotometery and the results were given as μ/g dry wt. The accumulation of heavy metal gradually increases in liver during the heavy metal exposure period. All the results were statistically significant at p < 0.001. The order of heavy metal accumulation in the gills and liver was Cd > Pb > Ni > Cr and Pb > Cd > Ni > Cr. Similarly, in case of kidney and flesh tissues, the order was Pb > Cd > Cr > Ni and Pb > Cr > Cd > Ni. In all heavy metals, the bioaccumulation of lead and cadmium proportion was significantly increased in the tissues of Cyprinus carpio (Common carp). 相似文献