溶解性有机碳（dissolved organic carbon，DOC）在全球碳循环过程中起着重要的作用。目前关于泛北极多年冻土区DOC的研究较多，青藏高原多年冻土区DOC的研究较少。为探讨青藏高原DOC的时空动态、来源，以及对气候变化和多年冻土退化的响应及其影响因素，以位于青藏高原长江源区内8个流域（直门达、沱沱河、雁石坪、风火山1~5）为研究区，通过对河流DOC观测、采样和分析，DOC输出通量计算，结合河流中{\delta }^{\mathrm{13}}C-DOC同位素的特征、流域水文特征、植被覆盖率、冻土覆盖率等观测数据，分析河流DOC输出的季节性变化规律和来源。结果表明：长江源多年冻土区河流DOC浓度全年较低，平均浓度在1.91~3.69 mg·L^-1之间，年内不同季节间变化率较小，上游DOC浓度大于下游DOC浓度。河流DOC的输出主要集中在夏、秋两季完全融化期，随径流量的增加而显著增加，而冬、春两季输出较少，DOC通量与径流量之间的相关系数达到0.92，与径流量的变化趋势一致。直门达水文站和风火山流域DOC年输出量分别为42 539.67 t和137.33 t，完全融化期输出占比分别为68.06%和79.85%，径流量和活动层冻融循环过程是导致DOC季节性输出差异的原因。季节尺度上长江源区{\delta }^{\mathrm{13}}C-DOC同位素变化趋势不显著，在-37.57‰~-21.06‰之间，完全融化期由于地下径流带来了更多{\delta }^{\mathrm{13}}C相对贫化的深层土壤有机碳，导致完全融化期{\delta }^{\mathrm{13}}C-DOC值相对较低。年内各季节下游地区{\delta }^{\mathrm{13}}C-DOC均较上游地区更富集。DOC来源{\delta }^{\mathrm{13}}C值在-37.69‰~-30.41‰之间， 表明DOC的主要来源为土壤有机质和C3植物。本研究有助于认识青藏高原冻土区河流碳迁移转化过程和机制。

Dissolved organic carbon （DOC） plays a pivotal role in the global carbon cycle. At present， there are many studies about DOC in permafrost catchments of the Arctic regions， yet some studies about DOC in permafrost catchments of the Qinghai-Tibet Plateau （QTP）. To explore the spatiotemporal variability， sources， the responses to climate warming and permafrost degradation and influence factors of DOC in QTP river， here we conducted field investigations of DOC in 8 catchments （ZMD， TTH， YSP， FHS1~5） in the Yangtze River source region （YRSR）. The seasonal variations and source characteristics of DOC were deciphered using stream sampling， laboratory analyses， flux calculation， stable carbon isotopic technique （{\delta }^{\mathrm{13}}C-DOC）， and hydrological observations. The catchment characteristics including vegetation coverage， and permafrost coverage were used to study the spatial controls of DOC. The results showed that riverine DOC concentrations were low and remained relatively steady through the whole year of the YRSR， with mean concentrations varied from 1.91 mg·L^-1 to 3.69 mg·L^-1. The riverine DOC concentrations of upstream sites were higher than DOC concentrations of downstream sites. The DOC export was mainly concentrated in summer and autumn during thawed season and was much higher than the export in spring and winter. The correlation coefficient between DOC flux and river runoff reaches 0.92， suggesting intimate controls of discharge on DOC flux. The annual DOC flux of YRSR and FHS watershed were 42 539.67 t·a^-1 and 137.33 t·a^-1， respectively. The thawed season DOC flux contributed 68.06% and 79.85% of the annual DOC flux in YRSR and FHS watershed， respectively. The runoff and active layer freeze-thaw cycle process were the main factors that affect the seasonal DOC flux. The carbon isotope of DOC （{\delta }^{\mathrm{13}}C-DOC） also remained relatively steady in different seasons， varied from -37.57‰ to -21.06‰. The carbon isotope of DOC （{\delta }^{\mathrm{13}}C-DOC） was relatively lower in thawed season， which may be due to the waterborne deeper thawed soil organic carbon with relatively depleted {\delta }^{\mathrm{13}}C supplied by subsurface runoff. The isotope was enriched in downstream rather than upstream in different seasons. The source carbon isotope of DOC （{\delta }^{\mathrm{13}}C-DOC） varied from -37.694‰ to -30.411‰， including the main sources of DOC were soil organic matter and C3 plants. This study helps to understand the process and mechanism of riverine carbon transfer and transformation in the permafrost region of the Qinghai-Tibet Plateau.