Analysis of changes in the Great Lakes hydro-climatic variables

A study of changes in hydro-climatology of the Great Lakes was performed incorporating the nonparametric Mann–Kendall trend detection test and a recently developed Bayesian multiple change point detection model. The Component Net Basin Supply (C-NBS) and its components (runoff, precipitation, evaporation) as well as water levels of Great Lakes were analyzed for gradual (i.e. trend type) and abrupt (i.e. shift type) nonstationary behaviors at seasonal and annual scales. It was found that the C-NBS experienced significant upward trends only in the lower Great Lakes (Erie, Ontario) during the summer portion of the year. At an annual scale upward trends were observed only in Lake Ontario. Change point analysis suggested an upward shift in Great Lakes C-NBS in the late 1960s and early 1970s. A combination of gradual and abrupt change analysis of Great Lakes water levels indicated a common upward shift along with a change in trend direction around the early 1970s. It was also found that precipitation and runoff are on a plateau and in some cases on a decreasing course following an increasing trend in the early twentieth century. Results obtained from this study show that the hydro-climatology of Great Lakes is characterized by nonstationary behavior. Changes in this behavior have caused the Great Lakes water levels to decrease during the last few decades. This study provides valuable insights into the nature of the nonstationary behavior of hydro-climatic variables of Great Lakes and contributes useful information to the future water management planning.     

珠江三角洲地区地下水中卤族元素质量浓度背景特征及成因分析

利用珠江三角洲地区1∶25万区域地下水污染调查评价项目所取得的水质数据,采用数理统计方法,在判断元素质量浓度分布类型的基础上,计算该地区卤族元素质量浓度的背景集中特征值和背景值范围,并对背景值统计特征及分布规律进行分析。结果表明,浅层地下水受人类活动影响较大,多呈偏态分布;地下水中卤族元素的分布主要受岩土性质、地下水径流条件、氧化还原环境的影响,另外,Cl、Br的背景质量浓度受海水入侵作用的影响明显,F的高背景质量浓度与温泉出露密切相关。对地下水中卤族元素质量浓度背景值的研究将为地方病防治工作提供重要科学依据。     

低水泥剂量稳定级配碎石基层典型结构分析

目的找寻适应不同交通等级的合理的低水泥剂量基层沥青路面结构．方法拟定低水泥剂量级配碎石基层沥青路面结构,利用有限元软件计算以低水泥剂量稳定级配碎石取代半刚性基层后对弯沉、沥青层底拉应力等设计指标的影响,并结合交通荷载分析各结构层厚度组合合理性．结果轻交通等级下,推荐使用5cm普通沥青混凝土面层＋22cm水泥质量分数为3％的低水泥剂量稳定级配碎石单基层;中交通等级下,推荐采用上基层厚度大于15cm的水泥质量分数为2．5％的低水泥剂量稳定级配碎石,半刚性下基层厚度至少为20cm结构组合形式;重交通等级下,推荐采用15cm水泥质量分数为2．5％的低水泥剂量稳定级配碎石上基层和15cm＋20cm半刚性双基层结构组合．结论在重、中交通荷载作用下,合理的低水泥剂量级配碎石基层能够在防治反射裂缝同时,较好地满足交通荷栽需求．     

铀矿井氡排出污染的模拟计算

铀矿开采会产生大量的氡排放到大气中,对环境产生一定程度的放射性污染。本文通过建立氡气扩散模型,对矿井排出的氡的污染程度和范围进行了合理的理论估算,讨论在不同的自然条件下选择适当高度的排风口和相应范围内的重点防护区域。计算结果表明：当排风口的选取在高出周围环境20 m以上时,排风口周围氡污染的程度不高,但考虑到经济、矿山地形以及通风条件等因素的影响时,选取排风口的位置和相应的重点防护区域应作最优化分析和设计。     

