调水工程对九龙江河口水环境的影响研究

为分析九龙江调水工程对河口水环境的影响,采用MIKE21构建了九龙江河口二维非稳态水环境数学模型,对调水前后的河口水动力、水质指标进行模拟。经分析,调水使西溪水闸下泄流量平均减少4.2 m^(3)/s,最大变化率达到10%。预测结果表明,北港、中港、南港典型点及河口国控点的流速变幅均为0.02 m/s,水位变幅均接近于0,氨氮浓度最大变化率为2.17%,盐度最大变化率为2.92%,西溪调水工程对河口区域涨落潮流场、氨氮浓度及盐度分布影响极小。该研究成果可为九龙江河口水环境保护与管理提供依据,也可为其他河口引调水工程的影响分析提供借鉴。

黄河三角洲典型潮沟发育演变过程分析

以黄河三角洲东部、侧弯丁坝北部为研究区域,基于1997—2021年内共8期Landsat系列遥感影像,采用目视解译的方法提取潮沟网络,通过分析不同时期潮沟数量、长度、密度等特征,揭示了潮沟阶段性演变规律。结果表明:潮沟的全生命周期可划分为幼年期、青年期、成熟期和退化期4个阶段,其中幼年期潮沟数量和长度增长率最大,是青年期的3倍以上;青年期潮沟数量和长度继续增加,但增长率明显降低,潮沟网络系统逐渐趋于稳定;成熟期潮沟系统发育基本完成,潮沟长度、数量、曲率等形态特征无明显变化;退化期部分潮沟萎缩、消亡、废弃,2005—2007年Ⅰ组潮沟每年消亡10.8%。

2022年后汛期长江口严重咸潮空间分布特征分析

2022年长江流域出现“汛期反枯”现象,9月长江口河段遭遇了历史罕见的咸潮入侵,对长江口沿江水源地造成严重威胁。为研究2022年后汛期(9~10月)长江口严重咸潮入侵的空间分布,掌握咸潮上溯的最上游位置,基于2022年9~11月长期站实测资料和咸潮应急监测资料及历年实测水文资料,定量分析了长江口咸潮的横向、纵向及垂向分布,结合FVCOM盐度数值模型进行模拟。结果显示,北港水域盐度底表层差异显著,底表层盐度比值平均为25;咸潮最严重时,影响到徐六泾节点段,最上游到达苏通大桥上游约1.0 km。研究结果对长江口应急水源地的规划选址具有指导意义。

极端干旱下长江口咸潮入侵成因及压咸补淡措施

2022年长江上游遭受极端干旱,长江口咸潮入侵加剧,区域用水安全受到严峻考验。为探究极端干旱天气下咸潮入侵成因和应对策略,基于长江口2019~2023年枯水期的实测盐度、潮水位、风速风向数据与同期上游大通站径流量数据,采用Spearman相关性分析、卡方分析等方法,分析了2022年9月起长江口咸潮入侵过程与长江口咸潮入侵的主要影响因素。分析结果显示:①2022年8月起长江干流枯水期提前,叠加台风和天文大潮情况,使得2022年9月至2023年4月长江口地区崇明洲头站、杨林站和六滧站的盐度大幅超标,分别达到1.922‰,0.585‰和2.134‰。②长江口3个主要盐度监测站点受上游来水影响时间存在前后差异,在大通站流量低于15000 m^(3)/s时,不同站点所属区域发生了不同程度的咸潮入侵情况。③2022年10月的压咸补淡措施在小潮期间作用于长江口地区,使得大通站流量高于12000 m^(3)/s,在南支上半段产生较好的压咸效果。研究成果可为长江口流域不同地区咸潮上溯成因分析和压咸补淡应对策略提供参考。

