The Tibetan Plateau is home to the largest aggregate of glaciers outside the Polar Regions and is a source of fresh water to 1.4 billion people. Yet little is known about the transportation and cycling of Hg in high-elevation glacier basins on Tibetan Plateau. In this study, surface snow,glacier melting stream water and lake water samples were collected from the Qiangyong Glacier Basin. The spatiotemporal distribution and transportation of Hg from glacier to lake were investigated. Significant diurnal variations of dissolved Hg(DHg) concentrations were observed in the river water, with low concentrations in the morning(8:00 am–14:00 pm) and high concentrations in the afternoon(16:00 pm–20:00 pm). The DHg concentrations were exponentially correlated with runoff, which indicated that runoff was the dominant factor affecting DHg concentrations in the river water. Moreover, significant decreases of Hg were observed during transportation from glacier to lake. DHg adsorption onto particulates followed by the sedimentation of particulate-bound Hg(PHg) could be possible as an important Hg removal mechanism during the transportation process. Significant decreases in Hg concentrations were observed downstream of Xiao Qiangyong Lake, which indicated that the high-elevation lake system could significantly affect the distribution and transportation of Hg in the Qiangyong Glacier Basin.
Black carbon(BC) deposited on snow and glacier surfaces can reduce albedo and lead to accelerated melt. An ice core recovered from Guoqu glacier on Mt. Geladaindong and analyzed using a Single Particle Soot Photometer(SP2) provides the ?rst long-term(1843-1982) record of BC from the central Tibetan Plateau. Post 1940 the record is characterized by an increased occurrence of years with above average BC, and the highest BC values of the record. The BC increase in recent decades is likely caused by a combination of increased emissions from regional BC sources, and a reduction in snow accumulation. Guoqu glacier has received no net ice accumulation since the 1980 s, and is a potential example of a glacier where an increase in the equilibrium line altitude is exposing buried high impurity layers. That BC concentrations in the uppermost layers of the Geladaindong ice core are not substantially higher relative to deeper in the ice core suggests that some of the BC that must have been deposited on Guoqu glacier via wet or dry deposition between 1983 and 2005 has been removed from the surface of the glacier, potentially via supraglacial or englacial meltwater.
Matthew JENKINSSusan KASPARIKANG Shi-ChangBjorn GRIGHOLMPaul A.MAYEWSKI
Rivers are critical links in the carbon and nitrogen cycle in aquatic,terrestrial,and atmospheric environments.Here riverine carbon and nitrogen exports in nine large rivers on the Tibetan Plateau—the"Water Tower of Asia"—were investigated in the monsoon season from 2013 to 2015.Compared with the world average,concentrations of dissolved inorganic carbon(DIC,30.7 mg/L)were high in river basins of the plateau due to extensive topographic relief and intensive water erosion.Low concentrations of dissolved organic carbon(DOC,1.16 mg/L)were likely due to the low temperature and unproductive land vegetation environments.Average concentrations of riverine DIN(0.32 mg/L)and DON(0.35 mg/L)on the Tibetan Plateau were close to the world average.However,despite its predominantly pristine environment,discharge from agricultural activities and urban areas of the plateau has raised riverine N export.In addition,DOC/DON ratio(C/N,~6.5)in rivers of the Tibetan Plateau was much lower than the global average,indicating that dissolved organic carbon in the rivers of this region might be more bioavailable.Therefore,along with global warming and anthropogenic activities,increasing export of bioavailable riverine carbon and nitrogen from rivers of the Tibetan Plateau can be expected in the future,which will possibly influence the regional carbon and nitrogen cycle.
Bin QuMika SillanpaaShichang KangFangping YanZhiguo LiHongbo ZhangChaoliu Li
