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151.
Katey M. Walter Melanie Engram Claude R. Duguay Martin O. Jeffries F.S. Chapin III 《Journal of the American Water Resources Association》2008,44(2):305-315
Abstract: Arctic lakes are significant emitters of methane (CH4), a potent greenhouse gas, to the atmosphere; yet no rigorous quantification of the magnitude and variability of pan‐Arctic lake emissions exists. In this study, we demonstrate the potential for a new method using synthetic aperture radar (SAR) imagery to detect methane bubbles in lake ice to scale up whole‐lake measurements of CH4 ebullition (bubbling) to regional scales. We estimated ebullition from lakes, which is often the dominant mode of lake emissions, by mapping the distribution of bubble clusters frozen in early winter ice across surfaces of seven tundra lakes and one boreal forest lake in Alaska. Applying previously measured ebullition rates associated with four distinct classes of bubble clusters found in lake ice, we estimated whole‐lake emissions from individual lakes. The percent surface area of lake ice covered with bubbles (R2 = 0.68) and CH4 ebullition rates from lakes (R2 = 0.59) and were correlated with radar return values from RADARSAT‐1 Standard Beam mode 3 for the tundra lakes, suggesting that with appropriate scaling and consideration for variability in lake‐ice conditions, this technique has the potential to be used for estimating broader‐scale regional and pan‐Arctic lake methane emissions. 相似文献
152.
Peter A. Cott Paul K. Sibley Andrew M. Gordon R.A. Bodaly Kenneth H. Mills W. Murray Somers Gerald A. Fillatre 《Journal of the American Water Resources Association》2008,44(2):328-342
Abstract: In northern regions, large volumes of water are needed for activities such as winter road construction. Such withdrawals, particularly from small lakes, can reduce oxygen concentrations and water levels, potentially affecting aquatic organisms. Withdrawal limits have been developed by regulatory agencies, but are largely theoretical. Water withdrawal thresholds were tested in two small lakes by removing 10% and 20% of their respective under‐ice volumes and comparing oxygen parameters, temperature, over‐wintering habitat, and northern pike (Esox lucius) abundance to reference conditions. Because of a milder winter, oxygen parameters were elevated in reference lakes in the period following withdrawal compared to the prewithdrawal period. The 10% withdrawal resulted in a ?0.2 m shift in the oxygen concentration profile at 4 mg/l in that lake, but had no effect on total volume‐weighted oxygen, or volume of over‐wintering habitat. In contrast, the 20% withdrawal caused 0.7 m reduction in the oxygen concentration profile at 4 mg/l compared to the previous year, a 26% decline in the volume‐weighted oxygen concentration, and a 23% reduction in the volume of over‐wintering habitat compared to prewithdrawal conditions. Water temperatures were slightly (≤ 10%) colder in the upper strata in the year following the withdrawal in both withdrawal and reference lakes. Northern pike abundance was not impacted by water withdrawals in either of the lakes. The results of this study show that the effects of water withdrawal on the parameters investigated reflected the characteristics of the lakes, and would therefore be expected to vary from lake to lake. Policy development to mitigate impacts must therefore reflect the site‐specific nature of water withdrawal. 相似文献
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154.
青藏高原冰川雪细菌与气候环境的关系 总被引:1,自引:0,他引:1
通过荧光显微镜测定细菌密度,利用DGGE图谱和Shannon-Weaver指数分析细菌种类多样性,对青藏高原北部老虎沟12号冰川、南部东绒布冰川和东南部海螺沟2号冰川雪坑的细菌密度和种类多样性做了差异性分析. 结果表明:老虎沟12号冰川雪坑细菌密度平均值比东绒布冰川和海螺沟2号冰川高,老虎沟12号冰川雪坑细菌种类多样性比东绒布冰川高,这与高原南、北部不同大气环流引起的大气微粒含量的差异性有关. 海螺沟2号冰川雪坑细菌种类多样性均最高,与该冰川所受的大气环流多样性最高相一致. 东绒布冰川雪坑细菌密度平均值与南极点相近,与其远离人类污染,因而大气环境本底值低有关. 海拔高的东绒布冰川雪坑细菌密度和种类多样性均比海拔低的海螺沟2号冰川和老虎沟12号冰川低,即二者与海拔高度呈反比. 相似文献
155.
156.
157.
Y.K. Pu F. Jia S.F. Wang T. Skjold 《Journal of Loss Prevention in the Process Industries》2007,20(4-6):462-469
The reactivity of a combustible dust cloud is traditionally characterized by the so-called KSt value, defined as the maximum rate of pressure rise measured in constant volume explosion vessels, multiplied with the cube root of the vessel volume. The present paper explores the use of an alternative parameter, called the maximum effective burning velocity (ueff,max), which also is derived from pressure–time histories obtained in constant volume explosion experiments. The proposed parameter describes the reactivity of fuel–air mixtures as a function of the dispersion-induced turbulence intensity. Procedures for estimating ueff,max from tests in both spherical and cylindrical explosion vessels are outlined, and examples of calculated values for various fuel–air mixtures in closed vessels of different sizes and shapes are presented. Tested fuels include a mixture of 7.5% methane in air, and suspensions of 500 g/m3 cornstarch in air and 500 g/m3 coal dust in air. Three different test vessels have been used: a 20-l spherical vessel and two cylindrical vessels, 7 and 22 l. The results show that the estimated maximum effective burning velocities are less apparatus dependent than the corresponding KSt values. 相似文献
158.
Stephen A. Norton 《Water, Air, & Soil Pollution: Focus》2007,7(1-3):93-98
Pollution of the atmosphere with cadmium (Cd), mercury (Hg), and lead (Pb) is a consequence of human activities. Natural archives
are necessary to reconstruct the long-term history of metal deposition because accurate measurement of atmospheric deposition
is a recent accomplishment. Reconstructions require: (1) accurate determination of concentrations of elements and isotopes,
(2) accurate chronology of archives, and (3) archives that faithfully record atmosphere deposition. The most useful long-term
archives are accumulations of ice and snow, peat, and lake sediment. Quantification of Cd deposition is uncommon because of
its low concentration and substantial chemical mobility. Nonetheless, trends in peat and lake sediment are similar to those
of Hg and Pb since ca. 1800 a.d. Both Hg and Pb are relatively chemically immobile and thus the peat and lake archives are believed to record historic trends
of atmospheric deposition. Isotopic and concentration studies of Pb indicate a history of northern hemisphere atmospheric
pollution extending back prior to 0 a.d. Although measurements of Hg concentration are now routine, isotopic measurements are in their infancy. Some Hg pollution
sources have unique isotopic ratios, thereby contributing unique signals to the total Hg. Maximum accumulation rates of Hg
and Pb occur up to 10 years later than for Cd (1970s versus 1960s in eastern North America, perhaps slightly later in Europe).
By 2004, deposition of Cd, Hg, and Pb had declined from peak values in eastern North America more than 75, 75, and 90%, respectively. 相似文献
159.
160.
Changes in the role of relict crustaceans in the zoobenthic communities of large subarctic Lake Imandra are analyzed over the long period of economic development in its drainage area. To date, Mysis relicta as a species highly sensitive to anthropogenic pollution has apparently disappeared from the lake fauna. The currently recorded maximum values of Pontoporeia affinis abundance and biomass are more than 20 times as great as those between 1968 and 1986. As in other lakes with mass development of P. affinis, the populations of this crustacean inhibit chironomid larvae in the communities of Lake Imandra. 相似文献