三峡水库调节典型时段对鄱阳湖湿地水情特征的影响

三峡工程建成运行将改变下游的水文过程,影响通江湖泊湿地生态系统.本文选取水文情势变化大且可能对植被乍长产生较大影响的汛末蓄水和汛前腾空两个时段,运用长江中游江湖耦合水动力模型计算了三峡水库不同凋节流量下湖泊水位变化特征,并结合湖泊高程和面积关系曲线,分析了不同增减下泄流量对洲滩湿地淹没出露的影响.结果表明,三峡水库汛末...     

中国东北地区中生代构造体制的转变:来自火山岩时空分布与岩石组合的制约

东北地区中生代经历了蒙古-鄂霍茨克构造体系向太平洋构造体系的转换,形成了不同期次火山活动。本文归纳总结了露头区与覆盖区中生代火山岩的年代学、空间分布、岩石组合以及地球化学特征,揭示了两个构造域的时空分布范围。该区火山岩锆石U-Pb年龄统计结果表明中生代存在五期火山活动:早-中侏罗世(190~160Ma)、晚侏罗世(160~145Ma)、早白垩世早期(145~120Ma)、早白垩世晚期(120~100Ma)、晚白垩世早期(100~90Ma)。早-中侏罗世火山岩分布较少,火山岩仅分布在大兴安岭西部满洲里地区和东部张广才岭以及南侧辽宁北票-朝阳地区,火山岩属于高钾钙碱性系列,为蒙古-鄂霍茨克海闭合和法拉隆板块双俯冲作用的产物。晚侏罗世东北地区火山活动明显增强,主要分布在大兴安岭地区,张广才岭以及小兴安岭也有少量分布。西部大兴安岭地区以粗面安山岩、粗面岩为主,属于同碰撞造山成因,为蒙古-鄂霍茨克海闭合造山环境产物。东部以中酸性、酸性岩为主,为法拉隆板块背离欧亚大陆,岩石圈伸展引起的壳源物质熔融产物。早白垩世早期火山活动最为强烈,火山岩主要分布在大兴安岭地区。岩性以高钾钙碱性系列的粗面玄武安山岩、粗面安山岩、安山岩、粗面岩为主,为蒙古-鄂霍茨克海闭合造山后伸展环境产物。早白垩世晚期火山岩主要分布在松辽盆地内部。火山岩以中酸性岩为主,属于中钾-高钾钙碱性系列,为伊泽奈崎板块俯冲引起的弧后拉张,软流圈上涌导致年轻地壳熔融的产物。晚白垩世早期火山岩仅分布在小兴安岭及吉林、黑龙江省东部地区。火山岩为一套玄武岩、玄武安山岩、安山岩和英安岩组合,属于中钾钙碱性系列,是伊泽奈崎-库拉板块高角度俯冲的大陆边缘岩浆活动产物。东北地区中生代不同期次火山岩记录了蒙古-鄂霍茨克构造域向太平洋构造域转换过程及其时空影响范围。     

鄂尔多斯盆地周边断裂运动学分析与晚中生代构造应力体制转换

基于对鄂尔多斯盆地西南缘构造带、中央断裂、东缘边界带和东北部地区的断裂几何特征、运动学及其活动期次的野外观察和测量,并根据断层面上滑动矢量的叠加关系和区域构造演化历史,确定了鄂尔多斯盆地周边地带晚中生代构造主应力方向、应力体制及其转换序列,提出了4阶段构造演化模式和引张-挤压交替转换过程。早中侏罗世,盆地处于引张应力环境,引张方向为N-S至NNE-SSW向。中侏罗世晚期至晚侏罗世,构造应力场转换为挤压体制,盆地周缘遭受近W-E、NW-SE、NE-SW等多向挤压应力作用。早白垩世,盆地构造应力场转换为引张应力体制,引张应力方向为近W-E、NW-SE和NE-SW向。早白垩世晚期至晚白垩世,盆地应力体制再次发生转换,从前期的引张应力体制转换为NW-SE向挤压应力体制。晚中生代构造应力体制转换和应力场方向变化不仅记录了不同板块之间汇聚产生的远程效应,同时记录了盆地深部构造-热活动事件,并对盆地原型进行了一定的改造。     

