Multi-tracer evidence of agritourism wastewater impacts and associated soil metal enrichment in a mountain headwater wetland.

Decentralized agritourism wastewater can introduce multiple contaminants into headwater wetlands, yet its coupled water-soil impacts remain poorly resolved. We combined nitrate dual isotopes, dissolved organic matter fluorescence, linear alkylbenzene sulfonate (LAS), fecal indicators, paired water-soil metal measurements, and a soil-column experiment across 11 fixed sites sampled in two seasons. δ15N-NO3- increased from 4.7 ± 0.5‰ upstream to 15.8 ± 1.4‰ in the agritourism reach, where the measured local domestic-wastewater end-member dominated the model-conditional source solutions. Independent tracer evidence consistently identified this reach as the principal wastewater-impact zone, with wastewater-associated indicators declining by 65-98% toward the reservoir. Cd, Hg, Pb, and Cr were concurrently enriched in soils, while Hg and Cd contributed 54.9% and 40.3%, respectively, of the screening-level ecological risk index. Soil-column experiments further showed matrix-dependent differences in metal breakthrough, with treated wastewater producing lower cumulative effluent deficits than untreated wastewater. These results reveal a clear cross-media contamination pattern and show that water-column attenuation does not necessarily indicate equivalent recovery of receiving soils, supporting targeted discharge surveillance and repeated soil monitoring focused on Hg and Cd.