| Futian Mangrove Reserves of Shenzhen is an important national mangrove reserves in China,and phytoplankton is important component in mangrove ecosystem and is the foundation for water control and environmental protection.In the present study,various phytoplankton samples were collected and analyzed from the water of Futian Mangroves,in four seasons of 2015 and 2016.Our studies were focused on composition,population distribution and community structure of phytoplankton in Futian Mangroves Reserve of Shenzhen(E113° 45?,N 22° 32?),combining with the environmental factors.And the influences of three single heavy metals(Cd2+,Pb2+ and Cr3+),salinity and pH value on extracellular polymeric substances(EPS)secreted by the dominant species Cyclotella meneghiniana were studied.The results are as following:1.There are significant seasonal differences in the surface water temperature of Futian mangrove.The surface water temperature varied from 18.0 to 31.0 ? and four stations have little differences.The seasonal variation tendency of four stations is consistent.The salinity varies greatly with season change,which varies from 2.0?17.5‰.So the study area belongs to brackish water.The variation range of pH value is between 6.62?9.54,the study area belongs to alkaline water.2.The contents of nitrogen and phosphorus in Futian mangrove area were over standard,showing irregular seasonal variation.The range of inorganic nutrients total nitrogen,total phosphorus and silicate were:0.95?6.28,0.04?0.51 and 0.87-6.33mg/L respectively.Comparing with previous data,there was a significant decline.3.A totally 135 species of phytoplankton belonging 58 genera were identify in all the stations sample,among which 89 taxa in 30 genera belonging to Bacillariophyta,28 taxa in 14 genera for Chlorophyta,8 taxa in 6 genera for Cyanophyta,3 taxa in 3 genera for Dinoflagellate,4 taxa in 3 genera for Euglenophyta and 3 taxa in 2 genera for Cryptophyta.In Futian mangroves,diatom is still the main group of phytoplankton,accounting for 65.93%of the total species number.In addition,the benthic and epiphytic diatoms accurred abundantly in four stations.4.Cyclotella meneghiniana,C.caspia,Thalassiosira weissflogii,Oscillatoria sp.,Merismopedia minima,Cryptomonas erosa and C.ovata were the dominant phytoplankton species of Futian mangroves.5.In 2015 and 2016,the average cell density of 2.37×106 cells/L and 3.95×106 cells/L respectively,showing an increasing trend.the average cell density in spring is 3.44×106cells/L,summer is 2.77×106cells/L,Autumn is 3.21×106cells/L and winter is 3.20×106cells/L.It was found that the cell density was highest in spring and decreased in summer and autumn.The cell density reached 106/L level.According to the evaluation standards of the water eutrophication,the water of Futian mangroves has reached the level of eutrophication.6.In 2015,the average cell density of Fengtang estuary was 2.02×106cells/L,Shazui Dock was 1.81 × 106cells/L,Birdwatching house was 2.50× 106cells/L,Jiwei fish ponds was 3.14×106cells/L?In 2016,the average cell density·of Fengtang estuary was 2.12 × 106cells/L,Shazui Dock was 2.75 X 106cells/L,Birdwatching house was 4.48 X 106cells/L,Jiwei fish ponds was 4.45 X 106cells/L.The cell density of Jiwei fish ponds was highest,and Fengtang estuary and Shazui Dock were low.And the cell density of the second year was more than the second years,which showed the water pollution in Futian mangrove area is moderately polluted,and the pollution is getting worse.the dominant phytoplanktons in various stations were Cyclotella meneghiniana,C.caspia,Thalassiosira weissflogii.In Jiwei fish ponds,the appearance of Oscillatoria sp.and Cryptomonas erosa was quite frequent.In Birdwatching house,the appearance of Crypto,monas erosa and C.ovata.And Merismopedia minima only became the dominant phytoplankton species of Shazui Dock while Cyclotella meneghiniana,C.caspia,Thalassiosira Weissflogii.were the dominant phytoplankton species of Fengtang estuary.7.Redtide causative algae were found in Futian mangroves,such as Skeletonema costatum,Thalassiosira weissflogii and Alexandrium tamarense.Pollution tolerant species were also found,such as Cryptomonas erosa,Oscillatoria sp.Gymnodinium aeruginosum and Euglena viridis.There are more pollution tolerant species in Futian mangroves.8.In 2015 and 2004,the diversity index of phytoplankton was 1.82 and 1.76 and the evenness index was 0.47 and 0.43 respectively,showing a slightly decline trend.According to the diversity index,evenness index and the degree of water pollution,it is considered that the water pollution in Futian mangrove area is moderately polluted,and the pollution is getting worse.9.Treament were conducted by different salinity gradient(15,25,35 ‰).After 7days,the growth rate of the algae was 2.7 ×104 cells/day in salinity 15,0.9 ×104 cells/day in salinity 25,3.2 ×104 cells/day in salinity 35.Treatment were conducted by different pH value gradient(6.0,7.0,8.0).After.7 days,the growth rate of the algae was 1.4 × 104cells/day in pH 6,1.8 × 104 cells/day in pH 7,1.4 × 104 cells/day in pH8.The results showed that the dominant species Cyclotella meneghiniana in low salinity and alkaline water grows well.The content of EPS in salinity 35 was significantly higher than that of salinity is higher than salinity 15 and 25(ANONA,p<0.05).The content of EPS in pH 6 was significantly higher than that of pH7 and pH8(ANONA,p<0.05).The results showed that under the stress of high salinity and low pH value,C.meneghiniana will secret abundant EPS.10.The reproduction of C.meneghiniana was inhibited by three single heavy metals(Cd2+,Pb2+ and Cr3+).The influences of three single heavy metals on EPS secreted by the dominant species C.meneghiniana were different.In the low concentration of Pb2+ and Cd2+ there was no significant difference in the content of EPS between control group and experimental group.In the Low concentration of Cr3+ the content of EPS in experimental group was significantly higher than control group(ANONA,p<0.05).And EPS accumulations were promoted by three single heavy metals in high concentration.The results showed that as the dominant species of phytoplankton in Shenzhen mangroves,C.meneghiniana has a strong receivable ability of heavy metal pollution. |
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