长江徐六泾黑碳的季节变化及环境意义

SEASONAL VARIATIONS OF BLACK CARBON IN XULIUJING WATER OF THE YANGTZE RIVER AND THEIR ENVIRONMENTAL IMPLICATIONS

2009年8月~2010年7月,每月在长江口徐六泾对水中悬浮颗粒物进行了采样,分析悬浮颗粒物中有机碳及黑碳含量,研究它们的季节变化特征,并计算出相应的输送通量。结果显示,水体中颗粒有机碳(Particulate organic carbon,POC)含量在0.34~0.92mg/L,黑碳(Black carbon,BC)含量在0.035~0.096mg/L;POC含量与水中总悬浮颗粒物(Total suspended material,TSM)含量有显著的正相关,但POC%随着TSM浓度的增加而减小;此外,水体中BC含量与人类的燃烧活动密切相关。观测期间长江的POC通量为2.34×106 t/yr,BC通量为2.77×105 t/yr,且BC通量占到颗粒有机碳通量的12.9%。

Suspended particulate matter(SPM)samples were collected from Xuliujing water of the Yangtze River from August 2009 to July 2010 to investigate the contents of particulate organic carbon(POC)and black carbon(BC),and calculate their fluxes.The results indicated the POC contents in the water ranged from 0.34 to 0.92mg/L,while BC contents ranged from 0.035 to 0.096mg/L.POC concentration and total suspended matter(TSM)in the water demonstrated clearly positive correlation,which indicated that SPM was the primary carrier of POC.In the meantime,the POC%in TSM(1.41±0.26%)was close to that of the paddy soil(1.25±1.43%),which indicated that the soil in the drainage basin was the main source of POC in the water.Furthermore,BC%showed obvious seasonal variations,in which BC%of SPM in dry seasons was higher than that in flood seasons.This may be caused by the following two reasons:(1)an decreased discharge in dry seasons causes a decrease in mineral matter,and an increase in BC%;(2)the dry season occurred mainly in the autumn and winter,equal to a residential large-scale heating,as well as the rural fire period,so BC output in this period tended to be higher than other time.During the period of observation in this study,the monthly fluxes of POC and BC at XLJ ranged from 4.40×105 t to 4.63×106 t and from 4.65×103 t to 5.64×103 t,respectively.Moreover,the percentage of the POC and BC fluxes in flood seasons were 82.5% and 80.4%,respectively,which was associated with hydrological dynamics in the Yangtze River Basin.In summary,the POC flux was estimated to be 2.34×106 t/yr,while BC was estimated to be 2.77×105 t/yr,which occupied 12.9%of the POC flux,and accounted for about2.69%of the total global river transportation.Finally,the emissions of BC in China by combustions were close to the fluxes in rivers,which was explained by the following reasons:(1)BC in the Yangtze River was derived not only from combustions,but also from older BC in soils and graphite BC by weathering;(2)the BC emmitted from biomass burning was associated with large uncertainties due to highly variable emission factors.The concentrations of the dissolved BC,as the intermediate of degradation,was not to be neglected.These results have important implications for the global carbon cycle.