Sediment Suspension and Deposition Across Restored Oyster Reefs of Varying Orientation to Flow: Implications for Restoration     

Allison M. Colden  Kelsey A. Fall  Grace M. Cartwright  Carl T. Friedrichs 《Estuaries and Coasts》2016,39(5):1435-1448

The eastern oyster, Crassostrea virginica, is a prominent ecosystem engineer, whose reefs exhibit strikingly consistent morphologies at multiple spatial scales throughout its North American range. These distinct morphologies are thought to form by interactions of nascent reef structures with hydrodynamics. We carried out two field studies to determine if historical reef configurations applied in a restoration context would improve reef persistence and restoration outcomes. We collected seabed and water column observations across constructed reefs of three orientations representative of those found historically throughout the oyster’s range: parallel or perpendicular to tidal currents or circular. Areas adjacent to reefs were sites of fine sediment trapping, with lower flow velocities, evidence of particle settling, and more fine sediments on the seabed relative to off-reef reference sites. The water column above the reef crest exhibited higher acoustic backscatter, higher flow velocities, and larger particles in suspension, consistent with local erosion of flocculated fine sediment from the reef crest. Perpendicular reefs produced conditions that were more conducive to reef persistence and improved oyster performance, including high flow velocities and enhanced resuspension of sediments from the reef, compared to parallel or circular reefs. Particle trapping in areas between reefs has the potential to inhibit reef growth between existing reef structures, providing support for hypotheses of landscape-scale reef pattern formation. Oyster reef restoration efforts can benefit from this improved understanding of biophysical interactions arising from reef orientation that contribute to sediment dynamics on constructed oyster reefs.  相似文献   

Late Pleistocene baldcypress (Taxodium distichum) forest deposit on the continental shelf of the northern Gulf of Mexico     

Kristine L. Delong  Suyapa Gonzalez  Jeffrey B. Obelcz  Jonathan T. Truong  Samuel J. Bentley Sr  Kehui Xu  Carl A. Reese  Grant L. Harley  Alicia Caporaso  Zhixiong Shen  Beth A. Middleton 《Boreas: An International Journal of Quaternary Research》2021,50(3):871-892

Approximately 13 km south of Gulf Shores, Alabama (United States), divers found in situ baldcypress (Taxodium distichum) stumps 18 m below the ocean surface. These trees could have only lived when sea level fell during the Pleistocene subaerially exposing the tectonically stable continental shelf. Here we investigate the geophysical properties along with microfossil and stratigraphical analyses of sediment cores to understand the factors that lead to this wood’s preservation. The stumps are exposed in an elongated depression (~100 m long, ~1 m deep) nested in a trough of the northwest–southeast trending Holocene sand ridges and troughs with 2–5 m vertical relief and ~0.5 km wavelength. Radiocarbon ages of the wood were infinite thus optically stimulated luminescence (OSL) dating was used to constrain the site’s age. Below the Holocene sands (~0.1–4 m thick), separated by a regional erosional unconformity, are Late Pleistocene mud-peat (72±8 ka OSL), mud-sand (63±5, 73±6 ka OSL), and palaeosol (56±5 ka OSL) facies that grade laterally from west to east, respectively. Foraminiferal analysis reveals the location of the terrestrial-marine transitional layer above the Pleistocene facies in an interbedded sand and mud facies (3940±30 (1σ) ¹⁴C a BP), which is part of a lower shoreface or marine-dominated estuarine environment. The occurrence of palaeosol and swamp facies of broadly similar ages and elevation suggests the glacial landscape possessed topographic relief that allowed wood, mud and peats to be preserved for ~50 ka of subaerial exposure before transitioning to the modern marine environment. We hypothesize that rapid sea-level rise occurring ~60 or ~40 ka ago provided opportunities for local flood-plain aggradation to bury the swamp thus preserving the stumps and that other sites may exist in the northern Gulf of Mexico shelf.  相似文献   

An Automatic Well Planner for Complex Well Trajectories     

Kristoffersen  Brage S.  Bellout  Mathias C.  Silva  Thiago L.  Berg  Carl F. 《Mathematical Geosciences》2021,53(8):1881-1905

Mathematical Geosciences - A data-driven automatic well planner procedure is implemented to develop complex well trajectories by efficiently adapting to near-well reservoir properties and geometry....  相似文献   

Social–ecological memory in urban gardens—Retaining the capacity for management of ecosystem services     

Stephan Barthel  Carl Folke  Johan Colding 《Global Environmental Change》2010,20(2):255-265

Many ecosystem services are in decline. Local ecological knowledge and associated practice are essential to sustain and enhance ecosystem services on the ground. Here, we focus on social or collective memory in relation to management practice that sustains ecosystem services, and investigate where and how ecological practices, knowledge and experience are retained and transmitted. We analyze such social–ecological memory of allotment gardens in the Stockholm urban area, Sweden. Allotment gardens support ecosystem services such as pollination, seed dispersal and pest regulation in the broader urban landscape. Surveys and interviews were preformed over a four-year period with several hundreds of gardeners. We found that the allotment gardens function as communities-of-practice, where participation and reification interact and social–ecological memory is a shared source of resilience of the community by being both emergent and persistent. Ecological practices and knowledge in allotment gardens are retained and transmitted by imitation of practices, oral communication and collective rituals and habits, as well as by the physical gardens, artifacts, metaphors and rules-in-use (institutions). Finally, a wider social context provides external support through various forms of media, markets, social networks, collaborative organizations, and legal structures. We exemplify the role of urban gardens in generating ecosystem services in times of crisis and change and conclude that stewards of urban green areas and the social memory that they carry may help counteract further decline of critical ecosystem services.  相似文献   

