Effect of groundwater chemistry on the swelling behavior of a Ca-bentonite for deep geological repository     

《Physics and Chemistry of the Earth》2013

The swelling properties of buffer material for high level radioactive waste repository in a near-field environment are of particular importance for achieving the low permeability sealing function. In this study, the free swelling behavior of a potential buffer material Zhisin clay is evaluated under simulated groundwater conditions such as immersion in NaCl, CaCl₂, and Na₂SO₄ solutions at various concentrations. Experimental results indicate that Zhisin clay, being a Ca-bentonite, exhibits reduced swelling strain in salt solutions. The amount of decrease in swelling strain upon saline water intrusion is affected by both the type and concentration of electrolyte. At the same concentration, the swelling strains in CaCl₂ solution are lower than those in NaCl solution due to the quasi-crystals formed in the presence of calcium ions. Also, the swells in Na₂SO₄ solution are found to be lower than those in NaCl solution. This is attributed to the precipitation of CaSO₄, which acts as binding agent and results in aggregation of clay particles.  相似文献   

Increasing temperature and flow management alter mercury dynamics in East Fork Poplar Creek     

Scott C. Brooks  Carrie L. Miller  Ami L. Riscassi  Kenneth A. Lowe  Johnbull O. Dickson  Grace E. Schwartz 《水文研究》2021,35(8):e14344

East Fork Poplar Creek (EFPC) is a mercury (Hg) contaminated creek in east Tennessee, USA. Stream restoration activities included the initiation of a flow management programme in 1996 in which water from a nearby lake was pumped to the head of the creek. We conducted regular water sampling for 2 years along the length of EFPC during active flow management and for 5 years after flow management stopped. Total Hg and total monomethylmercury (MMHg) concentration and flux decreased in the uppermost reaches of EFPC that were closest to the point of water addition. Most water quality parameters, including DOC concentration, remained unchanged after flow management termination. Nevertheless, SUVA₂₅₄, a measure of dissolved organic matter (DOM) composition, increased and coincided with increased dissolved Hg (Hg_D) concentration and flux and decreased Hg solid-water partitioning coefficients throughout EFPC. Higher SUVA₂₅₄ and Hg_D concentration have potential implications for bioavailability and MMHg production. Total and dissolved MMHg concentrations increased in lower reaches of EFPC after the end of flow management and these increases were most pronounced during spring and early summer when biota are more susceptible to exposure and uptake. A general warming trend in the creek after active flow management ended likely acted in concert with higher Hg_D concentration to promote higher MMHg concentration. Total and dissolved MMHg concentrations were positively correlated with water temperature above a threshold value of 10°C. Concentration changes for Hg and MMHg could not be accounted for by changes in creek discharge that accompanied the cessation of flow management. In addition to the changing DOM composition in-stream, other watershed-scale factors likely contributed to the observed patterns, as these changes occurred over months rather than instantaneously after flow management stopped. Nevertheless, similar changes in MMHg have not been observed in a tributary to EFPC.  相似文献   

Luquillo Experimental Forest: Catchment science in the montane tropics     

William H. McDowell  Miguel C. Leon  Michelle D. Shattuck  Jody D. Potter  Tamara Heartsill-Scalley  Grizelle González  James B. Shanley  Adam S. Wymore 《水文研究》2021,35(4):e14146

Catchments in the Luquillo Experimental Forest (LEF) of Puerto Rico are warm, wet and tropical with steep elevational relief creating gradients in temperature and rainfall. Long-term objectives of research at the site are to understand how changing climate and disturbance regimes alter hydrological and biogeochemical processes in the montane tropics and to provide information critical for managing and conserving tropical forest ecosystems globally. Measurements of hydrology and meteorology span decades, and currently include temperature, humidity, precipitation, cloud base level, throughfall, groundwater table elevation and stream discharge. The chemistry of rain, throughfall, and streams is measured weekly and lysimeters and wells are sampled monthly to quarterly. Multiple data sets document the effects of major hurricanes including Hugo (1989), Georges (1998) and Maria (2017) on vegetation, biota and catchment biogeochemistry and provide some of the longest available records of biogeochemical fluxes in tropical forests. Here we present an overview of the findings and the data sets that have been generated from the LEF, highlighting their importance for understanding montane tropical watersheds in the context of disturbance and global environmental change.  相似文献   

