Modelling and experimental study of coupled exchange of p,p′‐DDE and colloids in a flume simulated stream–streambed system          下载免费PDF全文

Celina Camarena  Doris Otero  Jianhong Ren 《水文研究》2016,30(1):40-56

Stream–subsurface exchange plays a significant role in the fate and transport of contaminants in streams. It has been modelled explicitly by considering fundamental processes such as hydraulic exchange, colloid filtration, and contaminant interactions with streambed sediments and colloids. The models have been successfully applied to simulate the transport of inorganic metals and nutrients. In this study, laboratory experiments were conducted in a recirculating flume to investigate the exchange of a hydrophobic organic contaminant, p,p′‐dichloro‐diphenyl‐dichloroethane (DDE), between a stream and a quartz sand bed. A previously developed process‐based multiphase exchange model was modified by accounting for the p,p′‐DDE kinetic adsorption to and desorption from the bed sediments/colloids and was applied to interpret the experimental results. Model input parameters were obtained by conducting independent small‐scale batch experiments. Results indicate that the immobilization of p,p′‐DDE in the quartz sand bed can occur under representative natural stream conditions. The observed p,p′‐DDE exchange was successfully simulated by the process‐based model. The model sensitivity analysis results show that the exchange of p,p′‐DDE can be sensitive to either the sediment sorption/desorption parameters or colloidal parameters depending on the experimental conditions tested. For the experimental conditions employed here, the effect of colloids on contaminant transport is expected to be minimal, and the stream–subsurface exchange of p,p′‐DDE is dominated by the interaction of p,p′‐DDE with bed sediment. The work presented here contributes to a better mechanistic understanding of the complex transport process that hydrophobic organic contaminants undergo in natural streams and to the development of reliable, predictive models for the assessment of impacted streams. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Scales and magnitude of hyporheic,river–aquifer and bank storage exchange fluxes          下载免费PDF全文

Roger H. Cranswick  Peter G. Cook 《水文研究》2015,29(14):3084-3097

Many studies have investigated the exchange processes that occur between rivers and groundwater systems and have successfully quantified the water fluxes involved. Specifically, these exchange processes include hyporheic exchange, river–aquifer exchange (groundwater discharge and river loss) and bank storage exchange. Remarkably, there are relatively few examples of field studies where more than one exchange process is quantified, and as a consequence, the relationships between them are not well understood. To compare the relative magnitudes of these common exchange processes, we have collected data from 54 studies that have quantified one or more of these exchange flux types. Each flux value is plotted against river discharge at the time of measurement to allow the different exchange flux types to be compared. We show that there are positive relationships between the magnitude of each exchange flux type and increasing river discharge across the different studies. For every one order of magnitude increase in river discharge, the hyporheic, river–aquifer and bank storage exchange fluxes increase by factors of 2.7, 2.9 and 2.5, respectively. On average, hyporheic exchange fluxes are almost an order of magnitude greater than river–aquifer exchange fluxes, which are, in turn, approximately four times greater than bank storage exchange fluxes for the same river discharge. Unless measurement approaches that can distinguish between different types of exchange flux are used, there is potential for hyporheic exchange fluxes to be misinterpreted as river–aquifer exchange fluxes, with possible implications for water resource management decisions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Variability in the vertical hyporheic water exchange affected by hydraulic conductivity and river morphology at a natural confluent meander bend          下载免费PDF全文

Jinxi Song  Guotao Zhang  Weize Wang  Qi Liu  Weiwei Jiang  Weiqiang Guo  Bin Tang  Haifeng Bai  Xinyi Dou 《水文研究》2017,31(19):3407-3420

River confluences and their associated tributaries are key morphodynamic nodes that play important roles in controlling hydraulic geometry and hyporheic water exchange in fluvial networks. However, the existing knowledge regarding hyporheic water exchange associated with river confluence morphology is relatively scarce. On January 14 and 15, 2016, the general hydraulic and morphological characteristics of the confluent meander bend (CMB) between the Juehe River and the Haohe River in the southern region of Xi'an City, Shaanxi Province, China, were investigated. The patterns and magnitudes of vertical hyporheic water exchange (VHWE) were estimated based on a one‐dimensional heat steady‐state model, whereas the sediment vertical hydraulic conductivity (K_v) was calculated via in situ permeameter tests. The results demonstrated that 6 hydrodynamic zones and their extensions were observed at the CMB during the test period. These zones were likely controlled by the obtuse junction angle and low momentum flux ratio, influencing the sediment grain size distribution of the CMB. The VHWE patterns at the test site during the test period mostly showed upwelling flow dominated by regional groundwater discharging into the river. The occurrence of longitudinal downwelling and upwelling patterns along the meander bend at the CMB was likely subjected to the comprehensive influences of the local sinuosity of the meander bend and regional groundwater discharge and finally formed regional and local flow paths. Additionally, in dominated upwelling areas, the change in VHWE magnitudes was nearly consistent with that in K_v values, and higher values of both variables generally occurred in erosional zones near the thalweg paths of the CMB, which were mostly made up of sand and gravel. This was potentially caused by the erosional and depositional processes subjected to confluence morphology. Furthermore, lower K_v values observed in downwelling areas at the CMB were attributed to sediment clogging caused by local downwelling flow. The confluence morphology and sediment K_v are thus likely the driving factors that cause local variations in the VHWE of fluvial systems.  相似文献   

