北江河水溶解无机碳同位素的季节变化

在有碳酸盐岩分布的河流流域, 河水地球化学主要反映的是风化速率较高的碳酸盐矿物风化的信息, 而硅酸盐矿物风化的信息往往被掩盖掉.北江流域碳酸盐岩和硅酸岩分布广泛, 为追踪其中的硅酸盐矿物风化的信息, 分析了北江河水中溶解无机碳同位素的时空变化.河水样品按4个季节自北江的上游到下游采集6个样点, 分析结果显示, 除上游武江的采样点同位素值季节变化不大外, 中下游采样点的同位素值有明显季节变化, 主要表现在6月份的δ13C_DIC显著变轻(-16‰~-19‰).在详细剖析矿物风化过程对碳同位素的影响后, 指出除了显著的碳酸盐矿物风化过程外, 北江流域在夏季还存在明显的硅酸盐矿物风化过程, 大大提高了流域的碳汇作用. 

Seasonal Variations of Dissolved Inorganic Carbon Isotope in the Beijiang River

In watershed with occurrence of carbonate minerals, information of carbonate weathering can be easily traced by river chemistry due to its higher weathering rate, whereas signals of silicate weathering tend to be concealed. In this study, temporal and spatial variations of carbon isotope of dissolved inorganic carbon are employed to trace silicate weathering in the Beijiang River, whose watershed is covered by both carbonate and silicate. Water samples were collected from six sites from upstream to downstream for all seasons. Our results show that there is an obvious seasonality in isotope values at sites in the midstream and downstream, displaying marked lighter values in June (-16‰ to -19‰) except for the upstream sites showing less varying carbon isotope values. Taking into consideration of constrains of various processes on dissolved inorganic carbon isotope, we propose that silicate weathering is greatly enhanced in summer in addition to carbonate weathering, which strengthens carbon sink significantly.