Hall et al. 2023 — MeHg production and bioaccumulation in tidal marsh food webs
This study characterized mesoscale spatial variation in methylmercury (MeHg) production and bioaccumulation across four hydrological and geomorphological marsh features (interiors, edges, first-order channels, third-order channels) at three tidal marshes along the Petaluma River, San Francisco Bay, California. Marsh interiors had biogeochemical conditions — greater organic matter, greater sulfate reduction rates, greater MeHg production potential — that led to greater MeHg concentrations in sediments and surface water particulates. Consumer tissue MeHg concentrations were greater from marsh edges and interiors than from channels, a spatial mismatch from sediment patterns that the authors attribute to consumer behavior and physiology governing the spatial scale over which MeHg is integrated into tissues.
Key numbers
Sediment MeHg concentrations differed among features (marsh interiors > other features, though not statistically significant at p = 0.09 due to modest sample sizes). Consumer tissue MeHg (µg/g dry mass) was significantly greater from marsh edges and interiors compared to channels (GLM with feature, site, trophic position, and dietary carbon source as predictors; likelihood ratio test significant).
Consumer genera sampled: Assiminea (n=6), Myostotella (n=6), Geukensia (n=19), Macoma (n=11), Traskorchestia (n=12), Bembidion (n=2), Pardosa (n=11), Palaemon (n=3), Hemigrapsus (n=6), Tridentiger (n=12), Acanthogobius (n=5), Gillichthys (n=1), Gambusia (n=5), Gasterosteus (n=16), Cottus (n=1). Total composited consumer samples: marsh interior n=20, marsh edge n=17, first-order channel n=29, third-order channel n=50.
MeHg analyzed in invertebrates by Battelle Marine Sciences Laboratory method (Bloom); THg in fish by USGS EPA Method 7473 (DMA-80). THg in fish treated as equivalent to MeHg (80–100% THg is MeHg in fish muscle per prior literature).
Methods (brief)
Three tidal marshes along Petaluma River, northern San Francisco Bay; sampling in spring (April) and summer (August) 2006. Composited surface sediments (0–2 cm). ICP-MS and USGS Mercury Research Laboratory (Middleton, WI) for THg and MeHg. Invertebrate MeHg by distillation-aqueous phase ethylation (Bloom method). Fish THg by DMA-80 (EPA Method 7473). Stable isotopes (δ¹³C, δ¹⁵N) for trophic position control. GLM with Tukey’s HSD for multiple comparisons.
Implications
Certification: Tidal marsh fish and shellfish from legacy-mercury-contaminated areas present elevated MeHg risks; bioaccumulation varies significantly by marsh microhabitat, not just by waterbody. Sourcing from specific marsh microhabitats matters for MeHg exposure assessment.
Courses: Classic illustration of MeHg biomagnification through marsh food webs; the spatial mismatch between sediment production hotspots and tissue accumulation hotspots is counterintuitive and pedagogically important.
App: Fish and shellfish sourced from tidal marsh environments near historic mining areas (Bay Area, California) warrant elevated MeHg flags; waterfowl and bivalves from such areas are also flagged.