The transport of fine-grained sediments in shallow waters     

Carl Kirk Ziegler  Wilbert Lick 《Environmental Geology》1988,11(1):123-132

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Jari: A pulp plantation in the Brazilian Amazon     

Dr. Carl F. Jordan  Dr. Charles E. Russell 《GeoJournal》1989,19(4):429-435

Jari plantation is the largest pulp growing operation in the humid tropics, and occupies about 1000 sqkm previously covered by tropical forest. A study of five sites at Jari in 1980 indicated declining soil fertility, and low productivity of pulpwood. Low pulp production at Jari was caused by several factors, one of which appeared to be low soil fertility. The sams sites were re-evaluated in 1987. There was no discernable trend in either nutrients or productivity since 1980.Although productivity and nutrient stocks may have stabilized, low profitability caused by low pulp production resulted in the sale of Jari in 1982, for a $ 720 million loss. Despite growth rates at Jari which were too low to produce a profit on original investment, another plantation is planned for the eastern Amazon which is 10 times the size of Jari.  相似文献   

Capture Zones for Simple Aquifers   总被引：1，自引：0，他引：1  

Carl D. McElwee 《Ground water》1991,29(4):587-590

Abstract. The protection and cleanup of aquifers is a matter of high priority for all states and the federal government. One concept that is receiving increased attention is that of wellhead protection. Capture zones showing the area influenced by a well within a certain time are useful for both aquifer protection and cleanup. If hydrodynamic dispersion is neglected, a deterministic curve defines the capture zone. Analytical expressions for the capture zones can be derived for simple aquifers. However, the capture zone equations are transcendental and cannot be explicitly solved for the coordinates of the capture zone boundary. Fortunately, an iterative scheme allows the solution to proceed quickly and efficiently even on a modest personal computer. Three forms of the analytical solution must be used in an iterative scheme to cover the entire region of interest, after the extreme values of the x coordinate are determined by an iterative solution. The resulting solution is a discrete one, and usually 100-1000 intervals along the x-axis are necessary for a smooth definition of the capture zone. The presented program is written in FORTRAN and has been used in a variety of computing environments. No graphics capability is included with the program; it is assumed the user has access to a commercial package. The superposition of capture zones for multiple wells is expected to be satisfactory if the spacing is not too close. Because this program deals with simple aquifers, the results rarely will be the final word in a real application. However, the program is useful as a first phase in developing wellhead protection or aquifer cleanup schemes.  相似文献   

Correction of the paper “A study of meteorite falls”     

Frans E Wickman  Carl D Palmer 《Journal of Earth System Science》1985,94(2):185-186

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Petrological evidence for the development of refolded folds during a single deformational event     

Carl E. Jacobson 《Journal of Structural Geology》1984,6(5):563-570

The Pelona Schist, which forms the lower plate of the Vincent thrust in the San Gabriel Mountains of southern California, has undergone a complex history of folding. The youngest folds in the schist (style 2 folds) range in shape from open to tight and fold both compositional layering and schistosity. These are superposed upon isoclinal folds with axial-plane schistosity (style 1 folds) that, in turn, overprint older isoclinal folds (also called style 1 folds). Samples from the hinges of style 2 folds contain two generations of muscovite. Muscovites of the older generation are parallel to the folded (style 1) schistosity. The newer muscovites recrystallized during and/or after style 2 folding. Microprobe analysis indicates that the two generations of muscovite are very similar in composition, although the new muscovites tend to have slightly higher paragonite and celadonite contents than the old muscovites. From the gross similarity of the two groups of muscovite, it is concluded that the style 1 and style 2 folds were produced during a single progressive deformation. The slightly higher paragonite and celadonite contents of the new muscovites are thought to indicate that both pressure and temperature were increasing during the deformation. This is consistent with the deformation being due to underthrusting of the Pelona Schist beneath the upper plate of the Vincent thrust.  相似文献   

Boundary-layer structure near the cold front of a marine cyclone during “ERICA”     

Bradford W. Berger  Carl A. Friehe 《Boundary-Layer Meteorology》1995,73(3):227-253

The boundary layer in the warm sector of a moderately deepening winter cyclone during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) is studied near the cold front. Data from the National Center for Atmospheric Research Electra research aircraft are used to examine mean and turbulence quantities. The aircraft data and supplemental data from ships, drifting buoys and moored buoys reveal an equivalent-barotropic pressure field. The area is found to be dominated by gradients in temperature and in turbulent fluxes, with changes occurring over 100 km horizontally being comparable to changes over 350 m vertically. The horizontal components of the gradients are found to be a maximum in a direction perpendicular to the front. Cross-sections perpendicular to the front are used to illustrate boundary-layer structure. Profiles of wind speed, stress, wind direction and stress direction are estimated from an Ekman model that is modified to take into account the equivalent-barotropic pressure field. Comparison of profiles from the model to the aircraft-measured data show reasonable agreement far from the front (100 km) when the model uses a constant eddy viscosity of approximately 6 kg m^–1 s^–1. Near the front there is less agreement with the model. Profiles of turbulent fluxes of momentum, heat and latent heat are divergent, with along-wind momentum flux negative and decreasing upward, cross-wind momentum flux positive and increasing upward, and heat flux and latent heat flux small, positive and decreasing upward. Far from the front, the turbulent kinetic energy budget shows that dissipation balances shear production. However, near-front behavior has an imbalance at low altitude, with shear production appearing as a TKE sink.  相似文献