This study investigated the nitrate dual isotopic compositions (δN and δO) of water samples to trace nitrate sources in Lake Sihwa, which encompasses various land-use types (e.g., urban, industry, wetland, and agriculture). The biogeochemical interactions of anthropogenic nitrogen sources (e.g., soil, road dust, and septic water) were also evaluated through multiple pathways from terrestrial boundaries to the water column. Based on increased concentrations of dissolved total nitrogen (DTN; 3.1 ± 1.6 mg/L) after typhoon, the variation of element stoichiometry (N:P:Si) in this system shifted to the relatively N-rich conditions (DIN/DIP; 14.1 ± 8.1, DIN/DSi; 1.4 ± 1.8), potentially triggering the occurrence of harmful algal blooms. Furthermore, discriminative isotopic compositions (δN; 4.0 ± 2.1 ‰, δO; 6.1 ± 4.3 ‰) after the typhoon suggested the increased DTN input of anthropogenic origins within Lake Sihwa would be mainly transported from urban sources (76 ± 9 %). Consequently, the isotopic-based approach may be useful for effective water quality management under increased anthropogenic activities near aquatic systems.

中文翻译：

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台风对韩国始华湖人为氮源的影响

本研究调查了水样的硝酸盐双同位素组成（δN 和 δO），以追踪始华湖的硝酸盐来源，其中涵盖了各种土地利用类型（例如城市、工业、湿地和农业）。人为氮源（例如土壤、道路灰尘和化粪池水）的生物地球化学相互作用也通过从陆地边界到水柱的多种途径进行了评估。基于台风过后溶解总氮浓度的增加（DTN；3.1 ± 1.6 mg/L），该系统中元素化学计量（N:P:Si）的变化转向相对富氮的条件（DIN/DIP；14.1） ± 8.1，DIN/DSi；1.4 ± 1.8)，可能引发有害藻华的发生。此外，台风后的同位素组成（δN；4.0±2.1‰，δ18O；6.1±4.3‰）表明始华湖内人为来源增加的DTN输入将主要来自城市来源（76±9％）。因此，基于同位素的方法可能有助于在水生系统附近人类活动增加的情况下进行有效的水质管理。