BIOGEOCHEMICAL INTERACTIONS AMONG THE ARSENIC, IRON, HUMIC SUBSTANCES, AND BACTERIA ACTIVITY IN MUD VOLCANOES IN SOUTHERN TAIWAN

Fluid and mud samples were collected from Hsiaokunshui (HKS), Wushanting (WST), Yenshuikeng (YSK), Kunshuiping (KSP), Liyushan (LYS), and Sinyangnyuhu (SYNH) mud volcanoes of southwestern Taiwan in order to characterize the interaction between major ions, humic substances (HS) and trace elements concentrations. Sulphate (SO₄^2-) reducing bacteria along with other geochemical processes may play role in release As from mud into fluids. Arsenic and iron (Fe) in mud has good correlation (r=-0.92) which implies that arsenic is strongly associated with Fe-oxhydroxide in mud sediments. However, in mud volcano liquid, As has good correlation with HS (r=0.99) which implies that humic substances play significant role for releasing As from mud into fluids. The more reduced condition (-38 ~ -326 mV) which is produced by breaking organic matter or humic substances in the mud volcanoes also favors the release of arsenic from the host minerals to the mud liquid. In addition, the SO₄^2- reducing bacteria may play significant role in reducing the chemical elements (for example As⁺⁵, Fe³⁺, or SO₄^2-) and also help to do some mineralogical interaction in mud liquid. A hypothetical model was developed to understand the mobilization process of As in mud volcano fluids from mud along with the interaction of SO₄^2- reducing bacteria and humic substances.