Distribution pattern of flocsand and its controlling factors in a saltwater-wedge estuary: A case study of the Modaomen Estuary of the Pearl (Zhujiang) River
-
摘要: 细颗粒泥沙絮凝是影响河口泥沙输移扩散的关键过程，受控于河口复杂动力结构，其中河口水体层化环境下絮凝体空间分布规律亟待探究。针对该问题，本文基于2020年珠江磨刀门河口枯季大面积走航原型观测数据，分析磨刀门河口絮凝体时空分布特征，探究不同动力对其影响作用，揭示水体层化下絮凝体分布规律。结果表明，观测期间磨刀门河口絮凝体中值粒径介于1.87～395.53 μm，体积浓度介于20.29～
1495.67 μL/L；垂向上，中表层水体中值粒径多大于底层，平面上最大值多位于中心拦门沙和西侧。采用多峰分解方法可将磨刀门河口絮凝体分解为基本颗粒和絮凝核（统称微絮团）、小絮团、大絮团等组分，大絮团占比最大；总体来讲，中表层水体微絮团和小絮团体积浓度小于底层，底层大絮团体积浓度小于中表层。这与盐水楔河口动力结构密切相关，强盐度层化抑制絮凝体在各水层间的交换，导致表层水体大絮团占比远高于中底层，而底层絮凝体受湍流剪切强度影响，以解絮为主，小絮团和微絮团占比高。本研究不仅有助阐明复杂动力结构下细颗粒泥沙絮凝机制，也能为磨刀门河口拦门沙治理、水沙调控及航道疏浚等提供技术支撑。Abstract: Flocculation of fine sediments is a key process affecting sediment transport and dispersion in estuaries, which is controlled by complex dynamic structure of estuaries, and spatial distribution of flocs in a stratification condition needs to be explored. To solve this problem, in this study, based on the hydrology and sediment cruising observation in the Modaomen Estuary of the Pearl River during the dry season in 2020, spatial and temporal distribution of flocs in the Modaomen Estuary was analyzed, impacts of dynamics factors were investigated, and distribution pattern of flocs in a stratification condition was uncovered. The results show that median floc size in the Modaomen Estuary during the observation period ranged from 1.87 μm to 395.53 μm, and volumetric concentration of flocs ranged from 20.29 μL/L to1495.67 μL/L. Vertically, median floc size in the middle and surface layers was generally larger than that in the bottom layer. The plane distribution characteristic of the median floc size is that the maximum values generally occurred at the central bar and the west side. Decomposition of multimodal floc size distributions indicates that the flocs in the Modaomen Estuary were composed of primary particles (Pp) and Flocculi (collectively known as Pico-flocs), microflocs (Micro), macroflocs (Macro), among which Macro was dominant. In view of vertical distribution, the volumetric concentration of Pico-flocs and Micro in the bottom layer tended to be larger than that in the surface and middle layers, while volumetric concentration of Macro in the surface and middle layers was generally larger than that in the bottom layer, which is closely related to dynamic structure in the salt water wedge estuary. Strong salinity stratification inhibited the exchange of flocs between different water layers, resulting in a relatively higher percentage of Macro in the surface layer than that in the middle and bottom layers. In the bottom layer flocs were affected by intensity of turbulent shear and deflocculation process was dominant. As a result, the percentage of Pico-flocs and Micro was higher than the surface and middle layers. This study is not only helpful to elucidate the flocculation mechanism of fine sediment under complex dynamics, but also provides technical support for regulation of mouth bar, goverment of water and sediment, and channel dredging in the Modaomen Estuary. -
图 1 研究区域：珠江三角洲口（a）和磨刀门河口（b）
Fig. 1 Sketch map of the study area: the Pearl River Estuary (a) and the Modaomen Estuary (b)
图 2 走航观测期间潮位（红色阴影区域表示观测时段）（a），OBS-3A标定悬沙浓度曲线（A船（b）和B船（c））
