A STUDY ON THE RELATIONSHIPS OF THE NUTRIENTS NEAR THE CHANGJIANG RIVER ESTUARY WITH THE FLOW OF THE CHANGJIANG RIVER WATER

Investigations from August, 1985 to July , 1986 showed that the high concentration area of PO4-P , SiO3-Si and NO3-N gradually reduced with the reduction of the area of the Changjiang River diluted water from summer, autumn to winter , and that the seasonal distributions and variations of the nutrients concentrations were mainly controlled by the river flow and were also related to the growth and decline of phytoplankton . The conservation of SiO3-Si and NO3-N in the estuary in the flood season was poorer than that in the dry season .. The behaviour of PO4-P in the estuary shows that aside from -biological removal, buffering of PCU-P is possible in the estuary . The highest monthly average concentrations and annual average concentrations in the river mouth were respectively 0.88 and 0.57 umol/L for PO4-P,191.5 and 96.2 umol/L for SiO3-Si, and 81.6 and 58.6 umol/L for NOs-N . The Changjiang’s annual transports of PO4-P , SiO3-Si and NO3-N to the sea were about 1.4×104tons , 204.4×104 tons and 63.

Effects of dissolved oxygen and nutrients from the Kuroshio on hypoxia off the Changjiang River estuary

The intrusion of the Kuroshio into the East China Sea(ECS)aff ects the development of hypoxia off the Changjiang(Yangtze)River estuary;however,quantitative analysis of its impacts is lacking.In this study,the Regional Ocean Modeling Systems(ROMS)model coupled with the Carbon,Silicate and Nitrogen Ecosystem(CoSiNE)model was used to investigate the relative importance of dissolved oxygen(DO)and diff erent nutrients(silicate,nitrate,and phosphate)in the Kuroshio on hypoxia in the ECS.Results show that changes in DO concentrations in the Kuroshio modify the distribution and intensity of hypoxia through direct onshore transport by hydrodynamic processes.An increase in Kuroshio DO concentration by 25%or 50%would result in a decrease of the maximum hypoxia extent(MHE)in the ECS by 76%or 86%,respectively,while a 25%decrease in Kuroshio DO would increase the MHE by up to 219%.The contribution of DO in the Taiwan Strait is almost negligible.In contrast to Kuroshio DO,nutrients aff ect hypoxia in the ECS through onshore transport by hydrodynamic and biochemical processes.Changes in phosphate and nitrate concentrations by 25%in the Kuroshio would change the MHE by up to 30%and 18%,respectively,accompanied by apparent changes in surface chlorophyll-a concentrations.The eff ect of silicate on hypoxia is negligible because a 25%change in silicate concentrations in the Kuroshio would result in less than 1%change in the MHE.Our results reveal a hierarchical rank of importance for environmental variables in the Kuroshio(i.e.,DO>phosphate>nitrate>silicate)in modifying the development of hypoxia in the ECS.

Variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang(Yangtze River) Estuary

Dissolved inorganic nutrient elements were analyzed from the samples collected in the South Passage of the Changjiang (Yangtze River) Estuary in March 2003, including NH4+, NO3-, NO2- and PO43-. The water samples were collected with a Niskin sampler hourly at the near-surface, middle and near-bottom depths at the three stations -A1, A2 and A3-during two complete tidal cycles of neap tide and spring tide. Results showed that 1) the concentrations of NH4+, NO3- and NO2- were a little higher respectively during the neap tide than those during the spring tide, while PO43- showed an opposite trend, and each was higher in the ebb tide than in the flood tide, either for the neap tidal cycle or the spring tidal cycle; 2) higher stratification of the nutrients existed obviously in this area, with the concentrations of which increased from the bottom to the surface, especially for NH4+ and NO3-; 3) the coefficient of variation (C.V.) values of all dissolved inorganic nutrients varied from 4.06% to 36.8% beyond different influences of the tidal current and Changjiang runoff; 4) with increasing suspended matter in the water column, the concentrations of PO43- became lower in the filtered water; and 5) the total transport of each tidal cycle was much more in the spring tide than in the neap tide, and the positive values indicated that the nutrients had been exported to the East China Sea. Studies on the variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang Estuary will provide the scientific basis for the study of the mechanism of red tide in the East China Sea.

