Abstract
Water samples were collected twice per month over a two-year period from the Longchuanjiang River (Yunnan Province, China) to understand monthly variations in major elements and solute fluxes as related to rock weathering and associated CO 2 consumption rates. Solute concentrations were 5 times the median of 65 mg/l for global average. Total cationic exchange capacity (Tz +) ranged from 2.4 to 6.1 meq/l; and the mean (4.4 meq/l) was significantly higher than that of the global river waters. Calcium and bicarbonate dominated the annual ionic composition, accounting for more than 70% of the solute flux that exceeded 71 × 10 6 kg/yr. Lower concentrations of most measured elements during the monsoon high flow period could be explained by dilution effects from precipitation. Three major reservoirs contributed to the dissolved load: carbonates, silicates and anthropogenic inputs, i.e., some 83% of the riverine cations from carbonates and 17% from silicates. The chemical weathering rate of 26.1 t/km 2/yr, with respective carbonate and silicate weathering rates of 20.3 t/km 2/yr (8.46 mm/kyr) and 5.75 t/km 2/yr (2.13 mm/kyr), was comparable to the average for global rivers, but higher than that for the Changjiang River in China. The CO 2 consumption rate was estimated to be 173.7 × 10 3 mol/km 2/yr and 202.9 × 10 3 mol/km 2/yr by silicate and carbonate weathering, respectively. The CO 2 consumed by rock chemical weathering in the upper Changjiang River reduced the atmospheric CO 2 level and constituted a significant part of the global carbon budget. Consequently the carbon sink potential of rock chemical weathering in the Qinghai-Plateau deserves extra attention. Population density and anthropogenic activities, particularly agricultural practices, contributed remarkably to dissolved solutes and associated CO 2 consumption worldwide, and anthropogenic inputs probably contributed some 10.4% to the dissolved solutes in the Longchuanjiang River.
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