筑坝粗粒料单线法湿化变形模型比较

粗粒土的湿化变形是一种普遍现象,对土石坝长期安全运行至关重要。针对已有多种经验公式拟合精度未知问题,对搜集的试验数据进行验证研究。结果表明：(1)各向等压湿化体变与围压用幂函数拟合效果较好;(2)湿化轴向应变与应力水平用指数函数拟合效果较好,指数函数参数与围压呈良好的线性关系;(3)湿化体变采用双线性模型,形式简单且拟合精度较幂线型及六参数型高;(4)湿化剪应变与应力水平呈良好的双曲线关系,与围压相关性较弱。最后,分析了湿化应变与不同应力水平的相关程度,建立了基于改进相对湿化应力水平的湿化应变经验公式。     

Export of mercury downstream from reservoirs

Environmental effects monitoring at the La Grande hydroelectric complex (Québec, Canada) revealed important increases in mercury levels in fish caught downstream from reservoirs. A study was carried out in 1997 immediately below the Caniapiscau Reservoir to identify by which components mercury is transported downstream from reservoirs and to assess the amount of mercury being exported. Stomach contents of lake whitefish (Coregonus clupeaformis) captured immediately below the Caniapiscau Reservoir were examined to determine which components transfer mercury from lower trophic levels to fish. The analyses of water samples and drifting organisms collected below the reservoir indicate that the dissolved fraction (< 0.45 microm) and the suspended particulate matter (0.45-50 microm) are the major components by which methylmercury is transferred downstream of reservoirs, accounting for 64 and 33%, respectively, of the total amounts exported. Drifting organisms such as plant debris, benthic invertebrates, fish, phytoplankton and zooplankton are much less important pathways for mercury export because of their very low biomass per water volume coming out of the generating station, as opposed to the high biomass of suspended particulate matter. However, zooplankton is the major component by which methylmercury is directly transferred to non-piscivorous fish downstream.     

A simple method to estimate lake phosphorus concentrations resulting from natural, background, loadings

The relation of mean total phosphorus concentrations to morphoedaphic index (calculated as the ratio between the mean depth and the alkalinity or the conductivity) has been examined for a large, diverse, widely distributed group of lakes.A highly significant correlation was found in lakes practically not affected by anthropogenic input of phosphorus. As a consequence the phosphorus concentration in a lake resulting from natural, background, loading could be calculated on the basis of the morphoedaphic index. The evaluation of natural phosphorus concentration allows the prediction of the maximum extent to which actual phosphorus concentrations could be reduced in culturally eutrophied lakes by eliminating the anthropogenic inputs and to calculate “permissible” loadings necessary to achieve natural trophic conditions that will not necessarily correspond to oligotrophy.     

方寸之中见无极——城市小建筑细节与空间建构漫谈

本文主要研究城市小型建筑的现状，并在此基础上，从细节设计、空间设计、功能整合三大设计手段方面对现有小型建筑进行归类研究，探讨其中的设计亮点及创新之处，肯定城市当中数量不多的可建造空间内数量不多的小建筑的存在价值。     

杆端弯矩直接计算法

根据位移法计算无侧移刚架和连续梁的原理，以杆端弯矩为基本未知量，建立了杆端弯矩方程基本式和等效结点力矩分配矩阵，便于计算和编制计算机程序．     

基于“双评价”的市县级国土空间“三区三线”技术方法探讨

国土空间规划编制要求以资源环境承载力评价和国土空间开发适宜性评价(以下简称"双评价")作为对国土空间格局和"三区三线"划定的重要支撑依据。本文旨在探讨"双评价"结果与"三区三线"划定如何科学合理对接,并对市县级国土空间"三区三线"的细化进行探讨。提出,"双评价"是国土空间规划的预判,"三区三线"需要结合地区的整体战略进行因地制宜的多视角研究,才能得到科学合理的结果。"双评价"预判需要与现行管控边界、发展实际进行校核,应遵循"生态保护红线只增不减"、"基本农田总量不变"、"城镇开发边界集约利用"等基本原则,最终明确国土空间的"三区三线"。建议国土空间以"三区一网络"全域全覆盖的功能分区、以"三线一附加"的细化"三线"刚性控制线体系来实现统筹管控,构建覆盖全域、上下传导的空间控制体系。