Concentration versus streamflow trends of major ions and tritium in headwater streams as indicators of changing water stores     

Ian Cartwright  Uwe Morgenstern  Harald Hofmann 《水文研究》2020,34(2):485-505

Documenting the processes that control the variations in stream geochemistry at different streamflows is important for being able to use chemical tracers to understand catchment functioning. The concentrations of most solutes, including reactive cations (e.g., Na, Ca, K, and Mg) and anions that are primarily derived from precipitation (Cl and Br), in five headwater streams from southeast Australia vary little with streamflow and are close to being chemostatic. By contrast, NO₃ and SO₄ concentrations are higher at high streamflows. There is also a systematic increase of ³H activities from as low as 1.1 to as high as 2.6 TU with increasing streamflow. The changes in geochemistry cannot be explained solely by increased mineral dissolution at high streamflows or enhanced baseflow driven by hydraulic loading. They are best explained by an increased baseflow input augmented by water mobilized from shallower stores as the catchments wet up. The mean transit times of the water sustaining streamflow varies from 35 to 70 years at low streamflows to <7 years at high streamflows. The use of a range of geochemical tracers, including radioactive isotopes, allows the different possible causes of chemostatic behaviour to be assessed and improves our understanding of catchment functioning.  相似文献   

塔里木盆地南缘策勒绿洲区地下水TDS空间变异及水化学特征分析   总被引：4，自引：1，他引：3  

代述勇  雷加强  赵景峰  谌莉  杨光华  范敬龙  范冬冬  曾凡江 《中国沙漠》2010,30(3):722-729

基于策勒绿洲78个取样点的地下水的观测资料,结合地理信息系统,运用地统计学方法和Sigmaplot10.0中的Piper模块,研究塔里木盆地南缘策勒绿洲区地下水TDS（Total Dissolved Solids）的时空变异,揭示地下水水化学特征及其演变的主要水化学过程。结果表明:①地下水TDS存在强烈的空间相关性,其空间相关距离为4.4 km,在步长为6 km范围之内,地下水TDS的空间变异是各向同性的,当步长大于6 km时,4个方向上的半变异函数发生了不同的变化;②绿洲南部区域为地下水TDS的低值区,最小值为551 mg·L-1,由南向北地下水TDS呈增加的趋势,在北部地下水埋深低值区的TDS最大值为7 192 mg·L-1;从地下水水流方向上看,即从绿洲西南的低值区向北,再转向东北区方向,地下水TDS逐渐增加,最大值为3 677 mg·L-1;③浅层地下水化学类型变化复杂,主要从Na-Ca—SO4-Cl-HCO3、Na-Ca—SO4-Cl型向Na—SO4-Cl-HCO3和Na—SO4-Cl型演化。  相似文献   

深圳沿海表层海水与地表水关系的地球化学分析   总被引：2，自引：2，他引：0       下载免费PDF全文

杨巧凤  李文鹏  王瑞久 《水文地质工程地质》2010,37(1):45-49

依据深圳沿海所取31件表层海水样品的水化学数据,对主要离子Ca2+、Mg2+、Na+、K+、SO42-和HCO3-与C l-以及B r-与C l-的关系作散点图分析。西海岸表层海水Ca2+、K+、SO42-和HCO3-与C l-的比偏离海水稀释线,源于其位于珠江河道影响范围,与珠江水有不同程度的混合;东海岸表层海水Ca2+、K+和HCO3-与C l-的比主要围绕海水稀释线波动,表明沿海表层海水流动缓慢,受表层海水蒸发和当地沿岸污染河水排泄的长期累积影响;靠近深圳湾的5件西海岸海水样品成分与东海岸表层海水相似。  相似文献   

