【作者】 王晓红；

【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， 2014， 博士

【摘要】 长江口及邻近水域（30.5°N-32°N,122°E-123°30′E）是我国近海富营养化的典型水域，其物质通量研究具有重要意义。传统的“水-盐-营养盐”箱式模型是海岸带陆海相互作用研究计划（LOICZ）研究河口与近岸物质通量的一种稳态模式。该模式没有充分考虑研究区域的水动力因素，模式结果受箱体划分影响很大，只能估算盐度差异明显的界面之间的物质通量，对与海岸线平行以及流系复杂多变水域的物质通量估算无能为力。针对长江口及邻近水域流系复杂多变的特点，本研究尝试对传统箱式模型进行改进。本研究将物质输运过程正交分解为水平方向的物质输运和垂直方向的物质输运，水平与垂直方向的物质输运分别分为对流引起的物质输运和扩散引起的物质输运。以区域海洋模式系统（ROMS）为基础，通过Matlab编程，将水动力模型的流场数据准确匹配到箱式模型的箱体边界上，实现了水动力模型与箱式模型的联接，成功构建了基于水动力模型的改进的箱式模型（本研究简称为“水动力箱式模型”）。运用构建的水动力箱式模型，计算并阐释了研究区域的水平水通量、垂向水通量和边界水通量的空间分布与季节变化，探讨分析了研究区域水通量的动力因素与机制，以及研究区域水体交换与缺氧之间的关系，为该水域物质通量研究提供了准确的水量基础。在此基础上，利用2005年2月、5月、8月、11月4个航次的监测数据，计算并阐释了研究区域营养盐的水平通量、垂向通量和边界通量及其营养盐结构的空间分布与季节变化，探讨分析了研究区域营养盐通量的动力因素与机制。研究表明，表层水体水平水通量的季节排序为冬季>秋季>夏季>春季；底层水体水平水通量的季节排序为夏季>春季>冬季>秋季；秋、冬季底层水通量约比表层小1个数量级，夏季底层水通量约为表层的1/2，春季表、底层水通量差别最小。研究区域水通量整体受季风控制，季风使水体在南-北方向上季节性交替输运，台湾暖流对春、夏季底层水体向北输运具有重要作用，CDW、地形、向岸风等多种因素对水通量的时空分布态势具有重要作用。夏季上升流水通量为18.53m3/s，春季为12.55m3/s，冬季为13.07m3/s，秋季为14.25m3/s。西边界水通量方向全年向海。南、北边界的表层水通量与季风方向总体一致。东边界水通量方向规律不明显。南、北边界的水通量约大于西边界一个数量级。东边界水通量，除春、秋季以外，明显小于西边界。秋、冬季南、北边界的表层水通量约比底层水通量大1个数量级，春季约为底层水通量的1/2，夏季约为底层水通量的两倍。经东边界直接进入123.5°E以东外海水域的水通量极少（夏季5.41m3/s），且明显小于春、秋季经东边界自东部外海流入的水通量（12.45m3/s、27.75m3/s）。全年计算，约187.73m3/s的水通量自南边界流出研究区域，后经海洋环流系统间接入海。研究区域水体交换主要依赖季风方向、同层水体之间的的水平水通量。该水域底层水体缺氧的本质原因是跃层阻隔了表、底层水体之间的氧气交换。表层水体水平营养盐通量的季节排序为冬季>秋季>夏季>春季；底层水体水平营养盐通量的季节排序为夏季>春季>冬季>秋季；表层水体水平营养盐通量的空间差异与季节变化均显著大于底层水体。研究区域营养盐通量主要受物理作用控制，以生化作用为辅。与水通量相似，季风使营养盐在南-北方向上季节性交替输运，台湾暖流对春、夏季底层营养盐向北输运具有重要作用，是春、夏季长江径流影响范围向东扩展的重要限制因子，此外，垂向营养盐通量补给、外海水团入侵和初级生产消耗等多种因素对营养盐通量的时空分布态势具有重要作用。垂向DIP通量是DIP的重要来源。垂向营养盐通量的总体特征主要是由上升流通量的时空分布决定的。同一季节的上升流营养盐通量显著大于向上扩散的营养盐通量，且上升流营养盐通量与向上扩散的营养盐通量的产生区域基本重合。春、夏季的上升流营养盐通量和向上扩散的营养盐通量均显著大于秋、冬季。DIP上升流通量(5.83mol/s)和向上扩散通量(5.55mol/s)最大值均发生在夏季，但春季垂向通量对其影响最大。春季DIN、DSI垂向通量分别比水平通量少3-7倍、3-5倍，DIP垂向通量与水平通量接近相等；夏季DIN、DSI、DIP垂向通量分别比水平通量少3-6倍、5-10倍和5-8倍；秋、冬季，三种营养盐垂向通量均比水平通量小2个数量级。研究发现，同一季节流经南、北边界的营养盐通量均显著大于流经东、西边界的营养盐通量。四个边界中，经东边界与东部外海水体交换的营养盐通量最小，比经西边界流入的营养盐通量小大约1-2个数量级。西边界营养盐通量方向终年向海，南、北边界营养盐通量方向与季风方向基本一致，秋、冬季南向，春、夏季北向。但秋季为季风转换期，北边界表、底层营养盐通量方向相反，表层南向，底层北向。东边界营养盐通量方向规律不明显。研究区域扮演着营养盐从黄海向东海输送的“中转站”角色。来自西边界的营养盐通量主要被局限在122.5°E以西的近岸区域，被直接输送到123.5°E以东外海的极少。全年计算，约7149.82mol/s DIN，4097.97mol/s DSI,115.42mol/s DIP自南边界流出研究区域。相比传统箱式模型，水动力箱式模型弥补了传统箱式模型未能充分考虑水动力因素的缺陷，对复杂水动力环境下的营养盐通量估算具有明显优势，为河口物质通量研究提供方法借鉴。更多还原

【Abstract】 A traditional box model is a stoichiometrically linked steady state model forwater-salt-nutrient budget to solve nutrient flux and budget among waters withdistinct salinity difference. However, a traditional model cannot cope appropriatelywith those without distinct salinity difference parallel to coastline or in a complexcurrent system, as the results are highly affected by box division in time and space,such as the Changjiang (Yangtze River) estuary (CE) and adjacent waters(30.5°N-32°N,122°E-123°30′E).Therefore, we tried to construct a coupled box model with a hydrodynamicmodel unit on the traditional model and the regional oceanic modeling system model(ROMS)（named as′′the hydrodynamic box model′′）.The mass transport wasorthogonally decomposed to be the horizontal and the vertical fluxes, each dividedinto the advection