Hydrology And Water Quality Dynamics Pattern And River Health In Songhua River Headstream Basin

Under the influence of human activities and climate change,the depletion of river flow,the deterioration of water quality and the change of natural river course have become the impact factors that damage the healthy development of river ecosystem.Songhua River Basin is one of the seven major river basins in China,the source of river basin is located in Changbai Mountain National Nature Reserve,ecological value is huge,Birthplace Changbai mountain Tianchi is also the border lake between China and North Korea.The health status of Songhua River headstream basin has a direct impact on people’s production and life in Northeast China,as well as the water security at home and abroad.Lack of the evolution analysis of long-term hydrological factors,water quality status and environmental factors of Songhua River headstream basin in the previous studies,and did not establish scientific quantitative river health status,which restricted the restoration of degraded water ecosystem and proposed scientific river management measures.Our research take the headstream basin of Songhua River as the research area,firstly discussed the characteristics and change of hydrological factors in 65 years,and then clarified the spatio-temporal change pattern and key impact factors of water environmental quality in the basin in the past 6 years,to reveal the ecological background of the basin such as hydrological conditions and water environmental conditions.Then the coupling relationship between water quality and hydrology and environmental factors was analyzed.Finally,explored the river health status of Songhua River headstream basin from five aspects: hydrologic integrity,chemical integrity,morphological and structural integrity,biological integrity and sustainability of social service function.The conclusions are as the following:(1)Analysis of evolution characteristics of hydrological elements and sensitivity in the headstream basin of the Songhua River: Precipitation increased,evaporation decreased and runoff fluctuated during the study period.The annual average precipitation in the Toudao Songhua River Sub-basin was higher than that in the Erdao Songhua River Sub-basin.The annual average evaporation and runoff of Toudao Songhua River Basin was lower than that of Erdao Songhua River Basin.The seasonal distribution of hydrological elements in the whole basin is uneven,with summer taking up the largest proportion and that in winter is the least.The spatial distribution of hydrological elements decreased from upstream to downstream.It can be seen that precipitation abrupt change occurred at both ends of the series,evaporation abrupt change of Toudao Songhua River Sub-basin occurred in 2000 and 2002,and Erdao Songhua River Sub-basin in 2005,runoff series that no mutation occurred in the Toudao Songhua River Sub-basin after 1961,while the Erdao Songhua River Sub-basin had frequent mutation during the study period.According to the sensitivity analysis of runoff to meteorological elements,precipitation is the main influencing factor of runoff in the basin.Overall,there is a significant positive linear relationship between annual runoff and precipitation(P<0.01).For every 10 mm increase of precipitation,runoff will increase by 7.3-8.5mm.The correlation between runoff and precipitation in spring,summer and autumn was significantly higher than that in winter.On the whole,evaporation is also a factor affecting runoff change,and the correlation between runoff and evaporation is weak in the basin,but there is a significant positive correlation in spring.In addition,the higher the runoff is,the less precipitation in the basin,and the runoff is more sensitive to precipitation.(2)Analysis of spatial and temporal distribution characteristics of water environment quality in the Songhua River headstream basin and established evaluation model: The water quality of the Songhua River headstream basin has been at the "good" level(reaching the national Class Ⅱ standard)from 2015 to 2020,and has been improving year by year.From the spatial change of water quality in the basin,the water quality condition gradually becomes worse from the upstream to the downstream.The water quality of Toudao Songhua River Subbasin is the worst in autumn,and that of Erdao Songhua River Sub-basin is the worst in summer,but the water quality of the two sub-basins is the best in winter.In addition,IWPImin water quality evaluation model with good stability and excellent performance was established.The model in Toudao songhua River Sub-basin and the Erdao Songhua River Sub-basin were composed of four key water quality parameters(chemical oxygen demand,ammonia nitrogen,total nitrogen and total phosphorus;permangnoate index,dissolved oxygen,chemical oxygen demand,5-day biochemical oxygen demand,respectively),the IWPImin model with entropy weight method has better water quality evaluation results than the WPImin model with maximum membership degree.(3)Variation characteristics of air temperature and water temperature and coupling relationship between hydrology and temperature on water quality in the headstream of Songhua River: Both air temperature and water temperature in the basin fluctuated during the study period,with significant seasonal differences.The air temperature and water temperature in Erdao Songhua River Sub-basin are higher than those in Toudao Songhua River Sub-basin.The overall water quality of the basin is significantly positively correlated with all water quality parameters,temperature and hydrological factors(except runoff of Erdao Songhua River Sub-basin),and the single action of water temperature and the interaction between temperature and meteorology had the greatest impact on water quality.Temperature is the key influencing factor in spring,summer and autumn of Toudao Songhua River Sub-basin.The key influencing factors in spring,summer and autumn are meteorological,temperature and runoff of Erdao Songhua River Sub-basin,respectively.In addition,Spring and autumn are also affected by the interaction between temperature and meteorology,winter is mainly affected by runoff.(4)The health evaluation grades of the Songhua River headstream basin were all at the healthy level(69.5,72.8),and the health evaluation grades of each river were also at the healthy level(66.4～76.7),the evaluation grades of the upper stream is better than those of the middle and lower stream.The scores of functional condition layer of each river section are higher than that of ecological condition layer of corresponding river section.The functional condition layer of the main stream of Toudao Songhua River is at a very healthy level,but the functional condition layer of other river sections and the ecological condition layer of all river sections are at a healthy level.The functional status layer and ecological status layer of the main stream of Erdao Songhua River are all at a very healthy level.In the headstream basin of Songhua River,the health evaluation levels of all the sub-criteria of biological integrity in all reaches of Toudao Songhua River and the sub-criteria of chemical integrity in the middle and lower reaches of Erdao Songhua River are unhealthy or sub-healthy,and the other sub-criteria levels are healthy or very healthy.The degree of ecological flow satisfaction is the key influencing index of the sub-criterion layer of hydrological integrity.Water functional zone is the key influence index of chemical integrity sub-criterion layer.In the sub-criterion layer of morphological structural integrity,there is a great difference in the index scores of the reasonable degree of sewage outlet layout,which has a great influence on this layer.The score of biointegrity sub-criterion was the lowest among the five levels and fish retention index was the key index of this sub-criterion layer.The sub-criteria of social service function sustainability scored higher overall,and the scores of Erdao Songhua River were higher than those of Toudao Songhua River.In our research,the spatial and temporal variation pattern of hydrology and water quality in the headwaters of Songhua River is recognized,the sensitivity of meteorological elements to runoff is explored,and an optimization model for water quality evaluation is established.Then the coupling relationship among hydrology,water quality and environmental factors was revealed.Finally,the health status of rivers in the headwaters of Songhua River is evaluated by constructing an adaptive river health evaluation system.It lays the foundation for scientific management,effective restoration and reasonable control of river health,and has important practical significance.