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971.
The potential consequences of bedload transport of postlarvae for patterns of distribution of marine invertebrates were explored
by developing a bedload transport model for juvenile bivalves in a small estuary in New Jersey, USA. A simple numerical model
of tidal current hydrodynamics was developed based on field measurements of shear stresses near the bottom. Burrowing behavior
of bivalves was incorporated into the model of bedload transport by using estimates of entrainment rates of Gemma gemma and Mya arenaria in a laboratory flume, and jump lengths of the bivalves were estimated by methods previously developed for noncohesive particles.
Based on the flood domination and strong gradient of shear stresses in the Navesink estuary, our model predicted that juvenile
bivalves would accumulate in the center of the estuary, traveling up to several kilometers over 30 days. Field distributions
of juvenile bivalves were consistent with the model predictions for other species of bivalves but not for G. gemma, for which field distributions of both <500- and >500-μm individuals were concentrated in the eastern end of the estuary.
Differences between the bedload model and G. gemma distributions suggest that spatial variation in burrowing behavior or biological interactions are playing an important role
in maintaining distribution patterns of this species in spite of high levels of bedload transport. This modeling approach
is applicable to other juvenile benthic invertebrates that disperse as bedload and is a useful model against which to compare
field observations of rates of transport and patterns of distribution and abundance. 相似文献
972.
Sensitivity of MM5 and WRF mesoscale model predictions of surface winds in a typhoon to planetary boundary layer parameterizations 总被引:1,自引:1,他引:1
Sea surface winds and coastal winds, which have a significant influence on the ocean environment, are very difficult to predict.
Although most planetary boundary layer (PBL) parameterizations have demonstrated the capability to represent many meteorological
phenomena, little attention has been paid to the precise prediction of winds at the lowest PBL level. In this study, the ability
to simulate sea winds of two widely used mesoscale models, fifth-generation mesoscale model (MM5) and weather research and
forecasting model (WRF), were compared. In addition, PBL sensitivity experiments were performed using Medium-Range Forecasts
(MRF), Eta, Blackadar, Yonsei University (YSU), and Mellor–Yamada–Janjic (MYJ) during Typhoon Ewiniar in 2006 to investigate
the optimal PBL parameterizations for predicting sea winds accurately. The horizontal distributions of winds were analyzed
to discover the spatial features. The time-series analysis of wind speed from five sensitivity experimental cases was compared
by correlation analysis with surface observations. For the verification of sea surface winds, QuikSCAT satellite 10-m daily
mean wind data were used in root-mean-square error (RMSE) and bias error (BE) analysis. The MRF PBL using MM5 produced relatively
smaller wind speeds, whereas YSU and MYJ using WRF produced relatively greater wind speeds. The hourly surface observations
revealed increasingly strong winds after 0300 UTC, July 10, with most of the experiments reproducing observations reliably.
YSU and MYJ using WRF showed the best agreements with observations. However, MRF using MM5 demonstrated underestimated winds.
The conclusions from the correlation analysis and the RMSE and BE analysis were compatible with the above-mentioned results.
However, some shortcomings were identified in the improvements of wind prediction. The data assimilation of topographical
data and asynoptic observations along coast lines and satellite data in sparsely observed ocean areas should make it possible
to improve the accuracy of sea surface wind predictions. 相似文献
973.
Catarina Vinagre João Salgado Henrique N. Cabral Maria J. Costa 《Estuaries and Coasts》2011,34(4):663-674
River flow variability is known to influence estuarine production, yet knowledge on its effect upon estuarine food webs dynamics
is still scarce. Stable carbon and nitrogen isotopes were used to assess the effect of river flow in the connectivity and
food web interactions between the two main fish nursery areas of the Tagus estuary. The aims of the present work were to investigate
the seasonal variation in food web structure and the exchange rate of individuals of marine juvenile fish among estuarine
nurseries, to compare the spring of a rainy year (2001) with that of an average year (2000), and to investigate the impact
of the winter floods of 2001. A low level of connectivity was observed for the fish species that use these areas as nurseries.
