『Abstract
　The major cation and anion compositions of waters from the Lake Qinghai river system (LQRS) in the northeastern Tibetan Plateau were measured. The waters were collected seasonally from five main rivers during pre-monsoon (late May), monsoon (late July), and post-monsoon (middle October). The LQRS waters are all very alkaline and have high concentrations of TDS (total dissolved solids) compared to rivers draining the Himalayas and the southeastern Tibetan Plateau. Seasonal variations in the water chemistry show that, except the Daotang River, the TDS concentrations is high in October and low in July in the LQRS waters. The forward models were used to quantify the input of three main rivers (Buha River, Shaliu River, and Hargai River) from rain, halite, carbonates, and silicates. The results suggest that (1) atmospheric input is the first important source for the waters of the Nuha River and the Shaliu River, contributing 36-57％ of the total dissolved cations, (2) carbonate weathering input and atmospheric input have equal contribution to the Hargai River water, (3) carbonate weathering has higher contribution to these rivers than silicate weathering, and (4) halite is also important source for the Buha River. The Daotang River water is dominated by halite input owing to its underlying old lacustrine sediments. The water compositions of the Heima River are controlled by carbonate weathering and rainfall input in monsoon season, and groundwater input may be important in pre-monsoon and post-monsoon seasons. After being corrected the atmospheric input, average CO2 drawdown via silicate weathering in the LQRS is 35×10³ mol/km² per year, with highest in monsoon season, lower than Himalayas and periphery of Tibetan Plateau rivers but higher than some rivers draining shields.

Keywords: Seasonal variation; Chemical weathering; Lake Qinghai river system』

Introduction
Study area
　Geological setting, climate, and vegetation
Sampling and analytical methods
Results and discussion
　General observations
　Sources of major ions
　　Carbonate and silicate weathering to major ions
　　Other sources for Na, Cl and SO4
　Relative contribution of silicate weathering versus carbonate weathering and uncertainties
　　Correction for atmospheric input
　　Uncertainties of atmospheric input correction
　　Quantification of chemical weathering sources
　Flux calculation
Conclusions
Acknowledgments
References