Study Of Algal Distribution Pattern And Its Correlation With Environmental Factors In Yangtze River Estuary Area

Estuaries are bodies of water usually found where rivers meet the sea with ecotone of freshwater and marine, and home for unique plant and animal communities. Estuaries are among the most productive ecosystems in the world, many animals rely on estuaries for food, places to breed, and migration stopovers. Algae is key primary producers in estuaries, and also plays an important role in estuarine ecosystem, so estuarine algae research has very important theoretical and practical significance. Yangtze River estuary is one of the largest estuaries worldwide. It is the important water source of Shanghai city, with shipping, land reclamation and ecological function etc. as well. The study of algae distribution and dynamic has important significance to explore material cycle, energy flow and water quality monitoring of aquatic ecosystem of Yangtze River Estuary. Based on the survey of algae in the Yangtze River Estuary area (including Suzhou River, Huangpu River, Jiuduansha and Chongming Dongtan) during 2004 to 2012, dynamics of algae species composition and quantity biomass were analyzed, various analysis software (SPSS, R etc.) and methods (CCA, PCA etc.) were used to explore algal distribution patterns and its correlation with environmental factors, and a mathematical model of algae in Yangtze River estuary was derived. This paper offered important data and scientific base on study of estuarine algae and ecological protection and scientific use of Yangtze River Estuary. Main results of the research are given in the following:1. The composition and characteristics of Algae in Yangtze River Estuary area: totally 626 species (including variety and forma) belonging to 169 genera,8 phyla were identified in the Yangtze River Estuary area. Bacillariophyta was the most diversified division with 322 species in 83 genera, Chlorophyta was ranked as second with 187species in 52 genera, Euglenophyta with 47 species in 6 genera, Cyanophyta with 42 species in 13 genera, Pyrrophyta with 13 species in 6 genera, Chrysophyta with 9 species in 6 genera in, Cryptophyta with 4 species in 2 genera, Xanthophyta with 2 species in one genus. One new species of diatom (Campylodiscus sinensis) was identified and described.The species number of algae was abundant in the confluence reaches of Yangtze River Estuary main river channel (from Wusongkou to Xiasha of Jiuduansha) and Huangpu River, but less in the middle stream of Suzhou River.141 species belonging to 58 genera,8 phyla were identified in Suzhou River; Chlorophyta was the most diversified division with 70 species; species number was higher in autumn and winter than in spring and summer, and in upstream and downstream than in middle stream.229 species belonging to 84 genera,8 phyla were identified in Huangpu River; Chlorophyta was the most diversified division with 99 species; species number was higher in summer and winter than in spring and autumn, and in upstream and downstream than in middle stream.345 species belonging to 127 genera,8 phyla were identified in Jiuduansha; Bacillariophyta was the most diversified division with 160 species in 56 genera; species number was higher in summer and winter than in spring and autumn, and in upstream and middle stream than in downstream. Diatom was mainly investigated in Chongming Dongtan,169 species of diatom belonging to 84 genera were identified; Nitzschia was the most diversified genus with 16 species; species number was higher in spring than in other seasons.2. Distribution and dynamics of dominant species of algae:the dominant species of algae in Yangtze River Estuary mainly included Skeletonema costatum, Cyclotella meneghiniana, Melosira granulata and its variaties, Fragilaria sp., Gyrosigma acuminatum, Navicula spp., Synedra acus, Pediastrum duplex and its variaties, Scenedesmus quadricauda, Oscillatoria sp., Dactylococcopsis rhaphidioides, Tribonema monochloron, Chroomonas acuta etc..The difference of major dominant species was remarkable among sampling areas. The dominant species in main river channel of Yangtze River Estuary mainly were Melosira granulata, Cyclotella meneghiniana and Chroomonas acuta etc.; the upstream of the main river channel was dominated only by Melosira granulata, Cyclotella meneghiniana, and Chroomonas acuta, and middle and downstream was dominated by Skeletonema costatum. The dominant species in Suzhou River were mainly Cyclotella meneghiniana, Melosira granulata and Pediastrum duplex. The dominant species in Huangpu River mainly were Melosira granulata, Cyclotella meneghiniana, Synedra acus, Oscillatoria sp., Chroomonas acuta and Scenedesmus quadricauda. The dominant species in Chongming Dongtan were various in different habitats, mainly were Skeletonema costatum and Navicula spp.The seasonal succession of major dominant species was remarkable in different rivers. Pediastrum duplex occured in Suzhou River during the summer time, Chroomonas acuta occured in main river channel during winter and spring, but there was no obvious seasonal difference in Huangpu River. Skeletonema costatum dominated the main river channel of Yangtze River Estuary over the whole year.Skeletonema costatum had overwhelming dominance