Nitrogen and phosphorus budgets of the Changjiang River estuary

Eutrophication has emerged as a key environmental problem in Chinese coastal waters, especially in the Changjiang (Yangtze) River estuary. In this area, large nutrient inputs result in frequent harmful algal blooms and serious hypoxia in bottom waters. Four cruises were made in the estuary in 2006 to assess the concentration and distribution of dissolved inorganic nitrogen (DIN) and phosphorus (DIP). The concentration of DIN decreased gradually in a linear relationship with salinity from the river mouth to outer waters, while DIP was relatively more dispersed. A modified box budget method was used to estimate nutrient fluxes in the estuary and its adjacent waters. Water and nutrient budgets as well as primary production and denitrification rates were estimated from the box budget model. Estimated water residence time in the estuary was about 11 d. The turbid mixing zone released 33% of DIN and 49% of DIP, while in the adjacent outer sea 17.9 mmol DIN/m2·d and 0.36 mmol DIP/m2·d were fixed. Dissolved inorganic phosphorus was imported from the deep open sea waters, supporting primary production and population growth in this zone. Net ecosystem production (NEP) was calculated at 38.2 mmol/m2·d in the outer estuary and the estimated rate (N-fixation minus denitrification) was negative (1.92 mmol/m2·d), implying that a large amount of input nitrogen was taken up by algae and recycled through denitrification in bottom water and sediment.

Nutrient fluxes in the Changjiang River estuary and adjacent waters——a modified box model approach

To solve nutrient flux and budget among waters with distinct salinity difference for water-salt- nutrient budget, a traditional method is to build a stoichiometrically linked steady state model. However, the traditional way cannot cope appropriately with those without distinct salinity difference that parallel to coastline or in a complex current system, as the results would be highly affected by box division in time and space, such as the Changjiang （Yangtze） River estuary （CRE） and adjacent waters （30.75°-31.75°N, 122°10′-123°20′E）. Therefore, we developed a hydrodynamic box model based on the traditional way and the regional oceanic modeling system model （ROMS）. Using data from four cruises in 2005, horizontal, vertical and boundary nutrient fluxes were calculated in the hydrodynamic box model, in which flux fields and the major controlling factors were studied. Results show that the nutrient flux varied greatly in season and space. Water flux outweighs the nutrient concentration in horizontal flux, and upwelling flux outweighs upward diffusion flux in vertical direction （upwelling flux and upward diffusion flux regions overlap largely all the year）. Vertical flux in spring and summer are much greater than that in autumn and winter. The maximum vertical flux for DIP （dissolved inorganic phosphate） occurs in summer. Additional to the fluxes of the ChanNiang River discharge, coastal currents, the Taiwan Warm Current, and the upwelling, nutrient flux inflow from the southern Yellow Sea and outflow southward are found crucial to nutrient budgets of the study area. Horizontal nutrient flux is controlled by physical dilution and confined to coastal waters with a little into the open seas. The study area acts as a conveyer transferring nutrients from the Yellow Sea to the East China Sea in the whole year. In addition, vertical nutrient flux in spring and summer is a main source of DIP. Therefore, the hydrodynamic ROMS-based box model is superior to the traditional one in estimating nutrient fluxes in a complicated hydrodynamic current system and provides a modified box model approach to material flux research.

Simulating the influence of various nutrient sources on hypoxia off the Changjiang River Estuary

Hypoxia is increasingly reported off the Changjiang River Estuary with the confluence of multiple high volume nutrient sources.The Regional Ocean Modeling System coupled with a biological model was used to analyze the effect of different nutrient sources on the development of hypoxia off the Changjiang River Estuary.By comparing to observed data,our model suitably captured the regional dynamics of chlorophyll a,dissolved oxygen,and nutrient concentration.A series of sensitivity experiments were conducted to investigate the hypoxia response to the various nutrient sources,such as loading from the Changjiang River,Kuroshio and Taiwan Warm Current.Our model results indicated that nutrients from different sources significantly influenced the hypoxia off the Changjiang River Estuary,and it was mostly affected by nutrients sourced from the Kuroshio.The nutrients input from the Changjiang River had larger impacts on the hypoxia in the north of 30°N than that in the south of 30°N.The nutrients sourced from the Taiwan Strait had a least influence on the hypoxia off the Changjiang River Estuary.

