【作者】 贾建军；

【导师】 高抒；

【作者基本信息】 中国科学院海洋研究所 ， 海洋地质学， 2001， 博士

【摘要】 潮汐汊道是砂质海岸常见的沉积地貌单元，是海岸带与内陆架的重要组成部分，其作为港口航道、旅游、海水养殖等方面的资源的重要性早已被认识；但是，潮汐汊道的沉积动力行为、浅海物质循环与通量、全球变化的区域响应等方面的研究尚未充分开展。月湖是山东半岛东北角的一个小型的泻湖——潮汐汊道系统，已有4000年的历史，具有很高的科研、经济、生态、休闲旅游价值。历史上的月湖是比较稳定的，1979之后，由于人为活动的影响，月湖的物理环境和生态环境质量呈恶化趋势。研究月湖的沉积与水动力现状，分析其变化的地貌动力学原因，有助于理解小型潮汐汊道系统的沉积动力行为，重视海岸带海湾在全球物质循环中的作用，具有现实和理论的意义。 1998年冬季和1999年夏季，在月湖进行了为期各一月的野外工作，采集了131个表层底质沉积样和9个岩芯，获得了冬夏各29天的潮位记录，观测了口门大小潮期间的潮位、潮流，并采集了同步的悬移质水样。在实验室分析测定了沉积物的粒度、颗粒态有机碳含量和²¹⁰Pb放射性活度，进行了粒径趋势分析和沉积速率估算。对潮位和潮流进行了调和分析，从湾内潮位记录推算出口门的干道垂线平均流速和断面平均流速，并计算了口门的推移质和悬移质的输运能力。在此基础上，结合历史资料（地形图、航片、前人的研究成果等），探讨了月湖的沉积物平衡、汊道稳定性、潮流不对称性、口门P-A关系等问题。另外，对于海岸带的海湾——泻湖系统在全球碳通量与碳循环过程中的作用进行了讨论。 月湖是一个小而浅的潮汐汊道系统，面积4.94km²，平均水深不足1m，无常年性淡水径流汇入。集水盆地属于低山丘陵地貌，面积15.2km²。月湖表层沉积物以细颗粒物质为主，从岸到湖心逐渐变细，泥和砂质泥占湾内面积的40％以上；表层沉积物的平均粒径与沉积物类型有比较好的对应关系。²¹⁰Pb数据分析表明，湖心的沉积速率高达18.2mm yr^-1，而湖区大部沉积速率在2-5mmyr^-1。从岩芯的垂向粒度变化所反映的信息来看，湖区的沉积速率大约是5-10mm yr^-1。 月湖的沉积物主要来自流域的坡面侵蚀、湖岸侵蚀、风尘沉降、生物物质、 涨潮流带入的悬移质和推移质；整个湖区的沉积通量为 10000l2000 t yTI．粒 径趋势分析表明，月湖的湾顶(西部与北部X涨潮三角洲和湖心等地貌单元是 沉积的优势区域． 月湖的潮汐属不规则半日潮，潮差小，日不等现象明显，冬夏两季有显著 差异；平均潮差 0．50 m，平均涨潮历时 5 ’J’时 19分，平均落潮历时 7小时 5 分，平均纳潮量 2刀X 106 m‘．月湖口门的潮流是不规则半日潮流，涨急、落急 流速可达 1刀 m s’‘以上；口门想流时刻正对应湾内的高人潮时，是典型的驻波． 月湖的潮流具有独特的不对称性，口门的干道垂线平均流速的主要模式为 落潮流速大于涨潮流速、且落潮历时长于涨潮历时，而断面平均流速以涨潮流 优势型占微弱优势．这种现象出现的原因是月湖的不规则潮汐特征，以及口门 的形态与潮位的特殊对应关系．其他潮汐汉道可能也存在类似的现象． 月湖所处海域的波浪作用并不强烈，沿岸输沙强度较小．实测悬浮体浓度 较低，在10人10‘mgL”‘左右．用口门干道垂线平均流速计算，月湖的悬移质和 推移质净输运均为向外海输出，悬移质的输运量不到推移质的1／10．但是，从 沉积物平衡的角度分析，涨潮流带入的悬移质和推移质可能是月湖湾内沉积物 的重要来源．人类活动对月湖的沉积过程可能有重大影响． 从平均大潮纳潮量与沿岸毛输沙量的比值来看，月湖应属于稳定性相当好 的潮汐汉道系统；如果仅考虑口门的形态及主干道的通畅性，这一判断是可以 接受的．可以认为，月湖当前的物理系统是脆弱而稳定的，但其生态系统的稳 定性和自适能力已经遭到了严重破坏． 月湖湖心的颗粒态有机碳通量为 0．34 kg m”‘p”’．推而广之，仅就有机碳通 量而言，整个黄、渤海沿岸的小型海湾具有和黄、渤海陆架泥区相同的数量级．因 此，在碳循环研究中应充分注意海岸带海湾的贡献． 均衡状态下的潮汐汉道系统，它的纳潮量与口门面积之间的确存在某种稳 定的卜A关系．传统方法得出的P．A关系有其固有的不准确性．应用沉积动力 学方法，每个潮汐汉道的P－A关系都受涨落潮历时、断面平均流速、口门形态(面 积和宽深比X纳潮量、淡水径流量、沿岸毛输沙量和沉积物粒度等因素的控制， 互互 对于上述因素的每一种组合，都有对应的均衡态卜A关更多还原

