Mercury volatilization from salt marsh sediments

Abstract

In situ volatilization fluxes of gaseous elemental mercury, Hg(0), were estimated for tidally exposed salt marsh sediments in the summer at the urban/industrial Secaucus High School Marsh, New Jersey Meadowlands (Secaucus, New Jersey) and in the early autumn at a regional background site in the Great Bay estuary (Tuckerton, New Jersey). Estimated daytime sediment‐air mercury volatilization fluxes at the Secaucus High School Marsh ranged from −375 to +677 ng m−2 h−1 and were positive (land to air flux) in 16 out of 20 measurement events. At the Great Bay estuary, mercury fluxes measured continuously over a 48‐h period ranged from −34 to +81 ng m−2 h−1 and were positive during the day and negative at night. At both sites, mercury volatilization fluxes peaked at midday, and cumulative mercury fluxes exhibited strong positive correlations with cumulative solar radiation (r2 = 0.97, p < 0.01) consistent with a light‐driven mercury volatilization efficiency of about 15 ng Hg mol PAR−1 or about 0.06 ng Hg kJ−1. No significant correlations were found between mercury fluxes and wind speed, air temperature, or tide height at either site. Thus despite a tenfold difference in sediment mercury concentration, photochemistry appears to be the dominant factor controlling mercury volatilization from these salt marsh sediments. The average mercury volatilization flux estimated for the Great Bay salt marsh in this study (17 ng m−2 h−1) compares well with other micrometeorological mercury fluxes for nonpoint source contaminated salt marsh and forest soils (8–18 ng m−2 h−1) and is more than 10 times higher than the average mercury emission flux from land (∼1 ng m−2 h−1). Annual mercury emissions from salt marsh wetlands may be comparable to individual industrial emissions sources in coastal states of the eastern United States.