广东省土地登记信息交换系统的设计与实现   总被引：1，自引：0，他引：1  

邱海泉 《测绘与空间地理信息》2016,(4):140-142,146

广东省各级土地登记部门经过多年的信息化建设,已经建成了一批土地登记信息管理系统,为业务的开展提供了有效的支撑,但由于缺乏统一的建设标准,这些系统之间无法进行信息共享。广东省通过建设土地登记信息交换系统,在省、市、县三级节点构建起了一套土地登记信息动态汇交体系,打破了信息孤岛,为全省土地登记信息监管系统的构建和运行提供了重要保障。本文重点介绍了该系统的需求分析、系统设计,以及在实现过程中采用的关键技术等。  相似文献   

Selection and quality assessment of Landsat data for the North American forest dynamics forest history maps of the US     

Karen Schleeweis  Samuel N. Goward  Chengquan Huang  John L. Dwyer  Jennifer L. Dungan  Mary A. Lindsey 《International Journal of Digital Earth》2016,9(10):963-980

Using the NASA Earth Exchange platform, the North American Forest Dynamics (NAFD) project mapped forest history wall-to-wall, annually for the contiguous US (1986–2010) using the Vegetation Change Tracker algorithm. As with any effort to identify real changes in remotely sensed time-series, data gaps, shifts in seasonality, misregistration, inconsistent radiometry and cloud contamination can be sources of error. We discuss the NAFD image selection and processing stream (NISPS) that was designed to minimize these sources of error. The NISPS image quality assessments highlighted issues with the Landsat archive and metadata including inadequate georegistration, unreliability of the pre-2009 L5 cloud cover assessments algorithm, missing growing-season imagery and paucity of clear views. Assessment maps of Landsat 5–7 image quantities and qualities are presented that offer novel perspectives on the growing-season archive considered for this study. Over 150,000+ Landsat images were considered for the NAFD project. Optimally, one high quality cloud-free image in each year or a total of 12,152 images would be used. However, to accommodate data gaps and cloud/shadow contamination 23,338 images were needed. In 220 specific path-row image years no acceptable images were found resulting in data gaps in the annual national map products.  相似文献   

土壤样品镉同位素分析中Cd与Sn有效分离方法的改进     

段桂玲  段瑞春  谭娟娟  顾涛  邵长生  路韬 《岩矿测试》2016,35(1):10-16

保证Cd的高回收率以及彻底的Sn干扰去除是获得精确镉同位素组成的前提,目前报道的多种Cd分离与纯化方法获得的Cd回收率有较大差异(42.6%~99.8%),且去除Sn干扰的效果也不同(去除率在87.8%~97.4%之间),Cd回收率和Sn去除率均不理想。本文对前人报道的分离方法进行对比实验,发现0.1 mol/L氢溴酸-0.5 mol/L硝酸是分离Cd和Sn的有效试剂,增加该组混合酸的用量可淋洗出样品中更多的Sn且不会损失Cd,当混合酸的淋洗用量增加至30 mL时,Sn的淋洗率达到99.8%以上,Cd的回收率亦达到99.0%±0.5%,可满足土壤样品镉同位素的测定要求。本工作为获得高精度的镉同位素组成奠定了基础,为研究土壤环境中镉的污染来源提供了技术手段。  相似文献   

利用LA-ICP-MS在16 μm和10 μm激光束斑条件下测定独居石U-Th-Pb年龄     

汪双双  韩延兵  李艳广  魏小燕  靳梦琪  程秀花 《岩矿测试》2016,35(4):349-357

我国锂钾主要矿产资源大多分布在西部偏远地区,其勘查找矿或综合利用迫切需要现场快速分析技术的支持。本文介绍了自行开发的便携式Li-K分析仪的主要性能及其在锂辉石中锂的分析应用。Li-K分析仪是一种基于大气压的液体阴极辉光放电光谱仪,以待测液体为放电阴极,实现样品中Li、K等元素的原子化和激发。该仪器以光纤传导CCD光谱仪作为检测器,其波长范围为345～1015 nm,分辨率3 nm;以Li 670.78 nm和K 769.90 nm分析谱线,在最佳仪器工作条件下测定Li、K的精密度（RSD,n=14）均低于2%,检出限为0.03 μg/mL,检测范围0.1～10 μg/mL。研究表明,不同酸度和酸的类型对谱线强度影响较大,且存在显著的样品基体效应,标准曲线法分析锂辉石中Li的结果偏差高达267%;而标准加入法可克服基体效应的影响,获得与ICP-OES一致性较好的分析结果,为现场开展固体样品中Li的测定奠定了基础。  相似文献   

