| The Three Gorges Project is one of the most comprehensive water conservancy hub in the world,playing an important role in flood control,power generation,shipping and water supply.However,with the periodic regulation of water storage and drainage,the water environment has undergone major changes.A series of environmental problems have also become increasingly prominent.In recent years,the occurrence of dinoflagellate blooms has been observed in many tributaries of the Three Gorges reservoir area,and the area of blooms has spread from the vicinity of the dam site to the upstream tributaries further aw ay from the dam.It is generally believed that in adverse conditions,dinoflagellates sink to the bottom to form cysts to survive short-term or long-term adverse living conditions;when the conditions are again suitable,the cysts will rapidly germinate into the water,and then dinoflagellate rapid increase in the formation of blooms.Therefore,in order to curb the growing trend of dinoflagellate blooms,the prevention work must be done.And understand the occurrence of dinoflagellate blooms is particularly important.As for the dinoflagellate blooms in the Three Gorges Reservoir area,although studies have been conducted at different levels,there have been few reports on the occurrence of dinoflagellate blooms in the reservoir area.In order to reveal the formation and extinction mechanism of dinoflagellate blooms in the Three Gorges reservoir area,it is particularly critical to clarify the interannual dynamic changes of the cysts in sediments and dinoflagellates in water bodies and their correlation with environmental factors.Ruxi River is located in the ventral area of the reservoir area and is one of the important primary tributaries of the Three Gorges reservoir area.And serious dinoflagellate blooms have occured every year from March to May in the tributaries of the Ruxi River since 2013.In this study,Tujing and Pingshan that the tributaries of Ruxi River were used as the study area.Quantitative PCR was used to quantify the amount of dinoflagellates in the water and sediment of the Ruxi tributary during the whole year.And the correlation analysis and redundancy analysis between dinoflagellate quantity and environmental factors were also carried out.The aims are to explore the ecological occurrence process of the dinoflagellate bloom in Ruxi River and provide theoretical support for the prevention of dinoflagellate bloom in the reservoir area.Research indicates:(1)After morphological identification,it was found that the dinoflagellate species in the water was Peridiniopsis niei.18 S and 28 S rDNA sequences were used to analyze the phylogeny of the dinoflagellates in Ruxi River.The result showed that there was a high similarity(more than 95%)was found among several species of Peridiniopsis and the species in the Ruxi River.Among them,the spec ies in the Ruxi River has a 99.7% similarity with Peridiniopsis niei in Xiangxi River and 100% similarity with Peridiniopsis niei in the East Lake.Therefore,the dinoflagellate species in Ruxi River was identified as Peridiniopsis niei based on molecular and morphological characterizations.(2)Through the verification of specific primer,uPr1 and Upf1can be selected to quantify the dinoflagellates in Ruxi River.Fluorescent quantitative PCR was carried out on Ruxi River water samples.In the upper water,dinoflagellate had the least amount in summer,and then began to grow in autumn until reaching its peak in spring.Environmental factors including water temperature,light,dissolved oxygen,nutrients in water,was found a greatest impact on the copy number of dinoflagellate.Therefore,the change process of dinoflagellate in the upper water body was as follows: the moderate temperature in spring combined with the high TN and TP in water caused a large number of dinoflagellates in the water body.However,with the increase of temperature and light intensity,the number of dinoflagellate decreased significantly in summer.When the water temperature and light intensity began to decrease in autumn and winter,the copy number of dinoflagellate was increasd with the increase of the content of TN and the dissolved oxygen in the water.(3)The variations of dinoflagellates in deeper water kept a same trend with that of the upper water,but the number of the dinoflagellates in latter one was significantly more than that of the former.In the deeper water,the environmental factors limited the number of dinoflagellates were mainly water temperature,TN and TP.In spring,with suitable temperature and higher TP content in water,as well as the vertical migration of dinof lagellate in the upper water body,the number of dinoflagellate in the water body dominates in the seasons.In summer and autumn,the water level in the reservoir area declined with the water discharge,TN,TP content were also relatively low,and there was a small number of dinoflagellate in the upper water body,so the amount of dinoflagellates in the lower layer of the summer and autumn seasons were small.But in winter,the upper layer of water dinoflagellate quantity were more,because the water temperature gradually probably near the temperature of water bloom,as well as TN,TP in the water body increased more than that in summer and autumn,so the amount of dinoflagellate increased greatly.(4)In sediments,the copy number of dinoflagellate was the most in spring,followed by winter,then by autumn and summer.After analyzing the physical and chemical parameters of the Ruxi River sediment,it was found that the sediment temperature in summer> autumn> spring> winter,and the temperature keept at about 20?in spring.The content of TN in the spring mud was the highest,while the TN content in the other three seasons did not show a significant difference.The content of TC in spring mud was generally higher than other seasons,followed by winter,and the content of TP was showed a trendency as winter> autumn> summer> spring.There have a great relationship between the amount of dinoflagellate and temperatureand nutrient in sediment.(5)By comparing and analyzing the copy number of dinoflagellate in the Ruxi River water and sediment,it was found that the copy numbers of dinoflagellate in the upper spring and the bottom mud had no significant difference,but more than those in the deeper stream.In summer,the copy number of dinoflagellate was the lowest in all four seasons,but the number of dinoflagellate copies in the deeper water> upper water> sediment.The differences among the three layers were not abvious in autumn but the highest in upper water.While in winter,the copy of dinoflagellate was significantly more than the lower water bodies and sediments.In general,the trends of dinoflagellate abundance in the upper,lower water bodies and the sediment basically remained the same throughout the year,and the quantity of dinoflagellate in the upper and lower sediment of each season was basically same,while the quantity of the lower body of water generally at least among the three. |
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