among algae in the main river channel of Yangtze River Estuary, its quantity biomass gradually decreased from Shangsha and Zhongsha to up and downstream. The salinity in Shangsha and Zhongsha was 2.38-16.67%o with maximum turbidity.The quantity biomass of Melosira granulata and Cyclotella meneghiniana reached the maximum in the confluence reaches of Suzhou River and Huangpu River, and gradually decreased to up and downstream, with increasing salinity in the main river channel.3. Distribution and dynamics of the quantity biomass planktonic algae:planktonic algae was sampled at 19 sampling sites in Yangtze River Estuary, including main river channel, Suzhou River and Huangpu River. Algae quantity biomass varied significantly in the 19 sites. The average quantity biomass of Yangtze River Estuary was 66.77×104 Ind/L, Bacillariophyta was the most abundant with 41.75x 104 Ind/L, accounting for 62.53% of the total; Chlorophyta was ranked as second with 19.26×104 Ind/L, accounting for 28.85% of the total; Cryptophyta was 2.36×104 Ind/L, accounting for 3.53% of the total; Cyanophyta was 1.54×104 Ind/L, accounting for 2.31% of the total; Euglenophyta was 1.02 x 104 Ind/L, accounting for 1.53% of the total; Xanthophyta, Pyrrophyta and Chrysophyta were very low, three of them accounting for 1.26% of the total.There were significant differences of the amount and composition of algae quantity biomass in different rivers. The algae quantity biomass of Suzhou River was the highest with 177.45 x 104 Ind/L, the main river channel of Yangtze River Estuary was ranked as second with 45.47×104 Ind/L, Huangpu River was the lowest with 22.29×104 Ind/L. Spatial dynamics were the similar in three rivers, presented as high in middle stream, and low in up and downstream. Chlorophyta dominated the composition of algae quantity biomass in Suzhou River, while Bacillariophyta dominated in Huangpu River and the main river channel of Yangtze River Estuary. Chlorophyta quantity biomass with 82.77×104Ind/L was the highest in Suzhou River, accounting for 46.65% of the total; Bacillariophyta was ranked as second with 74.32×104Ind/L, accounting for 41.88%. Bacillariophyta quantity biomass with 12.49×104 Ind/L was the highest in Huangpu River, accounting for 54.32% of the total; Chlorophyta was ranked as second with 5.82×104 Ind/L, accounting for 25.31%. Bacillariophyta quantity biomass with 41.05×104 Ind/L was the highest in the main channel of Yangtze River Estuary, accounting for 87.42% of the total; Chlorophyta was ranked as second.Seasonal succession of algae quantity biomass was dissimilar in different rivers. Algae quantity biomass was higher in summer and spring than in autumn and winter in Suzhou River, Chlorophyta dominated in summer, and Bacillariophyta dominated in winter. Algae quantity biomass was higher in summer and autumn than in spring and winter in Huangpu River, Bacillariophyta dominated all the year round. Algae quantity biomass was higher in summer and spring than in autumn and winter in main river channel of Yangtze River Estuary, Bacillariophyta dominated all the year round.4. Correlation of the environmental factor and planktonic algae in Yangtze River Estuary:The results of correlation analysis between community structure of planktonic algae and physicochemical factors indicated that algae spatial dynamic was mostly influenced by salinity, secondly by TP and COD. Multiple regression equations of algae species and quantity biomass were deduced from the correlation analysis of algae and environmental factors.Salinity was the main environmental factor which influenced the algae community structure. It ranged from 0.87%o to 17.67%o in the main river channel. The algae species number decreased with the increasing salinity, and tended to be stable when salinity was greater than 3.3%o. Algae quantity biomass was significantly affected by salinity, with rapid growth when salinity was less than 6.5%o, and slow decline when salinity was greater than 6.5%o; this regularity mainly caused by the biomass variation of Skeletonema costatum. Biomass of Bacillariophyta increased while biomass of Chlorophyta and Cyanophyta decreased with the increasing salinity.5. Algae diversity index:Shannon Wiener biodiversity index of different sites in Yangtze River Estuary ranged from 1.17 to 1.91. It was higher in the upstream of Huangpu River and lower in the downstream of main river channel. Main river channel of Yangtze River Estuary, Huangpu River and Suzhou River were in a-mesosaprobic stage assessed by Shannon Wiener biodiversity index. Margalef diversity index of different sites in Yangtze River Estuary ranged from 2.63 to 8.40. It was higher in the upstream of main river channel and lower in the midstream of Suzhou River.6. Variation trend of planktonic algae in Yangtze River Estuary:The analysis of investigation data of 2005 and 2012 indicated that the number of algae species declined 59% from 297 to 121 in the main river channel of Yangtze River Estuary, the decreasing range of Euglenophyta and Chlorophyta were 81% and 67%. There was no significant variation of algae biomass, but the proportion of diatom was increased to 91.77%(2012) from 61.58%(2005). The dominance of Skeletonema caustatum was significantly increased to 51.65%(2012) from 63.58%(2005).