天然海水硝酸盐氮同位素组成的蒸馏法测定     

杨志  陈敏  曹建平  邱雨生 《海洋学报》2012,34(3):72-79

建立了测定天然海水中硝酸盐氮同位素组成的蒸馏法,该方法主要是在碱性条件下利用戴氏合金将海水中的硝酸盐还原为氨,后利用稀盐酸吸收生产的氨,将得到的氨吸收液浓缩后干燥结晶,利用同位素比值质谱仪测定所得晶体的氮同位素组成。研究中开展了戴氏合金添加量及氨吸收溶液在不同条件下干燥结晶对氮同位素测值的影响研究。结果表明,戴氏合金添加量为3.0 g及60 ℃下直接干燥结晶为最佳的实验条件。所建立的氨蒸馏法氮空白值仅为(0.90±0.19) μmol,低于此前文献报道的氮空白值;氮同位素组成(δ15N)空白值为(-14.7±4.1)×10-3。运用所建立的氨蒸馏法实测得到的硝酸盐δ15N值与氨扩散法、硝酸盐直接测定法得到的数值非常吻合,进一步证明所建立氨蒸馏法的可靠性。改进后的氨蒸馏法适用于硝酸盐浓度在2~50 μmol/dm3内的天然海水硝酸盐氮同位素组成的测定,方法的标准偏差为±0.3×10-3。  相似文献   

海水中总溶解氮测定的高温燃烧法和湿化学氧化法的比较     

阎雪姣  王江涛 《海洋科学》2012,36(5):103-108

对测量海水中总溶解氮(TDN)的两种常用方法——高温燃烧法和过硫酸钾氧化法进行了比较。结果表明,两种方法在空白、精密度和准确度实验中不存在显著差异。对不同化合物的回收率均在92%～107%之间,加标回收实验回归曲线的斜率分别为0.93和0.92。对于现场海水样品的测定结果,两个断面拟合的斜率分别为0.92和0.97。HTC法比PO法对实际海水样品的氧化效率略高,在操作上也更方便、快捷。因此,高温燃烧法更适合海水中总溶解氮(TDN)的测定。  相似文献   

广东红海湾表层海水重金属含量的时空变化特征与污染水平评价   总被引：2，自引：0，他引：2  

李壮伟  罗荣真  陈鸿生  刘文辉 《台湾海峡》2012,31(1):20-26

2007年6月(夏季)和2008年1月(冬季)分别对广东红海湾的汕尾港周边海域35个站位进行了表层海水的采样,在实验室内使用XGY-1011A型原子荧光光度计和HY-1F型多功能极谱仪获得了海水中重金属Hg、Cu、Pb、Zn、Cd的含量,研究了其时空变化特征,并采用综合指数法(WQI)评价其污染程度.结果显示:Hg、Cu、Pb、Zn、Cd的含量范围分别为0.009～0.050、0.9～4.3、0.4～1.4、1.6～19.0、0.1～0.7μg/dm3,平均含量分别为0.025、2.4、0.8、9.4、0.2μg/dm3.该海域表层海水各重金属含量的平面分布总体上呈现以品清湖向汕尾港递减的变化趋势.各站位重金属元素的单项污染指数和综合污染指数(WQI)均小于1,海水受重金属的污染程度较轻微,符合国家二类海水水质标准值的要求.2008年1月(冬季)重金属综合污染指数的平均值(0.17)略大于2007年6月(夏季)的平均值(0.14),海水中重金属污染程度略有加重的趋势.采用多元线性回归方法分析重金属元素含量与环境要素测值的相关程度,相关系数按从大到小的排列顺序大致为:Zn>Cd>Cu>Hg>Pb.  相似文献   

基于模糊神经网络的海水水质综合评价   总被引：2，自引：0，他引：2  

刁美娜  温小虎  刘有刚  王德  高猛 《海洋通报》2012,31(2):228-232

根据俚岛镇海湾22个海洋观测点的水质监测数据,依据人工神经网络与模糊理论,建立模糊神经网络模型,对研究区海水水质进行了综合评价。结果表明,区域内40,91%的采样点属于Ⅰ类海水水质标准,其余为Ⅱ类海水水质。其中,水质Ⅱ类区位于临络湾与俚岛湾的半封闭海域,因该区造船业对水体造成污染且海水对流强度较弱,不利于污染物的扩散;而海水水质Ⅰ类区域靠近黄海,工业活动较少,水体对流较强,利于污染物扩散。  相似文献