The role of salinity in fluvio-deltaic morphodynamics: A long-term modelling study

Salinity difference between terrestrial river discharge and oceanic tidal water plays a role in modifying the local flow field and, as a consequence, estuarine morphodynamics. Although widely recognized, recent numerical studies exploring the long-term morphological evolution of river-influenced estuaries with two-dimensional, depth-averaged models have mostly neglected salinity. Using a three-dimensional morphodynamic model, we aim to gain more insight into the effect of salinity on the morphodynamics of fluvio-deltaic systems. Model results indicate that the resultant estuarine morphology established after 600 years differs remarkably when a salinity gradient is included. A fan-shaped river-mouth delta exhibits less seaward expansion and is cut through by narrower channels when salinity is included. The inclusion of salinity tends to generate estuarine circulation, which favours landward sediment transport and hence limits the growth of the delta while enhancing the development of intertidal areas. The formation of deltaic channel–shoal patterns resulting from morphodynamic evolution tends to strengthen salinity stratification, which is characterized by an increased gradient Richardson number. The direction of the depth-averaged residual sediment transport over a tide may be opposite to the direction of residual velocity, indicating the significant influence of baroclinic effects on the net sediment transport direction (and hence morphological change). The effect of salinity on morphological evolution becomes less profound when the strength of tidal or fluvial forcing is dominant over the other. The effects of sediment type and flocculation, which are particularly important when salinity gradients are present, are also discussed. Overall, this study highlights that neglecting salinity to simulate long-term estuarine morphodynamics requires more careful justification, particularly when the environment is characterized by fine sediment types (favouring suspended transport), and relatively large river discharge and estuarine depth (favouring baroclinic effects). © 2020 John Wiley & Sons, Ltd.     

Effects of riverbed incision on the hydrology of the Vietnamese Mekong Delta

The hydrogeomorphology of the Vietnamese Mekong Delta (VMD) has been significantly altered by natural and anthropogenic drivers. In this study, the spatiotemporal changes of the flow regime were examined by analysing the long-term daily, monthly, annual and extreme discharges and water levels from 1980 to 2018, supported by further investigation of the long-term annual sediment load (from the 1960s to 2015), river bathymetric data (in 1998, 2014 and 2017) and daily salinity concentration (from the 1990s to 2015) using various statistical methods and a coupled numerical model. Then, the effects of riverbed incision on the hydrology were investigated. The results show that the dry season discharge (i.e., in March–June) of the Tien River increased by up to 23% from the predam period (1980–1992) to the postdam period (1993–2018) but that the dry season water level at My Thuan decreased by up to −46%. The annual mean and monthly water levels in June at Tan Chau and in January and June–October at My Thuan in the Tien River decreased statistically, even though the respective discharges increased significantly. These decreased water levels instead of the increased discharges were attributed to the accelerated riverbed incision upstream from My Thuan, which increased by more than three times, from a mean rate of −0.16 m/year (−16.7 Mm³/year) in 1998–2014 to −0.5 m/year (−52.5 Mm³/year) in 2014–2017. This accelerated riverbed incision was likely caused by the reduction in the sediment load of the VMD (from 166.7 Mt/year in the predam period to 57.6 Mt/year in the postdam period) and increase in sand mining (from 3.9 Mm³ in 2012 to 13.43 Mm³ in 2018). Collectively, the decreased dry season water level in the Tien River is likely one of the main causes of the enhanced salinity intrusion.     

浙江南部海域富营养化和赤潮的探讨

本文探讨了浙江南部海域1990年春季发生赤潮期间的水化学特征和富营养化状况,及与赤潮生物的线性回归关系。分析结果表明,该海域出现高营养盐以至形成富营养化乃是江浙沿岸流和瓯江等河流径流及远岸区盐度锋辐聚的综合影响的结果。根据回归分析,NO_3-N,SiO_3-Si与浮游植物细胞密度之间存在着较为显著的负相关。亦即N,Si和高N/P比(35:1左右)可能是导致浮游植物(夜光藻)异常增殖的重要因素。     

Long‐term final void salinity prediction for a post‐mining landscape in the Hunter Valley,New South Wales,Australia

Opencast mining alters surface and subsurface hydrology of a landscape both during and post‐mining. At mine closure, following opencast mining in mines with low overburden to coal ratios, a void is left in the final landform. This final void is the location of the active mine pit at closure. Voids are generally not infilled within the mines' lifetime, because of the prohibitive cost of earthwork operations, and they become post‐mining water bodies or pit lakes. Water quality is a significant issue for pit lakes. Groundwater within coal seams and associated rocks can be saline, depending on the nature of the strata and groundwater circulation patterns. This groundwater may be preferentially drawn to and collected in the final void. Surface runoff to the void will not only collect salts from rainfall and atmospheric fallout, but also from the ground surface and the weathering of fresh rock. As the void water level rises, its evaporative surface area increases, concentrating salts that are held in solution. This paper presents a study of the long term, water quality trends in a post‐mining final void in the Hunter Valley, New South Wales, Australia. This process is complex and occurs long term, and modelling offers the only method of evaluating water quality. Using available geochemical, climate and hydrogeological data as inputs into a mass‐balance model, water quality in the final void was found to increase rapidly in salinity through time (2452 to 8909 mg l⁻¹ over 500 years) as evaporation concentrates the salt in the void and regional groundwater containing high loads of salt continues to flow into the void. Copyright © 2004 John Wiley & Sons, Ltd.     

