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221.
Jeffrey R. Knott Joanna M. Fantozzi Kelly M. Ferguson Summer E. Keller Khadija Nadimi Carolyn A. Rath Jennifer M. Tarnowski Michelle L. Vitale 《Quaternary Research》2012,78(2):363-372
Pluvial lake deposits are found throughout western North America and are frequently used to reconstruct regional paleoclimate. In Death Valley, California, USA, we apply the beach particle technique (BPT) of Adams (2003), Sedimentology, 50, 565–577 and Adams (2004), Sedimentology, 51, 671–673 to Lake Manly deposits at the Beatty Junction Bar Complex (BJBC), Desolation Canyon, and Manly Terraces and calculate paleowind velocities of 14–27 m/s. These wind velocities are within the range of present-day wind velocities recorded in the surrounding area. Sedimentary structures and clast provenance at Desolation Canyon and the Manly Terraces indicate sediment transport from north to south. Lake level, based on the elevation of constructional features, indicates that the hill west of the BJBC was an island and that the BJBC spits formed during simple lake regression. The data are consistent with the hypothesis that the present wind regime (velocity and direction) formed the pluvial Lake Manly features. 相似文献
222.
Sung-Chul Kim Jae E. Yang Dong-Kuk Kim Young-Wook Cheong Jeffrey Skousen Yeong-Sang Jung 《Environmental Earth Sciences》2012,66(1):327-335
Heavy metals in tailings and mining wastes from abandoned mines can be released into adjacent agricultural field and bioaccumulated
in crops or vegetables. Therefore, prediction of metal bioavailability has become an important issue to prevent adverse effect
of bioaccumulated metals on human health. In this study, single and sequential extraction methods were compared using multivariate
analysis to predict the bioavailability of Cd and As in contaminated rhizosphere soils. Single extraction using 0.1 M HCl
for Cd and 1.0 M HCl for As had an extraction efficiency of 8–12% for soil Cd and 14–17% for soil As compared to total concentration
extracted with aqua regia. Using sequential extraction, Fe–Mn-bound Cd (FR3) and residual Cd (FR5) were the dominant fractions
representing 43 and 41% of total Cd concentration. For As, the strongly absorbed form (FR2) was the most abundant chemical
fraction showing 45–54% of the total As concentration in soil. Multivariate analyses showed that single extraction with HCl
and total concentration of Cd and As in soil were significantly correlated to potato and green onion plant tissue metal concentration.
Although little information was obtained with multiple regression analysis because of multicollinearity of variables, the
result of principle component analysis (PCA) revealed that the highest positive loading was obtained using total concentration
of Cd and As in soil in the first principle component (PC1). In addition, total concentration of Cd and As in soil was independently
grouped with other chemical fractions by cluster analysis. Therefore, the overall result of this research indicated that total
concentrations of Cd and As in rhizosphere soils were the best predictors of bioavailability of heavy metals in these contaminated
soils. 相似文献
223.
Jeffrey Chiarenzelli Robin Lock Carol Cady Adria Bregani Benn Whitney 《Environmental Earth Sciences》2012,67(1):189-204
Water from four north-flowing rivers (Oswegatchie, Grasse, Raquette, and West Branch of the St. Regis) traversing three distinct geologic terranes (Adirondack Highlands, Adirondack Lowlands, St. Lawrence Valley), originating in the acidified northern Adirondack region, display rapid spatial changes in downriver multi-element chemistry and physical parameters. Downriver, most soluble elements increase (Ba, Ca, Cu, K, Mg, Na, Rb, S, and Sr) while statistically significant decreases in insoluble elements (Al, Ce, Dy, Er, Fe, Gd, La, Mn, Nd, Pr, and Y) also occur. Lithium, Si, and Zr did not show a consistent increasing or decreasing trend. Concentrations of most elements measured on June 5, 2008 were greater than 7?weeks later; however, greater discharge and lower pH enhanced Al concentrations occurred during the later sampling date. Elemental ratios track changes in lithology, anthropogenic influence, and pH. The Raquette River shows the least variation in elemental concentrations because of storage in numerous hydropower reservoirs and has non-detectable concentrations of some redox sensitive elements such as Co, Ni, and V. Oswegatchie tributaries display similar geochemical trends dependent upon their location and local bedrock and show geochemical trends along the trunks of major rivers that are also evident in smaller drainage basins. Comparison with analytical results from the Western Adirondack Stream Survey also indicates acidification is prevalent in the Adirondack Highlands, particularly in the Oswegatchie headwaters during periods of high flow, but acidity is rapidly buffered downriver due to interaction with marble in the Adirondack Lowlands. 相似文献
224.
Liming He Jing M. Chen Shaoliang Zhang Gustavo Gomez Yude Pan Kevin McCullough Richard Birdsey Jeffrey G. Masek 《International Journal of Applied Earth Observation and Geoinformation》2011
Forest disturbances such as harvesting, wildfire and insect infestation are critical ecosystem processes affecting the carbon cycle. Because carbon dynamics are related to time since disturbance, forest stand age that can be used as a surrogate for major clear-cut/fire disturbance information has recently been recognized as an important input to forest carbon cycle models for improving prediction accuracy. In this study, forest disturbances in the USA for the period of ∼1990–2000 were mapped using 400+ pairs of re-sampled Landsat TM/ETM scenes in 500m resolution, which were provided by the Landsat Ecosystem Disturbance Adaptive Processing System project. The detected disturbances were then separated into two five-year age groups, facilitated by Forest Inventory and Analysis (FIA) data, which was used to calculate the area of forest regeneration for each county in the USA. 相似文献
225.
