Vertical Migration Of Snow Melt Water And Nitrate Nitrogen During Snowmelt

In the northeastern part of China,snowfall in winter forms a layer of snow on the ground.The fresh water formed by the melting of snow is a very important water resource in spring,which is of great significance to people’s production,life and cultivation.Nitrogen in the snow infiltrates into the soil with the snow melt water,including nitrate nitrogen that can be absorbed and utilized by plants,but there are few studies on the infiltration law and simulation of nitrate nitrogen in the process of snow melting.Therefore,this paper uses the indoor simulation method to study the vertical migration process of snow melting water and nitrate nitrogen in the process of snow melting,and to explore its migration law and influencing factors.The test soil is the brown soil of the comprehensive experimental base of the College of Water Conservancy of Shenyang Agricultural University.The measurement indicators include snow melting depth,thawing depth,snow surface temperature,snow temperature,mixed layer temperature,snow layer water holding capacity,soil water content,snow melting water volume and NO₃^--¹⁵N abundance.The migration of nitrate nitrogen was carried out using the tracer method.Due to the limitations of natural snow extraction,this study used artificial snow instead of natural snow to test and analyze the difference between it and natural snow.After the test,the Hydrus-1D model was used to simulate the migration process of snowmelt water and nitrate nitrogen in the soil.The simulated values were compared with the measured valuesto determine the applicability of the model.The following main conclusions were drawn through experiments and simulations:（1）In the artificial snow and natural snow difference analysis test,the physical snow snow depth,snow melting water,snow surface temperature and snow temperature are not different from natural snow,and the correlation between artificial snow and natural snow melting depth The highest,the correlation coefficient reaches 1.000,the correlation coefficients of the snow surface temperature,snow temperature and snowmelt water volume are 0.961,0.969 and 0.967,respectively.And there is no significant difference between artificial snow and natural snow in the case of solute infiltration.Therefore,the subsequent related snowmelt simulation test can use artificial snow instead of natural snow.（2）The infiltration process of snowmelt water in natural snow is mainly related to the depth of snowmelt,the temperature of snow surface and the temperature inside snow.The depth of snowmelt affects it the most,and the temperature of snow surface and temperature in snow are second.Correlation,the amount of snow melted increases with the increase of the depth of snowmelt,and the law is the same as natural snow in artificial snow.（3）In the process of infiltration of frozen snow,the infiltration results are mainly reflected in the change of soil water content,and the soil thawing depth and soil water content are obviously linear with the snow infiltration.Under different soil thawing depth conditions,soil water content showed a trend of decreasing gradually.Correlation analysis was carried out between layered soil water content and soil depth.The correlation coefficient between the two was-0.904.As the soil temperature rises,the ice in the soil melts,and the infiltration capacity of the snow-melted water increases.When the soil is completely melted,the water content of each layer is greater than the initial value.The infiltration of snowmelt water in frozen soil is also related to snowmelt depth,snow surface temperature and mixed layer temperature.The increase of snow melting depth,snow surface temperature and mixed layer temperature can promote the infiltration of snowmelt water and it is found during the test.Two ice layers will be formed between the upper surface of the soil and the snow and between the soil.The first ice layer on the surface of the soil will not accumulate with the temperature after the thickness of the ice layer reaches about 1 cm in a certain amount of snow.Continuous growth.The second ice layer is in the middle of the soil layer.As the snow melts,the position of the second ice layer gradually moves to the depth of the soil.As the frozen soil continues to melt until it melts through,the second ice layer disappears.（4）The vertical migration process of NO₃^--¹⁵N in snow is mainly related to snow surface temperature,snow temperature,snow melting depth and snow melting water,and is not closely related to snow layer water content,including snow melting water volume and NO₃^--¹⁵N concentration.The relationship of change is the largest,and the two are significantly positively correlated.The correlation coefficient between artificial snow and natural snow is0.880.Principal component analysis of each factor shows that the first principal component is the snowmelt water factor and the second principal component is snow.The combination of internal temperature and snowmelt depth;regression analysis showed that the combined effect of snowmelt water and snowmelt depth was more correlated with NO₃^--¹⁵N.Artificial snow is consistent with natural snow conclusions.（5）The infiltration process of NO₃^--¹⁵N in frozen soil was significantly positively correlated with soil water content,and it always decreased with the decrease of soil water content,which was consistent with the infiltration law of NO₃^--¹⁵N in snow.At the same time,the infiltration of NO₃^--¹⁵N in frozen soil was significantly negatively correlated with the depth of soil thawing,and decreased with the increase of soil thawing depth.（6）Using the Hydrus-1D model to simulate the process of melting the snow layer,the process of snowmelt water migration in the soil and the migration process of nitrate nitrogen in the soil,and compare the simulated value with the measured value and the fitness test.The simulation of the snow melting process,R²<0.75,NSE value<0.8,indicates that the overall level is credible,but the simulation process error is large,RMSE=1.5093 cm,considering the general fitting effect.The simulation of the migration process of snowmelt water in the soil,except for the simulated effect of soil thawing 5 cm,the other three groups have better simulation results.The simulation of the migration process of nitrate nitrogen in the soil,under the conditions of soil thawing 5 cm,10 cm,15 cm and 20 cm,the measured value and the simulated value can be well matched except for the individual values;The fitting test of R²,NSE and RMSE was carried out,and the results of each parameter were combined to show that the simulation fits of the four groups were good.