Abstract

Fuhrmann B, Beutel M, Ganguli P, Zhao L, Brower S, Funk A, Pasek J. 2021. Seasonal patterns of methylmercury production, release, and degradation in profundal sediment of a hypereutrophic reservoir. Lake Reserv Manage. 37:360–377.

Profundal lake sediment is an important site of toxic methylmercury (MeHg) production by anaerobic bacteria. This study tracked sediment MeHg cycling in hypereutrophic Hodges Reservoir, in the United States. Sediment-associated MeHg was most elevated in the early spring during moderately reduced conditions. In the late spring, MeHg and iron were released into hypolimnetic water during the progression from iron-reducing to sulfate-reducing conditions at the sediment–water interface. A decrease in porewater sulfate in the early summer indicated enhanced sulfate-reducing bacteria (SRB) activity and was associated with sediment buildup of MeHg, likely due to enhanced sorption to iron sulfides. Depletion of sulfate in the sediment during the fall corresponded with a substantial decrease in both sediment and water-column MeHg, suggesting that methanogenic conditions led to enhanced MeHg degradation. Shortly afterward, MeHg increased in the hypolimnion, indicating an upward shift in the zone of SRB methylation. Our study suggests 2 “hot moments” of MeHg entry into the water column, where it is susceptible to uptake into the pelagic food web: a spring window of mildly reduced conditions that promote MeHg release from sediment, and a fall window where MeHg is produced in the upper hypolimnion. These hot moments may potentially be managed to lower mercury bioaccumulation via redox enhancement of the profundal zone with approaches such as bottom water oxygenation, which began operation in Hodges Reservoir in 2020. However, the complexity of biogeochemical responses to such management perturbations in regard to MeHg cycling makes it difficult to predict the ultimate effect of oxygenation on mercury bioaccumulation.

Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2021.1940397 .

摘要

Fuhrmann B、Beutel M、Ganguli P、Zhao L、Brower S、Funk A、Pasek J. 2021。超富营养化水库深部沉积物中甲基汞产生、释放和降解的季节性模式。湖泊保护区管理。37:360-377。

深湖沉积物是厌氧菌产生有毒甲基汞（MeHg）的重要场所。这项研究追踪了美国富营养化霍奇斯水库中沉积物甲基汞的循环。在适度减少的条件下，与沉积物相关的甲基汞在早春升高最多。在晚春，在沉积物 - 水界面从铁还原条件到硫酸盐还原条件的过程中，甲基汞和铁被释放到下沉水中。初夏孔隙水硫酸盐的减少表明硫酸盐还原菌 (SRB) 活性增强，并且与甲基汞的沉积物堆积有关，这可能是由于对硫化铁的吸附增强。秋季沉积物中硫酸盐的消耗与沉积物和水柱甲基汞的显着减少相对应，表明产甲烷条件导致甲基汞降解增强。此后不久，水下层中的甲基汞增加，表明 SRB 甲基化区域向上移动。我们的研究表明，甲基汞进入水体有 2 个“热点时刻”，在那里它很容易被吸收到远洋食物网中：促进甲基汞从沉积物中释放的温和减少条件的春季窗口，以及产生甲基汞的秋季窗口在上水层。这些高温时刻可能会通过深层区域的氧化还原增强和底水氧化等方法来降低汞的生物积累，该方法于 2020 年在 Hodges 水库开始运行。但是，

本文的补充数据可在 https://doi.org/10.1080/10402381.2021.1940397 在线获得。