Spatial and Habitat-Based Variations in Total and Methyl Mercury Concentrations in Surficial Sediments in the San Francisco Bay-Delta

Abstract

Recent studies indicate significant amounts of mercury (Hg) are annually transported into the San Francisco Bay-Delta (Bay-Delta) as a result of historic gold and Hg mining activities. We examined temporal and spatial variation in concentrations of total Hg (Hg(T)) and monomethylmercury (MMHg) in surficial sediments of various ecosystem types in the Bay-Delta. We sampled surficial sediments across the Bay-Delta system and found Hg(T) sediment concentrations in the central Delta were generally 100-200 ng g(-1) and increased westward through Suisun Bay to 250-350 ng g(-1). MMHg concentrations in the central Delta were between 1 and 3 ng g(-1), while those in sediments in the perimeter waterways and adjacent bays were less than 1 ng g(-1). Six sites were monitored monthly for over a year to identify seasonal changes in Hg sediment concentrations. Hgtau sediment concentrations ranged from 48 to 382 ng g(-1) and varied as a function of location not season. However, MMHg concentrations varied seasonally, increasing from 1 ng g(-1) during winter months to 6 ng g(-1) during spring and summer. Transects conducted at three marshes in the central Delta revealed MMHg sediment concentrations of 4-8 ng g(-1) at the interior and 2 ng g(-1) at the exterior of the marshes. Habitat type was a major factor controlling MMHg concentration and the MMHg to Hg(T) ratio in sediments of the Bay-Delta. MMHg was significantly correlated to Hgt (r2 = 0.49) in marsh sediments.

Mercury in coastal watersheds along the Chinese Northern Bohai and Yellow Seas

“…These results were in agreement with those reported in previous studies [62][63][64][65]. Based on the spatial distribution of Hg and MeHg in waters, sediments and biota (Figs.…”

Recent advances in the study of mercury methylation in aquatic systems

“…Both flow frequency and inundated area have been found to determine production potential, rather than flood magnitude alone (Singer et al 2016). Temporal flooding also results in an increased volume of sediment in which methylation can take place (Heim et al 2007;Sizmur et al 2013). Recent research suggests that prairie wetlands with temporal hydrological patterns of drying and re-flooding can promote methylation over permanently inundated environments, provided that the flooding periods are not sufficiently long to promote MeHg degradation (Sando et al 2007).…”

Tidal exchange of total mercury and methylmercury between a salt marsh and a Chesapeake Bay sub-estuary

“…Tidal salt marshes are important zones of net methylmercury (MeHg) production and accumulation within coastal ecosystems (Marvin-Dipasquale et al 2003;Canario et al 2007;Heim et al 2007;Hall et al 2008;Mitchell and Gilmour 2008). In situ production and accumulation of MeHg in tidal marshes place biota that utilize tidal marshes at risk to MeHg exposure (Eagles-Smith et al 2009;Greenfield and Jahn 2010).…”