Protozoan Community Structure Of The Yarlung Zangbo River And Its Relationship With Environmental Factors

The Yarlung Zangbo River is located on the Qinghai-Tibet Plateau and is located in Tibet.It is the longest plateau river in China and the largest river in Tibet.It has many tributaries and abundant water resources.It is known as the"Asian Water Tower".Due to the changes in the natural environment and the continuous enhancement of human activities,the stability of the water environment of the Yarlung Zangbo River has been changed,thereby affecting the community structure of aquatic organisms.Protozoa have the characteristics of wide distribution range,small individuals and short life cycle.They play an extremely important role in the material circulation and energy Flow of the ecosystem,and can respond accordingly to changes in the water environment.Therefore,in this study,the physical and chemical factors of the Yarlung Zangbo River water quality and the perennial protozoa were taken as the research objects.In 2017,the rain season(June-July),the medium season(October-November),and the 2018 dry season(March-April)26 sampling points in the main stream and tributaries of the Yarlung Zangbo River were sampled and surveyed.Based on the sampled data,the spatial and temporal changes of the Yarlung Zangbo River water environment were analyzed,and the quality of the water environment was discriminated.The response strategy of the protozoan community structure of Zhoucong to environmental factors can provide a theoretical basis for the establishment of a safety warning system for the Yarlung Zangbo River.The main findings are as follows:1.Characteristics of spatiotemporal changes of the water environment of the Yarlung Zangbo RiverBased on SOM clustering,26 sampling points of the Yarlung Zangbo River were collected,and the 25 water quality physical and chemical indicators in three seasons were clustered into 4 categories.The difference analysis of the 25 water quality physical and chemical indicators in these four categories was carried out by the Turkey method.The results show that it can be roughly divided into six categories:First,the physical and chemical indicators that are in a downward trend with increasing altitude,including:water temperature,iron,and total phosphorus,of which low altitude the water temperature in the area is high,maintained at about 15?,the water temperature in the high altitude area is low,at about 5?,the iron element is high in the low altitude area,about 1.5mg/L,the other three areas are almost the same,close to 0,the total Phosphorus is higher in low-altitude areas,around0.12mg/L,mid-altitude areas are around 0.05mg/L,and high-altitude areas are lower;the second is the physicochemical index that is increasing with increasing altitude,which is sulfate Ion,the higher altitude area is maintained at about 40mg/L,and the lower altitude area is maintained at about 25mg/L;the third is the physical and chemical indicators that show a"?"trend as the altitude increases,including:nitrate nitrogen,the low altitude area is more Low,salinity,and high altitude areas are low;the fourth is the physical and chemical index showing"N"trend as the altitude increases,which is the flow rate,and the higher the altitude,the faster the flow rate;the fifth is the"V"as the altitude increases The physical and chemical indicators of the trend include:ammonium nitrogen,total nitrogen,calcium,total hardness,silicate ions,and chlorophyll,of which the above indicators are higher in areas with higher altitudes,and lower in the middle areas.In addition,they also include The chemical oxygen consumption is higher in areas with lower altitudes and lower in other altitudes.Six is the physical and chemical indicators that show a“?”trend with increasing altitude,including:p H value,surface dissolved oxygen,The dissolved oxygen,bicarbonate,total alkalinity,magnesium,potassium,sodium,nitrate,chloride,and sulfide in the bottom layer are higher in the middle altitude area of the above physical and chemical indicators.In terms of seasons,the water environment in the wet season is mainly affected by the dissolved oxygen-related factors(surface dissolved oxygen,bottom layer dissolved oxygen);the dry water period is mainly affected by the p H-related factors(water flow rate,p H,bicarbonate,total alkalinity,magnesium Ion,potassium ion,sodium ion,sulfate ion,nitrate ion),but sampling points 4,11 and 26 are mainly affected by water trophic factors(ammonium nitrogen,nitrate nitrogen,total nitrogen,total phosphorus,sulfide,Chlorophyll);the flat water period is the transition period between the high water period and the low water period.The lower Yarlung Zangbo River maintains the rich water period and is affected by the dissolved oxygen-related factors.Influenced by factors,Palon Zangbu is mainly affected by dissolved oxygen related factors in water,but sampling points 11,13 are affected by dissolved oxygen consumption related factors(water temperature,iron,calcium,hardness,silicate ions,chemical oxygen consumption,Mineralization),the upper Niyang River,Lhasa River and Nianchu River are mainly affected by dissolved oxygen consumption factors.2.Judgment of water quality of the Yarlung Zangbo River and analysis of influencing factorsAccording to the weight judgment,the four types of water environment of SOM clustering are defined as the water quality physical and chemical indicators of light contribution,moderate contribution,high contribution and serious contribution according to the degree of contribution.Constructing the Yarlung Zangbo River Water Environment Quality Discrimination Index(Po S),which divides the Yarlung Zangbo River water environment into 5 categories,very good,good,normal,poor,and very poor.It is poor.The flat water period is the transition period between the high water period and the low water period,and the water environment quality varies greatly in each river section.Sort out the indicators that the relative contribution of the Yarlung Zangbo River in different seasons