Studies On The Community Characteristics Of The Phytoplankton And Water Quality Evaluation In Mudanjiang Basin

Mudanjiang watershed is the typical natural river system in northern cold region,showing obvious water rich period,flat water period and low water period.The growth and multiplication of phytoplankton are closely related to different seasons.At the same time,the growth and reproduction of phytoplankton are largely influenced by the change of water quality.In recent years,with the rapid progress of China's economy,the water pollution of the Mudanjiang river basin is aggravated and the water quality is obviously reduced,while the Ning'an section of the Mudanjiang River Basin and the tributary of the Mudanjiang River are the drinking water sources of the citizens of Ning'an city and the citizens of Mudanjiang,which directly affects the life safety of the residents of Ning'an city and the Mudanjiang urban residents.The water quality of the Mudanjiang basin also affects the downstream waters of the Songhua River directly.The water quality directly affects the ecological safety of aquatic organisms in the lower reaches of Songhua River.Therefore,the study of the corresponding relationship between the different water periods of the Mudanjiang basin,especially the phytoplankton and the environment,grasps the characteristics of phytoplankton community structure and succession law,and makes full use of the sensitive characteristics of phytoplankton to the environment,which is beneficial to the comprehensive and objective reflection of the quality of the water environment,and can provide a reliable scientific basis for the management decision of the Mudanjiang River Basin,especially the important water source.It is of great significance for improving water quality,ensuring water quality and ensuring the safety of urban residents.In this study,eight monitoring points were set up in the Mudanjiang main stream.Based on the environmental characteristics of the northern cold region,the paper investigated the Mudanjiang basin in the dry period,the flat water period and the abundant water period in 2013.Through the qualitative and quantitative analysis of phytoplankton and the water environmental factors at the corresponding sampling points,the community structure characteristics of the phytoplankton in the Mudanjiang basin were revealed.The relationship between phytoplankton biomass and water environmental factors was investigated by grey correlation analysis,and the aquatic nutrient status of various sampling points in Mudanjiang basin was evaluated by using phytoplankton biomass,diversity index,organic pollutant index and TLI index of comprehensive nutrition status.The results show that:It is found that the phytoplankton in the Mudanjiang basin belonged to 238species of 88 genera in the Mudanjiang River Basin.In general,the Mudanjiang basin is from the dry period,the flat water period and the abundant water period,and the succession of the phytoplankton species in different periods is diatom diatom+green algae-diatom+green algae.There are significant differences between phytoplankton abundance and biomass in sampling and dry season in Mudanjiang basin.The annual fluctuation range is 4.24×10⁵/L⁴.20×10⁶/L,the highest is the S6 sampling point at the flat water stage,and the lowest is the S1 sampling point in dry season.Biomass in the whole year is between 0.24 mg/L⁴.29 mg/L,the same is the S6 sampling point in the flat water period,and the lowest in the dry season isS1 sampling sites.The abundance and biomass time distribution of phytoplankton in the Mudanjiang River Basin were the highest in the flat water period and the lowest in the dry water period.The level distribution was higher in the lower reaches of the lower water period,higher in S5 and S6,lower in the lake reservoir area S1 and S7,higher in the flat water period except for the S4 sampling point,and the opposite in the water rich period,and the abundance and biomass of the S4 sampling point increased significantly.It is obviously different in different water environment factors.NH₄⁺-N and TN has the similar regulation in different water level and sites.It is that the values of upstream is lower middle stream and downstream,but TP has not similar regulation,except for in lower water level.The values of COD and BOD are obviously lower in S2 and S4.The values of Chla have not obviously in different sites and water level.The variations of water temperature,transparency,pH value,dissolved oxygen,ammonia nitrogen,biological oxygen consumption,permanganate index,total nitrogen,total phosphorus and chlorophyll content in different periods of the Mudanjiang River Basin in 2013 are the same.The trend of the changes in the water period,the sampling points of the ammonia nitrogen and total nitrogen is consistent.The collection is reflected in the upstream waters<middle reaches of the lower waters<the downstream waters,but the change of total phosphorus presents this rule in the dry period.Outside the law,the change trend of other sampling points is not obvious.As the water source of the S2 West Pavilion and the water source area of the sea wave River,the permanganate index and the biological oxygen consumption are significantly lower than those of the other sampling points,and the trend of each sampling point in each water period of the chlorophyll is different.The results of grey correlation analysis shows that the main factors affecting the biomass of phytoplankton in the Mudanjiang basin were TP,water temperature and BOD₅,and the main factors affecting the phytoplankton biomass in the Mudanjiang basin are TN,water temperature and pH,and the main factors affecting the phytoplankton in the Mudanjiang basin are pH,DO and water temperature.It can be seen that the main factors that affect the abundance of phytoplankton in different water periods are different.The most influential factors are the nutrient salt and the water temperature,and the most influential factors are pH and DO,and the water temperature is still the important factor affecting the phytoplankton in the cold region.The results of phytoplankton biomass,phytoplankton diversity index,organic pollution evaluation index and comprehensive nutritional status index are more consistent,but phytoplankton abundance indexes are heavily evaluated.Phytoplankton abundance should be abandoned to evaluate the water quality of Mudanjiang basin.According to the results of the comprehensive use of various indicators,the whole Mudanjiang basin is in the poor middle nutrient water body,but there is a potential eutrophication trend in the S6 and S7 sampling points with high phytoplankton biomass and high comprehensive nutritional status index,which should be paid close attention to.