Alteration of estuarine circulation pattern due to channel modification in the North Passage of the Changjiang River Estuary

The exchange flow structure was examined in the North Passage of Changjiang River Estuary,where a deep waterway project(DWP)was carried out to improve the navigability.Before the construction of the DWP,the friction effect played a significant role in shaping the transverse structure of the exchange flow.The turbulent eddy viscosity generated near the seabed can be transferred to the upper water column,which facilitated vertical momentum exchange.As a result,the landward inflow extended to–2 m below the water surface and the seaward outflow was concentrated on the shallow shoal on the southern side of the cross section.After the construction of the DWP,the turbulent mixing was suppressed as a result of density stratification.The friction felt by the water was constrained in the lower half of the water column and the vertical momentum exchange was reduced.Meanwhile,the channel became dynamically narrowed with a Kelvin number of 0.52.Therefore,the Coriolis played a minor role in shaping the transverse structure of the exchange flow.As a consequence,the exchange flow featured a vertically-sheared pattern,with outflow at the surface and inflow underneath.Additionally,the gravitational circulation was enhanced due to increase in along-channel density gradient and stratification.The exchange flow components associated with the lateral processes(residual currents induced by eddy viscosityshear covariance and lateral advective acceleration)were reduced,which suggests that lateral processes played a minor role in modifying the along-channel dynamics when the estuary becomes dynamically-narrowed.

Changes in nutrient uptake of phytoplankton under the interaction between sunlight and phosphate in the Changjiang (Yangtze) River Estuary

We conducted ship-board incubation experiments to investigate changes in nutrient uptake of phytoplankton under different phosphate concentrations and irradiances in the Changjiang River Estuary and its adjacent waters in China. Under 100% natural irradiance the uptake rates of phosphate, silicate, and nitrate were accelerated at high phosphate levels (1.84 μM), while under low irradiance (about 50% natural irradiance) their uptake rates were restrained at the high but stimulated greatly at the intermediate phosphate concentrations (1.26 μM), as the growth of phytoplankton, changes in nitrite and ammonium uptake didn't follow an obvious pattern. Our results also showed that there were linear relationships between nitrate, silicate and phosphate uptake at different phosphate concentrations under low and high irradiances, and the growth period of phytoplankton was prolonged both at the high phosphate concentrations under high irradiance and at the intermediate concentrations under low irradiance, suggesting that the limitation of phytoplankton growth mainly reflected changes in its growth period, and because no such environment (low irradiance and low phosphate concentrations) actually existed in a high turbidity zone, phytoplankton blooms hardly occurred there. In the absence of irradiance, denitrification occurred readily and phytoplankton was kept decreasing, which resulted in phosphate regeneration.

Benthic nutrient fluxes in the intertidal flat within the Changjiang (Yangtze River) Estuary

In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang (Yangtze River) Estuary. Except for NH4+, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrifica- tion rates, that utilizing NO3- transported from overlying water (DW) in Dongtan sediments, were estimated to be from -16 to 193 μmol·h-1·m-2 with an average value of 63 μmol·h-1·m-2 (n=18). These estimated values are still un- derestimates of the in-situ rates owing to the lack of consideration of DN, i.e., denitrification supported by the local NO3- production via nitrification.

