Chemical composition and triple Sr isotopes of Gang-Kou River, Southern Taiwan

Abstract

    Radiogenic Sr isotope (87Sr/86Sr) is a robust tool for provenance identification in hydrology, affected mainly by chemical weathering, lithological background and climatic changes while stable Sr isotope (δ88Sr) may provide complementary information about weathering, adsorption, or carbonate precipitation. In this study, river water samples from the mainstream and the major tributary located at Gang-Kou River catchment were collected seasonally for two years. Major ions, trace elements, and Sr isotopes were measured. The results show that the major anions are bicarbonate (2.35 to 5.24 mM), chloride (0.413 to 1.11 mM), and sulfate (0.187 to 0.817 mM). The major cations are sodium (0.567 to 1.41 mM), calcium (0.720 to 1.66 mM), and magnesium (0.508 to 0.922 mM). The Sr isotopes of river water in the mainstream decrease from upper steam to down steam (from 0.71287 to 0.71174) and are higher than the major tributary. In reverse, the Sr isotopes of major tributary increase from upper steam to down steam (from 0.71066 to 0.71136). The major tributary shows lower Sr isotopes during wet season while the mainstream shows no seasonal variations. The major tributary also shows slightly higher δ88Sr than the mainstream without seasonal variation. The result of major elements with Sr isotopes indicates silicate weathering dominates the river water chemistry while the major tributary shows slightly higher portion of carbonate weathering. Besides that, river water chemistry shows higher carbonate weathering contribution in wet season than dry season. To summary, Sr isotopes are more sensitive to the source variations in water chemistry than the chemical compositions. The results of dissolved phase in Gang-Kou River catchment indicate possible implication to the province identification of the sediments at the estuary.