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311.
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
312.
层次分析法在区域湖泊水资源可持续发展评价中的应用 总被引:40,自引:1,他引:39
依据可持续发展理论,区域可持续发展系统一般由人口、资源、环境、经浊和社会五个子系统组成。本文从四个方面(人对资源环境的需求;资源环境的需求;经济发展的需求;社会发展的需求)提出区域湖泊水资源可持续发展的5指标体系。并用层次分析法计算各指标的权重,用于评价区域湖泊水资源可持续发展的保证程度,结果表明:区域湖泊水资源可持续发展指标体系的26个指标中,与人民群众生活息息相关的居民对水物满意程度(P13) 相似文献
313.
314.
Assefa M. Melesse Xixi Wang 《Journal of the American Water Resources Association》2006,42(6):1647-1657
Abstract: An artificial neural network (ANN) provides a mathematically flexible structure to identify complex nonlinear relationship between inputs and outputs. A multilayer perceptron ANN technique with an error back propagation algorithm was applied to a multitime-scale prediction of the stage of a hydro-logically closed lake, Devils Lake (DL), and discharge of the Red River of the North at Grand Forks station (RR-GF) in North Dakota. The modeling exercise used 1 year (2002), 5 years (1998–2002), and 27 years (1975–2002) of data for the daily, weekly, and monthly predictions, respectively. The hydrometeorological data (precipitations P(t) , P(t-1) , P(t-2) , P(t-3) , antecedent runoff/lake stage R(t-1) and air temperature T(t) were partitioned for training and for testing to predict the current hydro-graph at the selected DL and RR-GF stations. Performance of ANN was evaluated using three combinations of daily datasets (Input I = P(t) ), P(t-l) , P(t-2) , P(t-3) , T(t) and R(t-l) ; Input II = Input-l less P(t) P(t-l) , P(t-2) , P(t-3) ; and Input III = Input-II less T(t) ). Comparison of the model output using Input I data with the observed values showed average testing prediction efficiency (E) of 86 percent for DL basin and 46 percent for RR-GF basin, and higher efficiency for the daily than monthly simulations. 相似文献
315.
Stratification and Circulation in a Shallow Turbid Waterbody 总被引:1,自引:0,他引:1
Shallow waterbodies are often assumed to be well mixed in the vertical. However, when they are characterised by high turbidity levels, absoption of solar heating within a relatively thin surface layer can produce thermal stratification. Results from an intensive monitoring program have been combined with three-dimensional circulation modelling to examine the diurnal stratification cycles in a small turbid waterbody. The waterbody, known as Rushy Billabong, is located in southeastern Australia and its high turbidity coupled with forcing by wind and solar radiation resulted in regular diurnal cycles of stratification and overturning. Under conditions of light wind and high solar radiation, the model results were generally consistent with the observed temperature field. However, under stronger winds, preferential cooling and sinking of shallow water around the edge of the lake began to contribute significantly to the interior stratification. Model estimates then became more sensitive to the detailed bathymetry and the choice of turbulence parameterisation. The level of stratification is also shown to influence the circulation in the billabong by trapping the wind-driven flow near the surface. Insights provided by the observations and modelling may have broader implications for the management of small turbid systems such as settling ponds, aquaculture ponds, and some natural wetlands. 相似文献
316.
达里诺尔湖化学特征与发展态势 总被引:2,自引:0,他引:2
通过对国家级自然保护区核心区达里诺尔湖水环境四年的研究,结果表明:有着典型代表的达里诺尔北方湖泊尔环境以含盐量高、碱度大为主要化学特征,而且随着生态环境的破坏、湖水蒸发量的逐年增加,湖泊水质有明显恶化趋势。 相似文献
317.
青山水库底栖动物群落初步研究 总被引:9,自引:0,他引:9
1996年10月-1997年7月对青山水库底栖大型无脊椎动物群落进行了4次采样调查,共发现大型底栖无脊椎动物16种,其中寡毛类5种,水生昆虫7种,软件动物2种,蛭类和线虫各1种。青山水库底栖动物群落密度和生物量的水平变化为库出口>库中心>进口。湖区底栖动物群落占优势的各类为:刺夹长足摇蚊(Tanypus punctipennis)、花翅前突摇蚊(Procladius choreus)和霍甫水丝蚓(Limnodrilus hoffmeisteri)。调查结果表明,目前青山水库底栖动物群落的种类组成指示该水体已属富营养型,但从生物量上分析,目前青山水库应属中营养。 相似文献
318.
319.
五元联系数在湖泊水质综合评价中的应用 总被引:1,自引:0,他引:1
集对分析是一种新的处理模糊和不确定问题的系统理论方法,运用同异反表达式可解决各种模糊不确定问题,而五元联系数又是集对分析理论的拓展. 针对当前众多湖泊富营养化评价方法过程复杂繁琐问题,提出利用基于五元联系数的系统态势对湖泊富营养化程度进行等级评价,其评价结果与其他评价方法基本一致;并且用集对分析法对湖泊富营养化程度进行等级评价,评价结果更符合实际情况,对监测数据的利用率高,对营养化程度的划分更细致,能够得到属于同一级别的湖泊富营养化程度的排序. 五元联系数克服了以往集对分析评价级别只有3个等级的缺点,扩大了评价等级范围,因此可在更多领域得到广泛应用. 相似文献
320.
开都河灌区灌溉引水对博斯腾湖面积影响的定量分析 总被引:4,自引:1,他引:3
开都河是注入博斯腾湖的最大河流,1958~2002年间平均入湖水量达23.62×108m3,占博斯腾湖总补给量的80%以上。1958年以来开都河灌区灌溉引水量维持在8.17×108m3~13.18×108m3之间,其中20世纪60年代灌溉引水量平均为10.14×108m3/a,占开都河径流量的31.1%;70年代引水量上升到12.15×108m3/a,为开都河径流量的36.5%;80年代引水量下降到11.29×108m3/a,但引水量仍占开都河径流量的36.5%;90年代灌溉引水量进一步降至9.85×108m3/a,仅占径流量的27.1%。通过水量平衡分析和相关回归计算,得出开都河灌区灌溉引水对博斯腾湖面积影响的数值:20世纪60年代平均值为62.4km2;70年代平均值为80.8km2;80年代、90年代分别为90.4km2、76.7km2,2000年以来平均仅为41.3km2。由此可见,45年来开都河灌区灌溉引水对博斯腾湖面积的影响经历了弱→强→弱的变化过程。 相似文献