中国広西チワン族自治区碧水堰地下圏における岩石の化学的風化とCO消費量の推移

Chemical weathering and CO consumption rates of rocks in the Bishuiyan subterranean basin of Guangxi, China.

• Pingping Jiang
• Guo Yu
• Qiang Zhang
• Yane Zou
• Qingjia Tang
• Zhiqiang Kang
• Pen Sytharith
• He Xiao

抄録

化学的風化がCO消費量に及ぼす影響を調べるために、中国広西チワン族自治区碧水堰地下水域において、水化学平衡法を適用した水化学分析を行った。その結果、全イオン濃度(TZ)の平均値は1,854.97μEq/Lであり、世界平均値(TZ=1,250μEq/L)を大きく上回った。CaとHCOが主なイオン性成分であった。SO及びNO濃度は他の陰イオン濃度と比較して相対的に高く、Cl濃度は一貫して最も低い値を示した。溶存負荷量モデルの結果は、炭酸塩風化、珪酸塩風化、大気流入が主なイオン源であり、炭酸塩風化＞珪酸塩風化＞大気流入の影響を受けていることが示されたが、太平を除く全流域では、炭酸塩風化よりも珪酸塩風化が顕著であった。また、岩石風化を介した侵食は、大気中のCOやアロゲン酸の影響を受けていることが明らかになりました。炭酸塩風化率の定量計算による推定収量は59.7t/(km年)であり、珪酸塩風化率の4.40倍であった。また、流域岩石の風化炭素沈下量に占める炭酸塩風化成分の割合は、それぞれ71.2%と28.8%であった。

To investigate the influence of chemical weathering on CO consumption, an analysis was performed of water chemistry by applying water chemistry equilibria methods in the Bishuiyan subterranean basin, SW China. The average value of total ion concentrations (TZ) was 1,854.97 μEq/L, which was significantly higher than the global average value (TZ = 1,250 μEq/L). Ca and HCO were the main ionic constituents in the waters. SO and NO concentrations were relatively higher than other anion concentrations, and Cl concentrations were consistently the lowest. Dissolved load balance models result showed that carbonate weathering, silicate weathering, and atmospheric input were the primary ionic contributors, wherein the effects of carbonate weathering > silicate weathering > atmospheric input for the whole catchment, with the exception of Taiping, where silicate weathering was prominent over carbonate weathering. In addition, these analyses indicated that the erosion via rock weathering was also affected by atmospherically derived CO and allogenic acids. The estimated yield by quantitative calculation for the carbonate weathering rate was 59.7 t/(kmyear), which was 4.40 times higher than that of silicate weathering rate. Further, the carbonate and silicate weathering components of the carbon sink accounted for 71.2% and 28.8%, respectively, of the total basin rock weathering carbon sink.