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251.
252.
Hurricane impact and recovery shoreline change analysis of the Chandeleur Islands,Louisiana, USA: 1855 to 2005 总被引:1,自引:0,他引:1
Sarah Mary Fearnley Michael D. Miner Mark Kulp Carl Bohling Shea Penland 《Geo-Marine Letters》2009,29(6):455-466
Results from historical (1855–2005) shoreline change analysis conducted along the Chandeleur Islands, Louisiana demonstrate
that tropical cyclone frequency dominates the long-term evolution of this barrier island chain. Island area decreased at a
rate of −0.16 km2/year for the relatively quiescent time period up until 1996, when an increase in tropical cyclone frequency accelerated this
island area reduction to a rate of −1.01 km2/year. More frequent hurricanes also affected shoreline retreat rates, which increased from −11.4 m/year between 1922 and
1996 to −41.9 m/year between 1982 and 2005. The erosional impact caused by the passage of Hurricane Katrina in 2005 was unprecedented.
Between 2004 and 2005, the shoreline of the northern islands retreated −201.5 m/year, compared with an average retreat rate
of −38.4 m/year between 1922 and 2004. A linear regression analysis of shoreline change predicts that, as early as 2013, the
backbarrier marsh that serves to stabilize the barrier island chain will be completely destroyed if storm frequency observed
during the past decade persists. If storm frequency decreases to pre-1996 recurrence intervals, the backbarrier marsh is predicted
to remain until 2037. Southern portions of the barrier island chain where backbarrier marsh is now absent behave as ephemeral
islands that are destroyed after storm impacts and reemerge during extended periods of calm weather, a coastal behavior that
will eventually characterize the entire island chain. 相似文献
253.
Rachel M. Jeffreys George A. Wolff Sarah J. Murty 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1816-1833
The Arabian Sea is subject to intense seasonality resulting from biannual monsoons, which lead to associated large particulate fluxes and an abundance of organic carbon, a potential food source at the seafloor for benthic detritivores. We used the stable isotopes of carbon and nitrogen alongside lipid analyses to examine potential food sources (particulate and sedimentary organic matter, POM and SOM respectively) in order to determine trophic linkages for the twelve most abundant megafaunal species (Pontocaris sp., Solenocera sp., Munidopsis aff. scobina, Actinoscyphia sp., Actinauge sp., Echinoptilum sp., Pennatula aff. grandis, Astropecten sp. Amphiura sp. Ophiura euryplax, Phormosoma placenta and Hyalinoecia sp.) at the Pakistan Margin between 140 and 1400 m water depth. This transect spans a steep gradient in oxygen concentrations and POM flux. Ranges of δ13C and δ15N values were narrow in POM and SOM (4‰ and 2‰ for δ13C and δ15N, respectively) with little evidence of temporal variability. Labile lipid compounds in SOM originating from phytoplankton did exhibit seasonal change in their concentrations at the shallowest sites, 140 and 300 m. Benthic megafauna had broad ranges in δ13C and δ15N (>10‰ and >8‰ for δ13C and δ15N, respectively) suggesting they occupy several trophic levels and utilize a variety of food sources. There is evidence for feeding niche separation between and within trophic groups. Lipid biomarkers in animal tissues indicate a mixture of food sources originating from both phytoplankton (C20:5(n-3) and C22:6(n-3)) and invertebrate prey (C20:1 and C22:1). Biomarkers originating from phytodetritus are conserved through trophic transfer to the predator/scavengers. Six species (Pontocaris sp., Solenocera sp., Actinoscyphia sp., Echinoptilum sp., Amphiura sp. and Hyalinoecia sp.) showed a significant biochemical response to the seasonal supply of food and probably adapt their trophic strategy to low food availability. Biotransformation of assimilated lipids by megafauna is evident from polyunsaturated fatty acid distributions, for example, Echinoptilum sp. converts C20:5(n-3) to C24:6(n-3). 相似文献
254.
255.
Ecosystems have been viewed both as chaotic, untamed nature, and as mechanical systems with predictable equilibrium states. A developing concept of ecosystems as “complex adaptive systems” lies between these extreme concepts, with recognizably patterned but not fully predictable behavior. Sustainability has also been redefined as humans have exploited and often depleted desirable natural resources. Fisheries management desires sustainable yield, but must rethink this concept within the ecosystem context. The most powerful union of “ecosystem” and “sustainability” acknowledges the defining characteristics of complex adaptive systems with the objective of identifying and sustaining healthy relationships within and between ecosystems, economies, and society. 相似文献
256.
