长江口及其邻近海域表层沉积物粒度的空间格局和近期变化

发布时间：2018-05-31 22:05

本文选题：沉积物 + 粒径　；参考：《华东师范大学》2016年硕士论文

【摘要】：粒径是沉积物特性的重要指标。河口海岸表层沉积物特性在沉积地貌学、生态学和工程学上都具有重要意义。长江口及其邻近海域不仅是多学科研究的热点区域,也是社会经济活动的重要场所。近三十年来,长江流域建坝、水土保持工程等人类活动导致入海泥沙通量锐减,对水下三角洲的冲淤造成了巨大变化影响。另一方面,河口多项重大水利工程也不同程度的改变了河势格局和沉积动力环境。在这样高强度人类活动影响的背景下,长江口及其邻近海域的表层沉积物粒径及其空间分布格局是否发生了显著变化?这是一个值得和有待探讨的重要科学问题。本文是基于近三十年在长江口及其邻近海域大范围密集采样分析资料,揭示表层沉积物粒径的分布现状,并与三十年前海岸带调查期间相同区域和位置表层沉积物粒径资料(采用相同的吸管-筛析法分析)进行对比,探讨沉积物粒径的时间变化及其主要原因,以期丰富人类活动影响下的河口沉积学认识。主要结果和结论如下：1)长江口及其邻近海域表层沉积物粒径分布呈明显的自上游向下游变细的变化趋势。现阶段表层沉积物中值粒径(D50)的平均值在北支上段为57μm、在北支下段为16μm；在南支为66μm,南港和北港上段为41μm,南槽、北槽、北港下段(拦门沙河槽区域)为25μm,口外海滨为20μm。砂的组分北支上段为49%、在北支下段为10%；在南支为45%,南港和北港上段为29%,南槽、北槽、北港下段(拦门沙河槽区域)为17%,口外海滨为10%。粉砂组分在北支上段为37%、在北支下段为63%；在南支为40%,南港和北港上段为53%,南槽、北槽、北港下段(拦门沙河槽区域)为61%,口外海滨为66%。粘土组分在北支上段为15%、在北支下段为27%；在南支为15%,南港和北港上段为19%,南槽、北槽、北港下段(拦门沙河槽区域)为22%,口外海滨为24%。该趋势反映了径潮流相互作用下的河口动力格局和沉积物从源到汇的选择性输运过程。现阶段口内河槽沉积物明显粗于拦门沙河槽和口外海滨沉积物的总体空间格局与30年前研究区沉积物粒径分布特点基本一致,但口内外差异有所减弱。2)30年来整体上北支河槽表层沉积物粒径变细。根据前后两个时段相同位置取样点的资料对比分析,发现北支表层沉积物D50从30年前的97μm减小为现阶段的35μm；砂的含量从30年前的76%下降为现阶段的28%,粉砂含量从30年前的17%增大为现阶段的51%,粘土含量从30年前的8%增大为现阶段的21%。该变化主要归因于北支自然萎缩趋势和人类围垦缩窄等综合影响下的水动力减弱。3)30年来南支系统口内河槽表层沉积物变细,不同区段变细程度存在差异。近30年南支系统口内河槽(含南支、北港上段和南港)表层沉积物D50从89μm下降为57μm；砂的含量从54%下降为42%,粉砂含量从32%增大为43%,粘土含量从14%上升为15%。采砂可能是这导致这一变化的主要原因。4)30年来口外海滨表层沉积物粒径明显变粗。近30年长江口外海滨表层沉积物D50从10μm上升为16μm；砂的含量从8%上升为9%,粉砂含量从52%上升68%,粘土含量从39%下降为24%。口外海滨表层沉积物粗化被主要归因于流域来沙减少后水下三角洲前缘出现的侵蚀以及近期长江入海泥沙D50的增大趋势。5)30年来长江口及其邻近海域表层沉积物的分选系数、偏度和峰度随着D5o发生了相应变化。研究区分选系数、偏度和峰度均与D50之间存在一定的统计关系。这些关系反映总体上沉积物越粗,分选越好,正偏度越大,峰度越大。因此,近30年来,随着长江口内表层沉积物变细,沉积物的分选性变差,正偏度减小、峰度降低；相反,口外海滨表层沉积物的分选性变好,正偏度增大、峰度上升。总之,近30年长江口及其邻近海域表层沉积物粒径发生了显著变化,其主要原因是人类活动的影响。不同地理单元区域的沉积物粒径变化特点和主控原因有所不同。北支表层沉积物变细主要归因于围垦-促淤加速了河槽的衰亡,使其动力减弱,细颗粒悬沙沉降淤积。南支系统口内河槽表层沉积物变细则主要归因于采砂等人类活动,这些活动不仅直接抽取了较粗的砂粒组分,还因沙体的消失扩大了过水断面,从而削弱了水动力,导致较细的泥沙淤积。口外海滨表层沉积物变粗主要反映流域建坝等背景下长江入海泥沙急剧减少后水下三角洲前缘从总体上快速淤积转向侵蚀的海底过程变化,同时也可能与近期长江中游河床侵蚀补偿悬沙使入海泥沙D50增大有关。研究表明,河口及其邻近海域表层沉积物粒径可因流域或三角洲高强度人类活动的影响而发生显著变化。这种变化对底栖生物和海底工程研究可能具有借鉴意义。鉴于流域-三角洲高强度人类活动在国内外的普遍性,长江口及其邻近海域表层沉积物粒径变化的认识可能对其它河口三角洲具有一定的启示作用。
[Abstract]:The grain size is an important indicator of the characteristics of sediment. The characteristics of the surface sediments of the estuarine and coastal areas are of great significance in sedimentary geomorphology, ecology and engineering. The Yangtze Estuary and its adjacent waters are not only a hot area of multidisciplinary research, but also an important place for social and economic activities. In the last thirty years, the dam construction of the Yangtze River Basin and the soil and water conservation project On the other hand, a number of major water conservancy projects in the estuary have changed the river pattern and the sedimentary dynamic environment in varying degrees. On the background of such high intensity human activities, the surface sediments of the Yangtze Estuary and its adjacent waters Is there a significant change in the particle size and its spatial distribution pattern? This is an important scientific problem to be discussed. This paper is based on a large range of dense sampling data in the Yangtze Estuary and its adjacent waters in the last thirty years, revealing the distribution of the grain size of the surface sediments and the same area as the survey of the coastal zone thirty years ago. Compared with the surface sediment