Marine fog inputs appear to increase methylmercury bioaccumulation in a coastal terrestrial food web

Coastal marine atmospheric fog has recently been implicated as a potential source of ocean-derived monomethylmercury (MMHg) to coastal terrestrial ecosystems through the process of sea-to-land advection of foggy air masses followed by wet deposition. This study examined whether pumas (Puma concolor) in coastal central California, USA, and their associated food web, have elevated concentrations of MMHg, which could be indicative of their habitat being in a region that is regularly inundated with marine fog. We found that adult puma fur and fur-normalized whiskers in our marine fog-influenced study region had a mean (±SE) total Hg (THg) (a convenient surrogate for MMHg) concentration of 1544 ± 151 ng g−1 (N = 94), which was three times higher (P < 0.01) than mean THg in comparable samples from inland areas of California (492 ± 119 ng g−1, N = 18). Pumas in California eat primarily black-tailed and/or mule deer (Odocoileus hemionus), and THg in deer fur from the two regions was also significantly different (coastal 28.1 ± 2.9, N = 55, vs. inland 15.5 ± 1.5 ng g−1, N = 40). We suggest that atmospheric deposition of MMHg through fog may be contributing to this pattern, as we also observed significantly higher MMHg concentrations in lace lichen (Ramalina menziesii), a deer food and a bioindicator of atmospheric deposition, at sites with the highest fog frequencies. At these ocean-facing sites, deer samples had significantly higher THg concentrations compared to those from more inland bay-facing sites. Our results suggest that fog-borne MMHg, while likely a small fraction of Hg in all atmospheric deposition, may contribute, disproportionately, to the bioaccumulation of Hg to levels that approach toxicological thresholds in at least one apex predator. As global mercury levels increase, coastal food webs may be at risk to the toxicological effects of increased methylmercury burdens.publishedVersio

Total and Monomethyl Mercury in Fog Water from the Central California Coast

[1] Total mercury (HgT) and monomethyl mercury (MMHg) concentrations in fog collected from 4 locations in and around Monterey Bay, California during June-August of 2011 were 10.7 ± 6.8 and 3.4 ± 3.8 ng L−1respectively. In contrast, mean HgT and MMHg concentrations in rain water from March-June, 2011 were 1.8 ± 0.9 and 0.1 ± 0.04 ng L−1 respectively. Using estimates of fog water deposition from 6 sites in the region using a standard fog water collector (SFC), depositions of HgT and MMHg via fog were found to range from 42–4600 and 14–1500 ng m−2 y−1, which accounted for 7–42% of HgT and 61–99% of MMHg in total atmospheric deposition (fog, rain, and dry deposition), estimated for the coastal area. These initial measurements suggest that fog precipitation may constitute an important but previously overlooked input of MMHg to coastal environments. Preliminary comparisons of these data with associated chemical, meteorological and oceanic data suggest that biotically formed MMHg from coastal upwelling may contribute to the MMHg in fog water

Sources of gaseous oxidized mercury and mercury dry deposition at two southeastern U.S. sites

Wet deposition measurements have shown that relative to other parts of the US, the southeastern region has the highest mercury (Hg) inputs. The source of this Hg has been investigated by multiple researchers and is suggested to be derived from local, regional and global sources. Here we focus on trying to understand potential sources of Hg to this area during periods dominated by dry gaseous oxidized mercury (GOM) deposition. Dry deposition of GOM to a surrogate surface was measured in conjunction with speciated atmospheric Hg, and ancillary parameters from September 2007 through September 2008 at two sites located within 25 km of coal-fired power plants (CFPPs) near Yorkville, GA, and Pensacola, FL. Mean weekly GOM dry deposition, daily GOM, and daily sulfur dioxide (SO2) concentrations were significantly (P \u3c 0.01) higher at the Yorkville site by factors of 1.5, 2.0, and 1.8, respectively. At both sites, GOM and SO2 concentrations were significantly correlated (P \u3c 0.05) in every season on hourly and daily time scales. Wind rose diagrams showed significantly enhanced GOM and SO2 concentrations when air moved to the sites from the direction of the nearest CFPPs. Most periods of enhanced GOM concentrations ([GOM] \u3e 98th percentile), were also associated with NOy/SO2 ratios that were within 25% of that reported for the local CFPPs (N = 27 of 33 at Yorkville, N = 18 of 26 at Pensacola). During these events, termed Category 1, mean GOM/SO2 enhancement ratios were 2.4 ± 0.1 and 2.3 ± 0.1 pg m−3 ppb−1 for Yorkville and Pensacola, respectively (range = 0.5 to 5.5). The remaining events at both sites (termed Category 2) displayed significantly lower SO2 concentrations, yet GOM concentrations were not significantly different compared to Category 1 events. The potential sources of GOM during the Category 2 events at OLF were investigated using gridded frequency distributions (GFD) of 72-h atmospheric back trajectories. During these periods there was a greater component of air mass transport from the free troposphere, and less precipitation along the trajectory paths compared to GFDs for Category 1 events. GFDs developed for the weeks when GOM dry deposition was in the upper quartile at both sites simultaneously revealed a similar pattern to the GFDs of Category 2 GOM concentration events, that is, greater free tropospheric transport and relatively little precipitation. Although dry deposition inputs are thought to represent \u3c15% of total annual Hg deposition in this region, we suggest that a significant portion of this Hg could be derived from sources outside the local area

