中国西南三江流域风化的季节性变化特征

Seasonal Variation Characteristics of Weathering in the Three Rivers Basin,Southwestern China

青藏高原的风化可能影响着全球碳循环和长时间尺度气候变化,其风化速率和影响机制一直受到科学界的关注。本研究对发源于青藏高原东部的三江——金沙江、澜沧江和怒江干流进行每月两次,为期一水文年的定点观测研究。结果表明三江水样的pH总体呈弱碱性,水中主要阴阳离子组成和TDS变化明显并且都有明显的季节性变化特征。本研究首先用正演模型评估了不同端元对三江水化学的贡献比例,并估算出金沙江石鼓以上、澜沧江维登以上和怒江六库以上流域的净CO2消耗速率分别为76.3×103 mol/(km2·a)、238.9×103 mol/(km2·a)和189.3×103 mol/(km2·a),雨季净CO2消耗速率可达旱季的2~4倍;反演法估算出的净CO2消耗速率与正演法的相差均在25%以内,表明估算结果的可靠性。

As the weathering of the Tibetan Plateau may affect the global carbon cycle and the long time-scale climate change,its weathering rate and influential mechanism have been subjected to the attention of the scientific community.In this study,the Jinshajiang River,the Lancangjiang River and the Nujiang River originating from the Eastern Qinghai-Tibet Plateau were monitored for one hydrological year and water samples were collected every other week.By analyzing basic physical and chemical properties,the pH of river water samples turn out to be mildly alkaline and the chemical composition have a noticeable seasonal variation.During the research,we used forward model to calculate the contribution of different end-members to the river water chemistry and net CO2 consumption rates by silicate weathering,around 76.3×103 mol/(km2·a),182.0×103 mol/(km2·a)and 238.9 ×103 mol/(km2·a)of the upper reach of Shigu(the Jinshajiang River),Weideng(the Lancangjiang River)and Liuku(the Nujiang River),respectively,the net CO2 consumption rate in rainy season can be twice to four times than that in dry season.At last,we used the inverse model to calculate the net CO2 consumption rate,and the results appeared to be quite good(within 25%).