Spatial and temporal distributions of nitrogen,phosphorus and heavy metals in the intertidal sediment of the Chang jiang River Estuary in China

Spatial and temporal distributions of nutrients （N and P） and heavy metals （Cu, Zn, Pb and Cd） in the intertidal sediments at Dongtan wetland of the Changjiang River （Yangtze River） Estuary were examined by laying one transect running seaward to landward during January, April, June, August and October of 2005. Total nitrogen （TN） and heavy metal concentrations in the intertidal sediment showed an increasing trend from open bare flat to the high marsh, with the maximum concentrations in the high marsh and the minimum values in open bare flat. In contrast, sediment total phosphorus （TP） concentrations changed little among sampling sites. One-way ANOVA found that there were significantly temporal variations of nutrients and heavy metals concentrations in the intertidal sediment （P 〈0.05）. The concentrations of heavy metals generally showed an increasing trend from January to October. As compared with other large estuaries, heavy metal contamination in the intertidal sediment of the Changjiang River Estuary was relatively low.

Estimation of dissolved inorganic nutrients fluxes from the Changjiang River into estuary

Because the estuary acts as either a trap or a source or both for nutrient elements and will modify greatly the riverine transport to the ocean, it is necessary to calculate the flux from river into estuary and that from estuary into sea, respectively. The present work aims to use a long-term record of nutrients concentrations and runoff discharges on H.e Datong section (625 km inland from the Changjiang River mouth) to identify the variability of nutrients concentrations and to estimate nutrients fluxes from the Changjiang River into the estuary.

Remote sensing of sea surface nutrient in the frontal zone of Changjiang diluted water and the Taiwan Warm Current

Field investigation was carried out during 4 to 15 April 2001 around the Changjiang River Estuary. The similar distribution of sea surface nutrients and suspended sediment （SS） concentration is attributed to the physical mixing of Changjiang diluted water （CDW） with the Taiwan Warm Current （TWC）. On the basis of the observed positive relationship between total phosphorus （TP） and SS concentration, the sea surface TP is inversed from satellite SS data. SS is believed to be an ideal eutrophic state assessing index substitution for TP, the eutrophication classification critical value of SS adopted in this research was based on the linear model： CTP =0. 000 6Css_ ＋0. 016 3, r^2 =0.564 5, n =32. Although lack of in-situ chromophoric dissolved organic matter （CDOM） measurement, a good relationship was observed between the in-situ DIN （dissolved inorganic nitrogen） concentration with near real time SeaWiFS absorption coefficient of CDOM （ACD） data： cDIN= 1. 406 5AACB_ - 0. 035 9, r^2 = 0. 741 5, n = 16. This empirical regression algorithm was also utilized for inversing the DIN concentration from SeaWiFS ACD data, and for establishing the eutrophication classification critical value of satellite ACD data. The established remote eutrophication classification sys- tem was later used for seawater eutrophic state assessment. The evaluation suggested that the Zhoushan Fishing Ground especially the western border is affected seriously with the nutrient input. The nutrient is mainly from the terrestrial source transported by the Changjiang River runoff. The seawater quality classification precision was assessed by in-situ data, which suggested the seawater quality distribution is similar to the two classification systems, and the remote classification error is below 25%.

长江口中肋骨条藻赤潮发生过程环境要素分析──营养盐状况

从长江口1990年6月的一次中肋骨条藻赤潮发生过程中营养盐含量变化可见，由于潮汐的作用，观测水域各营养盐要素都在不同程度上存在周日波动特征，其中NO3－N在一个潮周期内变化幅度可达1倍以上。赤潮发生时表层水体NO3－N，PO4－P和SiO3－Si值都呈下降趋势，降幅最大的PO4－P达3倍以上；N／P值则急剧上升，峰值为450。随着赤潮消亡，NO3－N，NO2－N和SiO3－Si浓度很快恢复正常，NH4－N浓度在赤潮发生时略有升高，但在赤潮末期明显下降，而且恢复过程相对较长。

