Reconstructing Atmospheric Chloride Deposition Using Chloride-Tritium Tracers Stored in Deep Loess

Atmospheric chloride deposition (ACD) is an essential parameter in estimating potential groundwater recharge. However, ACD observations are still limited to a few sparsely distributed sites and/or short time intervals, which are insufficient to characterize regional distribution over a longer time scale, putting into limitation the usefulness of the easily accessible environmental chloride method for tracking groundwater dynamics in future studies. Considering the mass balance between chloride input from precipitation and soil Cl storage in the unsaturated zone, we combined 3H- and Cl-based tracing techniques to inversely reconstruct the long-term average or historical time series of ACD from the Cl stored in soil profiles. Our results highlight the proposed methods can effectively exclude fertilization impacts and perform satisfactorily in estimating ACD. However climatic and geographic factors had should be taken seriously when reconstructing ACD. A better understanding of groundwater recharge in unsaturated zones is ultimately critical for water resource management, especially in semi-arid environments with deep soils.