and the diffusion one. The flow field data of the hydrodynamicmodel was matched to the boundary of the box model accurately, through which thehydrodynamic model and the box model was linked susccessfully through the Matlabprogramming.Horizontal, vertical and boundary water fluxes were calculated by thehydrodynamic box model. The characteristics, kinetic factors, mechanisms for waterflux and the relationship between water exchange and anoxia were discussed. Basedon the water flux and using data from four cruises in2005, horizontal, vertical andboundary nutrient fluxes were calculated, in which flux fields were depicted and themajor processes controlling the nutrient flux were discussed.It was found that horizontal water flux in upper layer in winter> that inautumn> that in summer> that in spring, while that in lower layer in summer> that in spring> that in winter> that in autumn. Horizontal water flux in lower layer wasabout one order of magnitude smller than that in upper layer in autumn and winter,and about1/2of that in upper layer in summer, with the smallest difference in springbetween the upper and lower layers. It was the monsoon that controlled the water fluxas a whole, making water being transported from north to south or from south to northseasonally; while it was the Taiwan Warm currents that played an important role in theprocess of lower waters being transported northwards in spring and summer，and theChangjiang diluted water(CDW), topography and the onshore wind all playedimportant roles in the spatial and temporal distribution of water flux. The upwellingwater flux was18.53m3/s in summer,12.55m3/s in spring,13.07m3/s in winter and14.25m3/s in aumtumn. The western boundary water flux flowed to the seathroughout the year, and the water flux across the southern and northern boundariesboth flowed with the monsoon on the whole.But there was no regulare pattern forwater flux across the eastern boundary. Water flux across the southern and northernboundaries was about one order of magnitude greater than that across the westernboundary. And water flux across the eastern boundary was obviously smaller than thatacross the western boundary. Water flux in upper layer across the southern andnorthern boudaries was about one magnitude greater than that in lower layer inautumn and winter, twice of that in lower layer in summer,and about1/2inspring.The Changjiang discharge was not dumped into the open seas east of123.5°Edirectly (5.41m3/s in summer), which was significantly smaller than water flux inacross the eastern boundary in spring and autumn(12.45m3/s、27.75m3/s).Water fluxwas transported out of the study area across the southern boundary first at the rate of187.73m3/s annually, and then to the open seas through the ocean current system.Under the strong monsoon, water exchange depended more on the horizontal waterflux in the monsoon direction, mainly in the same layer but not between the upper andlower layers. It was concluded that the ultimate cause of anoxia was the spring layerthat hindered the oxygen exchange between the upper and lower waters.Results showed that horizontal nutrient flux in upper