Fig. 2 Tidal level of two shipboard investigations (the red shaded areas represent the investigation periods) (a). Calibration curves in order to derive suspended sediment concentration from OBS-3A of ship A (b) and ship B (c)
图 3 絮凝体中值粒径和体积浓度平面分布
a−c：落潮期间表、中、底层中值粒径；d−f：涨潮期间表、中、底层中值粒径；g−i：落潮期间表、中、底层体积浓度；d−f：涨潮期间表、中、底层体积浓度
Fig. 3 Planar distribution of median floc size and volumetric concentration
a–c: Median floc size in the surface, middle, and bottom layers during the ebb period, respectively; d–f: median floc size in the surface, middle, and bottom layers during the flood period, respectively; g–i: volumetric concentrationin the surface, middle, and bottom layers during the ebb period, respectively; d–f: volumetric concentration in the surface, middle, and bottom layers during the flood period, respectively
图 4 中轴、东汊和西汊絮凝体中值粒径和体积浓度纵剖面
a, c, e: 涨潮期间中值粒径；b, d, f: 落潮期间中值粒径；g, i, k: 涨潮期间体积浓度；h, j, l：落潮期间体积浓度，黑色线为盐度等值线
Fig. 4 Longitudinal distribution of median floc size and volumetric concentration along different sections
a, c, e: Median floc size in the central bar, eastern bar and western bar sections during the flood period, respectively; b, d, f: median floc size in the central bar, eastern bar and western bar sections during the ebb period, respectively; g, i, k: volumetric concentration in the central bar, eastern bar and western bar sections during the flood period,respectively; h, j, l: volumetric concentration in the central bar, eastern bar and western bar sections during the ebb period, respectively. The black lines indicate the salinity contour lines
图 5 中轴、东汊和西汊水体盐度层化参数纵剖面
a, c, e：涨潮；b, d, f：落潮，由于部分站点Rig计算值为负数不能取对数，部分站点存在缺失值，图中以空白显示
Fig. 5 Longitudinal distribution of salinity stratification parameter along different sections
a, c, e: central bar, eastern bar and western bar sections during the flood period, respectively; b, d, f: central bar, eastern bar and western bar sections during the ebb period, respectively. Some of the sites have negative Rigvalues that do not have logarithms, so there are missing values at some of the sites, which are shown as blanks in the figure
图 6 河口微絮团体积浓度平面分布
a−c：落潮期间表、中、底层；d−f：涨潮期间表、中、底层
Fig. 6 Planar distribution of volumetric concentration of Pico-flocs in the estuary
a–c: Surface, middle, and bottom layers during the ebb period, respectively; d–f: surface, middle, and bottom layers during the flood period, respectively
图 7 河口小絮团体积浓度平面分布
a−c：落潮期间表、中、底层；d−f：涨潮期间表、中、底层
Fig. 7 Planar distribution of volumetric concentration of Micro in the estuary
a–c: Surface, middle, and bottom layers during the ebb period, respectively; d–f: surface, middle, and bottom layers during the flood period, respectively
图 8 河口大絮团体积浓度平面分布
a−c：落潮期间表、中、底层；d−f：涨潮期间表、中、底层
Fig. 8 Planar distribution of volumetric concentration of Macro in the estuary
a–c: Surface, middle, and bottom layers during the ebb period, respectively; d–f: surface, middle, and bottom layers during the flood period, respectively
图 9 中轴、东汊和西汊微絮团体积浓度纵剖面
a, c, e: 涨潮；b, d, f: 落潮，黑色线为盐度等值线
Fig. 9 Longitudinal distribution of volumetric concentration of Pico-flocs along different sections
a, c, e: Central bar, eastern bar and western bar sections during the flood period, respectively; b, d, f: central bar, eastern bar and western bar sections during the ebb period, respectively. The black lines indicate the salinity contour lines
图 10 中轴、东汊和西汊小絮团体积浓度纵剖面
