The understanding of the essential environmental factors affecting the spatiotemporal variation in methylmercury (MeHg) in river water is limited to date, despite its importance for predicting the effect of ongoing climate change on MeHg accumulation in freshwater ecosystems. This study aimed to explore the variation in MeHg concentration and related environmental factors in the downstream zone of the Yeongsan River under highly dynamic hydrologic conditions by using water quality and hydrologic data collected from 1997 to 2022, and Hg and MeHg data collected from 2017 to 2022. The mean concentration of unfiltered MeHg was 35.7 ± 13.7 pg L ( = 24) in summer and 26.7 ± 7.43 pg L ( = 24) in fall. Dissolved oxygen (DO), conductivity, nitrate, and dissolved organic carbon (DOC) were determined to be the most influential variables in terms of MeHg variation based on the partial least squares regression model, and their effects on the MeHg concentration were negative, except for DOC. Heatmaps representing the similarity distances between temporal trends of hydrologic and water quality variables were constructed to determine fundamental factors related to the time-based variations in DO, conductivity, nitrate, and DOC using a dynamic time warping algorithm. The heatmap cluster analysis showed that the temporal trends of these variables were closely related to rainfall variation rather than irradiance or water temperature. Overall, biogeochemical factors directly related to in situ methylation rate of Hg(II)—rather than transport of Hg(II) and MeHg from external sources—mainly control the spatiotemporal variation of MeHg in the downstream zone of the Yeongsan River.

中文翻译：

---

高动态水文条件下温带河流甲基汞及相关水质变量的时空变化


尽管对于预测持续气候变化对淡水生态系统中甲基汞积累的影响非常重要，但迄今为止，对影响河水中甲基汞 (MeHg) 时空变化的基本环境因素的了解仍然有限。本研究旨在利用1997年至2022年采集的水质和水文数据以及2017年至2022年采集的汞和甲基汞数据，探讨高动态水文条件下荣山江下游区域甲基汞浓度的变化及相关环境因素。夏季未过滤的甲基汞的平均浓度为 35.7 ± 13.7 pg L (= 24)，秋季为 26.7 ± 7.43 pg L (= 24)。基于偏最小二乘回归模型，溶解氧（DO）、电导率、硝酸盐和溶解有机碳（DOC）被确定为对甲基汞变化影响最大的变量，它们对甲基汞浓度的影响为负，除了对于文档。构建了代表水文和水质变量时间趋势之间相似距离的热图，以便使用动态时间扭曲算法确定与 DO、电导率、硝酸盐和 DOC 随时间变化相关的基本因素。热图聚类分析表明，这些变量的时间趋势与降雨变化密切相关，而不是与辐照度或水温密切相关。总体而言，与Hg(II)原位甲基化率直接相关的生物地球化学因素——而不是Hg(II)和MeHg从外部来源的迁移——主要控制着灵山江下游区域MeHg的时空变化。