Study On Accumulation And Migration Of Nitrogen And Phosphorus During Snow Cover And Snowmelt In Ridge Cropland In Black Soil Region Of Northeast China

Although the river runoff during the snowmelt period in Northeast China is not high,the river water pollution is relatively serious,which is closely related to the non-point source pollution during the snowmelt period,but so far there are few related studies.Although there have been some research results on snowmelt erosion and nitrogen-phosphorus migration in the cold season at home and abroad,the snowfall accumulation,the process of snowmelt erosion and the impact on nitrogen and phosphorus migration are rarely considered.The ridge cropland is widely distributed in the black soil area of??northeast China.In the snowmelt period,crop cover is lacking,and the exposed surface is more susceptible to snowmelt runoff erosion,which makes the nitrogen and phosphorus migration and deposition process during the snowmelt period different from the rainy season slope erosion.In order to explore the above problems,this study selected the Jixing small watershed in Meihekou of Jilin Province as the observational community.Through the arrangement of new snow,snow and snow melting observation communities,the characteristics of new snow,snow,snow melting chemical and nitrogen and phosphorus accumulation and migration were obtained.The following conclusions:?1?The average value of fresh snow p H is 5.11±0.51,which is acidic.Up to 66.9%of the acid snow water in the snowfall is neutralized,and the neutralization capacity is mainly provided by Ca²⁺and NH₄⁺.The conductivity of the 10 snowfalls varied from 34.1-51.5 us/cm with an average of 43.06 us/cm.The p H value is highly correlated with conductivity.The average concentration of anion and cation in fresh snow is NO₃^->SO₄^2->Cl^->PO₄^3->NO₂^-,Ca²⁺>K⁺>NH₄⁺>Mg²⁺>Na⁺,and the main cations and cations of Xinxue are NO3-And Ca2+,which accounted for 39.4%and 10.72%of the total ions,respectively.The coefficient of variation of NO₂^-content is the largest.The total nitrogen varies from 4.01 mg/L to 8.93mg/L.Organic nitrogen and nitrate nitrogen are the main components of total nitrogen.The change of total phosphorus content in fresh snow is not obvious,similar to PO₄^3-,indicating that the phosphorus content in the test area is unstable.The average content is 3.91 mg/L,and PO43--P accounts for 6.26%?33.93%of total phosphorus.?2?The p H of the snowy slope is between 5.57-6.87,with an average of 6.14,and the p H of the sunny slope is between 5.53-6.38,with an average of 5.86.The electrical conductivity of the shady slope is generally stable,with a range of 41.57us/cm-63.87us/cm,with an average of 52.63us/cm,and a solar slope conductivity range of 37.42us/cm-62.38us/cm.The average value is 49.86us/cm,and the conductivity is significantly negatively correlated with the depth of the snow layer.As the snow depth increases,the snow conductivity decreases gradually.In the snow,NO₃^-,SO₄^2-,Ca²⁺,Cl^-,Mg²⁺,K⁺,Na⁺content shading>sunny slope,in the snow period,the order of each ion is NO₃^->NH₄+>SO₄^2->Ca²⁺>Cl^->Mg²⁺>K⁺>Na⁺>NO₂^->PO₄^3-,NO₃^-the highest concentration,the average is 5.06mg/L,the NH₄⁺is 4.37mg/L,the Mg²⁺,Ca²⁺content surface layer 0-10cm is lower than the bottom layer 10-20cm,SO₄^2-,NO₃^-and NH₄⁺are consistent.Both the surface layer 0-10cm is larger than the bottom layer 10-20cm.The overall ion content decreased slightly with the accumulation of snow.The total phosphorus content in the sunny slope is less than that on the slope and the slope,and the total nitrogen content is higher than that on the slope and the slope.The total phosphorus content of the shady slope is>slope>slope>slope,the concentration is 3.21mg/L,2.75 mg/L,1.62 mg/L.The total nitrogen content of the sunny slope was less than that of the slope and the slope,and the concentrations were 4.48 mg/L,6.59 mg/L,and 6.22 mg/L,respectively.The total nitrogen in the snow is dominated by NO₃^-—N.The total nitrogen content in the surface of the sunny slope is larger than that of the bottom layer.With the extension of snow accumulation time,the surface layer content increases.The total nitrogen surface of the shady snow is 0-10cm larger than the bottom layer10-20cm,and the total nitrogen content of the surface of the shady slope is 3.31-5.94mg.Between/L,the average content of the bottom layer is between 3.18-5.69 mg/L.The stratification of total nitrogen and total phosphorus in snow is not obvious.?3?The Yin and Yang Slope snowmelt production flows lasted for 5 days,the sunny slope was from March 2 to March 6,and the shady slope was from March 10 to March 14.The snow melting on the sunny slope is mainly affected by radiation,and the snow melting on the shady slope is mainly affected by temperature.The daily instantaneous runoff of snowmelt gradually increases,and finally decreases slowly.The instantaneous runoff of the sun slope on March 3 at 12:28 is 7.8L/min.On the 11th of the year,the runoff was the largest,the daily runoff was the second on March 12,and the runoff was the smallest on March 10,because the temperature was high on March 11 and March 12,and the snow melted..The snow melting time on the sunny slope is 8 days earlier than the melting time of the snow on the slope.The p H value fluctuated with the number of snow melting days.The p H varied between5.22-5.655.The p H value of the sunny slope was slightly lower than the p H value of the shady slope.The reason for the analysis was that the surface soil of the shady slope melted and was released under the weathering of the rock.Part of Ca²⁺and CO₃^2-enter the snowmelt water,causing the p H to increase.The conductivity decreased first and then decreased with the number of snow melting days.The sunny slope ranged from 63.69us/cm to 118.19us/cm,and the shaded slope ranged from 54.37us/cm to 66.65us/cm.The conductivity of the sunny slope is smaller than that of the shady slope.The reason is that the surface soil of the shady slope melts,and some ions in the snowmelt runoff migrate into the topsoil.In the early stage of snowmelt,the ion content in the runoff is relatively high.The 30%snowmelt water produced by the ablation of the sunny slope releases 53%of the chemical ions in the snow,and the 30%of the snow melted by the ablation begins to dissolve 65%of the chemical in the snow.Ion release.The runoff is highly correlated with each ion.The total nitrogen content of the sunny slope increased first and then decreased with the number of snow-melting days.On the third day of snow melting,the maximum value reached 454.4g.The total nitrogen and total phosphorus content of the sunny slope was far greater than the total nitrogen and total phosphorus content of the shady slope.The reason is that the soil layer has begun to thaw when the snow on the slope is melted,and most of the snow melt water infiltrates into the soil,resulting in a decrease in total nitrogen content.The total phosphorus content in the yang and shady slopes increased first and then decreased with the snow melting days,and reached the maximum at 269.59g and 106.86g respectively on the third day of snow melting.