is high or serious(Q_f>10%).The water temperature appears 49 times,the silicate occurs 33 times,the sulfide appears 31 times,the ammonium nitrogen appears 18times,and the total nitrogen appears 14 times.The physical and chemical indexes of water quality with higher frequency appear,pointing out that the physical and chemical indexes that have greater impact on the Yarlung Zangbo River are water temperature,silicate,sulfide,ammonium nitrogen and total nitrogen.3.The structural characteristics of the protozoan community in the Yarlung Zangbo RiverA total of 33 genera of 31 families and 31 families of protozoa from Zhouluo were identified in the Yarlung Zangbo River.Among them,there are 2 families,18 families and 19genera in the wet season,mainly Difflugia,Cyphoderia,and Hemiophrys;in the flat water period,there are 2 families,16 families and 16 genera,mainly Difflugiaand and Glaucoma are the main species;there are 2 families,15 families and 15 genera in the dry season,mainly Difflugia and Tetrahymena.In terms of along the way,the protozoan species richness and richness index of the Lhasa River and Nianchu River periclusters during the high water period are significantly different from the main stream of the Yarlung Zangbo River and the lower reaches of the Palongzangbu River(P<0.05).The species richness,total abundance,Shannon index,and richness index are the highest,with average values of about 11,800/m~2,1.15,and 1.5 respectively,while the upper reaches of the Niyang River are the lowest,at 3,210/m~2,0.68,0.25,the evenness index of the main stream of the Yarlung Zangbo River and the lower reaches of the Palongzangbu is the highest,with an average value of 0.73,and the lowest is the Lhasa River and the Nianchu River,which is 0.44;,Richness index is higher than other sections of the Yarlung Zangbo River(P>0.05),while Shannon index and evenness index are just opposite(P>0.05),the species richness minimum value is less than 3,the maximum value is 3,total abundance,richness The minimum value of the index is about 8300/m~2,0.19,the maximum value is about9700/m~2,0.20,the minimum value of the Shannon index and the evenness index are about0.56 and 0.53,and the maximum value is about 0.64 and 0.53,respectively;the dry season is the lower reaches of the Yarlung Zangbo River The protozoan species abundance and total abundance of the periclusters are lower than those of other river sections,and the total abundance is significantly different(P<0.05).The species richness of the lower reaches is less than 3 and the total abundance is about 280/m~2.The species richness in the upper reaches exceeds 3,and the total abundance is around 9600/m~2.The Shannon index,evenness index,and richness index in the lower reaches of the Yarlung Zangbo River are higher than those in other reachs(P>0.05).The lower reaches are 0.87,0.97,and 0.26,respectively.The reach of the river is 0.80,0.66 and 0.25 respectively.In terms of seasons,the weekly protozoan species richness,Shannon index,evenness index,and richness index are the lowest in the flat water period,respectively around 3,0.6,0.5,0.2,and there is no significant difference between different seasons(P>0.05),the species richness,Shannon index and richness index are the highest in the wet season,around 4,0.8,and 0.5,respectively,and the evenness index is the highest in the dry season,about 0.7,and the total abundance in the wet season is lower than other seasons(P<0.05),700/m~2,and the highest abundance in the average period is 8,500/m~2.4.Analysis of the relationship between the protozoan community structure of the Yarlung Zangbo River and environmental factorsCanonical correspondence analysis(CCA)shows that the protozoan community structure of the Yarlung Zangbo River perimeter cluster is affected by multidimensional environmental factors.Among them,water temperature,total alkalinity,chemical oxygen consumption,salinity,and total nitrogen are the main environmental factors that affect the protozoan community structure in the rain season;elevation,water temperature,surface dissolved oxygen,and Flow velocity are the influences in the medium season.;altitude,p H value,surface dissolved oxygen,total nitrogen,and total phosphorus are the main environmental factors that affect the protozoan community structure in the dry season.The multiple regression tree(MRT)model was used to predict the influence of environmental factors on the spatial distribution of the protozoan community structure in the perimeter.The results show that total alkalinity,water temperature,and chemical oxygen consumption have a greater impact on the spatial distribution of the protozoan community structure in the rain season.Among them,total alkalinity is the first influencing factor,with a threshold of 54.98 mg/L.The value is 18.68?,and the chemical oxygen consumption threshold is 25.12mg/L.Altitude,p H value,water temperature and chlorophyll have a greater impact on the spatial distribution of the protozoan community structure in the medium season,of which altitude is the first influencing factor,the threshold is 2419m,the p H threshold is8.44,and the water temperature threshold is 3.4?,The chlorophyll threshold is 0.056mg/L.Altitude,Flow velocity,and surface dissolved oxygen have a greater impact on the spatial distribution of the protozoan community structure in the dry season.Among them,altitude is the first influencing factor,the threshold is 1524m,the Flow velocity is 0.035 m/s,and the surface dissolved oxygen 10.41mg/L.Based on the research results of this article,it is recommended to carry out long-term monitoring of the Yarlung Zangbo River water environment,strengthen the attention to the perennial protozoa and key environmental factors,increase the treatment of agricultural pollution and mining wastewater,improve the construction of urban sewage pipeline network,weaken from the source,Control the external pollution sources of water bodies,and actively promote the sustainable and healthy development of the ecological environment of the Yarlung Zangbo River waters.