layer in winter> that inautumn> that in summer> that in spring, and horizontal nutrient flux in lower layer in summer> in spring> in winter> in autumn. The spatical difference and seasonalchange of horizontal nutrient flux in upper layer was significantly greater than that inlower layer. Nutrient flux in the study area varied greatly in season and space,depending more on physical dilution than biochemical reactions. Similar to water flux,it was the monsoon that made nutrients being transported from north to south or fromsouth to north seasonally; while it was the Taiwan Warm currents that played animportant role in the process of nutrients in lower waters being transportednorthwards in spring and summer，being a limiting factor of the Changjiang dischargetransported eastwards to the open seas. Besides, vertical nutrient flux replenishment,open waters intrusion and primary production consumption all played important partsin the spatial and temporal distribution of nutrient flux.Upwelling flux outweighed upward diffusion flux in vertical direction.Upwelling flux and upward diffusion flux regions overlapped largely all the year.Vertical flux in spring and summer were much greater than that in autumn and winter.Vertical nutrient flux was a main source of DIP (dissolved inorganic phosphate). Themaximum vertical flux for DIP occurred in summer，but the most prominent affectfrom vertical flux was in spring. Vertical flux in spring was3-7times and3-5timessmaller than horizontal flux for DIN and DSI, respectively, while vertical flux for DIPcould match the horizontal flux. Vertical flux in summer was3-6times,5-10timesand5-8times smaller than horizontal flux for DIN, DSI and DSI, respectively. AndVertical fluxes in autumn and winter were both2orders of magnitude smaller thanhorizontal flux for DIN,DSI and DIP.Nutrient fluxes across the southern and northern boundaries were significantlygreater than those across the eastern and western boundaries in the same season.Nutrient flux across the eastern boundary was the smallest among the four boundaries,about1-2orders of magnitude smaller than that across the western boundary. Westernboundary nutrient flux flowes towards the sea throughout the year, and nutrient fluxesacross the southern and northern boundaries flowes with the monsoon on the whole,southward in autumn and winter and northword in spring and summer. But nutrientflux across the northern boundary in upper layer and lower layer in autumn was opposite, southward in upper layer and northward in lower layer. There was no regularpattern for eastern boundary nutrient flux.Nutrient flux from the western boundarywas mainly confined to coastal waters with little into the open seas east of123.5°E.The study area acted as a conveyer transferring nutrients from the Yellow Sea to theEast China Sea in the whole year at the rate of7149.82mol/s,4097.97mol/s and115.42mol/s for DIN, DSI and DIP respectively.Therefore, the hydrodynamic box model is superior to the traditional one inestimating nutrient fluxes in a complicated hydrodynamic current system and providesa modified box model approach to material flux research.更多还原