珠江河网水位与动力边界的联合依赖关系演变

珠江河网的水位变化是动力和地貌边界共同驱动的结果。然而,在强人类活动干预下,河网地貌边界发生异变,叠加动力边界(上游流量和口外海平面)变化影响,导致河网水位格局出现异变。探讨河网水位的异变问题,可为河口整治和水资源高效开发利用等提供重要指导。本研究采用Copula方法探究强人类活动驱动下河网日均水位与动力边界的联合依赖关系演变过程,并对极端日均水位风险进行了评估。结果表明:珠江河网水位与动力边界的联合依赖关系发生了显著变化,表现为相同流量或海平面条件驱动下,河网上部日均水位下降、中下部高水位下降但低水位抬升,而口门区域日均水位抬升。强人类活动前后珠江河网极端日均水位的风险变化表明,当河网上部水位与流量、海平面遭遇概率为10%~90%时,日均水位降幅为0.02~1.24 m;河网中下部水位与流量、海平面遭遇概率为90%时,变化与上部一致但降幅缩小为0.05~0.23 m,而遭遇概率为10%时,其日均水位抬升,幅度为0.01~0.07 m;在口门区域,水位与流量、海平面遭遇概率为10%~90%时,日均水位抬升0.02~0.09 m。综上所述,强人类活动后,动力边界对河网水位的影响明显减弱,河网日均水位整体抗风险能力下降,发生极端水位事件的风险加剧。

Examining the evolution of tidal creeks in the Huanghe River delta using multi-temporal Landsat images

Coastal tidal creeks are important channels for exchanges of material and energy between sea and land,and play an important role in the ecological protection of tidal flats.Although tidal creeks have evolved differently in various regions,the evolutionary process of tidal creeks in the Huanghe(Yellow)River delta of China,one of the most active deltas worldwide,is not entirely clear.Therefore,the evolution of tidal creeks in the delta from 1981 to 2021 was investigated by quantitatively analysing the tidal creeks and developing a standard for dividing their evolution periods.Visual interpretation and supervised classification methods were applied to the Landsat images to extract the tidal creek network,and 17 groups of tidal creek systems were selected.Results indicate that Creek S 1 was the most developed creek for having 113 tidal creeks totaling 65.8 km in length,while Creek E 3 had the fastest growth rate for having average annual increase of 1.9 km.Meanwhile,the level of tidal creeks increased,the average and median lengths of tidal creeks increased,and the number of tidal creeks decreased since 1981.The evolution of the tidal creek system could be divided into four stages,namely,rising,developing,stabilizing,and degrading.Analyses of a representative tidal creek show that there was no degenerated tidal creek during the rising period,with an increase in the number of 50 and a length increase of 57.9 km between 1981 and 1989.The proportion of new tidal creeks in the developing period was more than 50%and the new tidal creeks in the stabilizing period were equal to the degraded tidal creeks.Extinct tidal creeks were greater than 50%during the degrading period.There was no fixed order of tidal creek evolution in each period,and there may be a skip in evolution.Our findings provided a reference for studying the evolution of tidal creeks.

长江古河谷早中全新世沉积物碳埋藏通量与来源解析

为了研究长江古河谷地区早中全新世沉积物的碳埋藏速率及来源,进行了ZK1孔沉积物总有机碳(TOC)、总氮(TN)及δ^(13)C的测定,结合AMS^(14)C(植物碎屑、贝壳)测年、有孔虫及粒度数据,分析了长江古河谷碳埋藏的时空分布特征与TOC来源。采用历史地理学、沉积地质学结合测年数据进行了年代地层划分,自下而上分别为U1潮汐河道、U2河口湾、U3潮流砂脊和U4前三角洲。沉积物受到水深、径流、河口余环流、潮流、波浪、风暴与再矿化等作用或因素影响,TOC平均值为0.41%,低于长江河口表层沉积物基准值0.46%。ZK1碳埋藏通量(TOC_(BF))介于7.4~110.5g/(m^(2)·a)之间,差异较大。TOC_(BF)数值主要受控于沉积速率。δ^(13)C与TOC/TN(C/N)投影点结果表明,TOC来源表现为多源特征,且整体表现为偏陆源特征。C/N与δ^(13)C线性拟合相关性高,适合采用C/N与δ^(13)C进行TOC来源的定量分析。基于C/N与δ^(13)C采用三端源模型进行了TOC来源分析。U2、U3沉积期处于全新世大暖期,其海源碳与陆源碳较U1、U2沉积单元高,这主要与海洋、陆地初级生产力的提高有关。ZK1海洋浮游植物对TOC的贡献量平均值为31%。河口浮游植物对TOC的贡献量平均值为31%。陆源有机碳对TOC的贡献量平均值为38%。整体来看,陆源有机碳的贡献量大于河口浮游植物与海洋浮游植物的贡献量,这与图解法的分析结果基本一致。

