Dual-phase nitrogen transport from swine farms in a volcanic watershed of Jeju Island, South Korea: Insights from hydrochemical, isotopic and microbial analyses

초록

Intensive livestock farming in volcanic watersheds creates complex nitrogen pollution pathways that remain poorly understood. This study investigated nitrogen transport mechanisms in an ephemeral creek system on Jeju Island, South Korea, using an integrated approach combining hydrochemical analysis, dual isotope tracing, and microbial community profiling of 52 water samples from groundwater, springs, and surface runoff. Results revealed a two-stage nitrogen pollution mechanism: during dry periods, manure-derived nitrogen underwent volatilization, creating accumulated nitrogen reservoirs with enriched delta 15N signatures. Rainfall events subsequently triggered rapid mobilization of stored nitrogen through ephemeral creeks and subsurface pathways. Nitrate concentrations in spring water consistently exceeded Korean drinking water standard (44.4 mg/L NO3), with isotopic signatures confirming manure as the primary source. Dual isotope analysis demonstrated that microbial nitrification was the dominant transformation process, supported by key nitrifying bacteria (Acinetobacter, Comamonadaceae) along flow paths. Bayesian mixing models confirmed that runoff became the primary contributor to spring water nitrate during precipitation events. Advanced compositional data analysis validated the mixing of surface-derived nitrogen with groundwater. These findings highlight the vulnerability of spring water systems to delayed nitrogen inputs in fractured volcanic aquifers, emphasizing the need for management strategies that address both immediate and rainfall-triggered transport pathways in agricultural watersheds.

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