a, c, e: 涨潮；b, d, f: 落潮，黑色线为盐度等值线
Fig. 10 Longitudinal distribution of volumetric concentration of Micro along different sections
a, c, e: Central bar, eastern bar and western bar sections during the flood period, respectively; b, d, f: central bar, eastern bar and western bar sections during the ebb period, respectively. The black lines indicate the salinity contourlines
图 11 中轴、东汊和西汊大絮团体积浓度纵剖面
a, c, e: 涨潮；b, d, f: 落潮，黑色线为盐度等值线
Fig. 11 Longitudinal distribution of volumetric concentration of Macro along different sections
a, c, e: Central bar, eastern bar and western bar sections during the flood period, respectively; b, d, f: central bar, eastern bar and western bar sections during the ebb period, respectively. The black lines indicate the salinity contourlines
图 12 强盐度层化（a−c）和弱盐度层化（d−f）时刻表、中、底层粒度分布曲线
Fig. 12 FSDs in the surface, middle, and bottom water with strong salinity stratification (a−c) and weak salinity stratification (d−f)
图 13 流致底床剪切应力底层悬沙浓度平面分布
a, b: 涨、落潮底剪应力； c, d：涨、落潮底层悬沙浓度
Fig. 13 Planar distribution of current-induced bed shear stress and suspended sediment concentration in the bottom layer
a, b: Current-induced bed shear stress during the flood and ebb period; c, d: suspended sediment concentration in the bottom layer during the flood and ebb period
图 14 中轴、东汊和西汊G值纵剖面
a, c, e: 涨潮；b, d, f: 落潮
Fig. 14 Longitudinal distribution of G along different sections
a, c, e: Central bar, eastern bar and western bar sections during the flood period, respectively; b, d, f: central bar, eastern bar and western bar sections during the ebb period, respectively
图 15 盐水楔型河口絮凝体垂向分布模式示意
Fig. 15 Sketch of vertical distribution pattern of flocs in saltwater-wedge estuary
表 1 不同级配絮凝体多峰分解结果与实测结果皮尔逊相关系数平方
Tab. 1 Square of Pearson correlation coefficient between the decomposition of multimodal floc size distributions and observation of flocs with different size
粒组 微絮团（基本颗粒与絮凝核） 小絮团 大絮团 R2 0.97 0.74 0.98 
下载: 导出CSV
-
[1] Milliman J D, Farnsworth K L. River Discharge to the Coastal Ocean: A Global Synthesis[M]. Cambridge: Cambridge University Press, 2011: 384. [2] Bronick C J, Lal R. Soil structure and management: areview[J]. Geoderma, 2005, 124(1/2): 3−22. [3] Droppo I G, Ongley E D. Flocculation of suspended sediment in rivers of southeastern Canada[J]. Water Research, 1994, 28(8): 1799−1809. doi: 10.1016/0043-1354(94)90253-4 [4] 朱文武, 李九发, 姚弘毅, 等. 长江河口北槽河道悬沙絮团特性及其影响因素研究[J]. 海洋学报, 2016, 38(3): 88−97. doi: 10.3969/j.issn.0253-4193.2016.03.009Zhu Wenwu, Li Jiufa, Yao Hongyi, et al. Study on sediment floccules and the influence factors in the North Passage of the Changjiang Estuary[J]. Haiyang Xuebao, 2016, 38(3): 88−97. doi: 10.3969/j.issn.0253-4193.2016.03.009 [5] Manning A J, Baugh J V, Spearman J R, et al. Flocculation settling characteristics of mud: sand mixtures[J]. Ocean Dynamics, 2010, 60(2): 237−253. doi: 10.1007/s10236-009-0251-0 [6] 田枫, 欧素英, 杨昊, 等. 伶仃洋河口泥沙絮凝特征及影响因素研究[J]. 