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11.
The Tennessee–Tombigbee Waterway (Tenn–Tom) was one of the first and largest water resources projects constructed after the
enactment of the National Environmental Policy Act of 1969. This highly controversial project was in litigation for 9 of the
13 years it was under construction. Substantial and innovative measures were incorporated into the project design to minimize
environmental damage and to promote environmental protection. Additionally, a wide variety of environmental mitigation measures,
including the acquisition and management of 35,614 ha of wildlife habitat to compensate for unavoidable impacts. This paper,
which updates a paper published by the American Society of Civil Engineers in 1996, presents an update of the environmental
and restorative measures incorporated into the design, construction, operation, and management of the Tenn–Tom some 15 years
after it was opened for navigation. The paper examines the accuracy of selected predicted impacts, waterway utilization, and
the effectiveness of environmental measures.
Received: 13 March 2000 · Accepted: 12 June 2000 相似文献
12.
Hydrated mineral surfaces play an important role in many processes in biological, geological, and industrial applications. An energy force field was developed for molecular mechanics and molecular dynamics simulations of hydrated carbonate minerals and was applied to investigate the behavior of water on the calcite surface. The force field is a significant development for large-scale molecular simulations of these systems, and provides good agreement with experimental and previous modeling results. Simulations indicate that water molecules are significantly ordered near the calcite surface. The predominant surface configuration (75-80%) results from coordination of a water molecule with a single calcium cation-carbonate anion pair, while the less common situation involves water coordination with two ion pairs. Surface restructuring and variation in coordination in the water layers results in distinct distances for water oxygens above the calcite surface—a two-component first monolayer (2.3 and 3.0 Å) and a secondary monolayer (5.0 Å). The different coordinations also alter lateral displacement, hydrogen bonding, and surface-normal orientation of the water molecules. The ordering of water molecules and the formation of a unique hydrogen bonding network at the calcite surface influence the physical properties of the interfacial water. Surface exchange of water molecules is observed by molecular dynamics simulation to occur at a rate of one exchange per 10 ps. Diffusion coefficients derived from mean square displacement analysis of atomic trajectories indicate a dependence of water transport based on the distance of the water molecules from the calcite surface. 相似文献
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14.
Alberto M. V��squez Zhenguang Huang Ward B. Manchester IV Richard A. Frazin 《Solar physics》2011,274(1-2):259-284
A three-dimensional (3D) tomographic reconstruction of the local differential emission measure (LDEM) of the global solar corona during the whole heliosphere interval (WHI, Carrington rotation CR 2068) is presented, based on STEREO/EUVI images. We determine the 3D distribution of the electron density, mean temperature, and temperature spread, in the range of heliocentric heights 1.03 to 1.23 R ??. The reconstruction is complemented with a potential-field source-surface (PFSS) magnetic-field model. The streamer-core, streamer-leg, and subpolar regions are analyzed and compared to a similar analysis previously performed for CR 2077, very near the absolute minimum of Solar Cycle 23. In each region, the typical values of density and temperature are similar in both periods. The WHI corona exhibits a streamer structure of relatively smaller volume and latitudinal extension than during CR 2077, with a global closed-to-open density contrast about 6% lower, and a somewhat more complex morphology. The average basal electron density is found to be about 2.23 and 1.08×108 cm?3, in the streamer core and subpolar regions, respectively. The electron temperature is quite uniform over the analyzed height range, with average values of about 1.13 and 0.93 MK, in the streamer core and subpolar regions, respectively. Within the streamer closed region, both periods show higher temperatures at mid-latitudes and lower temperatures near the Equator. Both periods show ??>1 in the streamer core and ??<1 in the surrounding open regions, with CR 2077 exhibiting a stronger contrast. Hydrostatic fits to the electron density are performed, and the scale height is compared to the LDEM mean electron temperature. Within the streamer core, the results are consistent with an isothermal hydrostatic plasma regime, with the temperatures of ions and electrons differing by up to about 10%. In the subpolar open regions, the results are consistent with departures from thermal equilibrium with T ions>T e (and values of T ions/T e up to about 1.5), and/or the presence of wave-pressure mechanisms linear in the density. 相似文献
15.
