CLASSIFICATION AND TYPES OF PREFERENTIAL FLOW FOR A DARK CONIFEROUS FOREST ECOSYSTEM IN THE UPPER REACH AREA OF THE YANGTZE RIVER

Preferential flow is the ordinary phenomenon of rapid and non-equilibrium transport of water and solutes occurring in most soil. It causes latent pollution of ground and surface waters and affects runoff yield and flow concentration. This paper studies preferential flow for a dark coniferous ecosystem in the upper reach area of the Yangtze River, establishes a classification for the preferential flow and discusses types of preferential flow with a soil column experiment using a homemade apparatus and dye-tracer analysis. The preferential flow is mainly unsaturated gravitational flow in the upper layer of the slope deposit for mature forest soil, which is dominated by a wetness front, and the flow gradually transforms to macroporous flow as the soil layer deepens. The observed preferential flow in the young, middle-aged and over-mature forests that have grown on glacial lateral moraines is macroporous flow. The purpose of this research is to analyze systemically the behavior of soil water movement for a dark coniferous forest ecosystem in the upper reach area of the Yangtze River and to provide a theoretical basis for effective watershed management.     

Morphologic evolution of bifurcated reaches in a macrotidal estuary with mountain streams

A macrotidal estuary with mountain streams(MEMS) is characterized by rapidly rising and falling flood peaks and large tidal ranges and is a typical estuary type with strong flow dynamics that is found worldwide. Understanding the morphodynamic evolution of MEMSs has great significance for river management. The roles of the mountain stream river flood process and macrotides on the morphology evolution still needs further quantitative study. Taking the Oujiang Estuary as an example, the evolution ...     

早期华夏先民到达美洲的考究

1910年印第安人殷福布族所指的“浮桥岛”即现在的白令海峡。该海峡两岸最窄处为86km,晴天雨后可以隔海相望,水深只有30～50m,中间还有2个小岛(大、小代奥米德岛)。这时先民们徒徙到美洲与古海平面变迁,即第四纪晚期大陆冰川不断溶化,海平面不断上升有关。大约距今14000年左右,海平面回升到-100m,从亚洲到美洲在白令海峡确实存在阿拉斯加陆桥；到了距今12000年最后一次冰期结束,海平面上升到-60m时,该陆桥仍然存在；到了距今9000年左右,海平面上升到-25m时,陆桥开始沉没,但水很浅,特别是冬季结冰,两岸徒徙也并非难事；到距今7000年以后,处于人类文明的前夜时,海平面至少比现在低5～6m,只要依靠简单工具如“筏”、“独木舟”就可以到达美洲,因此,中国许多先民从这时开始到达了美洲,这在中国古书也都有专门的记载和描述。足见,中国很早以前也是一个航海大国。     

淮河上游地区干旱评价分析

利用淮河上游6个雨量站1964～2000年日降雨资料和邻近气象站气象资料,分别计算各站逐月Palmer干旱指标和雨量距平指标,并对计算结果进行对比分析.结果表明:淮河上游地区旱涝程度具有较强的持续性,夏季干旱多发,不过干旱等级多集中在轻微干旱和中等干旱;秋冬季节则是严重干旱多发的季节;极端干旱多发于春季;相比降雨量较大的淮南地区,淮北地区更为干旱.     

黄河中—上游地区是否普遍发生过“史前大洪水”事件的讨论

传说中发生于夏朝建立前夕的"史前大洪水"是否在大面积地区广泛存在,是学术界争议的问题之一。本文在综述黄河中—上游地区古洪水研究成果的基础上,对该区全新世以来的古洪水事件进行了统计分析。结果显示黄河中—上游大部地区可能在距今4 300~4 000 a时段曾集中发生过古洪水事件,同时该时段的古洪水事件在时间及空间范围上均能与传说中发生于黄河中游地区的"大禹治水"传说相对应。即本文的综述结果能够支持部分前人关于"史前大洪水"事件在黄河中—上游的广大地区可能真实存在的观点,且本文推测其很可能发生于距今4 300~4 000 a。此外,通过对比研究区周边气候记录,显示黄河中—上游地区古洪水事件发生的时段对应于全新世气候剧烈波动的时段,因此,本文认为,黄河中—上游大面积地区集中发生的古洪水很可能是对研究区全新世气候不稳定性的响应。     

渭河下游不同类型区农户生活用能排放差异研究

不同类型农村地区具有不同的能源消费取向,其造成的用能排放也呈明显的区域差异。研究农户生活用能排放分异,对深刻认识区域发展状况、制定合理的区域用能和环境管理政策具有重要意义。本文选取渭河下游临渭区为研究区,通过问卷调查与访谈方式获取基础数据,采用排放系数法测算平原地区、黄土台塬、秦岭山地的农户生活用能排放,利用灰色关联法识别用能排放差异的影响因素,结果发现:1不同类型地区农户生活用能排放差异显著。沼气比例较大的黄土台塬用能排放最低(1850.43 kg),薪柴为主的秦岭山地用能排放最高(2556.68 kg),多元化用能的平原地区排放居中(1863.20 kg)。2生活用能主要污染物CO2的排放量由平原向台塬、山区依次升高;其余污染物排放量高低,三类地区并无固定顺序:TSP排放秦岭山地居高,固体废弃物排放平原地区居多,这与各类地区主导用能类型相关。3影响用能排放差异的根本原因是区域能源供应能力,亦与区域环境影响下农户特征差异有关,依次为农户年龄结构、文化程度、家庭经济水平和职业结构。     

