The Spatial And Temporal Variations Of Benthic Diatom Communities In Different Estuarine Mudflats

The estuary mudflat is an important part of the coastal marine ecosystem.It has rich biological resources and huge ecological service value.It is the habitat,breeding ground and foraging place for hundreds of benthic organisms.Benthic diatoms are important primary producers in the estuary mudflat ecosystem.The temporal and spatial variation of their community structure can significantly affect the primary productivity of the estuary mudflat.During the period from 2014 to 2016,we carried out ecological surveys in the spring,summer,autumn and winter seasons in the Daliao River estuary of Liaoning,Hangu River estuary of Tianjin,Yellow River estuary of Shandong,Dagu River estuary of Qingdao,Northern Suzhou shoal of Jiangsu,Yangtze River estuary of Shanghai,South bank of Hangzhou Bay in Cixi,Zhejiang,Min River estuary of Fujiang,Jiulong River estuary of Xiamen,Pearl River estuary of Guangzhou,Dongzhai port of Hainan.Based on this investigation,the spatial and seasonal variation characteristics of benthic diatoms in estuarine mudflats in China were analyzed,and the main environmental factors affecting the structure of benthic diatoms in estuarine mudflats were further analyzed in combination with the temporal and spatial variation of several environmental factors.The main research results are as follows:(1)The species diversity of benthic diatoms in 11 estuarine mudflats showed significant spatial and seasonal differences.In terms of space,the species diversity of benthic diatoms was significantly different from north to south,and the ShannonWeaver Index in the estuary area south of the Yangtze river estuary was mostly higher than that north of the Yangtze river estuary.Among them,the high value area mainly occurs in the Minjiang River estuary of Fuzhou,Fujian,and the Jiulong River estuary of Xiamen,south of the Yangtze River estuary,while the low value area mainly occurs in the Shandong Yellow River estuary,north of the Yangtze River estuary.The species diversity of benthic diatoms also showed a significant difference between the north and the south in terms of seasonal change;In the estuary area north of the Yangtze River estuary,the Shannon-Weaver Index in autumn is significantly higher than the other three seasons.(2)The biomass(diatom absolute abundance and chlorophyll a concentration)of benthic diatoms in 11 estuarine mudflats also showed significant spatial and seasonal differences.Spatially,the diatom absolute abundance in the area south of the Yangtze River estuary is slightly higher than that in the north.In terms of seasonal variation,the change of season in the area north of the Yangtze river estuary was relatively large.The diatom absolute abundance in most estuaries was significantly higher in autumn than in other seasons,and slightly higher in summer than in winter and spring.The seasonal variation of diatom absolute abundance in the estuary area south of the Yangtze River estuary was not significant.The diatom absolute abundance in most estuaries was slightly higher in autumn,and there was no significant difference between other seasons.In space,the chlorophyll a concentration shows a high-low-high variation from north to south.The high value occurs at the Daliao River estuary of Liaoning and Hangu River estuary of Tianjin,while the low value occurs at the Northern Suzhou shoal of Jiangsu,Yangtze River estuary of Shanghai and South bank of Hangzhou Bay in Cixi,Zhejiang.In season,chlorophyll a concentration in most estuaries is higher in spring and lower in autumn.(3)The correlation analysis between benthic diatom community structure and various environmental factors showed that the spatial and seasonal characteristics of benthic diatom community were significantly affected by temperature precipitation and nutrient changes.The sediment grain size and DIN concentration in estuarine sediments may be the important factors causing the spatial difference of benthic diatom communities.The lowest species diversity and biomass in the yellow estuary may be related to the runoff of the river with larger grain size in the coarser sediments and the significant phosphorus limitation.The higher silicate concentration and lower Si/P ratio in autumn may be one of the reasons for the higher species diversity and biomass of benthic diatoms in most estuary mudflats.In addition,the foraging action of benthic animals would affect the biomass of living diatoms,resulting in a great difference between the concentration of chlorophyll a and the diatom absolute abundance.