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991.
Sediment transport and trapping in the Hudson River estuary 总被引:3,自引:0,他引:3
The Hudson River estuary has a pronounced turbidity maximum zone, in which rapid, short-term deposition of sediment occurs during and following the spring freshet. Water-column measurements of currents and suspended sediment were performed during the spring of 1999 to determine the rate and mechanisms of sediment transport and trapping in the estuary. The net convergence of sediment in the lower estuary was approximately 300,000 tons, consistent with an estimate based on sediment cores. The major input of sediment from the watershed occurred during the spring freshet, as expected. Unexpected, however, was that an even larger quantity of sediment was transported landward into the estuary during the 3-mo observation period. The landward movement was largely accomplished by tidal pumping (i.e., the correlation between concentration and velocity at tidal frequencies) during spring tides, when the concentrations were 5 to 10 times higher than during neap tides. The landward flux is not consistent with the long-term sediment budget, which requires a seaward flux at the mouth to account for the excess input from the watershed relative to net accumulation. The anomalous, landward transport in 1999 occurred in part because the freshet was relatively weak, and the freshet occurred during neapetides when sediment resuspension was minimal. An extreme freshet occurred during 1998, which may have provided a repository of sediment just seaward of the mouth that re-entered the estuary in 1999. The amplitude of the spring freshet and its timing with respect to the spring-neap cycle cause large interannual variations in estuarine sediment flux. These variations can result in the remobilization of previously deposited sediment, the mass of which may exceed the annual inputs from the watershed. 相似文献
992.
Harish Veeramani Daniel S. Alessi Juan S. Lezama-Pacheco Jonathan O. Sharp Urs Dippon John R. Bargar 《Geochimica et cosmochimica acta》2011,75(9):2512-6510
Reductive immobilization of uranium by the stimulation of dissimilatory metal-reducing bacteria (DMRB) has been investigated as a remediation strategy for subsurface U(VI) contamination. In those environments, DMRB may utilize a variety of electron acceptors, such as ferric iron which can lead to the formation of reactive biogenic Fe(II) phases. These biogenic phases could potentially mediate abiotic U(VI) reduction. In this work, the DMRB Shewanella putrefaciens strain CN32 was used to synthesize two biogenic Fe(II)-bearing minerals: magnetite (a mixed Fe(II)-Fe(III) oxide) and vivianite (an Fe(II)-phosphate). Analysis of abiotic redox interactions between these biogenic minerals and U(VI) showed that both biogenic minerals reduced U(VI) completely. XAS analysis indicates significant differences in speciation of the reduced uranium after reaction with the two biogenic Fe(II)-bearing minerals. While biogenic magnetite favored the formation of structurally ordered, crystalline UO2, biogenic vivianite led to the formation of a monomeric U(IV) species lacking U-U associations in the corresponding EXAFS spectrum. To investigate the role of phosphate in the formation of monomeric U(IV) such as sorbed U(IV) species complexed by mineral surfaces, versus a U(IV) mineral, uranium was reduced by biogenic magnetite that was pre-sorbed with phosphate. XAS analysis of this sample also revealed the formation of monomeric U(IV) species suggesting that the presence of phosphate hinders formation of UO2. This work shows that U(VI) reduction products formed during in situ biostimulation can be influenced by the mineralogical and geochemical composition of the surrounding environment, as well as by the interfacial solute-solid chemistry of the solid-phase reductant. 相似文献
993.
R. Nagarajan Priyadarsi D. Roy M.P. Jonathan Rufino Lozano Franz L. Kessler M.V. Prasanna 《Chemie der Erde / Geochemistry》2014
Multi-element geochemistry and mineralogy are used to characterize the chemical composition, degree of paleo-weathering, provenance and tectonic settings of the Neogene sedimentary rocks of Borneo Basin of east Malaysia. Sedimentary rocks are classified as extremely weathered sandstones (i.e. wacke, arkose, litharenite, Fe-sandstone and quartz arenite). Wacke, arkose, litharenite and Fe-sandstone are characterized by post-depositional K-metasomatism and zircon enrichment through sediment recycling. Geochemical characteristics suggest a mixed-nature provenance for the sandstones and the variable tectonic settings possibly mirror the complexity of the basin. Enriched Cr in quartz arenite and Fe-sandstone are related to the contribution from ophiolite or fractionation of Cr-bearing minerals. 相似文献
994.
995.