2022年长江口夏季咸潮入侵及影响机制研究

2022年长江流域降雨、干支流来水均严重偏少,江湖水位持续走低,发生了1961年有完整记录以来最严重的流域性气象水文干旱。受此影响,2022年8月下旬长江河口就遭遇咸潮入侵,为有咸潮入侵监测记录以来历史最早,随后入侵增强并持续影响长江口。针对2022年长江口罕见的夏秋季节咸潮入侵事件,利用长江口岸基、浮标观测资料,分析了2022年洪季咸潮入侵的变化过程,并结合FVCOM咸潮入侵数值模型,量化分析径流、潮汐及台风事件对咸潮入侵的影响。结果表明:2022年夏季长江径流量为历史极低值,导致长江口咸潮入侵时间提前,入侵频率增加,上溯距离增大,河道北侧盐度显著高于南侧。在低径流情况下咸潮入侵呈现显著的涨落潮、大小周期性变化,其中小潮后期为盐度的快速上升期,大潮至中潮位为盐度缓慢下降时段。除此之外,持续的偏北风会有利于外海水体向海内输送,导致水位抬升,增强咸潮入侵。2022年9月在北向型台风“轩岚诺”和“南玛都”的影响下,随着涨潮流的作用,长江口咸潮入侵程度在9月21日达到最大,上溯至东风西沙水库北部约10 km处。研究成果可为进一步认识长江口咸潮入侵规律及机理提供依据。

辫状河三角洲沉积特征与生长演变规律——水槽沉积模拟实验研究

辫状河三角洲是一类常见的沉积体系,也是一类常见的油气储层,其沉积特征、沉积演化过程及内部结构一直受到沉积学研究的关注。为明确辫状河三角洲沉积特征、演化过程及生长演变规律,笔者等通过水槽实验模拟辫状河三角洲在平缓的水下底形上逐步发育的过程,并采用三维激光扫描仪、延时拍照等手段进行精准的沉积地貌监测和定量沉积学分析。研究表明:(1)辫状河三角洲沉积演化过程中,三角洲的规模、水流分散样式、沉积体表面地貌特征及沉积物分布样式存在阶段性差异,可据此将实验辫状河三角洲的演化分为3个阶段。(2)在最初阶段,辫状河携带沉积物直接入“湖”堆积并形成朵状河口坝,入“湖”水流无明显的水道化特征,随着朵状河口坝逐渐堆积露出水面,三角洲平原初步形成,平原上河道开始分流并导致后续河口坝转变为连续的弧形坝分布于先期沉积体周缘,这一阶段三角洲平均半径快速增加;进入第二阶段后,三角洲平均半径增速减缓,供给河道进入三角洲平原后形成1~2条主干分流河道与多条次级分流河道,并在主干河道河口区形成弧形的前缘朵体;到第三阶段,三角洲平原面积已经较大,其平均半径增速进一步降低,平原上分流河道的分叉性更强、宽度更小,不同分流河道规模接近并可同时将沉积物输送到三角洲前缘多个部位发生沉积,在同一时期形成多个孤立的小规模的前缘朵体。(3)在整个沉积演化过程中,伴随着三角洲规模的逐渐增大,分流河道的宽度逐步减小、流程变长、分流河道数量逐步增加,三角洲前缘沉积由少量弧形的连续分布朵体转变为多个孤立分布的小规模朵体。(4)在第二、三阶段,分流河道表现为多个侵蚀—回填的自旋回演化过程,形成了多套自旋回沉积复合体。(5)辫状河三角洲前积层存在自下而上、由近向远表现为沉积连续性逐步减小、叠切规律逐渐复杂的特性。通过水槽实验揭示辫状河三角洲沉积演化过程及内部结构,可为露头解剖与地下储层研究提供参考。

