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Mary Jo Baedecker Robert P. Eganhouse Haiping Qi Isabelle M. Cozzarelli Jared J. Trost Barbara A. Bekins 《Ground water》2018,56(5):797-809
The composition of crude oil in a surficial aquifer was determined in two locations at the Bemidji, MN, spill site. The abundances of 71 individual hydrocarbons varied within 16 locations sampled. Little depletion of these hydrocarbons (relative to the pipeline oil) occurred in the first 10 years after the spill, whereas losses of 25% to 85% of the total measured hydrocarbons occurred after 30 years. The C6‐30 n‐alkanes, toluene, and o‐xylene were the most depleted hydrocarbons. Some hydrocarbons, such as the n‐C10–24 cyclohexanes, tri‐ and tetra‐ methylbenzenes, acyclic isoprenoids, and naphthalenes were the least depleted. Benzene was detected at every sampling location 30 years after the spill. Degradation of the oil led to increases in the percent organic carbon and in the δ 13C of the oil. Another method of determining hydrocarbon loss was by normalizing the total measured hydrocarbon concentrations to that of the most conservative analytes. This method indicated that the total measured hydrocarbons were depleted by 47% to 77% and loss of the oil mass over 30 years was 18% to 31%. Differences in hydrocarbon depletion were related to the depth of the oil in the aquifer, local topography, amount of recharge reaching the oil, availability of electron acceptors, and the presence of less permeable soils above the oil. The results from this study indicate that once crude oil has been in the subsurface for a number of years there is no longer a “starting oil concentration” that can be used to understand processes that affect its fate and the transport of hydrocarbons in groundwater. 相似文献
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Mary D. Curtis 《The Journal of geography》2019,118(3):130-142
Preparing learners for the future requires twenty-first-century teaching that integrates professional tools in the classroom. Geospatial technologies (GST), which represent geographical professional technologies, lack robust integration in high school geography. Researchers continue to ask why educators teach about rather than with GST. Understanding teacher decisions is paramount. This mixed methods study examined commonalities among teachers who use GST using Mishra and Koehler’s (2006) Technological, Pedagogical, Content Knowledge (TPCK) framework as a theoretical lens. This investigation examined whether geography teachers who exhibit stronger geospatial TPCK used GST more frequently than other teachers who exhibited a less developed knowledge base. 相似文献
166.
Potential climate-change impacts on the Chesapeake Bay 总被引:1,自引:0,他引:1
Raymond G. Najjar Christopher R. Pyke Mary Beth Adams Denise Breitburg Carl Hershner Michael Kemp Robert Howarth Margaret R. Mulholland Michael Paolisso David Secor Kevin Sellner Denice Wardrop Robert Wood 《Estuarine, Coastal and Shelf Science》2010
We review current understanding of the potential impact of climate change on the Chesapeake Bay. Scenarios for CO2 emissions indicate that by the end of the 21st century the Bay region will experience significant changes in climate forcings with respect to historical conditions, including increases in CO2 concentrations, sea level, and water temperature of 50–160%, 0.7–1.6 m, and 2–6 °C, respectively. Also likely are increases in precipitation amount (very likely in the winter and spring), precipitation intensity, intensity of tropical and extratropical cyclones (though their frequency may decrease), and sea-level variability. The greatest uncertainty is associated with changes in annual streamflow, though it is likely that winter and spring flows will increase. Climate change alone will cause the Bay to function very differently in the future. Likely changes include: (1) an increase in coastal flooding and submergence of estuarine wetlands; (2) an increase in salinity variability on many time scales; (3) an increase in harmful algae; (4) an increase in hypoxia; (5) a reduction of eelgrass, the dominant submerged aquatic vegetation in the Bay; and (6) altered interactions among trophic levels, with subtropical fish and shellfish species ultimately being favored in the Bay. The magnitude of these changes is sensitive to the CO2 emission trajectory, so that actions taken now to reduce CO2 emissions will reduce climate impacts on the Bay. Research needs include improved precipitation and streamflow projections for the Bay watershed and whole-system monitoring, modeling, and process studies that can capture the likely non-linear responses of the Chesapeake Bay system to climate variability, climate change, and their interaction with other anthropogenic stressors. 相似文献
167.
Hurricane impact and recovery shoreline change analysis of the Chandeleur Islands,Louisiana, USA: 1855 to 2005 总被引:1,自引:0,他引:1
Sarah Mary Fearnley Michael D. Miner Mark Kulp Carl Bohling Shea Penland 《Geo-Marine Letters》2009,29(6):455-466
Results from historical (1855–2005) shoreline change analysis conducted along the Chandeleur Islands, Louisiana demonstrate
that tropical cyclone frequency dominates the long-term evolution of this barrier island chain. Island area decreased at a
rate of −0.16 km2/year for the relatively quiescent time period up until 1996, when an increase in tropical cyclone frequency accelerated this
island area reduction to a rate of −1.01 km2/year. More frequent hurricanes also affected shoreline retreat rates, which increased from −11.4 m/year between 1922 and
1996 to −41.9 m/year between 1982 and 2005. The erosional impact caused by the passage of Hurricane Katrina in 2005 was unprecedented.
Between 2004 and 2005, the shoreline of the northern islands retreated −201.5 m/year, compared with an average retreat rate
of −38.4 m/year between 1922 and 2004. A linear regression analysis of shoreline change predicts that, as early as 2013, the
backbarrier marsh that serves to stabilize the barrier island chain will be completely destroyed if storm frequency observed
during the past decade persists. If storm frequency decreases to pre-1996 recurrence intervals, the backbarrier marsh is predicted
to remain until 2037. Southern portions of the barrier island chain where backbarrier marsh is now absent behave as ephemeral
islands that are destroyed after storm impacts and reemerge during extended periods of calm weather, a coastal behavior that
will eventually characterize the entire island chain. 相似文献
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169.
A collaborative programme searching for mmag pulsations in chemically peculiar stars in the northern hemisphere was initiated
in 1997 between Nainital, India, and Cape Town, South Africa. It was therefore named as theNainital-Cape Survey programme. The detection limits imposed by the observing conditions (including atmospheric noise and telescope size) at both
Manora Peak and Devasthal sites are described. The scintillation noise on the best photometric nights is≈ 0.1 to 0.2 mmag for these sites. Both places allow one to detect few mmag variation in bright stars(B ≤ 12 mag), and are therefore particularly well-suited for carrying out the proposed survey work. The main characteristics of
the three-channel photometer developed at ARIES for carrying out the observations are also presented. This excellent instrument
has been used extensively since 1999 at the f/13 Cassegrain focus of ARIES’ 104 cm telescope. In particular, it allowed the
survey to result in the discovery of δ Scuti like pulsations in four Am stars, in one rapidly oscillating Ap star, and in
a number of probable variables so far. The future prospects are then presented, which regard the acquisition of a high speed
time series CCD photometer, a project to build a 3-metre class telescope at Devasthal, and collaborative observations with
Indian and foreign astronomical sites. 相似文献
170.