【Abstract】 Tidal inlets are a common feature along littoral drift shores all over the world. Located in the eastern Shandong Peninsula. China, Yuehu is a small tidal inlet system with great values in terms of fish culture, tourism, environment and scientific research. Generally, the environment in the Yuehu area was stable before the 1 970s, but some inappropriate development activities (e.g. the artificial closure of the entrance in 1979, and reclamation of a large part of the intertidal land of 0.59 km2 within the tidal basin since 1986) have resulted in high deposition rate, degeneration of water quality and deterioration of the lagoon ecosystem. This indicates that this coastal embayment is fragile and sensitive to external forcing; the environment and ecosystem damage caused by human activities is difficult to recover naturally. Several aspects of the Yuehu Inlet system are of scientific research significance. First, as a typical tidal inlet system with special hydrodynamics characteristics, this system is an excellent case for sediment dynamics study. Moreover, the latest 20 years saw fast and disastrous environmental changes happening in Yuehu. Such changes deserve extensive research focusing on the interaction between human activities and physical environment evolution. Two phases of hydrodynamic observation and sediment sampling were undertaken in winter 1998 (from November 12 to December 11) and summer 1999 (from August 12 to September 9), respectively. During each period of fieldwork, tidal water levels of 29 days were recorded at the lagoon center using an Aanderaa Water-Level Recorder (Model 7 for winter and 8 for summer). Spring and neap tidal cycle measurements of the current velocity, tidal water level and suspended sediment concentrations were carried out within the entrance to the tidal basin. Further, 130 surficial sediment samples and 9 short cores were collected. During the sampling, the position was fixed using a (Magellan 2000XL) portable GPS. In the laboratory, grain size analysis was undertaken for the sediment samples using a CILAS 940L laser grain size analyzer and sieves, and grain size trends overthe lagoon were computed using the Gao-Collins model (Gao and Collins, 1991). Four short cores were selected for analysis of depoaition rate ( 0Pb method) and one for organic carbon content (using a Perkin-Elmer 240C Elemental Analyzer). Water level records were processed with TIRA (a program for harmonic analysis), and tidal currents within the inlet entrance were calculated on the basis of the law of conservation of mass and a method proposed by Gao and Collins (1994). Furthermore, bedload and suspended sediment transport rates at the inlet mouth were calculated. Historical data from scientific journals, maps and aerophotos were also collated in order to understand the evolution of the Yuehu Inlet. Yuehu has a small lagoon of 4.94 km2 in area and an average water depth of 1.0 m. The lagoon was separated from the open sea by a send spit. An entrance channel of 132 m (measured at MSL) in width connects the lagoon with the open sea. Five small rivers discharge seasonally into the lagoon; the catcbment basin, 15.2 km2 in area. is characterized by low hills. Longshore drift along the beach on the open sea side is relatively weak. The lagoon is generally dominated by fine-grained material, and mud and sandy mud account for about 40% of the lagoon area. The central part of the tidal basin is covered with muddy se更多还原