海洋学报, 2017, 39(3): 55−67. doi: 10.3969/j.issn.0253-4193.2017.03.005Tian Feng, Ou Suying, Yang Hao, et al. Study on the flocs characteristic and dynamics effects in the Lingdingyang Estuary[J]. Haiyang Xuebao, 2017, 39(3): 55−67. doi: 10.3969/j.issn.0253-4193.2017.03.005 [7] Guo Chao, He Qing, Guo Leicheng, et al. A study of in-situ sediment flocculation in the turbidity maxima of the Yangtze Estuary[J]. Estuarine, Coastal and Shelf Science, 2017, 191: 1−9. doi: 10.1016/j.ecss.2017.04.001 [8] Li Wenjie, Wang Jie, Yang Shengfa, et al. Determining the existence of the fine sediment flocculation in the Three Gorges Reservoir[J]. Journal of Hydraulic Engineering, 2015, 141(2): 05014008. doi: 10.1061/(ASCE)HY.1943-7900.0000921 [9] Gratiot N, Manning A J. An experimental investigation of floc characteristics in a diffusive turbulent flow[J]. Journal of Coastal Research, 2004, (S41): 105−113. [10] Zhang Ying, Ren Jie, Zhang Wenyan. Flocculation under the control of shear, concentration and stratification during tidal cycles[J]. Journal of Hydrology, 2020, 586: 124908. doi: 10.1016/j.jhydrol.2020.124908 [11] Liu Jinliang, Liang Junhong, Xu Kehui, et al. Modeling sediment flocculation in langmuir turbulence[J]. Journal of Geophysical Research: Oceans, 2019, 124(11): 7883−7907. doi: 10.1029/2019JC015197 [12] Markussen T N, Andersen T J. Flocculation and floc break-up related to tidally induced turbulent shear in a low-turbidity, microtidal estuary[J]. Journal of Sea Research, 2014, 89: 1−11. doi: 10.1016/j.seares.2014.02.001 [13] Mikkelsen O A, Curran K J, Hill P S, et al. Entropy analysis of in situ particle size spectra[J]. Estuarine, Coastal and Shelf Science, 2007, 72(4): 615−625. doi: 10.1016/j.ecss.2006.11.027 [14] Lee B J, Fettweis M, Toorman E, et al. Multimodality of a particle size distribution of cohesive suspended particulate matters in a coastal zone[J]. Journal of Geophysical Research: Oceans, 2012, 117(C3): C03014. [15] Lee B J, Toorman E, Fettweis M. Multimodal particle size distributions of fine-grained sediments: mathematical modeling and field investigation[J]. Ocean Dynamics, 2014, 64(3): 429−441. doi: 10.1007/s10236-014-0692-y [16] Huang Jie, Wang Simin, Li Xinran, et al. Effects of shear stress and salinity stratification on floc size distribution during the dry season in the Modaomen Estuary of the Pearl River[J]. Frontiers in Marine Science, 2022, 9: 836927. doi: 10.3389/fmars.2022.836927 [17] Lasareva E V, Parfenova A M, Romankevich E A, et al. Organic matter and mineral interactions modulate flocculation across arctic river mixing zones[J]. Journal of Geophysical Research: Biogeosciences, 2019, 124(6): 1651−1664. doi: 10.1029/2019JG005026 [18] Dyer K R, Manning A J. Observation of the size, settling velocity and effective density of flocs, and their fractal dimensions[J]. Journal of Sea Research, 1999, 41(1/2): 87−95. [19] Li Dongyi, Li Yunhai, XuYonghang. Observations of distribution and flocculation of suspended particulate matter in the Minjiang River Estuary, China[J]. Marine Geology, 2017, 387: 31−44. doi: 10.1016/j.margeo.2017.03.006 [20] 谢荣耀, 刘锋, 罗向欣, 等. 河控型河口盐度层化对悬沙的捕集机制——以洪季磨刀门河口为例[J]. 海洋学报, 2021, 43(5): 38−49.Xie Rongyao, Liu Feng, Luo Xiangxin, et al. Sediment trapping mechanism by salinity stratification in a river-dominted estuary: a case study of the Modaomen Estuary in flood season[J]. Haiyang Xuebao, 2021, 43(5): 38−49. [21] Zhang Ying, Ren Jie, Zhang Wenyan, et al. Importance of salinity-induced stratification on flocculation in tidal estuaries[J]. Journal of Hydrology, 2021, 596: 126063. doi: 10.1016/j.jhydrol.2021.126063 [22] Liu Feng, Chen Hui, Cai Huayang, et al. Impacts of ENSO on multi-scale variations in sediment discharge