Changes Of Nitrogen And Phosphorus Components And Their Influencing Factors In The Upper Reaches Of Shule River

Global warming has become an incontrovertible fact and has had significant effects on a global scale.Glacier and permafrost regions are particularly sensitive to temperature changes,with climate warming,various aspects such as temperature,precipitation,vegetation,soil,hydrology and nutrient cycle will inevitably change.The Shule River originates from the western section of the Qilian Mountains on the Qinghai-Tibet Plateau and is the second largest river in the Hexi Corridor.As an inland river in arid regions,its importance to the life,production and ecological environment of the people in the basin is self-evident.Some studies have analyzed the impact of climate change on the hydrological process of the Shule River,however,it is not clear how the concentrations of nutrients such as nitrogen and phosphorus components in the water in the upper reaches of the Shule River change with climate changing.In this study,different water bodies in the upper reaches of the Shule River in the central and western section of the Qilian Mountains on the Qinghai-Tibet Plateau were taken as the research objects that collected water samples from the Shule River,snow samples,groundwater and spring water samples in different months in 2018 and 2019.The pH,electrical conductivity（EC）,total nitrogen（TN）,total dissolved nitrogen（TDN）,ammonia nitrogen（NH₄⁺-N）,nitrate nitrogen（NO₃^--N）,total phosphorus（TP）,total dissolved phosphorus（TDP）and phosphate(PO₄^3--P)concentrations were measured respectively in each water sample,analyzing nitrogen and phosphorus components in river water samples and their temporal and spatial variation characteristics,conducting correlation analysis with nitrogen and phosphorus components in snow samples,spring water,and groundwater.In addition,according to the collected data of temperature and precipitation in the basin,the influence on the concentration of nitrogen and phosphorus components in river water was analyzed.The results of this study are as follows:（1）The average pH of the Shule River was 7.43,the river water was weakly alkaline;The average conductivity was 793.24μs·cm^-1,the lowest value in August,there was no obvious seasonal variation in pH and conductivity.（2）The nitrogen concentration in the Shule River water was 74.27-1265.83μg·L^-1,and the phosphorus concentration was 4.87-272.08μg·L^-1,which increased by 10.43%-29.79%compared with the previous year,the phosphorus concentration increased 25.26-51.99%.The nitrogen and phosphorus components showed obvious seasonal variation characteristics,in which the TN concentration was the highest in spring,followed by winter,summer and autumn,while the concentrations of TDN,NO₃^--N,NH₄⁺-N,and TP were relatively high in spring,the concentrations of TDP and PO₄^3--P were higher in summer,nitrogen increased in summer as a whole,the concentrations of TP and TDP in phosphorus increased in summer,the concentration of PO₄^3--P had no clear rule,while the changes in other seasons showed a fluctuating trend.The dissolved inorganic nitrogen in the river water was mainly in the form of NO₃^--N and NH₄⁺-N,and the phosphorus was mainly in the form of granular phosphorus.（3）The spatial variation of nitrogen and phosphorus component concentrations in Shule River water was relatively complex,the spatial variation of nitrogen and phosphorus components indicated that the effects of different seasons had inconsistent changes in river water nutrients,the sources of river water nutrients in different seasons were diverse.Among them,the impact of spring had a higher contribution rate to the spatial variation of TN concentration than other seasons;The spatial variation of TDN and NO₃^--N concentrations in summer was relatively stable,and the contribution ratios to nutrients in spring,autumn and winter were the same as TDP concentrations,which was no definite rule to follow;The spatial changes of NH₄⁺-N,TP,PO₄^3--P concentrations were mainly reflected in spring and autumn,indicating that except the main seasonal changes,their own stability was also an important factor.（4）The nitrogen concentration in Gahe ranged from 21.43 to 1866.25μg·L^-1,and the nitrogen concentration in Suli was from 23.75 to 1342.50μg·L^-1,the concentration of TN varied greatly between spring and autumn,but it was similar in summer,TDN and NO₃^--N concentrations were generally higher than those in Gahe,there was no significant difference in NH₄⁺-N concentration between the two groups,but the change trend was inconsistent,the main changes were related to the melting of glaciers and snow covered in the region.（5）The pH of precipitation in Shule River was about 6.79,the rain water was acidic;The conductivity was low,the average value overall 20.86μS·cm^-1,which was mainly related to the absorbed gas and ions in the precipitation process.The concentrations of TN,TP,TDP and PO₄^3--P showed no monotonous trend,while TDN showed an increasing trend in summer,NO₃^--N and NH₄⁺-N showed a decreasing trend in summer,the nitrogen concentration was 48.00-2867.5μg·L^-1,the concentrations of phosphorus ranged from 1.00μg·L^-1to 233.75μg·L^-1,there was a strong correlation between nitrogen and phosphorus components,showing the sources were consistent.（6）The overall pH of the groundwater in Shule River was 6.95,the groundwater was acidic;The average conductivity was 186.33μS·cm^-1,the pH and conductivity in the groundwater did not fluctuate greatly with the month.The nitrogen concentration of groundwater showed an increasing trend in summer,its concentrations ranged from 6.00 to 2111.25μg·L^-1,the concentration of phosphorus was 2.00-282.50μg·L^-1,TP,TDP and PO₄^3--P had no definite time variation except that they were abnormally high or low at the beginning of summer.（7）The background value of nitrogen in snow samples was in the range of 50.50-940.00μg·L^-1,phosphorus was in the range of 17.50-62.50μg·L^-1,which was generally lower than that of river water;the overall concentration of nitrogen and phosphorus components in spring water was in autumn>Spring>Summer,the nitrogen concentration in spring water ranged from 10.00-1045.00μg·L^-1,the phosphorus concentration was 12.50-101.25μg·L^-1,at the end of autumn,the concentrations of TN and NO₃^--N were higher than those of river water;Its combined action with precipitation and groundwater,as well as temperature and precipitation in different seasons were important factors affecting the changes of nitrogen and phosphorus components in river water at different altitudes.