Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes

Enduring legacy of a toxic fan via episodic redistribution of California gold mining debris

“…Since that time, sediment-bound Hg has contaminated fish and waterfowl of the San Francisco Bay-Delta (SFBD) (13,14). However, the dominant modern geographical sources of Hg, as well as the processes, patterns, and time scale of its delivery to this downstream ecosystem, are debated (15)(16)(17), partly due to the lack of a generic understanding of postmining fan evolution. It is unclear whether there are modern sources of Hg to this system and by what set of physical and biogeochemical processes Hg may penetrate these sensitive ecosystems.…”

Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining

“…Therefore, a small mass of high THg sediment from upstream could significantly alter the isotopic composition of Cache Creek sediment. Bear Creek sediment had δ 202 Hg (−0.31±0.17‰) and Δ 199 Hg (0.08±0.01‰; mean±1SD, n=3) that was comparable to unroasted Hg mine waste from New Idria (δ 202 Hg of −0.43 to +0.16‰) [39][40][41] and Hg ores from the CA Coast Range (δ 202 Hg of −0.64±0.84‰, mean± 1SD, n=91). 38 Sediment collected in Cache Creek was located 13 …”

“…[31][32][33][34][35] Hg isotopes have also been measured in a variety of Hg mine waste materials, including calcines and CA Coast Range Hg-ores. [36][37][38][39][40] Hg mine wastes can vary widely in isotopic composition over very small spatial scales (e.g., δ 202 Hg range of >5‰ within a single calcine sample), 31,32 but sediment downstream of individual mines is thought to largely integrate these different mining sources. 35,39,41 We hypothesized that the isotopic composition of high THg sediment in Cache Creek downstream of individual mining districts would enable us to distinguish the contribution of Hg mining (Coast Range) vs. Aumining (Sierra Nevada) Hg sources to Yolo Bypass.…”

Sediment-adsorbed total mercury flux through Yolo Bypass, the primary floodway and wetland in the Sacramento Valley, California

“…Much attention has been paid to mercury sources and sinks in the Sacramento River basin of California, due to the legacy of hydraulic gold mining in the Sierra Nevada and Hg mining in the Coast Ranges, which has created persistent contamination of lowland sediments and food webs (Bouse et al, 2010;Conaway et al, 2007;David et al, 2009;Davis et al, 2008;Domagalski, 2001;Eagles-Smith et al, 2009;Gehrke et al, 2011aGehrke et al, , 2009Greenfield et al, 2005;Greenfield and Jahn, 2010;Marvin-DiPasquale et al, 2009, 2003Roth et al, 2001;Rytuba, 2000). However, there is still great uncertainty in the mass balance of total mercury (THg) delivered to and stored in lowland floodplain environments from different source areas.…”

“…In total, between 1.4 and 4.5 × 10 6 kg of Hg are estimated to have been lost to the rivers draining the western slope of the Sierra Nevada (Alpers and Hunerlach, 2000;Churchill, 2000). This Hg has led to contamination of Sierradraining rivers in their piedmont courses that is registered in elevated bioaccumulation in the tissues of local aquatic species (Davis et al, 2008;Gehrke et al, 2011b;Hunerlach et al, 1999;Slotton et al, 1997;Slotton et al, 2003) and waterfowl (Eagles-Smith et al, 2009;Greenfield et al, 2005;Greenfield and Jahn, 2010), as well as in sediments (Alpers et al, 2005;Choe et al, 2004;Conaway et al, 2007;Domagalski, 2001;Domagalski et al, 2004;Gehrke et al, 2011a;James et al, 2009;Roth et al, 2001) at locations downstream of both gold and mercury mining sites in the basin.…”