Processes Of Phytoplankton Succession In Xinlin Bay Revealed By High-frequency Monitoring

This study analysis the relationship between landscape characteristics and phytoplankton chlorophyll based on remote sensing method in Houxi River watershed.Statistical analysis and redundancy analysis were also coupled to determine the linkage between environmental factors and phytoplankton biomass,photosynthetic activity and cell abundance for different sizes based on high-frequency monitoring from January 2016 to December 2017 in Xinglin Bay Reservoir.The correlations between photosynthetic activity,cell abundance of different sizes and phytoplankton biomass were also studied.The results were as follows:1.Forest were the dominant landuse in the upstream while the proportion of Built increased from upstream to downstream in Houxi River watershed.The results of Pearson correlation analysis showed that Forest and Orchard were negative correlated with chlorophyll while Cropland,Built,Grass and Other land had positive impact on chlorophyll.Patch density,Shannon's diversity index and location-weighted landscape index were also positively correlated with chlorophyll.The results indicating that extensive woodland played an important role in conserving water resources and protecting water quality,and Cropland and built land was the major source of total nitrogen and total phosphorus for water bodies,which promoted the growth of phytoplankton in the downstream.2.Seasonal changes of environmental factors in Xinglin Bay Reservoir are quite different:Precipitation decreased sharply from 2016 to 2017,with water temperature fluctuates periodically and dissolved oxygen dramatic changes in a short time.Water level,water temperature,salinity,pH,dissolved oxygen,total nitrogen and total phosphorus increased in 2017 compare to 2016,while precipitation,transparency and ratio of total nitrogen and total phosphorus decreased.The changes of chlorophyll and photosynthetic activity of phytoplankton were quite different among algae.The chlorophyll concentration of blues(cyanobacterial),greens(Chlorophyta)and browns(Bacillariophyta,Pyrophyta,Chrysophyta and Cryptophyta,collectively referred to as Chromophyta)from PHYTO-PAM were 0-198.58 ?g/L,0-322.40 ?g/L and 5.14--668.83 ?g/L,respectively.And the photosynthetic activity of blues,greens and browns were 0-0.91,0-0.85 and 0.34-0.68,respectively.The chlorophyll concentration and photosynthetic activity of blues and browns tended to increase while the chlorophyll concentration and photosynthetic activity of greens tended to decrease in the total monitoring period.3.Precipitation and ratio of total nitrogen and total phosphorus had negative effects on the biomass and photosynthetic activity of blues and browns and total biomass,but had positive effects on the biomass and photosynthetic activity of greens.Water temperature,sanility,pH,dissolved oxygen,total nitrogen and total phosphorus had positive effects on the biomass and photosynthetic activity of blues and browns and total biomass,and negatively affected biomass and photosynthetic activity of greens.The impacts of environmental factors on blues and greens were more significant in the wet season,and the impacts of environment factors on browns were more pronounced in the dry season.The effects of environment factors on the photosynthetic activity were similar to biomass.The results of redundancy analysis showed that the environmental factors in the wet season of 2016,in the dry season from 2016 to 2017,in the wet season of 2017 and from January 2016 to December 2017 explained 67.8%,39.1%,54.4%and 36.5%of the phytoplankton biomass changes,respectively,and explained 44.4%?47.1%?46.2%and 40.9%photosynthetic activity changes,respectively.4.During the monitoring period,the cell abundance of 3-10 ?m and 10-20 ?m were 555-205348 ind/mL and 2624-151711 ind/mL,respectively,which were 1 to 2 orders of magnitude higher than other sizes in most cases.The proportion of 3-10 ?m and 10-20 ?m contributed to 0.62-74.4%and 23.6-87.4%of total cell abundance,and the sum of these two sizes reached more than 80%in most of the time.The proportion of 20-60 ?m was higher in January,March and December than other months.Water level,transparency total nitrogen,total phosphorus and ratio of total nitrogen and total phosphorus were the main environmental factors affecting changes for the size structure of phytoplankton.Environmental factors accounted 30.1%for size structure changes.There was no significant correlation between cell abundance of 3-10?m and total biomass,but the correlations between other sizes and total biomass were significant and positive.