U.S. Geological Survey, Idaho Water Science Center, United States of America.
U.S. Geological Survey, Upper Midwest Water Science Center, United States of America.
Sci Total Environ. 2024 Jan 10;907:167961. doi: 10.1016/j.scitotenv.2023.167961. Epub 2023 Oct 20.
Understanding sources of mercury (Hg) and methylmercury (MeHg) to a water body is critical for management but is often complicated by poorly characterized Hg inputs and in situ processes, such as inorganic Hg methylation. In this study, we determined inorganic Hg and MeHg concentrations and loads (filter-passing and particulate fractions) for a semi-arid 164-kilometer stretch of the Snake River above the Hells Canyon Complex, a Hg-impaired hydroelectric reservoir complex on the Idaho-Oregon border, and used water quality measurements and Hg stable isotope ratios to create a comprehensive Hg source budget for the river. Results show that whereas most of the streamflow to the study reach comes from the main branch of the Snake River (i.e., the upstream watershed), major tributaries within the study reach contribute a greater proportion of inorganic Hg and MeHg loads. Mercury stable-isotope analyses highlight that Hg within the tributaries is predominantly associated with geologic deposits and snowmelt sources, the latter reflecting wet deposition. Surprisingly, irrigation return drains contribute 40-50 % of particulate inorganic Hg loads despite being ≤4.3 % of the overall water budget. Together, tributaries and irrigation return drains account for 97-100 % of the inorganic Hg and streamflow to the study reach, but ~65 % of the MeHg, indicating in-stream and riparian methylation may be an important and previously unrecognized source of MeHg. Streamflow, total suspended solids, dissolved organic carbon, and agricultural land cover were found to be important controls on the mobilization and transport of different Hg species and fractions. This study represents the first fluvial budget for Hg in the Snake River that accounts for particulate and filter-passing Hg species from both major tributaries and irrigation return drains, and expands our understanding of Hg sources and methylation processes within semi-arid environments. This information is critical to inform management decisions related to elevated Hg burdens in biota.
了解水体中汞 (Hg) 和甲基汞 (MeHg) 的来源对于管理至关重要，但由于 Hg 输入和原位过程（如无机 Hg 甲基化）特征描述较差，情况往往变得复杂。在这项研究中，我们测定了半干旱的蛇河 164 公里河段的无机 Hg 和 MeHg 浓度和负荷（过滤通过和颗粒部分），该河段位于爱达荷州-俄勒冈州边界的海尔斯峡谷复合水电库 Hg 受损区，利用水质测量和 Hg 稳定同位素比值为该河流创建了全面的 Hg 源预算。结果表明，尽管研究河段的大部分水流来自蛇河的主要支流（即上游流域），但研究河段内的主要支流贡献了更大比例的无机 Hg 和 MeHg 负荷。Hg 稳定同位素分析突出表明，支流中的 Hg 主要与地质沉积物和融雪源有关，后者反映了湿沉降。令人惊讶的是，尽管灌溉回流水仅占总水量的 4.3%，但其却贡献了 40-50%的颗粒态无机 Hg 负荷。总之，支流和灌溉回流水占研究河段无机 Hg 和径流量的 97-100%，但占 MeHg 的~65%，表明河流和河岸甲基化可能是 MeHg 的一个重要且以前未被认识到的来源。发现径流量、总悬浮固体、溶解有机碳和农业土地覆被是不同 Hg 物种和形态迁移和运输的重要控制因素。本研究代表了首次对蛇河 Hg 进行河流预算，其中包括来自主要支流和灌溉回流水的颗粒态和过滤态 Hg 物种，并扩展了我们对半干旱环境中 Hg 来源和甲基化过程的认识。这些信息对于告知与生物体内 Hg 负荷升高相关的管理决策至关重要。
