Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 48, Issue 16, Pages 9514-9522Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es502134t
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Funding
- NSF Divisions of Atmospheric Chemistry [ATM0961357]
- Chemical Oceanography [OCE1130549]
- Arctic Great Rivers Observatory team [NSF OPP-0732522, OPP-0732821, OPP-1107774]
- USGS Toxics program
- NSF GFRP
- 7FP GMOS
- ARRS program [P1-0143]
- Directorate For Geosciences
- Division Of Ocean Sciences [1130549] Funding Source: National Science Foundation
- Directorate For Geosciences
- Office of Polar Programs (OPP) [1107774] Funding Source: National Science Foundation
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [0961357] Funding Source: National Science Foundation
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Rivers are an important source of mercury (Hg) to marine ecosystems. Based on an analysis of compiled observations, we estimate global present-day Hg discharges from rivers to ocean margins are 27 +/- 13 Mmol a(-1) (5500 +/- 2700 Mg a(-1)), of which 28% reaches the open ocean and the rest is deposited to ocean margin sediments. Globally, the source of Hg to the open ocean from rivers amounts to 30% of atmospheric inputs. This is larger than previously estimated due to accounting for elevated concentrations in Asian rivers and variability in offshore transport across different types of estuaries. Riverine inputs of Hg to the North Atlantic have decreased several-fold since the 1970s while inputs to the North Pacific have increased. These trends have large effects on Hg concentrations at ocean margins but are too small in the open ocean to explain observed declines of seawater concentrations in the North Atlantic or increases in the North Pacific. Burial of Hg in ocean margin sediments represents a major sink in the global Hg biogeochemical cycle that has not been previously considered. We find that including this sink in a fully coupled global biogeochemical box model helps to balance the large anthropogenic release of Hg from commercial products recently added to global inventories. It also implies that legacy anthropogenic Hg can be removed from active environmental cycling on a faster time scale (centuries instead of millennia). Natural environmental Hg levels are lower than previously estimated, implying a relatively larger impact from human activity.
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