Research On Characteristics Of Snow In Forests And Snowmelt-runoff In Forest-watershed In Greater Xing’an Mountains

Snow was solid water in winter, it occupied important position in the processes ofwater circulation and energy flow in Greater Xing’an Mountains. The researches on characteristics of snow and sonwmelt in three types of forests which were Larix gmelinii forest, Populus davidiana and Betula platyphylla forest and Pinus sylvestris var. mongolica forest and processes of snowmelt-runoff were conducted throughthe use of locating observation in the forest-watershed of northern region of Greater Xing’an Mountains. The results:(1) The retention capacity of forests of snow from large to small were Pinus sylves tris var. mongolica forest, Larix gmelinii forest and Populus davidiana and Betula platy phylla forest, The rate of interception by canopy layer was 24.28%、13.98% and 4.99% r espectively. In gradually accumulating, snow water equivalentin in Populus davidiana an d Betula platyphylla forest was always the largest, snow water equivalent reduced most in sunny day, and snow water equivalent in Pinus sylvestris var. mongolica forest was fewest and snow water equivalent reduced least in sunny day, Larix gmelinii forest wa s in between. The rate of snowmelt from large to small were Populus davidiana and Bet ula platyphylla forest, Larix gmelinii forest and Pinus sylvestris var. mongolica forest.T he order of the amount of snow is identical with the order of the snowmelt in the thr ee types of forest, leading to snowmelt in the three types of forest needed almost the same time.(2) Snowmelt-runoff began on April 17 and ended on May 7, amount of snowmelt-runoff fluctuated from 0.076 m3/s to 1.09 m3/s in spring. The whole process of snowmelt-runoff had three different stages which were flood-stage, back-stage and stationary-stage, after the May 6, snowmelt-runoff tend to 0.46 m3/s. The flow was influenced by meteorological factors in the flood-stage, the temperature in the process of snowmelt-runoff existed obvious difference between day and night, snowmelt-runoff increased in 14:00-17:00 period and snowmelt-runoff lessened as temperatures reduced in other periods. Temperature impacted flow of snowmelt greatestly, sensitive coefficient was up to 0.54, surface temperature was second, the increase of shallow soil temperature would cut the snowmelt runoff, rainfall in spring can be formed mixed rain and snow runoff and the greater the rainfall, the greater the runoff through the sensitivity analysis.(3) The average concentration of anions in the snow outside the forest was higher than that of the cation, and the difference between the two was 6.94 times, the concentration of PO43- become the most numerous of all ions, the concentration was 7.98 mg/L, the concentration of Mn become the lowest numerous of all cations, the concentration was 0.078 mg/L. In addition to the K+, other 7 kinds of ions varied "first increased and then decreased" rules with number of snow increasing, the change of Ca2+ and PO43- was larger, however, the change of Mn and NO3- was smaller. In the process of snow accumulation under forest canopy shape, different forest types had different effects on calcium content of snow, the order of three types of forest in the degree of influence from high to low was Pinus sylvestris var. mongolica forest, Populus davidiana and Betula platyphylla forest and Larix gmelinii forest. The snow in the forest produced snowmelt-runoff as temperatures rise in Spring, Ca2+ and PO43- were the main components in snowmelt-runoff, both of them accounted for 78.50%.At the same time, Ca2+、PO43-、Mg2+ and K+ revealed leaching migration compared to atmospheric snowfall, the amount of migration of Ca2+ was the most, migration coefficient was 20.01, however, SO42-、NO3-、Cl- and Mn showed internal storage migration.(4) Snow in forest in addition to providing water and nutrients for the basin, but a certain thickness of snow cover on soil had temperature insulation effects. Snow depth gradually increased from 12.98cm to 28.48cm when the temperature reached to the value from 13.08℃ to 28.03℃ in the observation period, in the process, the change of temperature on bare land surface is severe, the change of temperature at the bottom of snow moderate, temperature difference of bare land surface was 14.61℃, and temperature difference of snow bottom was only 5.34℃, the temperature difference between the bottom of the snow and bare surface increased from 6.89℃ to 18.87℃, the results indicated that the snow cover with certain thickness had the function of buffering the cold air and keeping the temperature of the snow bottom.when snow depth reached above 27cm, and the effect of heat preservation is obvious. The snow-cover delayed the transmission of cold air to the subsoil, when the depth of snow increased from 14.44cm to 34.16cm, the gradient between 10-20cm and 20-30cm decreased by 52.17% and 43.75% respectively, that showed the snow cover can promote the soil temperature distribution. The simulation accuracy on the shallow soil temperature with the help of the long wave radiation, soil heat flux and air temperature is decreased with the depth of the soil layer in winter.