大兴安岭南段晚中生代双峰式火山作用

大兴安岭南段晚中生代克头鄂博组山岩表现出双峰式特征，主要由玄武质安山岩、英安岩和流纹岩组成。基性火山岩属于代钾拉斑系列，轻微富集LREE，Eu异常不明显（Eu/Eu=0.99-1.04)和HREE无明显分馏的特征（Dy/YbcN=1.030-1.089);富集大离子亲石元素（LILE）而亏损高场强元素（HFSE），尤其是强烈亏损Nb,Ta。英安岩和流纹岩为钙碱性系列，在REE配分模式上为LREE富集型，其中英安岩为Eu弱负异常（Eu/Eu=0.81-1.01)，流纹岩的Eu负异常明显（Eu^*/Eu=0.65-0.76)；在微量元素蛛网图上，英安岩类似于基性火山岩，流纹岩除了具LILE富集和HFSE亏损特征外，还显示出Sr,P,Ti等元素的强烈亏损，可能与岩浆演化过程中斜长石、磷灰石的分离结晶作用相关。晚中生代双峰式火山岩分离结晶的结果。流纹岩表现出较高的La/Sm比值和很高的K／P、K／Ti比值，其成因可能与地壳混染作用或与大陆中、下地壳重熔作用有关。结合区域晚中生代盆岭构造格局特征、大兴安岭南段晚中生代双峰式火山岩形成于造山后阶段，是岩石圈快速伸展体制下导致受早期流体交代的岩石圈地幔发生减压部分熔融作用的产物。     

A review of paired catchment studies for determining changes in water yield resulting from alterations in vegetation

Paired catchment studies have been widely used as a means of determining the magnitude of water yield changes resulting from changes in vegetation. This review focuses on the use of paired catchment studies for determining the changes in water yield at various time scales resulting from permanent changes in vegetation. The review considers long term annual changes, adjustment time scales, the seasonal pattern of flows and changes in both annual and seasonal flow duration curves. The paired catchment studies reported in the literature have been divided into four broad categories: afforestation experiments, deforestation experiments, regrowth experiments and forest conversion experiments. Comparisons between paired catchment results and a mean annual water balance model are presented and show good agreement between the two methodologies. The results highlight the potential underestimation of water yield changes if regrowth experiments are used to predict the likely impact of permanent alterations to a catchment's vegetation. An analysis of annual water yield changes from afforestation, deforestation and regrowth experiments demonstrates that the time taken to reach a new equilibrium under permanent land use change varies considerably. Deforestation experiments reach a new equilibrium more quickly than afforestation experiments. The review of papers reporting seasonal changes in water yield highlights the proportionally larger impact on low flows. Flow duration curve comparison provides a potential means of gaining a greater understanding of the impact of vegetation on the distribution of daily flows.     

华南早中生代从印支期碰撞构造体系向燕山期俯冲构造体系转换的形变记录

华南地区中生代动力体制经历了从特提斯构造域向滨太平洋构造域的转换,但对这种动力体制转换发生的时间和产生的地质效应则存在不同的认识。通过分析华南印支—早燕山构造层(D—J1-2)广泛发育的褶皱构造,识别了早中生代两个世代褶皱构造的横跨叠加型式,发现早期近东西向褶皱构造具有南北成带、晚期NNE向褶皱构造具有东西分区的区域展布特征。基于地层接触关系和早中生代岩浆岩和火山岩同位素年代学数据统计分析,认为这两组叠加褶皱构造清楚地记录了华南早中生代两期挤压事件,近东西向褶皱是对印支早期华南地块南北边缘碰撞造山事件的远程响应,NNE向褶皱则起源于燕山早期((170±5)Ma)古太平洋板块向华南大陆之下低角度俯冲作用,两者发生转换的时代在中晚侏罗世之交。伴随这两期构造挤压而产生的地壳增厚分别诱发了华夏地块三叠纪和晚侏罗世地壳深熔作用和岩浆侵入活动。华南两组叠加褶皱构造的识别为进一步探讨早中生代从碰撞动力构造体系向俯冲动力构造体系转换提供了关键的构造地质学依据。     

