Study On Dynamics Of Phytoplankton Community In Jiangdong Reservoir And Jiulong River Estuary By High Frequency Observation

As a sensitive zone between ocean and terrestrial ecosystems,estuary is greatly affected by human activities and climate changes.Estuary has been undergoing a serious of significant impacts,such as eutrophication and harmful algal blooms.However,the relevant researches which are based on manual sampling,can barely provide timely and effective information to reveal the succession and mechanism of estuary or predict for ecological disaster events.In this research we took a subtropical reservoir——Jiangdong Reservoir,and Jiulong River Estuary,Xiamen Bay as the study area,using the high spatial and temporal frequency technique to study the dynamics of phytoplankton community,then developed a model based on the empirical relationships between POC with turbidity and chlorophyll a fluorescence to estimate the dynamics of POC The main results can be summarized as follows:1.Dynamics of phytoplankton community in Jiangdong ReservoirWe identified phytoplankton includes 7 phylum,51 genera,consisting mainly of green algae,blue-green algae,diatoms and cryptophyta.Water temperature was the most important factor effecting the phytoplankton community succession.Diatoms and cryptophyta were dominant groups in autumn and winter;Green algae,blue-green algae developed into dominant groups in spring and summer.Diatoms biomass were maximum from February to April,and minimum in June;Cryptophyta biomass were maximum from December to February,minimum in June;Green algae biomass were maximum in May and August,minimum in June;Blue-green algae can adapt to high turbidity water,which makes them kept higher biomass in June and August,and lower in November.From functional groups' stand,P and Y were dominant from March to April;Then D,S1 MP groups greatly increased in March to June;From August to October F,J,Lo developed into dominant groups;Since November to January,X1 and J groups began to mass reproduce,meanwhile P and Y groups recovered their advantages.There was obvious diurnal periodicity of phytoplankton biomass in the Jiangdong Reservoir,with one peak in daily cycle,approximately between 12-16 pm.Chlorophyll a peak could exist longer time in spring and summer than autumn and winter.Compared to blue-green algae,green algae and cryptophyta had more stable diurnal periodicity.During the observation period,the system recorded 13 events of algae blooms,including 6 events in dry period,existed for about 6 days,when the dominant groups were diatoms,cryptophyta and green algae;5 events in wet period,existed for about 10.8 days,when green algae and blue-green algae were dominant groups;2 events in normal period,existed for about 8 days,which were both cryptophyta blooms.When in the dry period,the average interval between blooms was 5.1±1.1 days and it's more frequent than wet period(average interval is 24.3±22.1 days),but water temperature and irradiance can't support bloom for a long time in dry period.2.Dynamics of phytoplankton community in Jiulong River Estuary and Xiamen BayThere is significant spatial and temporal difference of phytoplankton dynamics Jiulong River Estuary and Xiamen Bay had,especially in Jiulong River Estuary.Relatively,the heterogeneity in Xiamen Bay was smaller.In spring,green algae and blue-green algae were dominant groups in upstream of Jiulong River Estuary,their relative contribution was up to 80%,and their biomass were maxrimum in midstream;Blue-green algae was dominant group in Xiamen Bay,maximum biomass occurred in Tongan Bay.In autumn,the dominant groups in upstream were blue-green algae and green algae,their relative contribution is nearly 80%,the highest Chlorophyll a biomass is up to 10 ?g/L;Blue-green algae and diatoms were advanced in the downstream and Xiamen Bay,green algae showed their advantages in the southern area,western area and Tongan Bay.In Xiamen Bay the most productive region was southern area,its Chlorophyll a biomass was nearly 6.3 ?g/L.In winter,diatoms dominated in the whole estuary,its relative contribution can reach to 79%,the highest Chlorophyll a biomass is up to 46 ?g/L,while in the downstream of Jiulong River Estuary,biomass decreased;The most productive waters in Xiamen Bay was western area and eastern area.3.Develop a POC estimation model for Jiangdong Reservoir,Jiulong River Estuary and Xiamen BayBased on the empirical relationships between POC with Chlorophyll a and TSM in different hydrological periods and area,we marked off normal period and flood period in Jiangdong Reservoir to estimate POC concentration,and the result showed that there were highest POC concentration in June(2.8±4.5 mg/L),with minimum contribution from algae carbon(nearly 0.1%)in this month,less in November(1.0±0.3 mg/L)and May(1.0±0.4 mg/L).Divided Jiulong River Estuary and Xiamen Bay into low salinity area and high salinity area to estimate POC,result showed that there was a POC front along the salinity gradient,while from upstream of estuary to downstream POC increased and then decreased quickly.The front of POC migrated upstream from wet period to dry period.Based on Chlorophyll a fluorescence and turbidity,this model can estimate POC efficiently.