Comparison of Suspended Sediment and Salinity Vertical Distributions Across the Turbidity Maximum Zoneinthe Yangtze Estuaryin Dry Seasons of 1982 and 2012
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摘要:
2012年1月在长江口北港、北槽和南槽水域纵断面开展枯季多船准同步观测，将获得的大小潮悬浮泥沙和盐度数据与1982年12月同水域调查结果进行对比分析。结果表明：2012年长江口最大浑浊带枯季悬沙浓度比1982年减小了约50%；北港、北槽、南槽相近测点的大潮垂向平均悬沙浓度相较于1982年分别减小了43%、60%和40%，2012年长江口表层平均悬沙浓度与1982年相比减少了约53%。北港断面浑浊带核心与1982年浑浊带核心位置相近；北槽浑浊带核心向内迁移；南槽浑浊带核心位置向外迁移。2012年与1982年枯季遥感反演的长江口同水域表层悬浮泥沙浓度也明显降低。在30年来入海泥沙持续减少背景下，长江口3条入海主汊的最大浑浊带特征依旧显著，径流与潮流的此消彼长、径流的季节分配不同以及口内汊道分流分沙比的变化影响了长江口最大浑浊带核心的移动，浑浊带悬沙浓度最高的地段也是盐度梯度最高的地区。
Abstract:Ten ships, three in North Channel, three in North Passage and four in South Passage of the Yangtze Estuary, were employed to collect water samples in January 2012, in a pattern of three longitudinal profiles in the large estuary. The sampling sites are rather similar with those in 1982. Based on the comparison of suspended sediment concentrations (SSC) and salinity values across the turbidity maximum zone (TMZ) of the Yangtze Estuary acquired in 1982 and 2012 respectively, the change in TMZ in the vertical profiles was discussed in this paper. Results suggest that during the past 30 years from 1982 to 2012, even the sediment load coming from the river basin has been continuously reducing, the SSC of the TMZ decreased about 50%; and the average vertical SSC values in the North Channel, in the North Passage and in the South Passage decreased about 43%, 60%, and 40%, respectively. The 2012 SSC maximum of the turbidity zone in the North Channel was similar to that in 1982; the 2012 SSC maximum position in the North Passage migrated inward, and the coincidence of the SSC maximum and salinity maximum position in the turbidity zone may lead the increase in silt in the North Passage and the deposition in the middle section, while the highest SSC position in the South Passage moved outward. The change in runoff, tidal current and the seasonal distribution of runoff dominated the movement of core TMZ of the Estuary. During the dry season, the salinity gradient is obvious. On the section of the core of TMZ, the upper stream transported to the sea, and the lower stream transported to the estuary. The area with the highest SSC value is also the area with the highest salinity gradient.
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表 1 卫星影像参数
Table 1. Parameters of Landsat series images used in this study
影像数据 过境时间 潮型 潮情 大通流量/(m3/s) 农历 枯季 Landsat TM 1982/01/23 大潮 涨急 11 800 腊月廿九 Landsat ETM 2012/01/23 大潮 涨急 11 600 正月初一 
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表 2 1982年与2012年长江口三条汊道测点垂线平均悬沙浓度
Table 2. Suspended sediment concentration values in the three channels of the Yangtze Estuary in 1982 and 2012
表层 中层 底层 1982 2012 1982 2012 1982 2012 北港 上段 0.31 0.22 1.12 0.32 2.03 0.35 中段 0.56 0.96 1.24 1.27 1.73 1.37 下段 0.35 0.32 1.43 0.48 1.98 0.50 北槽 上段 0.24 0.28 0.68 0.62 0.74 0.96 中段 0.47 2.14 4.53 下段 0.32 0.16 2.02 0.25 1.89 0.30 南槽 上段 0.21 0.13 0.39 0.56 0.87 0.33 中段 0.56 0.51 0.83 0.77 1.34 0.81 下段 0.41 0.39 1.97 0.55 2.76 0.64
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