Controls of accommodation to sediment-supply ratio on sedimentary architecture of continental fluvial successions

The applicability of sequence stratigraphic models to continental fluvial successions has long been topic for debate. To improve our understanding of how fluvial architectures record responses to changes in the ratio between accommodation rate and sediment-supply rate (A/S), two case studies are analyzed, including a densely drilled subsurface fluvial reservoir imaged with a seismic cube, and an outcropping fluvial succession. The subsurface dataset provides a larger, three-dimensional perspective, whereas the outcrop dataset enables observation at higher resolution. On the basis of both datasets, channel-body density, channel-body stacking patterns and their formative river types are interpreted at different scales, and how these may reflect responses to A/S change (the rate of accommodation creation relative to the rate of sediment supply) are discussed. The results indicate that (i) channel-body stacking patterns undergo four evolutionary stages along with the A/S increase, i.e., multi-story, mixed multi- and two-story, two-story, and isolated patterns;(ii) channel-body density decreases along with the channel-body stacking patterns varying from multi-story to isolated;(iii) formative rivers types are interpreted as evolving from braided planforms to braided-meandering planforms and then to meandering ones, with the increase of A/S.

1955年以来入洞庭湖的荆江三口分流变化

近70年来荆江三口分流持续减少,为分析各历史阶段三口分流变化的驱动因素,根据1955—2021年干支流水文、地形实测资料开展研究,并基于控制变量法识别各驱动因素贡献比例。结果表明:三口分流阶段性减少,且集中在5—11月。长江上游降雨减少导致的干流来流偏枯以及下荆江裁弯、葛洲坝拦沙造成的干流河道冲刷和三口口门淤积对三口分流减少促进作用明显,调弦口堵口对三口分流影响不大,三峡水库蓄水后干流河道与三口口门同步冲刷,三口分流变化不大。长江上游汛期降雨减少明显,对5—11月三口分流减少影响较大,且三口分流主要发生于汛期干流中洪水位时,导致在下荆江裁弯期干流河床大幅下切条件下5—11月分流显著减少;葛洲坝调度、三峡水库初期调度和试验性蓄水调度也集中于5—11月,使得5—11月三口分流量分别减小0.4×10^(8)、12.5×10^(8)和38.6×10^(8)m^(3)。调弦口堵口对三口分流的增大作用远小于降雨的减小作用,贡献比例为负值;下荆江裁弯对三口分流减少的贡献比例达85%;水库运用期降雨对三口分流减少的贡献最大,贡献比例大于50%,葛洲坝调度几乎不产生贡献、下游河道调整贡献比例为21%,三峡水库初期调度贡献比例增大至7%、下游河道调整贡献比例为10%,试验性蓄水期则分别上升至23%和19%。长江上游降雨减少至少持续到本世纪末,三口分流年均值将长期呈减少趋势,而荆江干流与三口口门同步冲刷,干流同流量下三口分流仍将变化不大。

珠江河网横向汊道水位演变特性及原因探究

珠江河网横向汊道体系是维持三角洲河网动力平衡的独特地貌结构,具有泄洪纳潮的重要功能,探讨该结构水位的阶段性演变及其影响因子辨识是河口动力学研究的重要科学问题。采用流量驱动的R_TIDE数据驱动模型,对研究区域内“容桂-凫洲水道”和“潭洲-前航道”两个典型横向汊道体系共8个站点的日均水位序列进行分解,分离出由上游流量驱动引起的水位变化及地形和海平面共同驱动的水位变化。结果表明,经过水库的调蓄作用,在“容桂-凫洲水道”,流量驱动导致冬季日均水位抬升(平均为0.04m),其余三季日均水位下降;“潭洲-前航道”则由于北江流量增大导致流量驱动的日均水位均有不同程度的抬升(平均为0.17 m)。由于地形下切和海平面上升,地形和海平面共同驱动的日均水位变化普遍为负值(除南沙、黄埔站分别为0.11、0.07 m),“容桂-凫洲水道”中下部河段在秋季受海平面上升(秋季海平面高程最大)影响大于河床地形下切效应导致水位抬升,而其余站点主要受到疏浚、采砂等人类活动引起的地形下降影响,水位下降,且上游变化幅度明显大于下游;对径潮动力方差贡献率的分析结果表明,“容桂-凫洲水道”和“潭洲-前航道”夏季径流对水位的方差贡献率平均分别减小10%和15%,冬季则平均分别减小5%和3%,显示出强人类干预后总体呈现泄洪压力减小,纳潮能力增强的变化趋势。

