The production and uptake of toxic methylmercury (MeHg) impacts aquatic ecosystems globally. Rivers can be dynamic and difficult systems to study for MeHg production and bioaccumulation, hence identifying sources of MeHg to these systems is both challenging and important for resource management within rivers and main-stem reservoirs. Riparian zones, which are known biogeochemical hotspots for MeHg production, are understudied as potential sources of MeHg to rivers. Here, we present a comprehensive quantification of the hydrologic and biogeochemical processes governing MeHg concentrations, loads, and bioaccumulation at 16 locations along 164 km of the agriculturally intensive Snake River (Idaho, Oregon USA) during summer baseflow conditions, with emphasis on riparian production of MeHg. Approximately one-third of the MeHg load of the Snake River could not be attributed to inflowing waters (upgradient, tributaries, or irrigation drains). Across the study reach, increases in MeHg loads in surface waters were significantly correlated with MeHg concentrations in riparian porewaters, suggesting riparian zones were likely an important source of MeHg to the Snake River. Across all locations, MeHg concentrations in surface waters positively correlated with MeHg concentrations in benthic snails and clams, supporting that riparian produced MeHg was assimilated into local aquatic food webs. This study contributes new insights into riparian MeHg production within rivers which can inform mitigation efforts to reduce MeHg bioaccumulation in fish.

中文翻译：

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河岸甲基汞生产增加了河流汞通量和食物网的浓度


有毒甲基汞 （MeHg） 的产生和吸收影响着全球的水生生态系统。河流可能是动态且难以研究 MeHg 产生和生物积累的系统，因此确定这些系统的 MeHg 来源对于河流和主干水库内的资源管理既具有挑战性又很重要。河岸带是已知的 MeHg 生产的生物地球化学热点，作为 MeHg 进入河流的潜在来源，尚未得到充分研究。在这里，我们全面量化了夏季基流条件下，在农业密集型蛇河（美国俄勒冈州爱达荷州）沿线 164 公里的 16 个地点控制 MeHg 浓度、负荷和生物积累的水文和生物地球化学过程，重点是 MeHg 的河岸生产。蛇河大约 1/3 的 MeHg 负荷不能归因于流入的水（上坡、支流或灌溉排水）。在整个研究范围内，地表水中 MeHg 负荷的增加与河岸孔隙水中 MeHg 浓度显著相关，这表明河岸区可能是 Snake 河中 MeHg 的重要来源。在所有地点，地表水中的 MeHg 浓度与底栖蜗牛和蛤蜊中的 MeHg 浓度呈正相关，这支持河岸产生的 MeHg 被同化到当地的水生食物网中。这项研究为河流中河岸 MeHg 的产生提供了新的见解，可以为减少鱼类中 MeHg 生物积累的缓解工作提供信息。