Seminar

The lithium (Li) isotopic system is widely used to investigate weathering status, constrain water-rock interaction, and reconstruct paleoclimate due to its distinctive isotopic fractionation during the processes of chemical weathering. Dissolved Li concentrations and isotopic compositions (δ⁷Li) were applied to explore weathering in the groundwater-fluvial system. It is indispensable to delineate the contribution of different origins to chemical weathering represented by δ⁷Li as it was the accumulating and mixing products of both surface and subsurface processes in the river basin. These processes include groundwater-rock/sediment interaction, shallow groundwater/surface water mixing, and deep geothermal groundwater dynamics. We fully investigated Li-δ⁷Li in the shallow groundwater, deep geothermal groundwater, and river water in a granite dominant river basin. It is believed that the weathering regime in the basin is subject to strong controls of subsurface processes, i.e., groundwater-rock interactions. We intend to establish a novel Li and δ⁷Li reactive-transport model to delineate the chemical weathering under the influences of the aforementioned surface and subsurface processes. Control factors of dissolution processes and secondary mineral precipitation are explored through the model, by respectively examining the damköhler numbers and adsorption/desorption coefficients in both surface and subsurface system. Rare earth elements of dissolved loads are investigated to provide more information of regional weathering progresses. We hope to provide a new vision to quantitatively and theoretically investigate how groundwater system reshapes the chemical weathering as revealed by Li isotopes and advocates a hydrogeological perspective when addressing the chemical weathering in the river basin locally, regionally, and globally.

Additional information: Miss Yanqiong HUANG, huangyq1@connect.hku.hk