particle size data (using the same suction sieve analysis method analysis), the temporal variation of sediment particle size and its main reasons are discussed in order to enrich the estuarine sedimentology understanding under the influence of human activities. The main results and conclusions are as follows: 1) the surface sediment particle size distribution in the Yangtze River Estuary and its adjacent sea area is obvious. The average value of the median particle size (D50) in the surface sediments at the present stage is 57 mu m in the upper part of the North Branch, 16 mu m in the lower North Branch, 66 in the South Branch and 41 in m in the South and north port, in the South and in the North, and in the lower part of the north port (the Shahe trough area of the gate) is 25 mu m, and the component of the North Branch of the 20 mu m. sand is 49 in the outer seashore. The lower part of the North Branch is 10%, the South Branch is 45%, the south port and the northern port are 29%, the South trough, the North trough and the lower north port (Shahe trough area) are 17%. The outer seashore is 37% in the North Branch and 63% in the North Branch, 40% in the South Branch, and 53% in the South and North ports, the South trough, the North trough and the lower north port (the Shahe trough area of the gate of the north port). 61%, the 66%. clay is 15% in the upper part of the northern branch, 27% in the lower North Branch, 15% in the southern branch, 19% in the South and the north port, 22% in the South trough, the North trough, and the lower part of the north port (the Shahe trough area of the gate), and the trend of the estuarine and the selectivity of sediment from source to sink to the trend of 24%.. At the present stage, the overall spatial pattern of the sediment in the river trough, which is obviously coarser than the Shahe trough and the seashore sediments, is basically consistent with the grain size distribution characteristics of the sediments in the study area 30 years ago, but the difference between the first and outside of the mouth is weakened by.2. In the last 30 years, the grain size of the surface sediments in the surface of the North Branch of the north branch becomes thinner. According to the same position in the front and back of the two periods, It is found that the surface sediment D50 of the North Branch decreased from 97 mu m 30 years ago to 35 mu m at the present stage, and the content of sand decreased from 76% to 28% at the present stage, and the silt content increased from 17% before 30 years ago to 51% at the present stage, and the content of clay content from 30 years ago to the present stage of 21%. is mainly attributable to the present phase. The surface sediments of the river trough in the southern branch of the southern branch of the South Branch of the South Branch of the South Branch of the South Branch of the South Branch of the South Branch of the South Branch of the southern branch (including the South Branch, the upper part of the north port and the South Port) decreased to 57 m from 89 mu m in the last 30 years, and the content of the sand is from 5 to 30 years. 