Mercury (Hg) is a widespread contaminant known to pose severe risks to wildlife and human health. While Hg emissions have declined in recent decades, legacy emissions and stored Hg will continue to impact watershed Hg cycling for the foreseeable future. Boreal forests are a major concern due to their capacity for storing Hg, vulnerability to disturbance, and record of high Hg concentrations in fish. Thus, there is a need to better quantify factors that influence Hg export from boreal forest catchments to inform watershed management decisions regarding Hg. Streamflow measurements, as well as approximately bi-weekly sampling for total mercury (THg), methylmercury (MeHg), and supporting stream chemistry were completed in 19 headwater streams near Dryden, Ontario during the ice-free season of 2019. The results were related to landscape and hydrological indices to elucidate the potential factors governing THg and MeHg export across these catchments. This study shows that while Hg concentrations are relatively low (0.50–20.46 ng l⁻¹ THg; < 0.04–1.21 ng l⁻¹ MeHg) across boreal streams in south central Canada, there are significant differences in Hg export. Catchments within boreal shield landscapes dominated by shallow soils and exposed bedrock export more methylmercury than catchments within glaciolacustrine plain landscapes dominated by thicker sand deposits. Coniferous forest cover is more significant than dissolved organic matter concentrations and more reliable than available % wetland cover data, two metrics commonly included in Hg transport models, for predicting THg and MeHg loads. In the absence of substantial mapped wetland cover, wet forest cover, as defined by the proportion of catchment cover by tree species favoring wet conditions, is shown to be an effective alternative metric. Considering the generally detailed and extensive data on tree species coverage available in Canada’s managed forests, wet forest cover, in addition to coniferous forest cover, could be useful for modelling Hg transport in boreal forest watersheds.

汞 (Hg) 是一种广泛存在的污染物，已知会对野生动物和人类健康构成严重威胁。虽然近几十年来汞排放量有所下降，但在可预见的未来，遗留排放物和储存的汞将继续影响流域汞循环。北方森林因其储存汞的能力、易受干扰以及鱼类体内汞含量高的记录而成为一个主要问题。因此，需要更好地量化影响北方森林集水区汞输出的因素，以便为有关汞的流域管理决策提供信息。在 2019 年无冰季节期间，在安大略省德莱顿附近的 19 条源头溪流中完成了溪流测量以及大约每两周一次的总汞 (THg)、甲基汞 (MeHg) 和辅助溪流化学采样。结果与景观和水文指数相关，以阐明控制这些流域中总汞和甲基汞出口的潜在因素。这项研究表明，虽然 Hg 浓度相对较低（0.50-20.46 ng l^-1总谐波失真；< 0.04–1.21 ng l ^-1MeHg) 在加拿大中南部的北方溪流中，汞出口存在显着差异。以浅层土壤和裸露的基岩为主的北方盾构景观中的集水区比以较厚的沙沉积物为主的冰湖相平原景观中的集水区出口更多的甲基汞。针叶林覆盖比溶解有机物浓度更重要，并且比可用的湿地覆盖率数据更可靠，这两个指标通常包含在 Hg 传输模型中，用于预测 THg 和 MeHg 负荷。在没有大量地图湿地覆盖的情况下，潮湿的森林覆盖率（由有利于潮湿条件的树种的集水区覆盖率定义）被证明是一种有效的替代指标。