Dramatic climatic change in the Arctic elevates the importance of determining the risk of exposure for people living in vulnerable areas and developing effective adaptation programs. Climate change assessment reports are valuable, and often definitive, sources of information for decision makers when constructing adaptation plans, yet the scope of these reports is too coarse to identify site-specific exposure to the impacts of climate change and adaptation needs. Subsistence hunters and gatherers in the Arctic are valuable knowledge holders of climate-related change in their area. Incorporating both their traditional ecological knowledge and information found in climate science assessment reports can offer adaption planners a deeper understanding of exposure to climate change and local adaptation needs. In this study, we compare information found in assessment reports of climate change in the Arctic with what we have learned from the Alaskans Sharing Indigenous Knowledge project from 2009 to 2012, a research project documenting traditional ecological knowledge in two Native villages in Alaska, Savoonga and Shaktoolik. Content analysis of the interviews with hunters and gatherers reveal the site-specific impacts of climate change affecting these two villages. We find that their traditional ecological knowledge is complimentary and largely corroborates the climate science found in assessment reports. Traditional ecological knowledge, however, is more current to the social and local conditions of the villages, and presents a more unified social and biophysical portrayal of the impacts of climate change. If taken together, these two forms of knowledge can focus adaptation planning on the pertinent needs of the communities in question. 相似文献
996.
Climate change, ambient ozone, and health in 50 US cities 总被引:2,自引:1,他引:2
Michelle L. Bell Richard Goldberg Christian Hogrefe Patrick L. Kinney Kim Knowlton Barry Lynn Joyce Rosenthal Cynthia Rosenzweig Jonathan A. Patz 《Climatic change》2007,82(1-2):61-76
We investigated how climate change could affect ambient ozone concentrations and the subsequent human health impacts. Hourly
concentrations were estimated for 50 eastern US cities for five representative summers each in the 1990s and 2050s, reflecting
current and projected future climates, respectively. Estimates of future concentrations were based on the IPCC A2 scenario
using global climate, regional climate, and regional air quality models. This work does not explore the effects of future
changes in anthropogenic emissions, but isolates the impact of altered climate on ozone and health. The cities’ ozone levels
are estimated to increase under predicted future climatic conditions, with the largest increases in cities with present-day
high pollution. On average across the 50 cities, the summertime daily 1-h maximum increased 4.8 ppb, with the largest increase
at 9.6 ppb. The average number of days/summer exceeding the 8-h regulatory standard increased 68%. Elevated ozone levels correspond
to approximately a 0.11% to 0.27% increase in daily total mortality. While actual future ozone concentrations depend on climate
and other influences such as changes in emissions of anthropogenic precursors, the results presented here indicate that with
other factors constant, climate change could detrimentally affect air quality and thereby harm human health. 相似文献
997.
An ensemble of six 22-year numerical experiments was conducted to evaluate the ability of Regional Climate Model version 3 (RegCM3) to simulate the energy and water budgets of the midwestern United States. RegCM3 was run using two surface physics schemes: Integrated Biosphere Simulator (IBIS) and Biosphere-Atmosphere Transfer Scheme 1e (BATS1e), and two convective closure assumptions: Fritsch & Chappell (FC80) and Arakawa & Schubert (AS74). Boundary conditions were provided by the National Centers for Environmental Prediction-Department of Energy Reanalysis 2 dataset and the ECHAM5 general circulation model. A companion paper examines the American Midwest under future climate scenarios. Overall, the model that reproduces the observed seasonal cycles of the midwestern United States climate system best is RegCM3 using IBIS and the AS74 convective closure assumption. IBIS simulates shortwave radiation more accurately, while BATS1e simulates longwave radiation more accurately. Summer two-meter air temperature is overestimated by the combination of IBIS and the FC80 convective closure assumption. All models contain a wet bias and overestimate evapotranspiration during the spring. Total runoff, surface runoff, groundwater runoff, and root zone soil moisture are best simulated by RegCM3 using IBIS and the AS74 convective closure assumption. While BATS1e does capture the seasonal cycle of total runoff, gross errors in the partitioning of total runoff between surface runoff and groundwater runoff exist. The seasonal cycle of root zone soil moisture simulated by RegCM3 using IBIS and the AS74 convective closure assumption is dry, but agrees with observations during the summer. The rest of the models underestimate root zone soil moisture. 相似文献
998.
999.
Wang T Lu Y Chen C Naile JE Khim JS Park J Luo W Jiao W Hu W Giesy JP 《Marine pollution bulletin》2011,62(8):1905-1914
Perfluorinated compounds (PFCs) in water, sediment, soil, and biota collected from estuarine and coastal areas of the north Bohai Sea, China, were determined by use of HPLC-MS/MS. Significant concentrations of PFCs were found in water (mean: 18.4 ng/l) and biologic samples (fish: 265 ng/g dw), while concentrations of PFCs in soils and sediments were less. The predominately detected compound was perfluorooctanesulfonate (PFOS), with a maximum concentration of 30.9 ng/l in water and 791 ng/g dw in fish. Concentrations of PFCs were significantly greater in the Liaohe River system than other locations, which suggests point sources in this urbanized and industrialized region. PFOS concentrations in water and biota were both less than the reported threshold concentrations. Detection of PFCs at relatively great concentrations in various environmental matrices from this region suggested that further studies characterizing concentrations of PFCs, their sources and potential risk to both humans and wildlife are needed. 相似文献