4% decreased to 42%, silt content increased from 32% to 43%, clay content increased from 14% to 15%. sand mining may be the main cause of this change. In the 30 years, the surface sediment grain size of the outer seashore of the mouth was obviously thickened. In the last 30 years, the surface sediments of the outer seashore of the Yangtze River increased from 10 mu to 16 mu m; the content of sand was increased from 8% to 9%, and the content of silt was from 5. 2% the increase of 68%, clay content from 39% to 24%. surface sediment coarsening is mainly attributable to the erosion of the subaqueous delta front of the river basin and the increasing trend of the sediment D50 of the Yangtze River in the near future.5). The separation coefficient, deflection and kurtosis of the surface sediments of the Yangtze River estuary and its adjacent sea area have occurred with the occurrence of D5o. The correlation between the separation coefficient, skewness and kurtosis of the study area has a certain statistical relationship with the D50. These relationships reflect the coarser sediment, the better the separation, the greater the positive skewness, the greater the kurtosis. Therefore, in the last 30 years, with the finer in the surface sediments in the Yangtze estuary, the separation of the sediments becomes worse, the normal degree decreases and the kurtosis decreases. On the contrary, the separation of surface sediments in the outer mouth of the mouth becomes better, the positive deviation increases and the kurtosis rises. In a word, the surface sediment particle size of the Yangtze River Estuary and its adjacent sea area have been significantly changed in the last 30 years. The main reason is the influence of human activity. The characteristics of the variation of sediment grain size and the main controlling reasons in different geographic units are different. The thinning of the layer sediments is mainly attributable to the decline of the river trough, which has accelerated the decline of the river channel and made its power weaken and the fine particles suspended sediment deposition. The detailed details of the sediment in the surface of the river trough in the southern branch of the system are mainly attributable to the human activities such as sand mining. These activities not only directly extract the coarser sand composition, but also expand the over water break of the sand body. It weakens the hydrodynamic force and leads to the fine siltation. The thickening of the surface sediments in the surface of the seashore mainly reflects the change of the seabed process of the lower delta front of the Yangtze River after the drastic reduction of the sediment in the Yangtze River, and may also compensate for the erosion of the river bed erosion in the middle reaches of the Yangtze River in the near future. The study shows that the surface sediment particle size of the estuarine and its adjacent sea area can be significantly changed by the influence of high intensity human activity in the river basin or delta. This change may be of reference to the study of benthic and seabed engineering. In view of the high intensity human activities in the River Delta and the Delta, D50 The understanding of the change of surface sediment grain size in the Changjiang Estuary and its adjacent waters may have implications for other estuarine deltas.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P736.21;P343.5

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