【作者】 李祥安；

【导师】 俞志明； 宋秀贤；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 环境科学， 2010， 博士

【摘要】 本论文以长江口富营养化水域为研究对象,综合分析了该水域溶解无机氮、磷和硅等营养盐、化学需氧量、悬浮物和叶绿素的分布特征和富营养化现状;根据陆海相互作用模型,利用箱式模型定量分析了长江口水域溶解无机氮(DIN)、磷(DIP)和溶解硅酸盐(DSi)的输送通量和输送过程,包括径流的营养盐输送量,外海水体的营养盐输送量,大气沉降量,近岸区域水体的营养盐释放量和外海高生产力海区的营养盐消耗量,底层营养盐的释放量,系统生产力和反硝化能力;在多个航次的调查基础上,分析了长江口水域底层溶解氧的季节分布特征和影响因素,探讨了低氧区的的形成机制。主要结果如下:长江口水域营养盐、悬浮物、化学需氧量和叶绿素存在着较明显的季节分布特征,其分布主要受到长江冲淡水的影响。长江口水域的特点是高溶解无机氮和硅酸盐,低磷酸盐,口门内和近岸区的营养盐浓度较高,从口门内到外海呈降低趋势,硝酸氮是溶解无机氮的主要形式,N:P和Si:P比值较高,Si:N的比值普遍大于1。硝酸盐和硅酸盐在中低盐度海水中的分布主要受到海水物理混合作用的影响,与盐度呈现一定的保守性。叶绿素a浓度的高值出现在春季和夏季的外海区域,观测到的叶绿素a最大值为26.22 mg m-3。长江口水域丰富的营养盐,浮游藻类的大量繁殖,加重了长江口水域的富营养化。长江口水域的营养盐主要来自于径流输送,年平均输送1.53×1011 mmol DIN day-1、2.22×109 mmol DIP day-1和2.97×1011 mmol DSi day-1,外海的输送量分别是9.05×1010 mmol DIN day-1、3.57×109 mmol DIP day-1和1.65×1011 mmol DSi day-1,大气沉降量分别是4.06×108 mmol DIN day-1、6.45×105 mmol DIP day-1和2.52×109 mmol DSi day-1,外海水体输送的无机磷是支持本区域水体生产力的一个重要来源。在从口门到外海的输送过程中,近岸区域年平均释放的DIN、DIP和DSi占输出通量的40%、51%和30%,由于近岸高浑浊度,藻类生长受到光限制,近岸水域属于异养型系统。外海水域消耗大量的营养盐,平均值是894μmol DIN m-3 day-1 ,18.0μmol DIP m-3 day-1和1418μmol DSi m-3 day-1,系统净生产力是38.15 mmol m-2 day-1。在底层低氧水体中,氮的固定作用与反硝化作用的差值是-1.92 mmol m-2 day-1,表明反硝化作用参与到氮的生物地球化学循环过程。长江口水域溶解氧的分布有着明显的季节性特征:冬季底层溶解氧浓度普遍比较高,夏季底层溶解氧浓度降至最低,出现大范围的缺氧区,从区域上看,水下河谷底层水体溶解氧浓度低于周围水体。长江口水域底层溶解氧的分布受到温度、地形、分层结构和生物活动的影响。在夏季,底层溶解氧的分布与温度成正相关关系,秋冬季节相反。长江口口门外的水下河谷充满了来自台湾暖流的水体,阻碍了水体的水平交换。春季和夏季的温跃层结构直接影响到溶解氧的垂直输送,阻挡的溶解氧输送通量达到4.08 g m-2?day-1。长江口水域过量的营养盐和高的生产力提供了大量的有机质,这些有机质在底层被分解,消耗了大量的溶解氧,日益严重的富营养化,也加重了低氧现象的发生。更多还原

【Abstract】 The distribution characteristic of nutrients, chemical oxygen demand, suspended particulate matter and chlorophyll a and status of eutrophication in the Changjiang Estuary were analyzed. A modified box budget approach was adopted to estimate nutrient fluxes and processes in the Changjiang Estuary and its adjacent waters, including the amount from river, the deep open sea, atmosphere, the amount of release in alongshore mixing zone and deep open sea water, and the amount of consuming in outer sea, as well as primary production and denitrification rate. The seasonal distribution characteristics and influencing factors of dissolved oxygen were also analyzed, and the formation mechanism of low oxygen area in the Changjiang Estuary was discussed in this paper.The main results are as follows:The distribution of nutrients, chemical oxygen demand, suspended particulate matter and chlorophyll a had obvious seasonal characters, and it was affected by dilute water. The Changjiang Estuary was characterized by high dissolved inorganic nitrogen (DIN) and dissolved silicate (DSi) concentrations, with low dissolved inorganic phosphate (DIP) concentrations. The mean concentrations of nutrients were high in inner estuary and Turbidity Maximum zone and they become small with the increasing distance to land. Nitrate was main component of dissolved inorganic nitrogen. The values of N:P and Si:P were high and the value of Si:N was currently above 1. The distribution of nitrate and silicate was conservative in the water of mid and low salinity, since they were influenced by physical mixing. The maximum Chl a concentration existed in the open sea in spring and summer and the observed maximum was 26.22 mg m-3. Excess nutrient and large phytoplankton in spring and summer accelerated the eutrophication in the Changjiang Estuary.The majority of the nutrient input to the estuary came from the river, for annual 1.53×1011 mmol DIN day-1, 2.22×109 mmol DIP day-1 and 2.97×1011 mmol DSi day-1. The budgets from the open sea were 9.05×1010 mmol DIN day-1, 3.57×109 mmol DIP day-1 and 1.65×1011 mmol DSi day-1, while the budgets from atmosphere were 4.06×108 mmol DIN day-1, 6.45×105 mmol DIP day-1 and 2.52×109 mmol DSi day-1 respectively. The dissolved inorganic phosphorus from the deep open sea served as a major source of support for primary production over the outer sea area. The alongshore mixing zone served as a source that supplies 40% of DIN, 51% of DIP and 30%of DSi for the amount of export during their transport along the estuary to the coastal water. The alongshore water system was heterotrophic for light-limited turbid condition and low phytoplankton biomass. The outer sea zone served as nutrient trap and the rate of consumption was about 894μmol DIN m-3 day-1, 18.0μmol DIP m-3 day-1 and 1418μmol DSi m-3 day-1. The net ecosystem metabolism was 38.15 mmol m-2 day-1. In the bottom oxygen-deficient water, the denitrification process was significant.The distribution of dissolved oxygen (DO) in the bottom water had obvious seasonal characters. The values of DO were high in winter and low in summer. Low values of DO might appear in spring and autumn for the temporal physical and biological status. The concentrations of DO in the bottom water in the trough were lower than those in the surrounding water. The low values of DO might appear in the north water tongue of the Changjiang Estuary in the summer of some years. The distribution of DO was influenced by temperature, topography, stratification and biological factors. In the summer, it was found that there was positive correlation between DO concentration and temperature, which was contrary in the autumn and winter. The trough obstructed the horizontal transport of DO and was filled by the TWC water. Strong halocline and thermocline appeared in spring and summer. Strong stratification obstructed the vertical transport of DO and the vertical transport of DO flux, which was obstructed by stratification, was calculated and reached 4.70 g m-2 day-1. Hypoxia was seasonal and occurred in summer. Large nutrient loading led to enhanced phytoplankton production, and more organic matter was decomposed, which could result in oxygen depletion. These special physical conditions and biochemical factors might result in the occurrence of hypoxia in the Changjiang Estuary.更多还原