东海赤潮高发区营养盐时空分布特征及其控制要素

东海长江口、舟山渔场附近海域是我国近海赤潮爆发严重的区域之一。在影响该海域营养盐分布的水团中 ,长江冲淡水向表层输入了大量的氮、磷、硅营养盐 ,台湾暖流主要对底层和长江口外上升流区有贡献 ,苏北沿岸水、闽浙沿岸水主要影响近岸区域。同时 ,营养盐在海水 -沉积物界面的交换作用 ,大气湿沉降作用等也影响着该海域营养盐的时空分布。结合2002年4月～2003年3月对29°00′～32°00′N、122°00′～124°00′E海域四季航次调查的营养盐分布规律 ,该海域可分为三片区域 ,由岸边向外海分别为高营养盐、低浮游植物区 ,较高营养盐、高浮游植物区和较低营养盐、低浮游植物区。随着近年来营养盐输入通量的增加 ,富营养化程度加大 ,受化学、物理、生物等因素综合作用 ,高浮游植物区赤潮爆发频率和规模逐年增加 。

长江入河口区生源要素的浓度变化及通量估算

利用近几十年长江大通断面的实测流量和生源要素 (C、N、P、Si)资料 ,讨论了C、N、P、Si较长时间序列浓度的变化特征和长江入河口区的通量。结果表明 ,HCO-3 浓度比较稳定 ,波动较小 ;NO-3 、NO-2 、PO3-4 主要呈上升趋势 ;游离CO2 、NH+4和SiO2 -3 浓度表现出一定下降趋势 ;估算并研究了长江C、N、P、Si入河口区年内各月的平均通量、年际间各年的通量和多年平均的年均通量和主要变化特征 ;利用月通量序列以及相应的流量序列 ,拟合出可以利用已知的月均流量预测进入河口区的月通量的关系函数。这些研究是进行河口区生源要素收支平衡计算的重要基础。

长江口邻近海域营养盐分布特征及其控制过程的初步研究

利用 1997年秋季和 1998年春季对长江口邻近海域两个航次的调查结果 ,对该海域营养盐分布、结构特征以及其主要控制过程进行了探讨 .结果表明 ,该海域的营养盐分布及结构具有明显的季节变化 ,秋季海水中NO3 - N、SiO3 2 - Si及PO43 - P、DOP、PP均高于春季 ,平均含量分别为 4 .97、11.6、0 .4 4、0 .2 6、0 .82 μmol·L-1,而春季则是NO2 - N、NH4+ N、DON、PN含量高 ,平均含量分别为 0 .70、2 .2 6、9.88、7.88μmol·L-1.PP(5 4 % )和PO43 - P(5 1% )分别为秋季和春季磷的主要形态 ,两个季节氮结构基本一致 ,均以DON和PN为主 .除春季PO43 - P外 ,营养盐受长江冲淡水等陆源输入的影响而呈现近岸含量较高 ,溶解无机氮秋季以NO3 - N为主而春季则以NH4+ N为主 ,秋季PO43 P同时来源于长江冲淡水和台湾暖流 ,而春季则主要来源于台湾暖流 ,显示出春季台湾暖流对调查海区的影响程度大于秋季 .

长江口地区大气湿沉降中营养盐的初步研究

为了解大气湿沉降对于赤潮发生的影响 ,2 0 0 0年 5月至 2 0 0 1年 4月在嵊泗群岛采集了 6 4个雨水样品 ,并分析了其中的N、P、Si等营养盐的浓度 .结果表明 ,营养盐月平均浓度之间相差较大 ,与风向即不同的污染物来源和降水量等因素有关 ;营养盐季节通量分布不均 ,季节性明显 ,除冬季外 ,其他 3个季节均能成为赤潮的诱发因子 ;NO3 - N、NH4+ N、NO2 - N、PO43 - P和SiO3 2 - Si的年均浓度依次为 2 0 .2 3、30 .14、0 .11、0 .0 4 5和 3.4 3μmol·L-1,年通量分别为 2 .6 7× 10 8、3.98× 10 8、0 .0 14× 10 8、0 .0 0 5 9× 10 8和0 .4 5× 10 8mol,与河流输入量相比 ,湿沉降对营养盐的年输入量较小 .

长江口及邻近海区营养盐结构与限制

通过研究长江口及邻近海域溶解无机氮(DIN=NO3-+NO2-+NH4+)、磷酸盐(PO34-)、硅酸盐(SiO23-)所表征的营养盐区域结构特征及影响因素,在分析营养盐绝对限制情况的基础上,划分了潜在相对营养限制区域。结果表明,123°E以西近岸表层区域DIN/P比值全年均高于16,而Si/DIN除秋季外基本小于1,显示出长江冲淡水影响下"过量氮"的特征。春夏季河口锋面区(31°～32.5°N,122.5°～124°E)硅藻的大量生长可使DIN/P异常升高和Si/DIN异常降低。秋季研究区域北部DIN/P西低东高且Si/DIN西高东低是由于在高DIN、低PO34-的长江冲淡水影响下,近岸受相对低DIN、高SiO23-的苏北沿岸流南下入侵影响而被分割而成。冬季长江口门东北部存在的高DIN/P和低Si/DIN区则主要由于寡营养盐的黑潮水深入陆架,向东北输送的部分长江冲淡水和增强的苏北沿岸流共同作用造成DIN升高所致。利用Redfield比值进行了不同站位表层潜在相对营养限制情况的区分。近岸123°E以西受高DIN、SiO23-长江冲淡水影响,四季多呈现PO34-潜在相对限制,而在春夏季由于浮游植物的大量吸收PO34-,造成局部PO34-绝对限制及潜在相对限制。春夏季氮限(DIN潜在相对限制)一般发生在外海部分站位,但较为零散。秋季除了东南外海大部分站位外,受苏北沿岸流影响在长江口北部近岸也存在氮限。随着低DIN/P的黑潮表层水(KSW)的入侵加强,冬季外海氮限站位增多。硅限(SiO23-潜在相对限制)在夏季发生在赤潮高发区,而冬季南部存在较多硅限站位表明KSW中SiO23-相对较为缺乏。

长江口最大浑浊带潮滩沉积物间隙水营养盐剖面研究

2005—03～2006—02对长江口崇明东滩高、中、低潮滩3个典型站点沉积物间隙水中各营养盐成分含量及其随深度的变化做了为期1a的逐月观测。结果显示，研究区域间隙水中NH4^＋和SiO3^2-的浓度一般在200～500μmol／l之间，高、中、低潮滩间显示出了不同的分布态势；与高潮滩和中潮滩相比，没有植被覆盖、粒径较粗的低潮滩往往具有较高的NH4^＋浓度和较低的SiO3^2-浓度；SiO3^2-随季节的变化主要受温度的影响，而NH4^＋的变化则较为复杂，较低值往往出现在植物生长旺盛的春、夏季，与NH4^＋和SiO3^2-的浓度相比，NO2^-＋NO3^-和PO4^3-在间隙水中的浓度往往要低2～3个数量级，但由于受到生物扰动等因素的影响，沉积物表层NO2^-＋NO3^-浓度在某些月份可能出现几十μmol／l。的高值，较高的NO2^-＋NO3^-浓度以及沉积物中氧化环境向还原环境的快速转变为显著的反硝化反应的发生提供了物质基础与环境基础，从而可能对生源要素在长江口陆海相互作用地区的生物地球化学行为产生深刻的影响。

长江口及邻近海域冬夏季浮游植物营养限制及其比较

2001年7月27日至8月11日，2002年1月8～19日在长江口及邻近海域进行了浮游植物限制因子测定的现场培养实验．结果显示：在近长江口透明度低于1m的海域，冬季和夏季浮游植物的生长均受到光的限制．调查海域范围内夏季高浮游植物生物量海区主要集中在舟山渔场和长江口以北两个区域，盐度范围在28～31．冬季高浮游植物量海区向东南方向移动．夏季浮游植物的生长按照受限情况划分为4个区域：Ⅰ．近河口光限制区；Ⅱ．磷潜在的限制区；Ⅲ．氮、磷潜在限制过渡区；Ⅳ．氮潜在限制区．冬季划分为3个区域：Ⅰ．近河口浮游植物光限制区；Ⅱ．磷潜在限制区；Ⅱ．非营养潜在限制区．