秋季长江口水体颗粒有机碳年际变化及影响因素分析

根据2007—2012年长江口及其邻近海域4个航次(11月)调查资料,探讨了长江口秋季颗粒有机碳(POC)时空分布特征;结合长江口环境要素和陆源输入(径流、输沙),分析了秋季POC分布的主要影响因素。结果表明:(1)2007—2012年秋季长江口POC浓度范围为0.03—16.95mg/L,均值2.30mg/L,底层POC浓度高于表层。长江口表层POC浓度存在显著的年际变化特征。(2)长江口区POC分布呈现沿长江径流入海方向降低的趋势,高值区出现在口门附近偏南部水域。口门内和近岸水域POC显著高于近海水域。口门水域POC年际间相对稳定,近岸和近海水域年际变化显著。(3)长江口POC分布与盐度呈非保守性变化,悬浮物是POC分布的主要控制因素,多数年份POC与叶绿素a相关程度较弱。(4)河口来水来沙量对POC浓度具有较强的制约性,径流的主要影响区域在口门内和近岸区,输沙的主要影响区域在最大浑浊带和长江口北部水域。(5)入海输沙量与长江口水域POC相关性最强。咸淡水交汇引起的悬浮物沉积和沉积物的再悬浮强度决定口门内水域POC浓度,浑浊度较高的近岸水体POC对陆源输入泥沙的依赖性较强,长江口外侧海域初级生产力水平成为POC浓度的重要影响因素。

INTERANNUAL VARIATION OF PARTICULATE ORGANIC CARBON AND ITS INFLUENCING FACTORS IN CHANGJIANG RIVER ESTUARY IN AUTUMN

Using investigation data collected in the autumns in Nov. 2007, 2009, 2011, and 2012 in the Changjiang (Yangtze) River estuary and its adjacent waters, temporal and spatial distributions of particulate organic carbon (POC) and their interannual variations were studied. Relationships between POC and environmental factors, and the effects of runoff and sediment flux into the estuary were analyzed, to identify the factors controlling the POC distribution. Result shows that the interannual variation of POC concentration was larger at the surface than at the bottom. In the partitioning area of the estuary, POC concentration in the inner mouth remained relatively stable, while in the nearshore and offshore waters POC concentration showed remarkable interannual changes. The horizontal distribution of POC displayed a descending trend off river mouth. High-concentration POC occurred in the southern part of nearshore waters, and significantly higher within the mouth and in nearshore waters than in the offshore. In addition, POC concentration varied less interannually within month and nearshore than in offshore regions. Not all the POC distribution increased with salinity increase, showing a non-conservative behavior with salinity. POC was positively correlated significantly with total suspended matters and weakly with chlorophyll a. Runoff and sediment discharge were major factors controlling POC distribution in the areas proximal to estuary. The areas under the impact of runoff situated mainly within the mouth and nearshore zones, especially in the maximum turbidity zone (MTZ). The MTZ and the areas to the north in the estuary were directly under the impact of sediment discharge, causing high POC concentration. Other factors may also affect the POC concentration, e.g., deposition and resuspension of sediments within and near mouth regions, and primary productivity for the offshore.