黄河中游小北干流段持续淤积期的主槽摆动特点

黄河中游小北干流河段为典型的游荡型河段,主槽经常发生摆动,揭示主槽摆动特点对研究该河段的河床演变规律具有重要意义.以1986-2001年小北干流段汛后卫星遥感资料与实测29个淤积大断面地形资料为基础,计算了断面及河段尺度的主槽摆动宽度与强度,定量分析了持续淤积期小北干流段的主槽摆动特点及其主要影响因素.计算结果表明:主...     

夏季东太湖光合有效辐射衰减特征及其对沉水植物恢复的指示

水下光照分布是影响水生态系统的重要因素,研究光合有效辐射衰减特征对于沉水植物恢复具有一定的指导意义.根据沉水植物生物量资料,将东太湖划分为沉水植物茂盛区、沉水植物稀疏区和无植物区3种区域.基于2019年夏季原位水下光场资料,探讨了东太湖光衰减特性和光照衰减因子的空间差异以及不同区域内的主导衰减因子,分析了东太湖的稳态阶段和富营养化水平,并阐述了真光层深度与透明度的关系,以期为东太湖沉水植物恢复和保护提供相关资料.结果表明:东太湖不同区域光衰减特性差异显著,光合有效辐射衰减系数(k d(PAR))在0.73~11.80 m^-1之间变化,真光层深度范围为0.39~6.31 m.不同区域的无机悬浮物和有机悬浮物浓度存在显著性差异,稀疏区叶绿素a浓度显著高于茂盛区,而与无植物区没有显著差异,有色可溶性有机物(CDOM)吸收系数在3种区域无显著性差异.k d(PAR)与无机、有机悬浮物的线性拟合效果较好,而与叶绿素a、CDOM拟合较差.水体吸收和散射作用是茂盛区光衰减的主要原因,无植物区域主导衰减因子仅有无机悬浮物,稀疏区由叶绿素a和无机悬浮物共同主导,是生态修复需要重点关注的区域,有机悬浮物和CDOM对东太湖光照衰减没有太大影响.东太湖目前正处于从草型稳态向藻型稳态过渡的阶段,整个湖泊属于富营养水平,真光层深度大约为透明度的2.7倍.     

敦化市区地下水动态特征

本文按不同地下水类型,从地下水的水位、水温、水质三个方面论述了敦化市规划区地下水的动态特征。     

Using sediment rating parameters to evaluate the changes in sediment transport regimes in the middle Yellow River basin,China

This study analyses the changes in sediment transport regimes in the middle Yellow River basin (MYRB) using sediment rating parameters. Daily streamflow and suspended sediment concentration data were collected at 35 hydrological stations from the 1950s to 2016, which can be divided into three periods based on the type and intensity of human activities: the base stage before 1970, the restraining stage from 1971 to 1989, and the restoration stage after 2002. Data within each period were fitted by log‐linear sediment rating curves and the sediment rating parameters were utilized to analyse the spatial and temporal variations in sediment transport regimes. The results show that sediment rating parameters are indicative of sediment transport regimes. In the base stage and the restraining stage, the hydrological stations can be categorized into four groups based on their locations on the rating parameter plot. The stations with small drainage basins were characterized by the highest sediment transport regime, followed by those located in the coarse‐particle zone, the loess zone, and the mountainous/forest zone. In the restoration stage, the difference in sediment transport regimes between different geomorphic zones became less distinguishable than in previous stages. During the transition from the base stage to the restraining stage, sediment rating parameters showed no significant changes in sediment transport regimes in all four geomorphic groups. During the transition from the restraining stage to the restoration stage, significant changes were observed in the coarse‐particle zone and the mountain/forest zone, indicating that the revegetation programme and large reservoirs imposed a stronger influence on sediment transport regimes in these two zones than in the rest of the MYRB. This study provides theoretical support for evaluating sediment transport regimes with sediment rating parameters.