长江近口段水动力特征对来水变异的响应

三峡水库的调蓄作用使长江中下游的径流动力发生异变,并诱使长江近口段的潮汐动力发生变化。本文基于长江近口段近20 a的流量和潮位资料,运用水文学、统计学和调和分析的方法研究长江近口段的水动力特征对三峡水库调蓄作用产生的来水变异的响应。研究结果表明:三峡水库的调蓄作用使长江近口段的径流动力发生变化,泄水期1—3月多年月平均流量增幅达20%以上;蓄水期9—11月多年月平均流量减少,10月的多年平均流量减少8 488 m³/s。长江近口段径流动力的变化使潮汐动力发生相应调整,大通-江阴段保证率为10%～70%的高、低潮位显著下降,而保证率为80%～100%的高、低潮位则小幅上升。泄水期1—3月平均潮差和M₂分潮振幅减小,近口段的潮汐动力减弱;蓄水期9—11月平均潮差和M₂分潮振幅增加,尤其是10月份潮差增加最为显著,近口段潮汐作用显著增强。     

长江中下游持续性异常降水的天气学特征分析

针对长江中下游持续性降水的研究多为个例诊断,很少从合成的角度考虑,利用长江中下游地区89站的1961~2011年的逐日降水资料和NCEP/NCAR逐日再分析资料,采用数理统计和合成分析的方法,统计长江中下游地区夏季持续性降水事件,并合成分析了其环流特征。结果表明:1961~2011年,长江中下游地区夏季持续性异常降水事件发生了50次,主要集中在6月和7月,长江中下游地区持续性异常降水事件平均每2~3年发生一次。厄尔尼诺次年多有持续性异常降水发生;长江中下游地区持续性异常事件发生时,总伴有环流场的异常调整,低纬西太平洋副热带高压西伸,南北经向风在长江流域交汇,高层上,南亚高压东移,长江中下游地区出现强的辐散中心,为异常降水提供了重要条件。水汽来源主要是索马里越赤道气流途径暖湿的阿拉伯海,孟加拉湾和我国南海北部,进入长江中下游地区。     

安徽濉溪石山子遗址古人类植物性食物资源利用情况的淀粉粒分析

利用淀粉粒分析方法,对安徽濉溪石山子遗址（约7000aB.P.,33°51'N、116°49'E）出土的5件石磨盘和5件石磨棒表面附着残留物进行了研究。结果表明,这批石器表面残留物中包含了种类丰富的植物淀粉粒,其可能的植物种属来源至少有8类,包括薏苡（Coix lacryma-jobi）、小麦族（Triticeae）、山药（Dioscorea opposita）、莲藕（Nelumbo nucifera ）、 莲子（Nelumbo nucifera）、豇豆属（Vigna）、燕麦属（Avena）和姜科（Zingiberaceae）等,此外还有一部分未知种属的疑似禾本科植物的淀粉粒。统计结果显示,来自薏苡、小麦族以及疑似禾本科植物的淀粉粒无论是绝对数量还是在器物表面的出现频次都远高于其他植物种属的淀粉粒,应为这批石器的主要加工对象,此外,来自山药、莲藕等块根块茎类植物的淀粉粒,其数量和出现频次也较高。石山子遗址出土石磨盘、石磨棒表面残留物中淀粉粒组成的多样性表明了这些石质工具加工食物种类的多样性和古人类植物性食物资源组成的多样性,同时,从观察到的淀粉粒植物种属来源来看,石山子遗址先民的生业模式似仍以采集经济为主,其农业经济的发展则相对滞后,这一特点的形成可能与该遗址所处的地理位置及自然环境有较大关系。研究结果为探索新石器时代中期淮河中游地区古人类对植物资源利用以及当时的农业发展状况等问题提供了新的科学依据。     

Adjustment of flood discharge capacity with varying boundary conditions in a braided reach of the Lower Yellow River

It is of necessity to investigate the adjustment of flood discharge capacity in the Lower Yellow River(LYR) because of its profound importance in sediment transport and flood control decision-making, and additionally its magnitude is influenced by the channel and upstream boundary conditions, which have significantly varied with the ongoing implementation of soil and water conservation measures in the Loess Plateau and the operation of the Xiaolangdi Reservoir. The braided reach between two hydrometric stations of Huayuankou and Gaocun in the LYR was selected as the study area. Different parameters in the study reach during the period 1986–2015 were calculated, covering bankfull discharge(the indicator of flood discharge capacity), the pre-flood geomorphic coefficient(the indicator of channel boundary condition), and the previous five-year average fluvial erosion intensity during flood seasons(the indicator of incoming flow and sediment regime). Functional linkages at scales of section and reach were then developed respectively to quantitatively demonstrate the integrated effects of channel and upstream boundary conditions on the flood discharge capacity.Results show that:(1) the reach-scale bankfull discharge in the pre-dam stage(1986–1999)decreased rapidly by 50%, accompanied with severe channel aggradation and main-channel shrinkage. It recovered gradually as the geometry of main channel became narrower and deeper in the post-dam stage, with the geomorphic coefficient continuously reducing to less than 15 m-1/2.(2) The response of bankfull discharge to the channel and upstream boundary conditions varied at scales of section and reach, and consequently the determination coefficients differed for the comprehensive equations, with a smallest value at the Jiahetan station and a highest value(0.91) at reach scale. Generally, the verified results calculated using the comprehensive equations agreed well with the corresponding measured values in 2014–2015.(3) The effect of channel boundary condition was more prominent than that of upstream boundary condition on the adjustment of bankfull discharge at the Jiahetan station and the braided reach, which was proved by a larger improvement in determination coefficients for the comprehensive equations and a better performance of geomorphic coefficient on the increase of bankfull discharge.