老爷岭多年冻土小流域春季冻融期径流溶解性有机碳变化特征

Characteristics of stream dissolved organic carbon in the Laoyeling permafrost watershed during spring freeze-thaw period

溶解性有机碳(DOC)的输移过程是流域碳循环中重要的组成部分,对全球碳循环产生重要影响。以大兴安岭多年冻土区的典型森林小流域—老爷岭流域为研究对象,获得2021年4月9日到6月30日冻融期降雨量、气温、土温等气象数据及逐日径流量、径流DOC浓度,计算了冻融循环期(4月9日—28日)和融化期(4月29日—6月30日)流域径流DOC的输出通量,揭示了径流DOC浓度及输出通量的影响因素。结果表明:(1)研究时段内,老爷岭流域径流DOC浓度变化范围为3.88—33.75 mg/L,流域上游的径流DOC浓度变化趋势与下游基本一致,DOC浓度随着温度的升高呈现下降趋势,4月份平均径流DOC浓度明显高于5、6月份。(2)研究时段内流域径流DOC总输出通量为3215.48 kg/km^(2),其中5月径流DOC输出通量高于4、6月份。径流量与径流DOC输出通量存在显著正相关关系(P<0.05),是流域DOC输出通量的主导因素。(3)研究时段内流域DOC浓度与平均气温呈极显著负相关(R^(2)=0.5048,P<0.001);降水样品中的DOC浓度变化范围为1.06—9.42 mg/L,显著低于径流DOC浓度;土壤中DOC含量变化趋势与径流DOC变化趋势一致,0—10 cm、10—20 cm土壤平均DOC浓度范围为77.57—133.99 mg/L。(4)冻融循环期平均日径流DOC浓度(24.02 mg/L)显著(P<0.05)高于融化期(14.64 mg/L),而融化期平均日DOC输出通量(48.02 kg/km^(2))是冻融循环期(9.52 kg/km^(2))的5倍。研究结果揭示了大兴安岭多年冻土小流域春季冻融期径流DOC的输移特征及其影响因素,对理解多年冻土区碳循环有重要意义。

Dissolved organic carbon(DOC)is the largest organic carbon pool in natural water body.The transport process of DOC is an important part of the carbon cycle in watersheds,which has significant impacts on the global carbon cycle.In order to investigate the characteristics of stream DOC flux and its influencing factors during the spring freeze-thaw,the rainfall,air temperature,soil temperature,daily runoff and daily stream DOC concentrations in a permafrost small watershed of Laoyeling in the Da Hinggan mountains were observed during the freeze-thaw period from April 9 to June 30 in 2021.The stream DOC flux was calculated from the freeze-thaw cycle period(April 9-28)and the thaw period(April 29-June 30),respectively.The results showed that:(1)during the study period,the stream DOC concentration in the study watershed varied in the range of 3.88-33.75 mg/L.The change trend of stream DOC concentration in the upper stream is consistent with that in the downstream of the study watershed.The average stream DOC concentration was significantly higher in April than that in May and June,and showed a decreasing trend associated with the increase of air temperature.(2)The total stream DOC flux was 3215.48 kg/km^(2) in the watershed during the study period,of which the stream DOC flux in May was higher than that in April and June.The stream DOC flux showed a significantly positive correlation(P<0.05)with the runoff,which was the dominant factor controlling flus of stream DOC in the study watershed.(3)During the study period,stream DOC concentration was significantly negatively correlated with air temperature(R2=0.5048,P<0.001).The variation range of DOC concentration in precipitation samples was 1.06-9.42 mg/L,which was much higher that of stream The dynamic of DOC concentration in soils was consistent with stream DOC.The average DOC concentration in 0-10 cm and 10-20 cm soil ranged from 77.57 to 133.99 mg/L.(4)The mean daily stream DOC concentration was significantly(P<0.05)higher during freeze-thaw cycle(24.02 mg/L)than that during thawing period(14.64 mg/L),while the mean daily DOC flux during thawing period(48.02 kg/km^(2))was five times higher than that during freeze-thaw cycle period(9.52 kg/km^(2)).The results reveal the transport characteristics of stream DOC and its influencing factors during the spring freeze-thaw period in a small permafrost watershed in Da Hinggan Mountains,which is of great significance for understanding the carbon cycle in the permafrost region.