Mercury deposition and methylmercury formation in Narraguinnep Reservoir, southwestern Colorado, USA

Abstract

Editorial handling by M. Kersten a b s t r a c t Narraguinnep Reservoir in southwestern Colorado is one of several water bodies in Colorado with a mercury (Hg) advisory as Hg in fish tissue exceed the 0.3 lg/g guideline to protect human health recommended by the State of Colorado. Concentrations of Hg and methyl-Hg were measured in reservoir bottom sediment and pore water extracted from this sediment. Rates of Hg methylation and methylHg demethylation were also measured in reservoir bottom sediment. The objective of this study was to evaluate potential sources of Hg in the region and evaluate the potential of reservoir sediment to generate methyl-Hg, a human neurotoxin and the dominant form of Hg in fish. Concentrations of Hg (ranged from 1.1 to 5.8 ng/L, n = 15) and methyl-Hg (ranged from 0.05 to 0.14 ng/L, n = 15) in pore water generally were highest at the sediment/water interface, and overall, Hg correlated with methyl-Hg in pore water (R 2 = 0.60, p = 0007, n = 15). Net Hg methylation flux in the top 3 cm of reservoir bottom sediment varied from 0.08 to 0.56 ng/m 2 /day (mean = 0.28 ng/m 2 /day, n = 5), which corresponded to an overall methyl-Hg production for the entire reservoir of 0.53 g/year. No significant point sources of Hg contamination are known to this reservoir or its supply waters, although several coal-fired power plants in the region emit Hg-bearing particulates. Narraguinnep Reservoir is located about 80 km downwind from two of the largest power plants, which together emit about 950 kg-Hg/year. Magnetic minerals separated from reservoir sediment contained spherical magnetite-bearing particles characteristic of coal-fired electric power plant fly ash. The presence of fly-ash magnetite in post-1970 sediment from Narraguinnep Reservoir indicates that the likely source of Hg to the catchment basin for this reservoir has been from airborne emissions from power plants, most of which began operation in the late-1960s and early 1970s in this region.Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Role of Settling Particles on Mercury Methylation in the Oxic Water Column of Freshwater Systems

“…Indeed, the genes responsible for Hg-methylation ( hgcAB ) were rarely found in oxygenated layers of the open ocean, suggesting that an unidentified metabolic pathway could be responsible for MeHg production in this environment. In fresh water ecosystems, MeHg formation has been extensively investigated in sediments ,− and biofilms − but rarely in the hypolimnetic waters. , MeHg formed in hypolimnetic waters compartment may actually represent a significant source of MeHg to the food chain when the volume of such water is larger than the volume of surface sediments . Recent studies suggest that atmospheric Hg can be methylated and even accumulated in food chains within 24 h after its deposition.…”

Warming increases methylmercury production in an Arctic soil

“…A survey of an area of continuous permafrost and interstitial tundra at BEO, Barrow, Alaska, showed MeHg concentrations ranging 0.3 to 2.3 ng L -1 in ponded surface water and active layer soil pore waters (Table S2), which is more than 10 times higher than those typically found in uncontaminated soils and sediments at lower latitudes (Gray et al, 2014). The respective total Hg and MeHg concentrations per gram dry weight soil in the core sample before incubation were 55.2 ± 1.3 and 0.08 ± 0.01 ng in the organic layer, and 54.0 ± 1.2 and 0.07± 0.01 ng in the mineral layer.…”

Mercury and methylmercury in aquatic sediment across western North America

“…The MeHg/THg ratio in this compilation was generally low across the landscape with a median value of 0.7% and a 90 th percentile of 3.1%, although more than 100 locations exceeded the 6% benchmark (Figure 4b). Several other studies have reported similar central tendencies for MeHg/THg ratios: estuarine sediment in southern Florida (0.8%, Kannan et al, 1998), estuarine sites in New England (0.4%, Taylor et al, 2012), reservoirs in Colorado (0.2% to 0.3%, Gray et al, 2014), and mine-dominated large-scale watersheds in the USA (1%, Krabbenhoft et al, 1999). However, much higher mean MeHg/THg ratios were reported in northeastern lakes and streams (4%, Loukmas et al, 2006) and watersheds across the USA (3.2%, Scudder et al, 2009), particularly in mixed agricultural-forested watersheds (10%, Krabbenhoft et al, 1999).…”