In low river flow conditions, two isotopically distinct food webs were established in each nursery area. These food webs were
very sensitive to small variations in the freshwater input. Winter floods seem to disrupt the localized food webs that are
established in low river flow periods, leading to the re-establishment of a wider food web. While in rainy years this wide
food web is maintained until spring, in average years the food web undergoes fragmentation into two localized and isotopically
distinctive food webs. The increase in frequency of droughts due to climate change should lower the connectivity of the estuarine
fish nurseries food webs, causing habitat fragmentation and consequent loss in complexity and resilience. 相似文献
974.
Dhananjay A. Sant Sudesh K. Wadhawan Rajinder K. Ganjoo Nathani Basavaiah Prabhin Sukumaran Sourabh Bhattacharya 《Journal of the Geological Society of India》2011,78(2):147-156
The paraglacial sequence in the Leh valley, Ladakh Himalaya preserves imprints of various processes active during deglaciation
in the late phase of Last Glacial. In present work, a high resolution sedimentological record generated for Spituk is presented
identifying aeolian episodes, mudflow events from Ladakh Range and debris flows extending from Zanskar Range across present
Indus River. Two temporal phases of water ponding within Spituk Sequence are also identified. The seismites recorded at various
stratigraphic depths and their association with the sediment facies signifies gravity induced process besides possible seismic
activity as an added phenomena. Linkage between paraglacial processes since Last Glacial to Recent is tracked and evaluated. 相似文献
975.
D. Purushotham A. Narsing Rao M. Ravi Prakash Shakeel Ahmed G. Ashok Babu 《Journal of the Geological Society of India》2011,77(6):539-548
Maheshwaram watershed is situated in Ranga Reddy district of at a distance of about 30 km south of Hyderabad. The watershed
has an area of 53 km2 and has hard rock aquifers with semi-arid climate. The study area has been expanding at a fast pace and now has the distinction
of being one of the fastest growing urban centers, facing the problem of groundwater depletion and quality deterioration due
to the absence of perennial source of surface water and also due to over exploitation. Human activities involving industrial
and agricultural development and the inadequate management of land and water resources have, directly or indirectly resulted
in the degradation of environment viz. water and soil. 相似文献
976.
This paper assesses how far community led rural visions accord with the current thrust of rural planning policy delivery in
the UK. Adapting conventional visioning methods, qualitative techniques were used on eight different communities across urban,
exurban and rural Wales to elicit views relating to the kind of local countryside(s) that were desired. The results show that
the communities’ visions reflect an emerging consensus around local countryside priorities: multifunctionality, integration,
wider countryside protection, development based on need, and local distinctiveness according with the thrust of current planning
policy at national and local levels. However, there is a clear dichotomy between this and the reality of what communities
actually experienced in developments affecting their countryside. Here, universal criticism was encountered over the type,
pace and scale of development, the lack of rural specificity and the failure to take account of local community needs and
priorities. It is hypothesized that tensions between national and local politics and stakeholder power relations are playing
a crucial role in distorting the delivery of town and country planning. It is recommended that rural policy delivery must
become more “joined up” and rural proofed at national and local levels concomitant with a change in the operational culture
of agencies at the forefront of rural delivery. Essentially, effective engagement of top down approaches synergising with
bottom up community led ideas is long overdue. 相似文献
977.