Glacier recession and human vulnerability in the Yanamarey watershed of the Cordillera Blanca, Peru 总被引:2,自引:0,他引:2
Jeffrey T. Bury Bryan G. Mark Jeffrey M. McKenzie Adam French Michel Baraer Kyung In Huh Marco Alfonso Zapata Luyo Ricardo Jes��s G��mez L��pez 《Climatic change》2011,105(1-2):179-206
Glaciers in the Cordillera Blanca, Peru, are undergoing rapid retreat, in large part due to climate change. These changes are significantly altering water availability in the region and pose critical risks to local populations that are highly dependent on these resources for livelihoods. We examine these issues through an interdisciplinary and linked evaluation of hydrological change and livelihood vulnerability in the Yanamarey watershed. Physical observations of the Yanamarey glacier show acceleration in frontal retreat at a rate of 8 m decade???1 since 1970, accompanied by total volume loss on the order of 0.022 km3. Hydrological and hydrochemical analyses document a possible transformation of stream flow over the past decade as the seasonal storage capacity of the glacier has degraded. Recent stream discharge measurements from the proglacial lake below the glacier are more coincident with the highly variable seasonal precipitation than they were during the 1998?C1999 hydrological year. Local household perceptions of glacier recession and seasonal hydrological variability agree with this trend, which is increasing human vulnerability in the watershed. Household case-study survey results demonstrate that shifting water resources, increasing weather extremes and climate-related threats to tourism are all new vectors of vulnerability for household livelihoods. 相似文献
226.
Santos RG Martins AS Farias Jda N Horta PA Pinheiro HT Torezani E Baptistotte C Seminoff JA Balazs GH Work TM 《Marine pollution bulletin》2011,62(6):1297-1302
To show the influence of coastal habitat degradation on the availability of food for green turtles (Chelonia mydas), we assessed the dietary preferences and macroalgae community at a feeding area in a highly urbanized region. The area showed low species richness and was classified as degraded. We examined stomach contents of 15 dead stranded turtles (CCL = 44.0 cm (SD 6.7 cm)). The diet was composed primarily of green algae Ulva spp. (83.6%). In contrast, the macroalgae community was dominated by the green alga Caulerpa mexicana. We found a selection for red algae, seagrass and Ulva spp., and avoidance for C. mexicana and brown alga Dictyopteris delicatula. The low diversity of available food items, possibly a result of environmental degradation, likely contributed to the low dietary diversity. The nutritional implications of this restricted diet are unclear. 相似文献
227.
Christina L. Lopano Peter J. Heaney Jeffrey E. Post 《Geochimica et cosmochimica acta》2011,75(14):3973-3981
In this study, we applied time-resolved synchrotron X-ray diffraction (TRXRD) to develop kinetic models that test a proposed two-stage reaction pathway for cation exchange in birnessite. These represent the first rate equations calculated for cation exchange in layered manganates. Our previous work has shown that the substitution of K, Cs, and Ba for interlayer Na in synthetic triclinic birnessite induces measurable changes in unit-cell parameters. New kinetic modeling of this crystallographic data supports our previously postulated two-stage reaction pathway for cation exchange, and we can correlate the kinetic steps with changes in crystal structure. In addition, the initial rates of cation exchange, R (Å3 min−1), were determined from changes in unit-cell volume to follow these rate laws: R = 1.75[]0.56, R = 41.1[]1.10, R = 1.15[]0.50. Thus, the exchange rates for Na in triclinic birnessite decreased in the order: Cs ? K > Ba. These results are likely a function of hydration energy differences of the cations and the preference of the solution phase for the more readily hydrated cation. 相似文献
228.
Assessing potential repositories for geologic sequestration of carbon dioxide using numerical models can be complicated, costly,
and time-consuming, especially when faced with the challenge of selecting a repository from a multitude of potential repositories.
This paper presents a set of simple analytical equations (model), based on the work of previous researchers, that could be
used to evaluate the suitability of candidate repositories for subsurface sequestration of carbon dioxide. We considered the
injection of carbon dioxide at a constant rate into a confined saline aquifer via a fully perforated vertical injection well.
The validity of the analytical model was assessed via comparison with the TOUGH2 numerical model. The metrics used in comparing
the two models include (1) spatial variations in formation pressure and (2) vertically integrated brine saturation profile.
The analytical model and TOUGH2 show excellent agreement in their results when similar input conditions and assumptions are
applied in both. The analytical model neglects capillary pressure and the pressure dependence of fluid properties. However,
simulations in TOUGH2 indicate that little error is introduced by these simplifications. Sensitivity studies indicate that
the agreement between the analytical model and TOUGH2 depends strongly on (1) the residual brine saturation, (2) the difference
in density between carbon dioxide and resident brine (buoyancy), and (3) the relationship between relative permeability and
brine saturation. The results achieved suggest that the analytical model is valid when the relationship between relative permeability
and brine saturation is linear or quasi-linear and when the irreducible saturation of brine is zero or very small. 相似文献
229.
George O. Marmorino W.D. MillerGeoffrey B. Smith Jeffrey H. Bowles 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(3):316-321
Airborne hyperspectral and thermal infrared imagery collected over the Florida Current provide a view of the disintegration of a Sargassum drift line in 5 m s−1 winds. The drift line consists mostly of rafts 20-80 m2 in size, though aggregations larger than 1000 m2 also occur. Rafts tend to be elongated, curved in the upwind direction, and 0.1-0.5 °C warmer than the surrounding ocean surface. Long weed ‘trails’ extending upwind from the rafts are evidence of plants dropping out and being left behind more rapidly drifting rafts. The raft line may be a remnant of an earlier Sargassum frontal band, which is detectible as an upwind thermal front and areas of submerged weed. Issues are identified that require future field measurements. 相似文献
230.