北江流域水化学时空变化及化学风化特征

为了研究我国南方湿润地区河流水化学时空变化特征及控制因素，选择珠江流域第二大水系的北江为研究对象，通过分析2015年6月（汛期）和12月（非汛期）干流和支流河水基本水质参数及主量离子，利用化学计量法及质量守恒法定量评估了自然过程及人类活动共同影响下的流域化学风化特征及其通量.结果表明:①北江河水主量离子浓度非汛期高于汛期.岩石的区域分布和矿山活动构成了河水离子浓度和水化学类型的空间异质性，其中北江干流和支流连江为Ca-HCO₃型，而支流滃江则以Ca-SO₄型为主.②岩石对北江流域化学风化贡献率依次为碳酸岩（78.44%）>硅酸岩（14.43%）>降水源（5.42%）>蒸发岩（1.71%）.基于碳酸岩是北江径流水化学的主要控制因素，滃江流域的矿山开采活动加速了碳酸岩的风化，其对北江流域化学风化的贡献为7%.③汛期与非汛期的碳酸岩风化速率分别为7.49和5.29 t/（km2·月），年化学风化速率为87.63 t/（km2·a）.研究显示，由于受水热条件、流域面积以及岩性的影响，北江流域年化学风化速率略大于西江流域，远高于东江以及全球流域化学风化平均值，北江对整个珠江流域的风化贡献较大. 

Spatial and Temporal Variation of Hydro-Chemistry and Chemical Weathering Characteristics in the Beijiang River Basin

In order to investigate the spatial and temporal variations of hydro-chemical characteristics and its controlling factors in humid regions of southern China, water samples were collected from the Beijiang River and its tributaries in June and December 2015, respectively. Based on chemical parameters and major ions concentration, the chemical weathering and ions fluxes were estimated by the stoichiometry and mass conservation to identify the effects of natural and anthropogenic processes in the basin scale. The result showed that (1) The concentrations of main ions were higher in the non-flood season than that in the flood season. The geological features and mining activities affected greatly the chemical components in the river waters, resulting in the hydrochemistry type as Ca-HCO₃ in the Beijiang River and Lianjiang River, and Ca-SO₄ in the Wengjiang River. (2) The contribution of rock weathering to river chemistry is in the order of carbonate minerals (78.44%) > silicate minerals (14.43%) > precipitation (5.42%) > evaporite (1.71%). Since carbonatite is the main rock found widely in the basin, the mining activities accelerated dissolution of carbonatite, accounting about 7% of the total chemical weathering in the Beijiang River Basin. (3) The weathering rates of Beijiang River Basin were 7.49 t/(km²·month) in the flood season and 5.29 t/(km²·month) in the non-flood season, with the rate of 87.63 t/(km²·a). The annual chemical weathering rate in the Beijiang River is similar in the Xijiang River, but much higher than the Dongjiang River even the global average of rivers. Therefore, the chemical weathering in Beijiang River is very important for hydrochemistry in the Pearl River basin.