A33H-0283
Mercury and Other Chemical Constituents in Pacific Marine Fog Water: Results from Two Summers of Sampling in FogNet

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Ossian Sahba1, Scott Conrad1, Robert Moranville1, Peter Scott Weiss-Penzias1, Kenneth H Coale2, Wesley Alan Heim3, Alex Olson3, Holly Chiswell3, Daniel Fernandez2, Andrew J Oliphant4, Celeste Dodge5, Dave Hoskins6 and James P Farlin7, (1)University of California Santa Cruz, Santa Cruz, CA, United States, (2)California State University Monterey Bay, Seaside, CA, United States, (3)Moss Landing Marine Laboratories, Moss Landing, CA, United States, (4)San Francisco State University, San Francisco, CA, United States, (5)Pepperwood Preserve, Santa Rosa, CA, United States, (6)Humboldt Marine Labs, Trinidad, CA, United States, (7)University of California Davis, Davis, CA, United States
Abstract:
The principle goal of FogNet is to make measurements of monomethylmercury (MMHg), total mercury (HgT) and major ions in Pacific Coast marine fog water samples taken from eight land stations from Big Sur to Trinidad, California in order to calculate the flux of MMHg and HgT to the terrestrial ecosystem, and observe their spatial and temporal patterns and relationships to major ion concentrations in fog water. During the summers of 2014 and 2015, fog water samples were analyzed and mean concentrations and standard deviations were found (number of samples shown in parentheses): MMHg = 1.9 +/- 2.4 ng L-1 (119), HgT = 28.7 +/- 26.8 ng L-1 (86), NH4+ = 2.5 +/- 2.0 mg L-1 (49), Cl- = 7.1 +/- 13.7 mg L-1 (52), SO42- = 15.3 +/- 26.0 mg L-1 (52), NO3- = 5.9 +/- 7.7 mg L-1 (48), and pH = 5.4 +/- 0.8 (38). For comparison, MMHg in rain is ~0.1 ng L-1 from previous studies. A temporal pattern in MMHg concentrations in fog was observed with monthly means of all samples for June, July, August and September 2014 (in ng L-1) of 4.2, 2.4, 1.4, and 0.8, respectively (see figure). No such temporal pattern was observed for HgT concentrations. The coastal site at Humboldt State University Marine Labs had fog water samples with the highest concentrations of MMHg (4.0 +/-4.3), whereas the inland site of Pepperwood had the lowest mean concentration of 0.7 +/- 0.5 ng L-1 among all sites. The temporal and spatial patterns observed in MMHg concentrations in fog water are consistent with a marine source. By combining the measured concentrations of analytes in fog water with an estimate of deposition from collocated 1 m2 passive fog collectors, the fluxes of MMHg and HgT for the summer of 2014 were 0.003-0.14 and 0.04-0.55 mg m-2 y-1, respectively. For MMHg, the mean fog water flux is about 4 times larger than that calculated for rain, and for HgT, the mean fog water flux is about 10% that calculated for rain.
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