桂林漓江水体溶解无机碳迁移与水生光合碳固定研究
Study on dissolved inorganic carbon migration and aquatic photosynthesis sequestration in Lijiang River, Guilin
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摘要: 河流溶解无机碳含量昼夜变化主要受碳酸盐反向沉积、水生光合利用和脱气作用控制,被水生光合利用的溶解无机碳是岩溶碳汇的组成部分,脱气作用比例的大小是影响碳汇稳定性的决定因素。本文以漓江中游省里—冠岩之间15 km长河段为研究对象,开展昼夜高分辨率水化学自动化监测与高频取样,分析水生植物光合作用利用HCO3-1及相关钙沉降过程。结果表明,监测河段水生光合利用的无机碳转化通量为859 kgC?d-1,单位流程光合作用溶解无机碳转化量和钙沉降量分别为2.06 t?(d?km)-1和0.78 t?(d?km)-1。光合作用与钙沉降消耗DIC约占总转化量的70 %,以光合有机碳和CaCO3形式储存于河床,成为岩溶碳汇组成部分。无机碳转化量约占输入DIC总量的6.0 %(其中1.7%以CO2形式返回大气),说明夏季低水位期间强烈的水生植物光合利用溶解无机碳,可有效遏制白天水气界面CO2脱气过程发生,低脱气比例证实漓江水体的溶解无机碳还是比较稳定的。Abstract: Daily changes of dissolved inorganic carbon in river mainly are controlled by carbonate back-precipitation,aquatic photosynthesis and CO2 degassing at water-air interface. Dissolved inorganic carbon uptake by aquatic photosynthesis is a part of karst carbon sink,and the size of degassing proportion values acts as the determinant factor for carbon sink stability. To analysis of the loss of bicarbonate caused by aquatic photosynthesis and relevant calcite precipitation processes,high resolution monitoring for water chemistry and high-frequency water sampling in daily scale were conducted in a 15 km-long section between Shengli and Guanyan in middle course of Lijiang River. The results showed that the flux of photosynthesis uptake of dissolved inorganic carbon in monitoring section is about 859 kgC?d-1. DIC removal value by photosynthesis and calcite precipitation value are 2.06 t?(d?km)-1 and 0.78 t?(d?km)-1, respectively. CO2 degassing value accounts for 28.4 % of total carbon removal,namely,approximately 70% of carbon removal was converted into organic carbon and precipitated in riverbed in form of calcite,thus constitute a part of karst carbon sink. DIC removal accounts for about 6.0 % of total input,in which 1.7 % returned to the atmosphere in the form of CO2,indicating DIC uptake by aquatic photosynthesis during the summer low water level can restrain CO2 degassing process in air-water interface effectively during the day time. The low degassing proportion suggested that DIC in water body of Lijiang River is relatively stable.
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