[Driving mechanism of dissolved inorganic carbon on the carbon sink/source changes in Tianchi Lake, Huaying Mountain, Sichuan, China].

内容摘要

Dissolved inorganic carbon (DIC) formed by carbonate weathering in karst water has a significant fertilization effect on aquatic photosynthetic organisms (mainly phytoplankton), which can promote the fixation of inorganic carbon through the biological carbon pump (BCP) and increase carbon sinks. However, the source-sink attributes and their driving mechanisms in karst lakes and reservoirs under different temporal scales and disturbance events remain unclear. Taking Tianchi Lake in Huaying Mountain, Sichuan Province as the study area, we combined high-frequency online monitoring, the Bookkeeping model and the generalized linear mixed model to investigate the dynamics and driving mechanisms of net ecosystem productivity (NEP, net carbon sink) under the DIC fertilization effect at multiple scales (annual, seasonal, diurnal, and rainfall events). The results showed that the annual NEP of Tianchi Lake was 9.15 g C·m-2·a-1 during the monitoring period, with significant seasonal variations. The net carbon sink in summer was 53.86 g C·m-2, which could offset the total carbon emissions in spring, autumn, and winter (NEP was -6.74, -36.95 and -4.02 g C·m-2, respectively). On the diurnal scale, there was a pattern of "carbon fixation during daytime and carbon emission during nighttime", with the largest amplitude in summer (64.06 g C·m-2) and the smallest in winter (2.30 g C·m-2). Rainfall events drove NEP to form a three-stage pulse response of "inhibition-rebound-decay", with the increases of NEP after heavy rainstorm (10.41 g C·m-2·d-1) being 9.7 times that of moderate rain event (1.07 g C·m-2·d-1). On the annual scale, solar radiation dominated the changes in carbon sink/source. On the seasonal scale, carbon limitation in summer was dominated by the coupling effect of "high pH and low CO2 partial pressure", with a contribution rate of more than 80%; other seasons were affected by solar radiation and temperature factors. On the diurnal scale, the periodic rhythm of solar radiation was the core driver. Rainfall events alleviated carbon limitation through exogenous DIC input and pH decrease, thus driving the dynamic changes of NEP. 岩溶水体中碳酸盐岩风化形成的溶解无机碳(DIC)对水生光合生物(主要是浮游植物)具有显著的“施肥效应”,能促进水生光合生物通过生物碳泵(BCP)固定无机碳,增加碳汇。然而,岩溶湖库水体不同时间尺度和干扰事件下的源汇属性及其驱动机制仍不明确。本研究以四川华蓥山天池湖为研究区,结合高频在线监测、Bookkeeping模型与广义线性混合模型,探讨DIC施肥效应下净生态系统生产力(NEP,净碳汇量)在全年、季节、昼夜及降雨事件多尺度下的动态变化与驱动机制。结果表明:监测期间天池湖全年NEP为9.15 g C·m-2·a-1,且具有明显季节性差异。夏季净碳汇量为53.86 g C·m-2,能够抵消春、秋、冬季的碳排放总量(NEP分别为-6.74、-36.95和-4.02 g C·m-2)。昼夜尺度上,华蓥山天池湖呈现“昼固碳-夜排碳”模式,且夏季振幅最大(64.06 g C·m-2)、冬季振幅最小(2.30 g C·m-2)。降雨事件驱动NEP形成“抑制-反弹-衰减” 3阶段脉冲响应,大暴雨后NEP增幅(10.41 g C·m-2·d-1)为中雨事件(1.07 g C·m-2·d-1)的9.7倍。全年尺度上,太阳辐射主导碳汇/源变化;季节尺度上夏季的碳限制由“高pH、低二氧化碳分压”耦合作用主导,贡献率超过80%,其他季节则受太阳辐射和温度因素影响;在昼夜尺度,太阳辐射的周期性节律是驱动其变化的核心因子;降雨事件则通过外源DIC输入与pH下降缓解碳限制,驱动NEP动态变化。.