Source Tracing Techniques for Groundwater Contamination in Land-Sea Interaction Zone: A Critical Review

The land-sea interaction zone, as an ecologically sensitive interface linking terrestrial and marine systems, features complex material and energy exchange processes. The identification of contaminant sources in coastal groundwater is challenging due to the dual influence of anthropogenic activities and complex surface water-groundwater interactions. Over the years, various source tracing techniques have been developed from multiple perspectives, such as indicators, analytical methods, and data processing. This paper systematically reviews main contamination source tracing techniques applied in coastal groundwater, basing on chemical, geophysical prospecting, inverse modeling and biological methods. The advantages and limitations of these techniques in terms of tracing principles, applicable scope, and effectiveness are discussed comprehensively. A major challenge is that most existing source tracing techniques require a large number of sampling points, provide only coarse spatial resolution, and lack sufficient accuracy in identifying contamination source types. This study aims to offer technical references for tracing groundwater contamination sources in land-sea interaction zones. Future research should focus on developing more advanced tracing techniques based on information-rich microbial communities and organic matter fingerprints, integrated with machine learning techniques.