Li-Da Xing Jin Ba Martin G.Lockley Hendrik Klein Sheng-Wu Yan Anthony Romilio Chun-Yong Chou W.Scott Persons IV 《古地理学报》2018,(1)
Upper Triassic and Middle Jurassic strata of the Xichang Basin in Sichuan Province, southwestern China, yielded important dinosaur ichnofossils. From the Xujiahe Formation of the Yiguojiao tracksite, we report a Late Triassic footprint assemblage in China and the first discovery of diagnostic Triassic sauropodomorph tracks in this region. The tracks share a number of features in common with the ichnogenera Eosauropus(Late Triassic) and Liujianpus(Early Jurassic). The neighboring Bingtu tracksite is stratigraphically younger(Shaximiao Formation, Middle Jurassic) and preserves small tridactyl theropod tracks that represent the first occurrence of the ichnotaxon Carmelopodus in China and Asia. While these tracks are morphologically comparable to those from the Middle Jurassic type locality in North America, the specimens from China show the proximal margin of the digit IV impression in a more cranial position, which may indicate a trackmaker with a relatively short metatarsal IV. In addition to the skeletal record, the Carmelopodus footprints document the presence of small theropods in the dinosaur fauna of the Middle Jurassic Shaximiao Formation. 相似文献
16.
Is seagrass an important nursery habitat for the Caribbean spiny lobster,panulirus argus,in Florida?
Donald C. Behringer Mark J. Butler IV William F. Herrnkind John H. Hunt Charles A. Acosta William C. Sharp 《新西兰海洋与淡水研究杂志》2013,47(1):327-337
Caribbean spiny lobster (Panulirus argus) settle preferentially in macroalgal‐covered hard‐bottom habitat, but seagrass is more prevalent in Florida (United States) and the Caribbean, so even low settlement of lobsters within seagrass could contribute substantially to recruitment if post‐settlement survival and growth were high. We tested the role of seagrass and hard‐bottom habitats for P. argus recruitment in three ways. We first explored possible density‐dependent regulation of early benthic juvenile lobster survival within cages deployed in seagrass and hard‐bottom habitats. Second, we compared settlement and survival of P. argus in both habitats, by comparing the recovery of microwire‐tagged early benthic juveniles from patches of seagrass and hard‐bottom. Finally, we assessed the relative abundance of juvenile lobsters in each habitat by deploying artificial structures in seagrass sites and compared these data with data from similar deployments of artificial structures in hard‐bottom habitat in other years. More early benthic juvenile lobsters were recovered from cages placed in hard‐bottom than in seagrass, but mortality of the early benthic life stage was high in both habitats. In regional surveys, the mean number of lobsters recovered from artificial shelters deployed within seagrass was lower than in any year that we sampled hard‐bottom, indicating that fewer lobsters reside naturally in seagrass, particularly large juveniles >40 mm carapace length. The greater abundance (and likely survival) of juvenile P. argus that we observed in hard‐bottom habitat as opposed to seagrass, combined with previous studies demonstrating that postlarval P. argus are attracted to, settle in, and metamorphose more quickly in red macroalgae, confirm that macroalgae‐dominated hard‐bottom habitat appears to be the preferred and more optimal nursery for Caribbean spiny lobster. 相似文献
17.
He Qing Xing Lid Zhang Jianping Martin G. Lockley Hendrik Klein W. Scott Persons IV Qi Liqi Jia Chengkai 《《地质学报》英文版》2013,87(6):1477-1485
A pterosaur-bird track assemblage from a sandstone-siltstone-mudstone sequence of the Lower Cretaceous Tugulu Group of Xinjiang comprises the first pterosaur track record from this province and the largest specimen thus far known from China.The pterosaur tracks are assigned to the ichnogenus Pteraichnus based on the triangular overall-shape,the four elongate digit traces and the robust manual digit trace Ⅲ.Supposed trackmakers were dsungaripterid pterodactyloids whose skeletal remains are well known from the Tugulu Group.The bird tracks that occur on the same surface,are those of typical shorebirds,known from different other localities in southeast Asia.The congruence with Koreanaornis dodsoni described from the same stratigraphic level justifies an assignment to this ichnospecies.This is a further evidence of the co-occurrence of pterosaurs and birds in a typical iakeshore environment with possible seasonal alteration of water supply and aerial exposure indicated by wave ripples,mudcracks and repeated cycles of coarse to fine sediment.Pterosaurs and birds frequented the shoreline and may have fed also on the numerous invertebrates such as the Scoyenia tracemaker that left abundant burrows. 相似文献
18.