珠江黄茅海河口湾滩槽结构演变及动态平衡研究

河口湾常由滩、槽地貌系统组合而成,其滩槽结构演变及动态平衡既是河口海岸研究的重要科学问题,又是河口规划治理与港口航道建设的理论基石。本文以黄茅海河口湾为研究靶区,采用“动力−沉积−地貌”的研究思路,基于不同历史年代的海图资料,运用地貌信息熵等分析方法,研究黄茅海河口湾滩槽结构的系统演变特征及动态平衡机制,主要发现包括:(1)黄茅海河口湾半个多世纪以来的地貌演变,大致以2007年为转折点,经历由淤积到冲刷的状态转换,其在1940-2007年呈淤积状态,年均淤积率为1.4cm/a,在2007-2015年呈冲刷状态,年均冲刷率为1.2cm/a。(2)黄茅海河口湾的滩槽结构发生转换,在2003-2007年之间由“三滩两槽”的结构转换为“两滩一槽”的结构,受围垦和疏浚工程影响,滩槽分异趋于加强,呈现浅滩淤浅、深槽刷深的演变特征。(3)黄茅海河口湾地貌信息熵熵值先减后增,从缓慢淤积相对稳定的有序状态向人为干预下冲淤格局变化及滩槽演变的不确定性增加转换;滩槽结构的稳态存在差异,浅滩相对于深槽显示出更高的不确定性。(4)人类活动将滩槽结构的原有稳态打破,疏浚工程使得东槽的活力提升,促进深槽自适应重构平衡向有序方向发展。西滩和东滩经历围垦等人类活动干扰平衡,浅滩失稳呈无序演变。

Factors Influencing the Thermal Conductivity of Silt in the Yellow River Delta

The thermal conductivity of marine sediments is an important thermophysical parameter in the study of seafloor heat flow and marine engineering construction.Understanding the effect of thermal conductivity of marine sediments in the environment has a major engineering value and theoretical significance.In this work,a modified test method was used to measure the thermal conductivity of silt in the Yellow River Delta under different void ratios,moisture contents,temperatures,and salinities.Results showed that the thermal conductivity of silt in the Yellow River Delta decreased with the increase in the void ratio and increased with the water content.Compared with sand and clay,silt in the Yellow River Delta was the least affected by the void ratio and moisture content.Under low temperatures,the heat transfer of soil was controlled by the average velocity of the phonons;therefore,the thermal conductivity of silt in the Yellow River Estuary increased with temperature.The thermal conductivity of pore water decreased with increasing salinity.Moreover,certain salinity levels resulted in a phenomenon known as the‘compressing twin electrical layer’,which led to an increase in the contact area between soil particles.With the increase in salinity,the thermal conductivity of silt in the Yellow River Delta experiences an initial decline and a subsequent increase.The proposed thermal conductivity test method is more accurate than the existing technique,and the findings provide a basis for further study on the thermal characteristics of submarine sediments.

