江苏中部海岸盐沼前缘的地貌动力过程

发布时间：2018-03-16 17:27

  本文选题：地貌动力过程　切入点：后退速率　出处：《南京大学》2015年硕士论文　论文类型：学位论文

【摘要】：盐沼作为滨海湿地的重要生态类型,对于保护海岸带环境及滨海城市、加速沿海土地增长、扩大海岸带的人类可利用空间、增加碳埋藏、减缓全球气候变暖以及为海岸带生物提供栖息场所等具有重要研究价值。同时盐沼对沉积结构和构造的良好连续性和保存潜力,使其成为判别古环境和研究古海平面变化的重要材料。互花米草盐沼前缘作为盐沼-潮滩耦合系统中两者相交界的重要地带,发育有独特的地貌形态,研究其动态变化过程有助于深化对盐沼-潮滩耦合系统的认识以及预测盐沼未来的演变趋势。2012年12月、2013年9月和2014年7月在江苏中部海岸盐城湿地珍禽国家级自然保护区的核心区测量了互花米草盐沼边缘陡坡的形态参数,应用边缘波理论对陡坡韵律性形态的形成机理进行初步解释;观测了互花米草盐沼前缘光滩上的潮流、波浪以及悬沙浓度,并采集了光滩底质表层样和短柱样进行粒度分析,初步分析了盐沼前缘的沉积动力过程;结合2008～2014年的滩面高程数据和2005～2014年的遥感影像资料,探讨了该研究区盐沼前缘的地貌演化过程以及未来演化趋势。根据盐沼边缘陡坡形态参数及其相关性,可将韵律性陡坡形态划分为两种类型,凹槽长度、宽度和陡坡高度较大但空间分异较小的陡坡(第一种类型)和凹槽长度、宽度和陡坡高度较小但空间分异较大的陡坡(第二种类型),分别对应盐沼边缘陡坡演化的不同阶段。边缘波理论仅能够解释第一种陡坡韵律性形态的成因,这可能与第二种类型陡坡形态未达到均衡态有关。通过计算潮流和波浪引起的流速及底部切应力以及分析互花米草盐沼前缘光滩的底质粒径特征,发现该研究区光滩底质以砂质粉砂和粉砂质砂为主,观测期间波浪作用占主导,沉积物以悬移输运为主;悬沙浓度为1.0～4.0 g/L;沉积物的悬移输运率为0.01～0.3 kg/m/s。滩面高程变化率在-10~(-5) m/s量级,相当于0.2 m/yr的下蚀速率。对比遥感影像识别方法、地形测量对比方法和沉积动力计算方法,分析结果表明研究区光滩出现侵蚀后退的时间不晚于2010年,侵蚀后退速率在200 m/yr左右,下蚀速率达0.2～0.5 m/yr;互花米草盐沼边缘出现侵蚀后退的时间不晚于2012年,侵蚀后退速率在20 m/yr左右。用于计算盐沼边缘后退速率的Schwimmer经验公式方法在该研究区不适用。互花米草盐沼前缘水动力条件、沉积动力过程的分析结果表明,波浪是光滩和盐沼边缘侵蚀后退的主要水动力。结合互花米草生态位和研究区沉积物供应状况,分析认为互花米草盐沼边缘后退时尚未达到生态位下限,目前出现的侵蚀后退主要是由沉积物供应减少和波浪作用加强引起的。沉积物供应减少,光滩不断侵蚀后退,至盐沼边缘时导致盐沼前缘滩面坡度增大,波浪作用增强而作用于盐沼边缘,导致盐沼边缘陡坡的形成。盐沼边缘陡坡形态的演化发育过程正是盐沼边缘侵蚀后退的过程,在光滩侵蚀后退至盐沼边缘时,波浪下切导致局部根垫倒塌形成凹口切入平直的盐沼边缘,然后凹口溯源侵蚀形成凹槽和盐沼残留脊,最后残留脊被切断,以开始下一回次的侵蚀过程。
[Abstract]:As an important coastal wetland marsh ecological types, for the protection of coastal environment and coastal city, to accelerate the growth of coastal land, the coastal zone can be used to expand the human space, increase carbon burial, slowing global warming and provide habitat for coastal biological etc. it has important research value. At the same time on the deposition and structure of salt marsh for good and the preservation potential, make it become an important material for distinguishing the environment and study the sealevel changes. The marsh front as an important area for salt marsh tidal coupling system in two intersecting circles, the development has unique landform and its dynamic change process is helpful to deepen the understanding of salt marsh tidal coupling system.2012 and the future trend forecast in December and July 2014 September 2013, in Jiangsu, the central coast of Yancheng Wetland National Reserve. The core area of the measurement of morphological parameters of the marsh edge slope, application of edge wave theory in steep rhythm form the forming mechanism of the preliminary explanation; the marsh on the beach front light wave and tide observation, suspended sediment concentration, and collect the light flat substrate surface layer and short column sample size analysis, preliminary analysis of the sedimentary dynamic process of salt marsh in front of; the combination of remote sensing image data of 2008~2014 years of the beach surface elevation data and 2005~2014 years of the study area, the salt marsh pioneer landform evolution and future evolution trend. According to the morphological parameters of the steep slope marsh edge and its correlation can be rhythmic form steep slope is divided into two types. The length, width and height of a large but steep spatial differentiation of small slope (the first type) and groove length, width and height of slope is small but the spatial differentiation of large The steep slope (second types), corresponding to the different stages of evolution. The marsh edge slope edge wave theory can only explain the genesis of the first steep rhythmic patterns, which may be related to second types of slope morphology did not reach equilibrium. And the bottom velocity caused by calculating the tidal current and wave shear stress and analysis of Spartina alterniflora front mudflat sediment grain size characteristics found in the study area, mudflat sediment with sandy silt and silty sand, during the observation wave dominated by suspended sediment transport; suspended sediment concentration is 1 ~ 4 g/ L; suspended sediment transport rate is 0.01 ~ 0.3 kg/m/s. height of beach the rate of change in the sediment of -10~ (-5) m/s magnitude, erosion rate equivalent to 0.2 m/yr. Compared the recognition method of remote sensing image, calculation method of topographic contrast method and sedimentary dynamic analysis results show that the study area, mudflat eroded Back no later than 2010, the erosion rate is about 200 m/yr, erosion rate of 0.2 ~ 0.5 m/yr; the marsh edge erosion occur no later than 2012, the erosion rate was about 20 m/yr. For Schwimmer empirical formula method to calculate the rate of back marsh edge is not applicable in the study area. The marsh in front of the hydrodynamic conditions, the analysis results of sediment dynamic processes show that the wave is the main hydrodynamic mudflat and salt marsh edge erosion. Combined with the ecological niche and the study area of Spartina alterniflora sediment supply situation, analysis the marsh edge back has yet to reach niche limit, there is mainly backward erosion reduced by sediment supply and wave action strengthening caused. Sediment supply reduced, mudflat eroded back to the marsh edge lead salt marsh front Beach The increase of the slope wave enhanced and the effect on the marsh edge, resulting in the formation of steep slope. The evolution of salt marsh edge edge steep shape development process is the marsh edge erosion, beach erosion in the light back to the marsh edge, waves lead marsh edge local root mat collapse cut straight notch is formed, then notch headward erosion groove is formed and salt marsh residual ridge, the residual ridge was cut off, to start the next time the erosion process.

【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P748;P737
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本文编号：1620911