量化不同化學風化速率及其對二氧化碳淨收支之影響-以造山帶島嶼臺灣為例

Quantifying different chemical weathering rates and their relevant CO2 budget in active mountainous island, Taiwan

張宸菲(Chen-Fei Chang)

指導教授 ： 黃誌川

國立臺灣大學/理學院/地理環境資源學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202200391

摘要

化學風化因大氣中碳酸的參與，而成為影響全球碳循環的一個重要機制。然而，含硫礦物氧化（如：pyrite oxidation）所產生的硫酸可能取代碳酸進行反應，反而會釋放二氧化碳至大氣中成為碳源。活動造山帶的小河流域（如：台灣）常因高化學風化速率，被認為是吸收二氧化碳的重要熱點，然而黃鐵礦產生的硫酸對全島二氧化碳的收支的影響，尚缺乏量化評估。因其複雜的耦合作用，確切量化化學風化不同路徑所造成的淨二氧化碳收支極為重要，以了解造山帶是否符合有效碳匯的假說。本研究旨在分析台灣島河流之三種化學風化速率及其區域特性，並進一步衡量其對長期大氣二氧化碳淨收支之影響。本研究收集2014年至2016年間43個集水區之河水化學調查，並藉由端源模式分析各集水區的矽酸鹽與碳酸鹽端源，來探討台灣風化過程的變化特性。結果顯示，全流域產出的化學風化速率CWRsil, CWRcarb, CWRpyrite分別為40, 249, 143 ton/km2/yr。其中矽酸鹽風化可吸收 8.27 × 105 mol/km2/yr的二氧化碳，然而由於黃鐵礦風化釋放11.74 × 105 mol/km2/yr的二氧化碳，最終造成長時間尺度 3.47 × 105 mol/km2/yr的二氧化碳淨釋放。研究證實台灣北部流域有較高的二氧化碳淨消耗，而東部則多為淨碳源，顯示台灣黃鐵礦氧化產生的硫酸調節著化學風化路徑，及二氧化碳長期釋放量。

關鍵字

化學風化 ； 二氧化碳 ； 造山帶 ； 碳源 ； 岩性

並列摘要

Chemical weathering which silicate mineral reacts with carbonic acid is the main agent to absorb atmospheric CO2, yet the sulfuric acid from sulfide oxidation could be a stronger agent to hinder the involvement of carbonic acid, resulting in the conversion of CO2 consumption into release. Small rivers in active orogens, such as Taiwan, is hypothesized as a hotspot of CO2 consumption due to the expected high chemical weathering, yet the effect of sulfuric acid, which from pyrite spreading in sediment and metamorphic rock of Taiwan, on the CO2 budget island-wide is lack of assessment. This study aims to investigate the spatial and temporal variations in patterns of chemical weathering and the CO2 budget induced by chemical weathering in Taiwan. We analysis the river water samples from 43 catchments during 2014 to 2016, and analyzed the endmembers by inverse end-member mixing model to explore the characteristics of weathering processes in Taiwan. The result shows CWRsil, CWRcarb, CWRpyrite around Taiwan catchments are 39.9, 248.8 and 142.9 ton/km2/yr, respectively. Among them, silicate weathering absorbs up to 8.27 × 105 mol/km2/yr of CO2, however, 11.74 × 105 mol/km2/yr of CO2 is released due to pyrite weathering, resulting in a net CO2 release to the atmosphere of 3.47 ×105 mol/km2/yr. This study confirmed that the northern Taiwan has a high net consumption of atmospheric CO2, while the eastern side is mostly a net carbon source, demonstrating that the sulfuric acid produced by pyrite oxidation modulates the chemical weathering path and the long-term carbon dioxide emission in rapidly uplifting catchments.

並列關鍵字

chemical weathering ； carbon dioxide ； orogens ； carbon source ； lithology

參考文獻

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