Marine fog inputs appear to increase methylmercury bioaccumulation in a coastal terrestrial food web

Coastal marine atmospheric fog has recently been implicated as a potential source of ocean-derived monomethylmercury (MMHg) to coastal terrestrial ecosystems through the process of sea-to-land advection of foggy air masses followed by wet deposition. This study examined whether pumas (Puma concolor) in coastal central California, USA, and their associated food web, have elevated concentrations of MMHg, which could be indicative of their habitat being in a region that is regularly inundated with marine fog. We found that adult puma fur and fur-normalized whiskers in our marine fog-influenced study region had a mean (±SE) total Hg (THg) (a convenient surrogate for MMHg) concentration of 1544 ± 151 ng g−1 (N = 94), which was three times higher (P < 0.01) than mean THg in comparable samples from inland areas of California (492 ± 119 ng g−1, N = 18). Pumas in California eat primarily black-tailed and/or mule deer (Odocoileus hemionus), and THg in deer fur from the two regions was also significantly different (coastal 28.1 ± 2.9, N = 55, vs. inland 15.5 ± 1.5 ng g−1, N = 40). We suggest that atmospheric deposition of MMHg through fog may be contributing to this pattern, as we also observed significantly higher MMHg concentrations in lace lichen (Ramalina menziesii), a deer food and a bioindicator of atmospheric deposition, at sites with the highest fog frequencies. At these ocean-facing sites, deer samples had significantly higher THg concentrations compared to those from more inland bay-facing sites. Our results suggest that fog-borne MMHg, while likely a small fraction of Hg in all atmospheric deposition, may contribute, disproportionately, to the bioaccumulation of Hg to levels that approach toxicological thresholds in at least one apex predator. As global mercury levels increase, coastal food webs may be at risk to the toxicological effects of increased methylmercury burdens

Fog Water Collection Effectiveness: Mesh Intercomparisons

To explore fog water harvesting potential in California, we conducted long-term measurements involving three types of mesh using standard fog collectors (SFC). Volumetric fog water measurements from SFCs and wind data were collected and recorded in 15-minute intervals over three summertime fog seasons (2014–2016) at four California sites. SFCs were deployed with: standard 1.00 m[superscript 2] double-layer 35% shade coefficient Raschel; stainless steel mesh coated with the MIT-14 hydrophobic formulation; and FogHa-Tin, a German manufactured, 3-dimensional spacer fabric deployed in two orientations. Analysis of 3419 volumetric samples from all sites showed strong relationships between mesh efficiency and wind speed. Raschel mesh collected 160% more fog water than FogHa-Tin at wind speeds less than 1 m s[superscript –1] and 45% less for wind speeds greater than 5 m s[superscript –1]. MIT-14 coated stainless-steel mesh collected more fog water than Raschel mesh at all wind speeds. At low wind speeds of < 1 m s[superscript –1] the coated stainless steel mesh collected 3% more and at wind speeds of 4– 5 m s[superscript –1], it collected 41% more. FogHa-Tin collected 5% more fog water when the warp of the weave was oriented vertically, per manufacturer specification, than when the warp of the weave was oriented horizontally. Time series measurements of three distinct mesh across similar wind regimes revealed inconsistent lags in fog water collection and inconsistent performance. Since such differences occurred under similar wind-speed regimes, we conclude that other factors play important roles in mesh performance, including in-situ fog event and aerosol dynamics that affect droplet-size spectra and droplet-to-mesh surface interactions. Keywords: Fog mesh, Fog water collection efficiency, Raschel mesh, Hydrophobic coatingNational Science Foundation (U.S.) (Grant OCE-1333976)Geological Survey (U.S.). Climate and Land Use Change Mission AreaNBD NanotechnologiesNational Science Foundation (U.S.). Small Business Innovation Research Program (Award 2015-33610-23832

The Estimated Six-Year Mercury Dry Deposition Across North America

Dry deposition of atmospheric mercury (Hg) to various land covers surrounding 24 sites in North America was estimated for the years 2009 to 2014. Depending on location, multiyear mean annual Hg dry deposition was estimated to range from 5.1 to 23.8 μg m^–2 yr^–1 to forested canopies, 2.6 to 20.8 μg m^–2 yr^–1 to nonforest vegetated canopies, 2.4 to 11.2 μg m^–2 yr^–1 to urban and built up land covers, and 1.0 to 3.2 μg m^–2 yr^–1 to water surfaces. In the rural or remote environment in North America, annual Hg dry deposition to vegetated surfaces is dominated by leaf uptake of gaseous elemental mercury (GEM), contrary to what was commonly assumed in earlier studies which frequently omitted GEM dry deposition as an important process. Dry deposition exceeded wet deposition by a large margin in all of the seasons except in the summer at the majority of the sites. GEM dry deposition over vegetated surfaces will not decrease at the same pace, and sometimes may even increase with decreasing anthropogenic emissions, suggesting that Hg emission reductions should be a long-term policy sustained by global cooperation