Study on strength properties and soil behaviour type classification of Huanghe River Delta silts based on variable rate piezocone penetration test

Fine-grained silt is widely distributed in the Huanghe River Delta(HRD)in China,and the sedimentary structure is complex,meaning that the clay content in the silt is variable.The piezocone penetration test(CPTu)is the most widely approved in situ test method.It can be used to invert soil properties and interpret soil behavior.To analyse the strength properties of surface sediments in the HRD,this paper evaluated the friction angle and its inversion formula through the CPTu penetration test and monotonic simple shear test and other soil unit experiments.The evaluation showed that the empirical formula proposed by Kulhawy and Mayne had better prediction and inversion effect.The HRD silts with clay contents of 9.2%,21.4%and 30.3%were selected as samples for the CPTu variable rate penetration test.The results show as follows.(1)The effects of the clay content on the tip resistance and the pore pressure of silt under different penetration rates were summarized.The tip resistance Q_t is strongly dependent on the clay content of the silt,the B_(q)value of the silt tends to 0 and is not significantly affected by the change of the CPTu penetration rate.(2)Five soil behavior type classification charts and three soil behavior type indexes based on CPTu data were evaluated.The results show that the soil behavior type classification chart based on soil behavior type index ISBT,the Robertson 2010 behavior type classification chart are more suitable for the silty soil in the HRD.

Spatial differentiation and dynamic mechanism of micro-geomorphology based on acoustic spectrum data of the Huanghe(Yellow)River Delta

Submarine micro-geomorphology is a geo-morphological type occurring in shallow and surface areas of seabed.The combined relationships and distribution of the micro-geomorphology indirectly reflect coupling relationships among the sediment deposition,dynamic environment,and geomorphologic evolution.Spatial differentiation and dynamic changes in micro-geomorphology were studied based on acoustic data interpretation from a wide range(3200 km^(2))of the Huanghe(Yellow)River delta(HRD).The combination of the sub-bottom profiler and the side-scan sonar methods allowed for the identification of submarine shallow micro-geomorphologic types,as well as their scale and spatial distributions.There were seven typical micro-geomorphologic features in the shallow and surface areas of the HRD,including buried ancient channels,stratigraphic disturbances,scour troughs,sand waves,pits,erosional remnants,and sand spots.The coupling and superposition of the sediment,sediment characteristics,seabed scouring and silting,and hydrodynamic conditions of the Huanghe River had combined effects on the patterns of micro-geomorphologic types,characteristics,and ranges.From the perspective of acoustic profile interpretations,the scale,range,and spatial locations of the microgeomorphology in the HRD revealed seasonal variation characteristics,and the spatial distributions displayed significant regional differentiation characteristics.In addition,strong stratigraphic disturbances and areas with densely distributed buried ancient channels reflected the activity and instability of the submarine shallow strata.Through the interpretation of the sub-bottom profile detection data,the diversion processes of the flow paths in the lower reaches of the Huanghe River were obtained for a certain historical period in the coastal waters of the HRD.This study further clarified the relationships between the micro-geomorphologic features and spatial combinations,which is important for research on micro-geomorphologic features and their dynamic mechanisms.

Mechanism of the Impact of Floods and Typhoons on the Morphological Evolution of the Yangtze Estuary

In the last two decades,the Yangtze Estuary has undergone significant changes under the influence of reduced sediment inflow and estuary engineering.This study investigates the influence of floods and typhoons on sediment concentration and the morphological evolution of shoals and channels in the Yangtze Estuary.The analysis is conducted through the utilization of topographic data measured pre-and post-flood events and observations of hydro-sedimentary changes during typhoons.By using a generalized estuary mathematical model,this study examines the interplay between varying tidal ranges,tidal divisions,runoff volumes,and regulation projects on the erosion and deposition of shoals and channels in bifurcated estuaries.The results show that due to the implementation of river and waterway regulation projects,the impact of the 2020 flood on the main channel and shoal was significantly less than that of the1998 flood.The swing amplitude of the South Branch main channel decreased.However,local river sections such as the Southern Waterway of Baimao Shoal exhibited erosion.During typhoons,sediment concentration in the 20 cm above the bottom increased significantly and was closely related to wave processes,with a weakened correlation to tidal dynamics.After typhoons,high shoals in South Passage above 0 m were silted up,while the terrain on one side of the tail of Jiuduan Shoal in the downstream deep-water area was generally scoured due to strong wave action.The generalized mathematical model of the bifurcated estuary revealed that M2 tidal component contributed most to the ero sion and deposition evolution of estuary shoals and channels,with floods exhibiting characteristics of sedime ntation on shoals and erosion on channels.With the implementation of a branch rectification project,branch resistance increased,diversion decreased,and the riverbed changed from pre-project erosion to post-project sedimentation,with an increase in erosion in non-project branches.