from the Pearl River to the South China Sea[J]. Geomorphology, 2017, 293: 24−36. doi: 10.1016/j.geomorph.2017.05.007 [23] Liu Feng, Yuan Lirong, Yang Qingshu, et al. Hydrological responses to the combined influence of diverse human activities in the Pearl River delta, China[J]. CATENA, 2014, 113: 41−55. doi: 10.1016/j.catena.2013.09.003 [24] Tan Chao, Huang Bensheng, Liu Feng, et al. Recent morphological changes of the mouth bar in the Modaomen Estuary of the Pearl River Delta: causes and environmental implications[J]. Ocean & Coastal Management, 2019, 181: 104896. [25] Jia Liangwen, Wen Yi, Pan Shunqi, et al. Wave-current interaction in a river and wave dominant estuary: aseasonal contrast[J]. Applied Ocean Research, 2015, 52: 151−166. doi: 10.1016/j.apor.2015.06.004 [26] 贾良文, 吕晓莹, 程聪, 等. 珠江口磨刀门月际尺度地貌演变研究[J]. 海洋学报, 2018, 40(9): 65−77. doi: 10.3969/j.issn.0253-4193.2018.09.006Jia Liangwen, Lü Xiaoying, Cheng Cong, et al. Study on the morphological evolution of the Modaomen Estuary in monthly scale[J]. Haiyang Xuebao, 2018, 40(9): 65−77. doi: 10.3969/j.issn.0253-4193.2018.09.006 [27] 卢陈, 吴尧, 杨裕桂, 等. 珠江磨刀门河口环流结构动力特征分析[J]. 海洋学报, 2022, 44(12): 9−18.Lu Chen, Wu Yao, Yang Yugui, et al. Characterizing the circulation flow structure in the Modaomen Estuary of the Zhujiang River[J]. Haiyang Xuebao, 2022, 44(12): 9−18. [28] Hussein T, dal Maso M, Petäjä T, et al. Evaluation of an automatic algorithm for fitting the particle number size distributions[J]. Boreal Environment Research, 2005, 10(5): 337−355. [29] Whitey K T. The physical characteristics of sulfur aerosols[J]. Atmospheric Environment, 2007, 41Suppl: 25−49. [30] Li Haiwei, Yang Qingshu, Mo Sihao, et al. Formation of turbidity maximum in the Modaomen Estuary of the Pearl River, China: the roles of mouth bar[J]. Journal of Geophysical Research: Oceans, 2022, 127(12): e2022JC018766. doi: 10.1029/2022JC018766 [31] Stacey M T, Rippeth T P, Nash J D. Turbulence and stratification in estuaries and coastal seas[J]. Treatise on Estuarine and Coastal Science, 2011, 2: 9−35. [32] Geyer W R, MacCready P. The estuarine circulation[J]. Annual Review of Fluid Mechanics, 2014, 46: 175−197. doi: 10.1146/annurev-fluid-010313-141302 [33] 孙剑雄, 张文祥, 史本伟. 基于潮间带现场数据的底部切应力算法对比[J]. 海洋学研究, 2022, 40(1): 21−32. doi: 10.3969/j.issn.1001-909X.2022.01.003Sun Jianxiong, Zhang Wenxiang, Shi Benwei, et al. Comparison of methods for calculating bottom shear stress based on intertidal flat field data[J]. Journal of Marine Sciences, 2022, 40(1): 21−32. doi: 10.3969/j.issn.1001-909X.2022.01.003 [34] 邹志利. 海岸动力学(第四版)[M]. 北京: 人民交通出版社, 2009: 94.Zou Zhili. Coastal hydrodynamics (4th edition)[M]. Beijing: China Communication Press, 2009: 94. [35] Miles J W. On the stability of heterogeneous shear flows[J]. Journal of Fluid Mechanics, 1961, 10(4): 496−508. doi: 10.1017/S0022112061000305 [36] Byun J, Son M. On the relationship between turbulent motion and bimodal size distribution of suspended flocs[J]. Estuarine, Coastal and Shelf Science, 2020, 245: 106938. doi: 10.1016/j.ecss.2020.106938 [37] Guo Chao, He Qing, van Prooijen B C, et al. Investigation of flocculation dynamics under changing hydrodynamic forcing on an intertidal mudflat[J]. Marine Geology, 2018, 395: 120−132. doi: 10.1016/j.margeo.2017.10.001 -
计量
- 文章访问数: 53
- HTML全文浏览量: 26
- PDF下载量: 17
- 被引次数: 0
