A preliminary study on distribution characteristics of total organic carbon in sediment in upper reaches of the Yarlung Zangbo River
To investigate the spatial characteristics of total organic carbon(TOC)content in sediment in upper and tributary streams of the Yarlung Zangbo River(YZR)and its influencing factors,responses of TOC content in sediment on particle size were studied and effects of land use in the watershed on spatial trends of TOC were analyzed based on the random forest analysis(RFA).The results indicate that the mean TOC[(6.56±6.37)g·kg-1]in upper reaches of the YZR is lower than that of other large-and medium-sized rivers,which ranges from 5.95 to 49.06 g·kg-1 with a mean value of(19.77±14.05)g·kg-1.With the lowest TOC in sediment[(2.57±0.97)g·kg-1]in headwater,TOC is highly positively correlated(r=0.64,P<0.01)with clay content in sediment in the YZR.Based on literatures and results of this study,a highly significant exponential correla-tion between TOC in sediment and the content of particles smaller than 63 µm(r=0.77,P<0.01)was found across rivers,and thus,the content of particles smaller than 63 µm could be an indicator of TOC in sediment in rivers.Furtherly,RFA results indicate that in upper reaches of the YZR,TOC in sediment is majorly terrestrial-ly sourced from grassland(48.12%)and increased spatially along the direction of water flow due to transition-ing of land use from low-coverage grassland and bare land in headwater to medium,high-coverage grassland,as well as to agricultural,pastoral,and industrial(Class M1)land in upper-middle and upper-end sections of the YZR.We,therefore,concluded that the lower TOC in upper reaches of the YZR can be generally attributed to less anthropogenic activities and predominant sandy texture.
upper reaches of the Yarlung Zangbo Rivertotal organic carbon in sedimentgranularityspatial heterogeneity
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