九龙江河口水体粪类有机质污染时空变化特征研究

河口是陆源污染物入海的主要通道,在全球气候快速变化和人类活动加剧的背景下,河流入海污染物通量急剧增加,导致河口、海湾及其周边海域水体污染、生态受损等严峻的环境问题发生。本文选取了受极端事件和人类活动影响显著的我国东南强潮型的九龙江河口,利用粪甾醇有机标志物手段开展河口环境粪类污染示踪研究,探讨九龙江河口区粪类污染物(“源”)进入河流后的入海行为(“到”),揭示粪类有机质在近河口海域时空分布特征及受控因素(“汇”)。研究发现,不同季节的河口径流过程和潮汐作用影响粪类有机污染物的时空分布,潮汐过程对中上游河口区水体环境中粪甾醇的赋存影响较大,呈现高潮低浓度而低潮高浓度的潮周期变化特征;河口区粪甾醇在陆−海输运过程的赋存特征还受控于最大浑浊带复杂的水体和沉积动力过程,对粪类有机污染物有一定的净化作用;研究还通过对比人为源贡献主导的氨氮等河流输入的营养盐说明粪甾醇在河口区的时空分布特征与人类活动密切相关。

柴达木盆地英东地区浅水三角洲形成条件及沉积特征

柴达木盆地英东地区沉积特征复杂。据研究区沉积背景、古构造特征、古生物特征及古气候特征等分析认为,古近纪柴达木盆地西南部主要为干旱、半干旱气候条件下的浅水三角洲沉积。该区古水体浅且动荡,湖平面升降频繁,水体深浅旋回变化,表明英东地区发育浅水三角洲古地理环境。研究区岩性以粉砂岩和细粉砂岩为主,夹棕红、灰紫色泥岩,垂向上多个间断正韵律相互叠置,表明在频繁湖平面升降期间具较强河流冲刷作用。A、B、C区块上下油砂山组沉积相平面展布特征为干旱、半干旱条件下的浅水辫状河三角洲及湖相沉积。据研究区发育延伸远,多叉的水下分流河道,河口坝不发育等特征,综合分析建立河控远源-细粒型浅水三角洲沉积模式。

全新世呼伦湖区植被和气候变化的孢粉记录

文章详细分析了内蒙古呼伦湖HL06岩芯沉积的孢粉组合,基于AMS^(14)C年代标尺,恢复了全新世湖区植被演变过程;并根据我国北方和蒙古表土孢粉数据和气象资料,建立了孢粉-气候参数转换函数,定量重建了呼伦湖区降水和气温的变化历史。结果表明,11000～8000aB.P.,湖区植被以蒿、藜占优,为干草原景观,气候暖干;8000～6400aB.P.,湖区禾本植物扩张,山地桦林发育,降水显著增加,气温逐渐降低;6400～4400aB.P.,湖区旱生草本植物增加,降水减少,气温继续下降;4400～3350aB.P.,耐旱藜科植物大量生长,湖区荒漠化,气候极端干旱;3350～2050aB.P.,湖区草原植被有所恢复,降水略有增加,气温有所回升;2050～1000aB.P.,湖区蒿属植物减少,山地松林发育,气温降至全新世最低;最近1000年,藜科、禾本科等伴人植物大量出现,反映出人类活动对湖区自然环境的影响。全新世呼伦湖区气温变化在轨道尺度上受控于北半球太阳辐射量的变化,而在亚轨道尺度上可能与东亚夏季风强度有关。距今8000年前湖区降水较弱可能因为早全新世北半球高纬残存冰盖抑制了东亚季风雨带的北上,季风降水的千年-百年尺度波动与热带西太平洋海气相互作用密切相关。