| With the global climate change,extreme weather events except more frequency,and extreme hydrological events triggered by extreme weather is becoming more and more attention.The spring snowmelt and summer peak flow are two important hydrological events of the river runoff,and the effects of climate change on these two hydrological processes are particularly acute.Two spatial scales including a plot area of 625 m~2 and a cathment area of 150 hm~2 were the research object which were monitored atmospheric precipitation and output of river runoff throughout the year,and explored soluble organic carbon(DOC)output time dynamic and try to analyze the reasons for such changes during two hydrological events including snowmelt and flood peak periods by high frequency sampling investigation.The snowmelt period in this paper was from March 21,2014 to May 1,2014.The inputs of water and DOC into the soil during the snowmelt period of a water balance plot were 74.2 mm and 0.25 g/m~2,respectively,while the where we outputs were 15.6 mm and 0.22 g/m~2,respectively.The runoff rate reached approximate 21%,but the input and output of DOC were roughly balanced.The relationships between DOC concentration and instantaneous water flow rate varied with soil depths during the peak period of snowmelt.DOC concentration and instantaneous water flow rate were not correlated significantly(P>0.05)at the 5 cm and 35 cm soil depths,but significantly correlated negatively at the 65 cm soil depth(R~2=0.29,P<0.05)and positively at the 95 cm soil depth(R~2=0.43,P<0.05).The instantaneous DOC flux and water flow rate were linearly correlated significantly for all the soil depths(R~2>0.9,P<0.001),with steeper slopes of the linear equations for the soil layers with greater instantaneous water flow rates,suggesting a hydrologically-driven DOC loss.Both DOC and water exported at different soil depths during the snowmelt period followed the order of 35>5>65>95 cm.The amount of water and DOC exported at the 5 and 35 cm soil depths accounted for 70%of the total in the soil profile.The variability in the DOC concentrations tended to converge to low concentration with the soil depth increasing due to the effect of soil retention.The inputs of water and DOC into the catchment during the snowmelt period of a water balance plot were 84 mm and 0.29 g/m~2,respectively,while the where we outputs were 84 mm and 0.38 g/m~2,respectively.Peak period of snowmelt period river runoff flow gradually increased,and fluctuations in the basic remained stable after reaching gentle period;the change trend of river base flow was the same with runoff trend.The base flow index of peak and gentle period were 0.73 and 0.90,respecticvely.This explains regional groundwater was the main supply path for river during snowmelt period.DOC concentration of river also increased significantly during peak period,and significantly reducted and stabled.River DOC concentration during peak and gentle period were range of 2.3-12.4 mg/L and 2.1-7.4 mg/L,resprctively.There were six flood peak during 2014 year.The input and output of catchment were 322 and213 mm respectively,during flood peak period,and the DOC input by atmospheric precipitation and output from river flow were 0.53 and 1.36 g/m~2.As river runoff increase the DOC concentration also increased,but due to the limited DOC pool,DOC concentration of river was quickly reduced.During flood peak period,DOC concentration of river runoff range of 3.21-23.27 mg/L,and the mean was 6.36 mg/L.As time goes by,the relationship between DOC concentration and runoff linear slope was increased,during runoff peak,maybe caused by land soil carbon pool changed.The input of water and DOC in the catchment through atmospheric precipitation was 648 mm and 1.79 g/m~2 respectively,from November 12,2013 to November 11,2014,and the output of water and DOC through river runoff was 538 mm and 3.15 g/m~2 respectively.May and July was the main rainfall time through all the year.Due to the snow cover pass through the winter,although there was less water input,but the input of DOC was the highest.DOC concentration fluctuation throughout the year in atmospheric precipitation was range from 0.13 to 14.24 mg/L,and the average concentration of 0.27 mg/L.The DOC concentration of precipitation was higher in early and late growth period,but lower in middle growth period,and the concentration of the DOC drops gradually in continuous rainfall.DOC concentration of river runoff throughout the year was range from 2.15 to 23.27 mg/L,and the average DOC concentration was 5.86 mg/L.DOC concentration was increased obviously during snowmelt and flood peak period.DOC concentration and river runoff has significant linear positive correlation,and there was the same relationship between DOC concentration and the water temperature.But DOC concentration was negatively related with the water temperature in May and June,and October and November,due to a river runoff flow on its impact.Contrast snowmelt period and flood peak period of river water carbon output contribution throughout the year,We found that snowmelt period DOC output was only about 12%for the year,and the river water volume was only 14%,and snowmelt period DOC rivers concentration of 4.45 mg/L,below the average for the whole year.During flood peak period,water and DOC output of rivers runoff was 43 and 39%in the year and the region has a balanced contribution to the annual carbon output.Average concentration of DOC was 6.36 mg/L,slightly higher than the annual average concentration.Therefore DOC output in snowmelt period did not produce special contribution,and this may be caused by a lack of snowmelt water input and permeability of soil was higher.Flood peak period was the main river water and carbon output time,but the water and carbon output was mainly due to the increased runoff caused,and DOC concentration of river runoff contributed less concentration. |
PDF Full Text Request