It is generally believed that the heating of the solar corona is caused by waves originating in the photosphere and propagating into the corona where their energy is dissipated. The medium through which these waves propagate is in general permeated by magnetic fields complicating the behaviour of this propagation considerably. We have therefore analysed the wave motions in a plasma permeated by constant magnetic and gravitational fields. In general, three waves modes were found, which we called the + mode, –mode, and the Alfvén mode. Each mode was found to be strongly coupled to each of the three kinds of motion; acoustic, gravity, and hydromagnetic. However, the Alfvén mode was found to be separable from the dispersion relation, and therefore independent of compressibility and gravity. The local dispersion relation is derived and expressed in nondimensional form independent of the constants that describe a particular atmosphere. From the dispersion relation one can show that rising waves propagate either with a constant or a growing wave amplitude depending on the magnitudes and directions of the gravitational field, magnetic field, and the wave vector. The variation of the density with height is taken into account by a generalized W.K.B. method. Equations are found which give the height at which wave reflection occurs, giving the upper bound for possible wave propagation.Work supported by the National Aeronautics and Space Administration under Research Grant NGR-29-001-016.On leave of absence from the Desert Research Institute and Department of Physics, University of Nevada, Reno, Nevada, U.S.A. 相似文献
19.
Martin F. Hilfinger IV Henry T. Mullins Adam Burnett Matthew E. Kirby 《Journal of Paleolimnology》2001,26(3):293-305
A series (N = 12) of short (< 1 m) sediment cores were collected from meromictic Green Lake in Fayetteville, New York to investigate potential anthropogenic impacts on the watershed during historic time and environmental change over the past ~ 2,500 years. Stratigraphic data document an abrupt basinwide change during the early 1800's A.D. from brown laminated sediments to grey varved sediments separated by a transition zone rich in aquatic moss. Deforestation of the region by European settlers during the early 1800's A.D. resulted in a flux of nutrients and increased biological productivity followed by a 7fold increase in sediment accumulation rates. Elemental geochemical data document the anthropogenic loading of lead to the to the lake basin via atmospheric fallout. Stable oxygen isotope (18O calcite) data also provide evidence for an abrupt shift in the isotopic composition of lake water ~ 150–200 years ago. This isotopic shift could have been a local phenomenon related to an increased supply of summer enriched precipitation following removal of forest vegetation, or it might have reflected broader scale climatic changes. We hypothesize that the 18O calcite shift was the result of the polar front jet stream migrating from a more southerly prehistoric position to a contracted, northerly configuration ~ 150–200 years ago. Such a shift could have been natural, associated with the end of the Little Ice Age or it may have been anthropogenically forced. 相似文献
20.
David F. Naar Fernando Martinez R. N. Hey Thomas B. Reed IV Seth Stein 《Marine Geophysical Researches》1991,13(4):287-309
The Pito Rift area is the site of actively deforming oceanic lithosphere that has been primarily under extension for at least the past million years, based on kinematic reconstructions. The major morphologic features, Pito Deep and Pito Seamount, are aligned toward the Euler pole for relative motion between the Easter and Nazca plates. SeaMARC II side-scan and bathymetry data indicate that there are two general modes of faulting currently active in the Pito Rift area. One is associated with incipient rifting of old (3 Ma) Nazca lithosphere by large NW-SE normal faults, and the other is associated with a broad area of right-lateral transform shear between the Nazca and Easter plates. This transform shear is distributed over a broad region because of the northward growth of the East Rift and parallel tectonic rifting within the Pito Rift area. The majority of the Pito Rift area is composed of preexisting blocks of Nazca plate that are back-tilted away from Pito Deep and strike perpendicular to present and previous relative plate motions. This observation suggests that block-faulting and back-tilting are the primary mechanisms responsible for the distributed lithospheric extension, in agreement with gravity and magnetic analyses (Martinez et al., this issue).The only recent volcanic flows observed in side-scan data are from the Pito Seamount area and to the outside of the outer pseudofault of the East Rift. The significance of the young flows near the outer pseudofault is not understood. We interpret the flows extending northwest from the Pito Seamount as representing a newly formed seafloor spreading axis within the Pito Rift area. Gravity and magnetic analyses (Martinez et al., this issue) together with SeaMARC II bathymetry and side-scan data support this interpretation.Based on the tectonic evolution of the Easter microplate, we propose an evolutionary model for the formation of the Pito Rift area, where new tectonic grabens form immediately west of the previous graben and with slightly more counterclockwise orientation. The duration and history of tectonic activity for each graben are not well constrained. 相似文献