本文選題：沉積物 + 粒徑　； 參考：《華東師范大學(xué)》2016年碩士論文

【摘要】：粒徑是沉積物特性的重要指標(biāo)。河口海岸表層沉積物特性在沉積地貌學(xué)、生態(tài)學(xué)和工程學(xué)上都具有重要意義。長江口及其鄰近海域不僅是多學(xué)科研究的熱點區(qū)域,也是社會經(jīng)濟活動的重要場所。近三十年來,長江流域建壩、水土保持工程等人類活動導(dǎo)致入海泥沙通量銳減,對水下三角洲的沖淤造成了巨大變化影響。另一方面,河口多項重大水利工程也不同程度的改變了河勢格局和沉積動力環(huán)境。在這樣高強度人類活動影響的背景下,長江口及其鄰近海域的表層沉積物粒徑及其空間分布格局是否發(fā)生了顯著變化?這是一個值得和有待探討的重要科學(xué)問題。本文是基于近三十年在長江口及其鄰近海域大范圍密集采樣分析資料,揭示表層沉積物粒徑的分布現(xiàn)狀,并與三十年前海岸帶調(diào)查期間相同區(qū)域和位置表層沉積物粒徑資料(采用相同的吸管-篩析法分析)進行對比,探討沉積物粒徑的時間變化及其主要原因,以期豐富人類活動影響下的河口沉積學(xué)認(rèn)識。主要結(jié)果和結(jié)論如下：1)長江口及其鄰近海域表層沉積物粒徑分布呈明顯的自上游向下游變細(xì)的變化趨勢�，F(xiàn)階段表層沉積物中值粒徑(D50)的平均值在北支上段為57μm、在北支下段為16μm；在南支為66μm,南港和北港上段為41μm,南槽、北槽、北港下段(攔門沙河槽區(qū)域)為25μm,口外海濱為20μm。砂的組分北支上段為49%、在北支下段為10%；在南支為45%,南港和北港上段為29%,南槽、北槽、北港下段(攔門沙河槽區(qū)域)為17%,口外海濱為10%。粉砂組分在北支上段為37%、在北支下段為63%；在南支為40%,南港和北港上段為53%,南槽、北槽、北港下段(攔門沙河槽區(qū)域)為61%,口外海濱為66%。粘土組分在北支上段為15%、在北支下段為27%；在南支為15%,南港和北港上段為19%,南槽、北槽、北港下段(攔門沙河槽區(qū)域)為22%,口外海濱為24%。該趨勢反映了徑潮流相互作用下的河口動力格局和沉積物從源到匯的選擇性輸運過程�，F(xiàn)階段口內(nèi)河槽沉積物明顯粗于攔門沙河槽和口外海濱沉積物的總體空間格局與30年前研究區(qū)沉積物粒徑分布特點基本一致,但口內(nèi)外差異有所減弱。2)30年來整體上北支河槽表層沉積物粒徑變細(xì)。根據(jù)前后兩個時段相同位置取樣點的資料對比分析,發(fā)現(xiàn)北支表層沉積物D50從30年前的97μm減小為現(xiàn)階段的35μm；砂的含量從30年前的76%下降為現(xiàn)階段的28%,粉砂含量從30年前的17%增大為現(xiàn)階段的51%,粘土含量從30年前的8%增大為現(xiàn)階段的21%。該變化主要歸因于北支自然萎縮趨勢和人類圍墾縮窄等綜合影響下的水動力減弱。3)30年來南支系統(tǒng)口內(nèi)河槽表層沉積物變細(xì),不同區(qū)段變細(xì)程度存在差異。近30年南支系統(tǒng)口內(nèi)河槽(含南支、北港上段和南港)表層沉積物D50從89μm下降為57μm；砂的含量從54%下降為42%,粉砂含量從32%增大為43%,粘土含量從14%上升為15%。采砂可能是這導(dǎo)致這一變化的主要原因。4)30年來口外海濱表層沉積物粒徑明顯變粗。近30年長江口外海濱表層沉積物D50從10μm上升為16μm；砂的含量從8%上升為9%,粉砂含量從52%上升68%,粘土含量從39%下降為24%�？谕夂I表層沉積物粗化被主要歸因于流域來沙減少后水下三角洲前緣出現(xiàn)的侵蝕以及近期長江入海泥沙D50的增大趨勢。5)30年來長江口及其鄰近海域表層沉積物的分選系數(shù)、偏度和峰度隨著D5o發(fā)生了相應(yīng)變化。研究區(qū)分選系數(shù)、偏度和峰度均與D50之間存在一定的統(tǒng)計關(guān)系。這些關(guān)系反映總體上沉積物越粗,分選越好,正偏度越大,峰度越大。因此,近30年來,隨著長江口內(nèi)表層沉積物變細(xì),沉積物的分選性變差,正偏度減小、峰度降低；相反,口外海濱表層沉積物的分選性變好,正偏度增大、峰度上升�？傊�,近30年長江口及其鄰近海域表層沉積物粒徑發(fā)生了顯著變化,其主要原因是人類活動的影響。不同地理單元區(qū)域的沉積物粒徑變化特點和主控原因有所不同。北支表層沉積物變細(xì)主要歸因于圍墾-促淤加速了河槽的衰亡,使其動力減弱,細(xì)顆粒懸沙沉降淤積。南支系統(tǒng)口內(nèi)河槽表層沉積物變細(xì)則主要歸因于采砂等人類活動,這些活動不僅直接抽取了較粗的砂粒組分,還因沙體的消失擴大了過水?dāng)嗝?從而削弱了水動力,導(dǎo)致較細(xì)的泥沙淤積�？谕夂I表層沉積物變粗主要反映流域建壩等背景下長江入海泥沙急劇減少后水下三角洲前緣從總體上快速淤積轉(zhuǎn)向侵蝕的海底過程變化,同時也可能與近期長江中游河床侵蝕補償懸沙使入海泥沙D50增大有關(guān)。研究表明,河口及其鄰近海域表層沉積物粒徑可因流域或三角洲高強度人類活動的影響而發(fā)生顯著變化。這種變化對底棲生物和海底工程研究可能具有借鑒意義。鑒于流域-三角洲高強度人類活動在國內(nèi)外的普遍性,長江口及其鄰近海域表層沉積物粒徑變化的認(rèn)識可能對其它河口三角洲具有一定的啟示作用。
[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.
【學(xué)位授予單位】：華東師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：P736.21;P343.5

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