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71.
Simone Daniela Langhans Urs Richard Janine Rueegg Urs Uehlinger Peter Edwards Michael Doering Klement Tockner 《Aquatic Sciences - Research Across Boundaries》2013,75(3):335-348
Quantifying spatial and temporal dynamics of organic matter (OM) is critical both for understanding ecosystem functioning and for predicting impacts of landscape change. To determine the influence of different habitats and coarse particulate OM (CPOM) types upon floodplain OM dynamics, we quantified aerial input, lateral surface transfer, and surface storage of CPOM over an annual cycle on the near-natural floodplain of the River Tagliamento in NE-Italy. Using these data, we modelled floodplain leaf dynamics, taking account of the spatial distribution and hydrologic connectivity of habitats, and using leaf storage as a response variable. Mean aerial CPOM input to the floodplain was similar from riparian forest and islands, but surface transfer was greater from islands, supporting the suggestion that these habitats act as “islands of fertility” along braided rivers. Leaves were the lateral conveyor of energy to more open parts of the floodplain, whereas CPOM was mainly stored as small wood in vegetated islands and riparian forest. Simulating the loss of habitat diversity (islands, ponds) decreased leaf storage on the whole floodplain, on exposed gravel and in large wood accumulations. In contrast, damming (loss of islands, ponds and floods plus floodplain overgrowth) greatly increased storage on exposed gravel. A random shuffle of habitats led to a storage increase on exposed gravel, while that in large wood accumulations and ponds declined. These results disentangle some of the complexities of CPOM dynamics in floodplain ecosystems, illustrate the value of models in understanding ecosystem functioning at a landscape level, and directly inform river management practice. 相似文献
72.
Jacek?StankiewiczEmail author Michael?H.?Weber Ayman?Mohsen Rami?Hofstetter 《Pure and Applied Geophysics》2012,169(4):615-623
In the framework of the Dead Sea Integrated Research project (DESIRE), 59 seismological stations were deployed in the region
of the Dead Sea Basin. Twenty of these stations recorded data of sufficiently high quality between May and September 2007
to be used for ambient seismic noise analysis. Empirical Green’s functions are extracted from cross-correlations of long term
recordings. These functions are dominated by Rayleigh waves, whose group velocities can be measured in the frequency range
from 0.1 to 0.5 Hz. Analysis of positive and negative correlation lags of the Green’s functions makes it possible to identify
the direction of the source of the incoming energy. Signals with frequencies higher than 0.2 Hz originate from the Mediterranean
Sea, while low frequencies arrive from the direction of the Red Sea. Travel times of the extracted Rayleigh waves were measured
between station pairs for different frequencies, and tomographically inverted to provide independent velocity models. Four
such 2D models were computed for a set of frequencies, all corresponding to different sampling depths, and thus together giving
an indication of the velocity variations in 3D extending to a depth of 10 km. The results show low velocities in the Dead
Sea Basin, consistent with previous studies suggesting up to 8 km of recent sedimentary infill in the Basin. The complex structure
of the western margin of the Basin is also observed, with sedimentary infill present to depths not exceeding 5 km west of
the southern part of the Dead Sea. The high velocities associated with the Lisan salt diapir are also observed down to a depth
of ~5 km. The reliability of the results is confirmed by checkerboard recovery tests. 相似文献
73.
74.
James Flocks Michael D. Miner David C. Twichell Dawn L. Lavoie Jack Kindinger 《Geo-Marine Letters》2009,29(6):359-378
The barrier-island systems of the Mississippi River Delta plain are currently undergoing some of the highest rates of shoreline
retreat in North America (~20 m/year). Effective management of this coastal area requires an understanding of the processes
involved in shoreline erosion and measures that can be enacted to reduce loss. The dominant stratigraphy of the delta plain
is fluvial mud (silts and clays), delivered in suspension via a series of shallow-water delta lobes that prograded across
the shelf throughout the Holocene. Abandonment of a delta lobe through avulsion leads to rapid land subsidence through compaction
within the muddy framework. As the deltaic headland subsides below sea level, the marine environment transgresses the bays
and wetlands, reworking the available sands into transgressive barrier shorelines. This natural process is further complicated
by numerous factors: (1) global sea-level rise; (2) reduced sediment load within the Mississippi River; (3) diversion of the
sediment load away from the barrier shorelines to the deep shelf; (4) storm-induced erosion; and (5) human alteration of the
littoral process through the construction of hardened shorelines, canals, and other activities. This suite of factors has
led to the deterioration of the barrier-island systems that protect interior wetlands and human infrastructure from normal
wave activity and periodic storm impact. Interior wetland loss results in an increased tidal prism and inlet cross-sectional
areas, and expanding ebb-tidal deltas, which removes sand from the littoral processes through diversion and sequestration.
