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981.
Chapin TP Nimick DA Gammons CH Wanty RB 《Environmental monitoring and assessment》2007,133(1-3):161-167
Recent work has demonstrated that many trace metals undergo dramatic diel (24-h) cycles in near neutral pH streams with metal
concentrations reproducibly changing up to 500% during the diel period (Nimick et al., 2003). To examine diel zinc cycles in streams affected by acid rock drainage, we have developed a novel instrument, the Zn-DigiScan,
to continuously monitor in situ zinc concentrations in near real-time. Initial results from a 3-day deployment at Fisher Creek,
Montana have demonstrated the ability of the Zn-DigiScan to record diel Zn cycling at levels below 100 μg/l. Longer deployments
of this instrument could be used to examine the effects of episodic events such as rainstorms and snowmelt pulses on zinc
loading in streams affected by acid rock drainage. 相似文献
982.
Native trout species, such as the redband trout (Oncorhynchus mykiss), occupy thermally harsh stream habitats in hot, arid rangeland basins of the western United States. Declines in the distribution
and abundance of these species has generated interest in understanding how these cold water species survive in these systems,
as well as in identifying opportunities to restore these species to their former ranges. The purpose of this study was to
assess the potential for thermal stratification to provide thermal refuge for redband trout in stream pools characterized
by warm intermittent flow conditions on arid rangelands. We studied vertical thermal stratification in two pools during three
summers on Boles Creek located on the Modoc Plateau in extreme northeastern California. Water and air temperature data were
collected on a 0.5 h time step from 15-Jun through 15-Sep during 1996, 1997, and 2000 using commercial temperature data-loggers.
Water temperature was measured at the top (0.3 m below pool surface) and bottom (0.3 m above pool substrates) of each pool.
Vertical thermal stratification occurred within these pools creating conditions as much as 7.6 ˚C cooler and consistently
more constant at the bottom of pools compared to pool surface waters. Thermal stratification was dependent upon air temperature
with the magnitude of stratification increasing as air temperature increased. The magnitude of thermal stratification varied
significantly from year to year, likely reflecting variation in annual weather conditions. The thermal regime in the study
pools was often near the upper lethal limit reported for redband trout, but temperatures at the bottom of these pools did
offer refuge from lethal temperatures realized near the pool surface. Temperatures at pool bottom were consistently above
optimal levels published for redbands. 相似文献
983.
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
984.
985.
Chiyoji Ohkubo Hideyuki Okano Akira Ushiyama Hiroshi Masuda 《The Environmentalist》2007,27(4):395-402
Authors review the importance of studying the effects of electromagnetic fields (EMF) on microcirculatory system, especially
in respect of possibility that vasculature may have direct and indirect role in interaction of static magnetic fields (SMF).
We outline the physiological importance of microcirculation and relatively new methods of evaluation technique in vivo and
explain in details the local and/or whole body exposure effects of SMF with␣range of 0.3–180 mT, power frequency EMF with
range of 0.1–30 mT and microwaves at 1.5 GHz with range 0.08–8 W/kg brain average specific absorption rate (SAR) on microcirculatory
systems in different tissues in experimental animals. 相似文献
986.
为研究建筑火灾增长阶段室内温度的时间变化规律,提出了高温烟气的主要几种热损失的计算方法,发展了受火室与未受火室及环境的热平衡方程,并采用牛顿-拉菲尔森法迭代得到受火室的温度变化.计算了慢速、中速、快速、超快速四种火灾增长速率下,受火室气相温度及烟气热损失随时间的变化.本文的研究方法及有关结果可以为建筑防火及安全疏散提供有力依据. 相似文献
987.
988.
989.
哈尔滨市热岛效应与植被的关系——基于RS和GIS的定量研究 总被引:8,自引:0,他引:8
利用遥感和地理信息系统技术对Landsat ETM+热红外遥感数据进行处理,反演和计算了哈尔滨城区的地面亮温和植被指数。通过剖面分析,研究了城区温度场的空间格局与植被盖度的关系;通过多元回归分析,揭示了城区热岛效应同多个指数的相关关系。结果表明:市内的道外区是热岛效应的主要分布区,道里区、香坊区的情况也比较严重;铁路沿线区域是城区主要的热岛效应地带;植被盖度和地面亮温呈反相关关系;植被和水体区域可以缓解城市的热岛效应。通过对市区热岛效应分析,可以监测城市化进程,为城市热环境质量评价和热源调查提供准确、丰富的信息。 相似文献
990.