Effects of surface flux parameterization on the numerically simulated intensity and structure of Typhoon Morakot (2009)     

Jie Ming  Jun A. Zhang 《大气科学进展》2016,33(1):58-72

The effects of surface flux parameterizations on tropical cyclone(TC) intensity and structure are investigated using the Advanced Research Weather Research and Forecasting(WRF-ARW) modeling system with high-resolution simulations of Typhoon Morakot(2009).Numerical experiments are designed to simulate Typhoon Morakot(2009) with different formulations of surface exchange coefficients for enthalpy(C_K) and momentum(C_D) transfers,including those from recent observational studies based on in situ aircraft data collected in Atlantic hurricanes.The results show that the simulated intensity and structure are sensitive to C_K and C_D,but the simulated track is not.Consistent with previous studies,the simulated storm intensity is found to be more sensitive to the ratio of C_K/C_D than to C_K or C_D alone.The pressure-wind relationship is also found to be influenced by the exchange coefficients,consistent with recent numerical studies.This paper emphasizes the importance of C_D and C_K on TC structure simulations.The results suggest that C_D and C_K have a large impact on surface wind and flux distributions,boundary layer heights,the warm core,and precipitation.Compared to available observations,the experiment with observed C_D and C_K generally simulated better intensity and structure than the other experiments,especially over the ocean.The reasons for the structural differences among the experiments with different C_D and C_K setups are discussed in the context of TC dynamics and thermodynamics.  相似文献   

气象、农业和水文干旱之间关联性分析     

胡彩虹  赵留香  王艺璇 《气象与环境科学》2016,39(4):1-6

干旱具有发生频率高、持续时间长、波及范围广的特点。而干旱预报为科学地进行防旱抢险提供了决策支持。选取反映不同类型干旱的指标,即标准化降雨指标(SPI)、标准化土壤湿度指标(SSWI)和标准化径流指标(SRI),通过SWAT模型和带有时滞的灰色关联判断了各干旱之间的时滞。以陆浑水库控制流域为例进行了分析,结果表明:SWAT模型在该流域有很好的适用性,1975—2009年间发生各类干旱的次数在增加,且变率上从气象干旱、农业干旱到水文干旱有所增加,同时不同类型干旱之间表现出了一定的时滞关系,气象干旱对农业干旱的响应时间为1个月;水文干旱对气象干旱的响应时间为4个月;水文干旱对农业干旱的响应时间为2个月。  相似文献   

Reactive transport impacts on recovered freshwater quality during multiple partially penetrating wells (MPPW-)ASR in a brackish heterogeneous aquifer     

《Applied Geochemistry》2016

The use of multiple partially penetrating wells (MPPW) during aquifer storage and recovery (ASR) in brackish aquifers can significantly improve the recovery efficiency (RE) of unmixed injected water. The water quality changes by reactive transport processes in a field MPPW-ASR system and their impact on RE were analyzed. The oxic freshwater injected in the deepest of four wells was continuously enriched with sodium (Na⁺) and other dominant cations from the brackish groundwater due to cation exchange by repeating cycles of ‘freshening’. During recovery periods, the breakthrough of Na⁺ was retarded in the deeper and central parts of the aquifer by ‘salinization’. Cation exchange can therefore either increase or decrease the RE of MPPW-ASR compared to the RE based on conservative Cl⁻, depending on the maximum limits set for Na⁺, the aquifer’s cation exchange capacity, and the native groundwater and injected water composition. Dissolution of Fe and Mn-containing carbonates was stimulated by acidifying oxidation reactions, involving adsorbed Fe²⁺ and Mn²⁺ and pyrite in the pyrite-rich deeper aquifer sections. Fe²⁺ and Mn²⁺ remained mobile in anoxic water upon approaching the recovery proximal zone, where Fe²⁺ precipitated via MnO₂ reduction, resulting in a dominating Mn²⁺ contamination. Recovery of Mn²⁺ and Fe²⁺ was counteracted by frequent injections of oxygen-rich water via the recovering well to form Fe and Mn-precipitates and increase sorption. The MPPW-ASR strategy exposes a much larger part of the injected water to the deeper geochemical units first, which may therefore control the mobilization of undesired elements during MPPW-ASR, rather than the average geochemical composition of the target aquifer.  相似文献