| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 107 === Chemical weathering plays a vital role in the global carbon cycle over geological time scales. The central themes focus on the pathways of acid production, rock availability for dissolution, and correlations between rates and climatic or tectonic forcing. Most previous efforts are diverted to measure great exports of solutes and sediments from large rivers systems. As small rivers in active orogens across Asia and Oceania could deliver solutes and sediments at a rate surpassing large rivers on the per area basis, the exact flux and reaction pathway of chemical weathering in these catchments remain poorly quantified.
This study aims to investigate the spatial and temporal variations in patterns of chemical weathering along the Beinan-Sinwulyu river in southeastern Taiwan where uplifting rates range up to 3 cm/yr and fluxes of sediment export are among the largest in Taiwan. Analysis of river water collected from different tributaries between 2016 and 2018 yields Ca2+, SO42- and dissolved inorganic carbon as the major constitutes. In particular, SO42- concentrations are two to sixteen times higher than the world average value of ~300 μM, which is primarily attributed to be produced from pyrite oxidation. Using a new computational approach to evaluate these solute data, we demonstrate that the major proportion of solutes was contributed from carbonate weathering driven by sulfuric acid at all sites. The catchment-wide flux derived from chemical weathering is at least three orders of magnitude greater than the average of global large rivers. The computation also indicates that the CO2 efflux was correlated with the flux of pyrite-derived carbonate weathering with the net emission occurring in upstream, mountainous regions in all seasons and the net consumption in the downstream plain to estuarine regions in dry seasons. Overall, these results demonstrate a strong modulation of the oxidation of pyrite inherited with metamorphic rocks in chemical weathering and CO2 emission in a rapidly uplifting catchment.
|
|---|
