Mountain regions supply a large amount of fresh water for the people in arid and semiarid regions, however, there is great uncertainty of the water quantification from mountains to lower areas. In order to assess the hydrological significance of mountains and the hydrological linkage of mountains and plains, the measured and simulated hydrological data of the arid region in northwest China were used in the present research which followed a catchment-based approach. Firstly, the Heihe River Basin, a well-documented area, was selected as a specific watershed to reveal the hydrological relationship between highlands (mountains) and lowlands (plains); and then, the significance and disproportion of mountain runoff of 8 river basins as cases in the arid region of northwest China were analyzed and compared following the above analysis. The results of the study showed that the proportion of mountain runoff in total basinal runoff (PMR) of most rivers is above 50%. The PMR are between 50%-95% in the rivers originated in the northern slope of the Tianshan Mountains where the aqueous vapor is relatively sufficient. And that, almost all the flow of the rivers originating from the Qilian Mountains, the southern slope of the Tianshan Mountains, and the northern slope of the Kunlun Mountains come from mountain regions. Also the PMR gradually increases from west to east in northwest China. The hydrological significance and disproportion of mountains water in the arid region of northwest China were given a systematic and thorough assessment, and the results could give potential guides for the scientific utilization of water resources in these regional areas for relieving the more and more serious shortage of water resources due to climate warming and population expansion.
The profound impacts exerted by climate warming on the Tibetan Plateau have been documented extensively, but the biogeochemical responses remain poorly understood. This study was aimed at seasonal variations of total organic carbon(TOC) and total organic nitrogen(TON) in stream water at two gauging sections(TTH, ZMD) in the upper basin of Yangtze River(UBYA) and at fourgauging sections(HHY, JM, JG, TNH) in the upper basin of Yellow River(UBYE) in 2013. Results showed that concentrations of TON exhibit higher values in spring and winter and lower values in summer. TOC exhibits higher concentrations in spring or early summer and lower concentrations in autumn or winter. Seasonal variations of TOC and TON fluxes are dominated by water flux. In total, the UBYE and UBYA delivers 55,435 tons C of organic carbon and 9,872 tons N of organic nitrogen to downstream ecosystems in 2013. Although the combined flux ofTOC from UBYA and UBYE is far lower than those from large rivers, their combined yields is higher than, or comparable with, those from some large rivers(e.g. Nile, Orange, Columbia), implying that organic carbon from the Tibetan Plateau may exert a potentially influence on regional and/or global carbon cycles in future warming climate.
LI Xiang-yingDING Yong-jianHAN Tian-dingXU Jian-zhongKANG Shi-changWU Qing-baiMika Sillanp??YU Zhong-boYU Cong-rong