First- and second-order adaptation to natural hazards and extreme events in the context of climate change 总被引:2,自引:1,他引:2
Jörn Birkmann 《Natural Hazards》2011,58(2):811-840
This paper deals with coping and adaptation processes to natural hazards and (potential) climate change impacts. Selected
response measures to natural hazards are critically reviewed with respect to the actual and potential consequences that these
measures might imply for additional adaptation needs and changes within social-ecological systems. In this context, the author
introduces the concept of first- and second-order adaptation processes in order to underline the cascade process that adaptation
implies, the potentials for failure, and the limits of adaptation. Important aspects of first- and second-order adaptation
processes as well as the issue of the limits of adaptation are illustrated based on observations and empirical work conducted
in Vietnam. In its final part, the paper discusses the findings in light of selected theoretical approaches that might help
to understand how stabilization and destabilization processes are influenced or even triggered by adaptation measures. 相似文献
978.
Monometamorphic metasediments of Paleozoic or Mesozoic age constituting Schneeberg and Radenthein Complex experienced coherent deformation and metamorphism during Late Cretaceous times. Both complexes are part of the Eoalpine high-pressure wedge that formed an intracontinental suture and occur between the polymetamorphosed Ötztal–Bundschuh nappe system on top and the Texel–Millstatt Complex below. During Eoalpine orogeny Schneeberg and Radenthein Complexes were south-dipping and they experienced a common tectonometamorphic history from ca. 115 Ma onwards until unroofing of the Tauern Window in Miocene times. This evolution is subdivided into four distinct tectonometamorphic phases. Deformation stage D1 is characterized by WNW-directed shearing at high temperature conditions (550–600°C) and related to the initial exhumation of the high-pressure wedge. D2 and D3 are largely coaxial and evolved during high- to medium-temperature conditions (ca. 450 to ≥550°C). These stages are related to advanced exhumation and associated with large-scale folding of the high-pressure wedge including the Ötztal-Bundschuh nappe system above and the Texel–Millstatt Complex below. For the area west of the Tauern Window, F2/F3 fold interference results in the formation of large-scale sheath-folds in the frontal part of the nappe stack (formerly called “Schlingentektonik” by previous authors). Earlier thrusts were reactivated during Late Cretaceous normal faulting at the base of the Ötztal–Bundschuh nappe system and its cover. Deformation stage D4 is of Oligo-Miocene age and accounted for tilting of individual basement blocks along large-scale strike-slip shear zones. This tilting phase resulted from indentation of the Southern Alps accompanied by the formation of the Tauern Window. 相似文献
979.
We have calculated the compressional, vibrational, and thermodynamic properties of Ni3S2 heazlewoodite and the high-pressure orthorhombic phase (with Cmcm symmetry) using the generalized gradient approximation
to the density functional theory in conjunction with the quasi-harmonic approximation. The predicted Raman frequencies of
heazlewoodite are in good agreement with room-temperature measurements. The calculated thermodynamic properties of heazlewoodite
at room conditions agree very well with experiments, but at high temperatures (especially above 500 K) the heat capacity data
from experiments are significantly larger than the quasi-harmonic results, indicating that heazlewoodite is anharmonic. On
the other hand, the obtained vibrational density of states of the orthorhombic phase at 20 GPa reveals a group of low-frequency
vibrational modes which are absent in heazlewoodite. These low-frequency modes contribute substantially to thermal expansivity,
heat capacity, entropy, and Grüneisen parameter of the orthorhombic phase. The calculated phase boundary between heazlewoodite
and the orthorhombic phase is consistent with high-pressure experiments; the predicted transition pressure is 17.9 GPa at
300 K with a negative Clapeyron slope of −8.5 MPa/K. 相似文献
980.
Sebastien Fleuret 《GeoJournal》2011,76(2):177-189
New organizations of care and social service delivery (especially the development of coordination and networks) are leading
to the definition new spaces. This article is based on examples of restructuring of health care systems in France and in Quebec.
Both are moving towards more integration of delivery of care. In Quebec, 95 territories were created with a leading structure:
the center for health and social services. This structure is responsible for bringing all the providers of services into a
network and for giving to the population the guarantee of continuity and quality of care. It results in a new geography of
health at the local scale. In France, continuity and quality of care are also used as arguments to justify changes in the
organization of the system. 相似文献