Sources, transportations and variation characteristics of dissolved inorganic carbon in Lake Poyang, China

Abstract

为深入理解鄱阳湖水体溶解性无机碳（DIC）、碳同位素时空分布特征及其影响因素，继而了解鄱阳湖碳通量及其主要碳源贡献率，于2019—2020年典型水文季节对鄱阳湖湖区及“五河”入湖口进行样品采集分析，采用统计学方法初步分析鄱阳湖及入湖口水体中DIC及其同位素（δ¹³C_DIC）分布特征.结果表明：（1） DIC浓度丰水期大于枯水期，而δ¹³C_DIC值则相反，枯水期偏正，丰水期相对偏负；（2）鄱阳湖丰水期DIC月通量为266.1~268.4 t，平均值为267.3 t，枯水期DIC月通量为2.88~5.94 t，平均值为4.41 t，丰水期DIC通量是枯水期的60.6倍.CO₂水-气交换对鄱阳湖碳通量贡献率最大，为73.07%，其次为河流输入，为15.53%；（3）溶解碳酸盐岩风化是控制流域DIC来源及其δ¹³C_DIC组成的主要机制，季节性降雨形成的径流量变化是不同碳源对鄱阳湖碳通量贡献的主要控制因素.;Water samples of Lake Poyang and its five inflow river were collected in typical hydrological seasons from 2019 to 2020, to reveal the spatial variations of dissolved inorganic carbon (DIC) and its isotopic composition, as well as to estimate the carbon flux and the sources of the three main carbons in Lake Poyang. The results indicated that DIC concentrations in wet seasons were higher than those in dry seasons whereas both higher δ¹³C_DIC and the δ¹³C_DIC in dry seasons. The DIC flux in the surface water of Lake Poyang ranged from 266.1 to 268.4 t/month (the average was 267.3 t/month) in wet seasons, and ranged from 2.88 to 5.94 t/month (the average was 4.41 t/month) in dry seasons, exhibiting a difference nearly 60.6 times in different seasons. The contribution of gas CO₂ exchange between lake water and atmosphere to the DIC flux in Lake Poyang was the largest, accounting for 73.07%, followed by river input with 15.53%. The weathering of carbonate rock by H₂CO₃ was the dominating reaction controlling both DIC sources and δ¹³C_DIC compositions, and the variation of seasonal rainfall runoff was the main controlling factor of the contribution of different carbon sources to the carbon flux in Lake Poyang.