Shoreface erosion of the deltaic headlands does not provide sufficient sand to balance the loss, resulting in thinning and
dislocation of the islands. Abatement measures include replenishing lost sediment with similar material, excavated from discrete
sandy deposits within the muddy delta plain. These sand bodies were deposited by the same cyclical processes that formed the
barrier islands, and understanding these processes is necessary to characterize their location, extent, and resource potential.
In this paper we demonstrate the dominant fluvial and marine-transgressive depositional processes that occur on the inner
shelf, and identify the preservation and resource potential of fluvio-deltaic deposits for coastal management in Louisiana. 相似文献
75.
Albert M. Fowler K. Michael Merrill William Ball Arne Henden Fred Vrba Craig McCreight 《Experimental Astronomy》2002,14(1):61-68
The Orion program is a project to develop a 2K × 2K infrared focal plane using InSb p-on-n diodes for detectors. It is the
natural follow-up to the successful Aladdin 1K × 1K program started in the early 90's. The work is being done at the Raytheon
Infrared Operations Division (RIO, previously known as the Santa Barbara Research Center) by many of the same people who created
the Aladdin focal plane. The design is very similar to the successful Aladdin design with the addition of reference pixels,
whole array readout (no quadrants), two-adjacent-side buttability, and a packaging design that includes going directly to
the ultimate focal plane size of 4K × 4K. So far we have successfully made a limited number of hybrid modules with InSb detectors.
In this paper we will describe the design features and test data taken from some of these devices.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
Tomas?O.?H??kEmail author Edward?S.?Rutherford Shannon?J.?Brines Doran?M.?Mason David?J.?Schwab Michael?J.?McCormick Timothy?J.?DeSorcie 《Estuaries and Coasts》2003,26(1):21-29
The identification and protection of essential habitats for early life stages of fishes are necessary to sustain fish stocks.
Essential fish habitat for early life stages may be defined as areas where fish densities, growth, survival, or production
rates are relatively high. To identify critical habitats for young-of-year (YOY) alewives (Alosa pseud oharengus) in Lake Michigan, we integrated bioenergetics models with GIS (Geographic Information Systems) to generate spatially explicit
estimates of potential population production (an index of habitat quality). These estimates were based upon YOY alewife bioenergetic
growth rate potential and their salmonine predators’ consumptive demand. We compared estimates of potential population production
to YOY alewife yield (an index of habitat importance). Our analysis suggested that during 1994–1995, YOY alewife habitat quality
and yield varied widely throughout Lake Michigan. Spatial patterns of alewife yield were not significantly correlated to habitat
quality. Various mechanisms (e.g., predator migrations, lake circulation patterns, alternative strategies) may preclude YOY
alewives from concentrating in areas of high habitat quality in Lake Michigan. 相似文献
77.
In laboratory experiments, the influence of inflow and outflow sequences on the behavior of fine sedi-ment was investigated. The experimental set-up consisted of two interconnected rectangular basins, between which water was moved back and forth. Suspended sediment concentration in the main basin as well as the sediment exchange rates were derived from turbidity measurements.The suspended sediment ratio, SSR, and sediment exchange rates (influx sediment rate, ISR, and evacuated sediment rate, ESR) were measured. In twenty test runs, a parametric study on the magnitude and frequency of inflow and outflow cycles, the relative duration between inflow and outflow sequences, the initial sediment concentration, and the intake position was done. An initial test with stagnant water described the set-tling behavior of fine sediment and served as a reference scenario.The test results show that settling of fine particles near the intake/outlet structure can be considerably reduced by the nature of the inflow and outflow sequences. High cycle magnitude and frequency lead to maximum suspended sediment ratio in the system. For low discharges, the evolution of suspended sediment concentration cannot be directly correlated to the inflow and outflow cycles. However, compared to"no operation"conditions, the suspended sediment ratio could be increased by 10%to 40%locally. For high discharge, the evolution of suspended sediment concentration correlated with discharge cycles and suspended sediment ratios between 50%and 80%higher than for stagnant water could be achieved. Similar ratios could be obtained when the intake is located closer to the bottom or to the free water surface.Meanwhile, the overall sediment balance remained in equilibrium over the test period, indicating that the influx and evacuated sediment rates are not significantly influenced by the inflow and outflow cycles. 相似文献
78.
79.
80.
Michael E. McCormick 《Ocean Engineering》1976,3(3):133-144
The analysis of a pneumatic-type wave-energy conversion buoy is developed assuming independence of the buoy heaving motion and the motion of the water column within the center pipe. Results of the analysis are then compared with experimental data in a study of the relative air velocity within the turbine passage. The results compare very well. The effect of the variation of the center pipe length is found to be significant for periods about the surge chamber resonance but is negligible in the neighborhood of the heaving resonance period. Further, the theory is applied to a prototype buoy study of the U.S. Coast Guard, and a dimensionless design curve is developed from the results of the prototype analysis. 相似文献