化學風化為碳循環中的主要作用之一，岩層中的矽酸鹽及碳酸鹽與環境中的碳酸、硫酸反應，將影響大氣中二氧化碳的消耗與釋放。因碳酸由二氧化碳與水結合而形成，因此矽酸鹽與碳酸的風化反應，在地質時間尺度能消耗大氣中的二氧化碳。然而在造山帶環境，如台灣西南部麓山帶，高聳陡峭的地勢與持續的抬升運動使地層不斷出露大量礦物新鮮面，硫化礦物（特別是黃鐵礦）經氧化反應後產生硫酸，能夠驅動風化礦物反應。相較於碳酸，硫酸對於碳酸鹽反應速率更快、風化作用更具優勢，兩者反應產生的陽離子與碳酸氫根在海洋碳酸鈣補償時間尺度以上，沉澱碳酸鈣的過程則會造成二氧化碳釋放。然而硫酸風化的貢獻在現有的評估及二氧化碳通量計算方法中，不論是在空間及時間上皆需更多觀測數據來完備。由於河水溶解離子組成能夠代表岩石風化的溶解物質，故可透過河水化學分析不同風化途徑的貢獻。本研究針對台灣西南部六條主要河川（八掌溪、急水溪、鹽水溪、後堀溪、二仁溪、高屏溪）橫跨乾、濕季七個時間點進行時間序列採樣，以評估不同水文條件下，台灣西南部河川風化作用對於二氧化碳通量的控制及影響。河水樣品由感應耦合電漿光譜儀測得主要離子濃度，進一步計算碳酸及硫酸造成的二氧化碳通量及風化速率。此外，亦透過多接收器感應耦合電漿質譜儀量測硫同位素比值（δ34S），評估自然源或人為源硫酸的貢獻。計算結果顯示台灣西南部的河水溶解物質中碳酸鹽約占近七成、矽酸鹽約占三成；其中，約有四成來自硫酸的作用，且主要為碳酸鹽礦物的風化。濕季流量越大，硫同位素比值越趨近黃鐵礦端元，支持由硫化礦物產生硫酸進而造成風化的推論。此外，河川流量與硫酸風化貢獻比例、風化產生的二氧化碳相當濃度皆呈正相關。最終，由計算結果結合河水流量數據做出的線性回歸模型，能夠以流量數據預測台灣西南部來自風化作用的二氧化碳通量：河川流量4.5 m3/s為一關鍵閾值，在碳酸鈣補償時間尺度以上，河川流量超過該閾值，二氧化碳通量將由淨消耗轉變為淨釋放。

Carbonate weathering mediated by sulfuric acid can release CO2, in contrast to the CO2 consumption associated with the weathering of silicate minerals, as previously discussed. Southwestern (SW) Taiwan is located in an orogenic belt with concentrated periods of rainfall, where the oxidation of sulfide minerals, primarily pyrite, within the rock formations produces sulfuric acid, which then reacts with other minerals.
River water chemistry can be used to determine mineral weathering processes and estimate relevant CO2 fluxes. We conducted seven time-series samplings over one year, from the summer of 2022 to the summer of 2023, across six rivers in SW Taiwan. The concentrations of major ions were measured using ICP-OES to calculate CO2 fluxes from weathering caused by carbonic and sulfuric acids. Additionally, sulfur isotope ratios (δ34S) were analyzed to determine the sources of sulfuric acid, whether natural or anthropogenic.
The proportion of sulfuric acid-mediated weathering and the concentration of CO2 produced by weathering were positively correlated with river discharge. Sulfur isotope observations indicate that during the wet season, the sulfur isotope ratios of the samples approach the pyrite endmember, supporting the inference that sulfide minerals are oxidized to produce sulfuric acid, which then drives the weathering process.
A linear regression model combining calculation results with river discharge data predicts CO2 fluxes in southwestern Taiwan. When river discharge exceeds 4.5 cms, the CO2 flux shifts from net consumption to net release on a timescale beyond the calcium carbonate compensation.

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