Tim Beach Sheryl Luzzadder-Beach Nicholas Dunning John Jones Jon Lohse Tom Guderjan Steve Bozarth Sarah Millspaugh Tripti Bhattacharya 《Quaternary Science Reviews》2009,28(17-18):1710-1724
In the Maya Lowlands of Mexico, Belize, and Guatemala two main types of wetlands have played important roles in human history: bajos or intermittently wet environments of the upland, interior Yucatán and perennial wetlands of the coastal plains. Many of the most important Maya sites encircle the bajos, though our growing evidence for human–wetland interactions is still sparse. The deposits of these wetlands record two main eras of slope instability and wetland aggradation: the Pleistocene–Holocene transition as rainfall increased and forests eclipsed savannas and the Maya Preclassic to Classic as deforestation, land-use intensity, and drying increased. The ancient Maya adapted with terraces around these bajo margins but retracted in the Late Preclassic in some areas. The perennial wetlands of the coastal plains have different histories, and the first conceptual model of human–wetland interaction described intensive wetland agriculture in the Preclassic through Classic based on raised fields and canals. But a second model arose that interpreted the wetland stratigraphy and canals as more indicative of natural aggradation by accelerated erosion and gypsum precipitation that buried Archaic and Preclassic fields and there was little Classic era use. We present new data on a third and fourth model in this study. The third is a hybrid of the models one and two, including the Archaic to Preclassic aggradation of the second model, and the first model's Classic period fields and canals as piecemeal attempts by the Maya to adapt to these and other environmental changes. The fourth conceptual model describes a very Late/Terminal Classic, preplanned project on a floodplain. These wetland fields were short-lived, aggraded rapidly but with some reoccupation in the Postclassic. All of these new models display the burgeoning evidence for intricate Maya interactions with wetlands, and the diversity of evidence from the relatively few studies underscores the infancy of our understanding of Maya interaction with tropical wetlands. 相似文献
257.
258.
Laserprobe 40Ar–39Ar data from fault‐related pseudotachylytes and granitic host‐rocks from the Tatra Mountains (Central Western Carpathians) resolve the controversy over the age of propagation of the sub‐Tatra detachment fault. This major structure has resulted in exhumation of crystalline basement to the north‐west, and subsidence and sediment deposition in the Palaeogene Central Carpathians Basin to the south‐east. Host‐rock biotite ages range from 331 Ma to 322 Ma, and pseudotachylyte spot ages range from 164 Ma to 28 Ma. Of these, the youngest group identify the maximum timing of the early stages of Tatra Mountains uplift, which continued in the Miocene (20–10 Ma) and culminated during the Quaternary. The wide‐ranging older ages are an artefact of an unsupported 40Ar component that is most likely a combination of both inherited and excess argon. 相似文献
259.
A traversing micro-erosion meter (TMEM) was used to measure micro-scale surface changes in a 45 cm2 area of an intertidal mudstone shore platform on Kaikoura Peninsula, New Zealand, with hourly readings taken over 5 days for two seasons, within 4 h either side of low tide. For all monitoring events, the relative height of a total of 120 co-ordinates were obtained, resulting in 4200 and 4800 measurements for the summer and winter seasons respectively. Within seasons, samples were grouped according to the presence of rain or no rain. Significant changes were found in the micro-topography with variations in temperature and among rain and no rain sample groups. For both seasons, in the absence of rain, there were positive linear relationships between rock surface temperatures and rock surface elevations, and regression analysis explained 42.3% and 46.5% of this variation for the summer (y = 0.098 + 0.004x; p-value = 0.007) and winter (y = 0.007 + 0.012x; p-value < 0.001) seasons respectively. It is suggested that incorporating weather readings alongside measurements of surface change could not only improve extrapolations of shore platform erosion from short-term studies, but also differentiate fluctuations in rock surfaces due to changes in rock surface temperatures from other processes involved in shore platform erosion. 相似文献
260.
The introduction of invasive bivalves such as the zebra mussel (Dreissena polymorpha) can have profound effects on aquatic ecosystems, including decreases in phytoplankton biomass and changes in the taxonomic
composition of phytoplankton. Zebra mussel introductions have been associated with increased dominance of cyanobacteria, especiallyMicrocystis, but this change may depend on interacting physical, chemical, or biotic conditions. We used a 12-yr record in the Hudson
River to explore the relationship between phytoplankton composition and zebra mussel filtration. During this period (1993–2005),
the mean July–September filtration rate of the zebra mussel (ZMF) varied by 8-fold, and the mean biovolume of cyanobacteria,
which was dominated byMicrocystis, varied from 0 to 4.2 mm3 1−1 and comprised up to 52% of total phytoplankton biovolume. There was a tendency for high cyanobacterial biomass to be associated
with low rather than high ZMF. Neither the absolute nor the relative amounts of either total cyanobacteria orMicrocystis were significantly correlated to ZMF alone or in combination with total phosphorus or any other, physical or chemical parameters
that we measured. Cyanobacteria dominance and abundance were both strongly correlated to temperature, and over 80% of the
among year variance in cyanobacterial dominance could be explained by temperature in a linear model. Temperature in combination
with dissolved SiO3 explained 90% of the variation in cyanobacterial dominance. At higher temperatures and lower dissolved SiO3, cyanobacterial abundance increased, at the expense of diatoms that dominated at lower temperatures and a higher SiO3 years. The high explanatory value of temperature is surprising as the variation in temperature among years was relatively
low (24.0–26.8°C). The results suggest that event slightly increased temperatures could lead to higher biomass and dominance
of cyanobacteria in some aquatic systems. 相似文献