HR: 0830h
AN: B51D-1002    [PDF]
TI: Vegetated terrestrial ecosystems are large sources of Hg to the atmosphere
AU: Obrist, D
EM: dobrist@cabnr.unr.edu
AF: University of Nevada, Reno Environmental and Resource Science, Mail Stop 370, Reno, NV 89557
AU: * Gustin, M S
EM: msg@unr.nevada.edu
AF: University of Nevada, Reno Environmental and Resource Science, Mail Stop 370, Reno, NV 89557
AU: Arnone, J A
EM: jarnone@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512
AU: Schorran, D E
EM: daves@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512
AU: Verburg, P S
EM: pverburg@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512
AU: Johnson, D W
EM: djw@cabnr.unr.edu
AF: University of Nevada, Reno Environmental and Resource Science, Mail Stop 370, Reno, NV 89557
AB: Industrial processes, especially coal combustion and metal refining, have led to significant releases of Hg to the atmosphere during the last century. It has been hypothesized that a large percentage of this Hg has been deposited to terrestrial ecosystems via wet and dry deposition. Recent measurements of net Hg exchange between soils and the atmosphere indicate that terrestrial ecosystems are a source of Hg to the atmosphere, rather than the hypothesized sink, but very few measurements have been performed over vegetated terrestrial ecosystems. The objective of this study was to continuously measure net Hg exchange between a grassland ecosystem and the atmosphere during an entire year using the Ecologically Controlled Enclosed Lysimeter Laboratory (EcoCELLs) at Desert Research Institute. The EcoCELLs are unique open flow gas exchange systems that allow for the measurement of whole-ecosystem gas fluxes from large soil-plant monoliths under precisely controlled environmental conditions. Our results indicate that daily net ecosystem Hg exchange was positive (i.e., net Hg loss from the ecosystem to the atmosphere) during most of the year with the exception of the winter months when we observed net deposition of Hg to the ecosystem. Soil Hg fluxes only contributed between 10 % and 25 % of measured ecosystem Hg emissions. Ecosystem Hg fluxes showed pronounced diel patterns with higher daytime Hg emissions compared to nighttime Hg fluxes indicating that solar radiation, temperature, and evapotranspiration are important factors controlling Hg emissions. The cumulative annual Hg budget over one year indicated that the grassland ecosystem in our study was a relatively large Hg source to the atmosphere, ranging from 20 to 100 $\mu$ g Hg m$^{-2}$. Based on this study it appears that grassland ecosystems are sources of Hg to the atmosphere during most of the year, with vegetation greatly enhancing total emissions, possibly through transpiration, and that vegetated terrestrial ecosystems are large, yet still poorly quantified, sources of Hg to the atmosphere.
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting