The Characteristic And Effects Of Nutrient During The Process Of HAB In Changjiang River Estuary And Its Adjacent Area

The Changjiang River Estuary and its adjacent area has become the frequentHarmful Algal Blooms (HAB) occurrence area of our country in recent years.Thehigh frequency of HAB in this area is closely related to the increment of nitrogenousand phosphorous fluxes drainaged to this area by many resources year after year.Therefore one of the most important tasks about researching mechanism of HAB inthis area is to study the main nutrient resources and their fluxes,recognize theirinfluences on the HAB scale and realize the role of nutrient during the process ofHAB in East China Sea (ECS).Based on the data of field investigations through cruises in the area influenced byChangjiang Diluted Water from 2002 to 2007,the nutrient fluxes to ECS from mainresources and their variation patterns were systematically calculated.Then thenutrient characteristic of spatial distribution and seasonal variation in this area wereanalyzed.The difference of nutrient level between frequent HAB occurrence area andrare HAB occurrence area was compared.The characteristic of the nutrient during theprocess of HAB is analyzed and the relationship between nutrient flux and HABoccurrence is summarized.The main results are as follows:1.The main nutrient resources and their fluxes in Changjiang River Estuary and itsadjacent area1) During the mixture process of freshwater and seawater in Changjiang RiverEstuary and its adjacent area,SiO₃-Si is of conservative characteristic according to thegood linear relationship between its concentration and salinity.While DIN and PO₄-Pis of complemental function.The relationship between concentration and salinity ofDIN and PO₄-P shows a well curve,which accords with the equation of MnMolecular.2) The Changjiang River nutrient flux varies with its runoff.There is an obviousseasonal variation of nutrient flux in studied area.The input fastigium period occursfrom May to August every year and June is the fastigium.During the wholeinvestigation period,the nutrient input fluxes of the year 2002,2003 and 2005 arerelatively high while those of 2006 and 2007 are relatively low.The nutrient inputflux reached the lowest level in year 2004.3) The main nutrient resource of the research area is the Changjiang River,whose DIN flux to ECS accounts for 52%,PO₄-P accounts for 33% and SiO₃-Siaccounts for 56% of the whole drainge.The nutrient flux exchange with the open seawater makes great contributions to the flux PO₄-P (27%) and SiO₃-Si (21%) of thisarea.Some other rivers runoff makes great contribution to the flux of DIN (17%) andSiO₃-Si(23%).The atmosphere deposition accounts for the DIN (18%) flux.Besidesthe sediment-water nutrient flux works well with the nutrient budgets in the researcharea.2.The nutrient condition of Changjiang River Estuary and its adjacent area1) The contour of DIN,PO₄-P,SiO₃-S in this area has a relatively largeconcentration grads between 122.0～122.5°E.In winter and spring,the nutrientcontour parallels with the coastline and the high value nutrient area mainly locating inthe long and narrow zone from Changjiang Estuary to south coastal area of Zhejiang.While in summer and autumn,the contour turns to a fan-shape extending to the opensea and the high value nutrient area mainly locates north area of Zhoushanarchipelago.2) The primary factor affecting the horizontal distribution characteristic ofnutrient in Changjiang River Estuary and its adjacent area is such terrestrial input asChangjiang River.The high concentration value of nutrient extends as the increase ofthe Changjiang nutrient flux and the eutrophic area transfers as the ChangjiangDiluted Water turns around.Therefore attempering the amount and pervading mode ofChangjiang nutrient flux will affect the nutrient horizontal distribution characteristicand the eutrophic condition of the research area.3) The nutrient concentration level and its seasonal variation pattern in theChangjiang River Estuary and its adjacent area depends on balance between nutrientsupplement and consume of phytoplankton.In summer,the explosive growth andreproduction of phytoplankton in this area cause the huge demand of nutrientexceeding the supplement,which can explain the variation characteristic of averagenutrient concentration in this area reaches the highest in autumn,the lowest insummer,relative higher in autumn and winter and lower in spring and summer.4) There is an obvious difference of the value of S,PO₄-P,SiO₃-S and DINbetween frequent HAB occurrence area and rare HAB occurrence area.FrequentHAB occurrence area is mainly located on those areas who have nutrient relativelyhigh concentration and lower variation range.3.The characteristic of HAB in Changjiang River Estuary and its adjacent area1) According to the HAB records and Chlorophyll a concentration variationmode in the research area,the process of blooms of Diatom or Dinoflagellate can becompartmentalized to 5 stages:lag phase(Chlorophyll a＜1.5μg·L^-1),initiation stage,exponential phase(Chlorophyll a＜10ug·L^-1),stationary phase (Chlorophyll a =10μg·L^-1) and dissipation phase (Chlorophyll a＜10μg·L(-1)).2) The variation characteristic of several main parameters in the process of HAB is concluded.The bloom of diatom is initialized usually with low temperature and lowsalinity while the blooms of dinoflagellate usually with high temperature and lowsalinity.Before blooms of diatom,the nutrient concentration is relatively high whilelow before blooms of dinoflagellate.DIN,PO₄-P,SiO₃-S concentrations drop rapidlyduring the process of diatom bloom while slowly in dinoflagellate bloom..TheDiatom bloom would be initiation,exponential growth and dissipation with theinvasion of open seawater,while dinoflagellate bloom with the supplement ofChangjiang Diluted Water.During the whole process of HAB,the value of nutrientconcentration mainly depends on the phytoplankton's consuming speed and thesupplementing speed of nutrient.3) The temporal variation characteristic of each element during the process ofHAB in this area in 2005 is concluded.Before diatom blooms breakout,thetemperature and salinity is relatively low,the nutrient concentration is relatively highand in eutrophic condition.Then the diatom blooms would be prior occurred.Finallydiatom bloom would be dissipated quickly following with the sharp concentrationdecrease of PO₄-P and SiO₃-S.Before dinoflagellate bloom breakout,the temperatureis high and salinity and nutrient concentration are relative low.When dinoflagellatebloom occurs in large scale,the nutrient supplement increases.After a long retentionstage,dinoflagellate blooms dissipates when the temperature is too high fordinoflagellate and the DIN content reaches the lowest.4) The relationship of HAB condition and Changjiang nutrient flux's annualvariation and seasonal variation is concluded.There is a good exponential increasingcurve relationship between nutrient flux and HAB scale.The increment of nutrientflux will cause the exponential increase of frequency and area of HAB.The DIN inputflux has the best pertinency with HAB scale.5) The relationship of Changjiang nutrient flux in each cruise and averageconcentration of Chlorophyll a is concluded.In spring and summer,the averageconcentration of Chlorophyll a has a perfect lineal relationship with Changjiangnutrient flux.The increase of nutrient flux will cause the biomass linear increase inthis area。...