激光拉曼光谱法在单个流体包裹体研究中的应用进展

激光拉曼光谱法以其非破坏性、高灵敏度和高分辨率等特性,一直以来都是研究流体包裹体的重要方法之一。近年来,围绕激光拉曼光谱在流体包裹体中的应用而展开的研究主要集中在半定量-定量测试方面,即在准确定性的基础上,采用高斯-洛仑兹去卷积分峰、低温原位等定量方法获取流体包裹体的成分和含量,从而克服了激光拉曼光谱法应用于溶液中阳离子的定量分析的灵敏度、准确度较低的问题,不仅能获得流体包裹体中一些常温下不具拉曼活性的盐类物质拉曼特征峰信息,还能根据特征峰与浓度、内压之间的线性关系,进一步对盐度和压力等性质进行测定,从而拓展了激光拉曼光谱法在流体包裹体中的应用范围。本文对激光拉曼光谱法应用于分析流体包裹体成分、盐度、同位素和压力所取得的最新进展进行了评述,并认为随着分析测试技术的不断进步,激光拉曼光谱法未来的分析方向也将继续围绕多元复杂体系及其定量方面的研究展开。     

Diatoms and ostracods as mid-Holocene palaeoenvironmental indicators,North Stromatolite Lake,Coorong National Park,South Australia ∗

The Holocene carbonate sequence of perennial North Stromatolite Lake, located adjacent to the Coorong Lagoon near Salt Creek, South Australia, includes a prominent sapropelic unit (7 – 12% total organic carbon), in places more than 2 m thick, that was sampled for the purpose of radiocarbon dating and documenting its diatom and ostracod biostratigraphy. The recovered ostracods were also subjected to carbon and oxygen isotopic analysis. The bulk organic matter at the base of the sapropel yielded an uncalibrated ¹⁴C age of 6080 ± 60 y BP. Diatoms, where preserved, are almost exclusively benthic. Stratigraphic variation of the proportions of key indicator species in diatom assemblages records a marked oscillation between oligosaline and eusaline conditions in the hypolimnion during deposition of the sapropel. Ostracod carbon isotope data indicate that the lake at this time was eutrophic, thereby enriching the dissolved inorganic carbon of the hypolimnion in ¹³C. However, the observed secular variation in δ¹³C implies a mid-sapropel drop in productivity, caused by a freshening of the lake. Ostracod δ¹⁸O values display an overall increase through the sapropel consistent with the rising salinity of the hypolimnion. The existence of a flourishing benthic ostracod community, together with the valve ornamentation of Osticythere baragwanathi, indicates that the bottom waters were well oxygenated. Thus, anoxia was not a prerequisite for sapropel accumulation. The biostratigraphy and chemostratigraphy of the sapropel concur in suggesting a lack of climatic uniformity during its deposition, a period of ～1200 years. This study therefore highlights the potential of diatoms and ostracods in shallow perennial alkaline lakes along the Coorong coastal plain as proxies for short-term (10² – 10³ years) Holocene palaeoenvironmental change in southeastern Australia.     

高温高盐高黏油藏缔合聚合物-表面活性剂二元驱技术

针对大港油田孔南地区高温、高盐、中低渗、稠油等制约化学驱提高采收率的瓶颈技术问题,以官109 1断块枣Ⅴ油组为目标油藏,在优选适合缔合聚合物和表面活性剂基础上,进行聚合物-表面活性剂二元驱技术室内实验和现场应用研究。通过室内实验优选,缔合聚合物AP P7和表面活性剂BHS 01二元体系溶液与常规体系相比,具有较好的耐温抗盐性,拓展了常规二元驱适用油藏的温度和矿化度范围;缔合聚合物经过岩心剪切后仍能够有效建立阻力系数和残余阻力系数;通过岩心驱替实验,体系能有效提高稠油油藏的采收率,拓宽了聚合物驱适用的原油黏度范围;矿场单井试注后,注入井注入压力和启动压力升高,纵向吸水剖面得到改善,说明该体系在高温高盐条件下仍能保持较高黏度,能够有效改善水油流度比,效果明显。     

华北平原深层淡水在开采条件下接受上覆咸水越流补给——以天津平原为例

分析物探测井曲线和地下水位动态发现，天津平原深层孔隙地下淡水在开采条件下接受上覆咸水的越流补给，而且咸水底界未大量向下位移。本文讨论了咸质含水组底部钙化粘土微观粘粒与水溶液的相互作用，提出了“滤盐层”的概念。     

泥质砂岩复电阻率的频散特性实验

不同孔隙流体特性的岩石复电阻率频散实验,是复电阻率测井资料评价水淹层和低阻油层的岩石物理基础。通过水驱水、水驱油、油驱水的岩石复电阻率频散特性的实验研究,发现泥质砂岩的复电阻率频散特性受含油饱和度的影响较大,受地层水矿化度的影响较小,尤其是异相电阻率,受地层水矿化度的影响更小;与含水泥质砂岩相比,含油泥质砂岩的相角相对较大,且随着含油饱和度的增加而增大;含水岩石和含油岩行在频散特性上存在着较大差异。实验研究结果表明,利用基于岩石频散特性发展起来的复电阻率测井技术,可以有效地识别油水层。     

音频大地电磁法在地下水质评价中的应用

以西北某区的地下水勘查为例,对音频大地电磁法的野外工作方法技术作了较详细的介绍,并对其应用效果进行分析。音频大地电磁法因其装备相对轻便,勘探深度相对较大,应用效果良好,在地下水勘查中有着广泛的应用前景。