NSF Org:	EAR Division Of Earth Sciences
Recipient:	THE REGENTS OF THE UNIVERSITY OF COLORADO
Initial Amendment Date:	July 28, 2010
Latest Amendment Date:	July 25, 2011
Award Number:	0952068
Award Instrument:	Standard Grant
Program Manager:	Enriqueta Barrera EAR  Division Of Earth Sciences GEO  Directorate for Geosciences
Start Date:	August 1, 2010
End Date:	July 31, 2015 (Estimated)
Total Intended Award Amount:	$325,395.00
Total Awarded Amount to Date:	$406,288.00
Funds Obligated to Date:	FY 2010 = $325,395.00 FY 2011 = $80,893.00
History of Investigator:	Joseph Ryan (Principal Investigator) joseph.ryan@colorado.edu George Aiken (Co-Principal Investigator)
Recipient Sponsored Research Office:	University of Colorado at Boulder 3100 MARINE ST Boulder CO  US  80309-0001 (303)492-6221
Sponsor Congressional District:	02
Primary Place of Performance:	University of Colorado at Boulder 3100 MARINE ST Boulder CO  US  80309-0001
Primary Place of Performance Congressional District:	02
Unique Entity Identifier (UEI):	SPVKK1RC2MZ3
Parent UEI:
NSF Program(s):	Geobiology & Low-Temp Geochem
Primary Program Source:	01001011DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s):	OTHR
Program Element Code(s):	729500
Award Agency Code:	4900
Fund Agency Code:	4900
Assistance Listing Number(s):	47.050

ABSTRACT

Intellectual merit: Mercury mobilized by forest fire is accumulating in aquatic organisms in lakes and reservoirs in the Rocky Mountain region. Recent research has focused on mercury emitted to the atmosphere during forest fires, but fire also releases mercury to streams, lakes, and reservoirs. Soil organic matter effectively sequesters most of the mercury deposited in forested watersheds, and fire results in the destruction or erosion of most of the soil organic matter. Fire also results in the development of anoxic, sulfate-reducing conditions in the lakes and reservoirs receiving runoff from fire-disturbed watersheds, and under these conditions, mercury is biologically converted to methylmercury, the form that readily accumulates in aquatic organisms and concentrates up the food chain. In this proposal, research is outlined to examine the effect of fire on the ability of soil organic matter to strongly bind mercury and prevent methylation and bioaccumulation. The research is driven by three
hypotheses addressing the transformations caused by fire in the oxidation state of sulfur in soil organic matter and the effect of these changes on mercury binding. The hypotheses are (1) that forest fire increases the oxidation state of sulfur in soil organic matter, (2) that forest fire decreases the strong mercury binding capacity of soil organic matter because of the increase in the oxidation state of the sulfur, and (3) that sediment burial restores, or increases, the strong mercury binding capacity of soil organic matter because of incorporation of hydrogen sulfide in the lake and reservoir sediments. Soil and lake/reservoir sediment sampling will be carried out in watersheds affected by wildfire and prescribed burn. Mercury adsorption to and desorption from the soils, sediments, and extracted organic matter, will be examined using furnace heating to reproducibly assess the effect of heat on sulfur oxidation and mercury binding. In addition, the sulfur and mercury in these materials will be characterized with x?]ray absorption near edge structure (XANES) and extended x?]ray absorption fine structure (EXAFS) spectroscopy.

Broader Impact: The broader impacts of this proposal involve three unique features: (1) growth of the San Juan Collaboratory, an initiative of the University of Colorado, Fort Lewis College, the Mountain Studies Institute, and federal, regional, and state land management agencies in the San Juan Mountains region, (2) recruitment of under-represented graduate students through well-established and successful programs at the University of Colorado and University of Illinois, and (3) establishment of the Colorado Water Quality Outreach Center (CWQOC) at the University of Colorado. The San Juan Collaboratory was recently formed to enhance and establish research and educational programs for the southwestern Colorado area. The Colorado Water Quality Outreach Center is being established with the support of the University of Colorado Outreach Committee to provide a state-wide avenue for watershed stakeholder groups and municipalities dealing with water quality problems to seek assistance from faculty and students with water quality problems.

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

The transport and deposition of mercury from natural and anthropogenic sources has led to enrichment of mercury in soils on a global scale.  In arid climates, such as the southwestern United States, the common occurrence of wildfire mobilizes mercury from soils.  Some of the mercury is mobilized to the atmosphere and some is mobilized to natural waters.

Limited evidence indicated that transport of mercury from forest soils to streams, lakes, and reservoirs leads to transformation of mercury into a form -- methylmercury -- that results in accumulation of mercury in aquatic organisms.  To better understand the effect of fire on mercury bioaccumulation, we conducted field and laboratory studies in several forested watersheds in Colorado, United States, subjected to historical and recent wildfire.

Simulated wildfire heating of soil was conducted using a furnace to observe the influence of heat on the oxidation of sulfur, which was thought to be responsible for binding mercury to organic matter in soils. Experiments were conducted on soils to assess the release of mercury from burned, unburned, and laboratory-heated soils to water.  To examine the nature of sulfur and mercury following ash and sediment deposited in a reservoir, we examined the chemistry of these elements in cores from two reservoirs.  Transitions in the chemical conditions controlling oxidation state of the elements during sediment deposition were simulated using small-scale simulations of the reservoir sediments (microcosms).  We used a synchrotron-based spectroscopic technique to assess the effects of oxidation (simulations of fire heating) and reduction (reservoir deposition) on the chemistry of sulfur and mercury.  Changes in capacity of the reservoir sediments to bind mercury were quantified using a technique that measured competition for mercury binding.

For one of the field sites, Mesa Verde National Park, we found that soils affected by historical wildfires contained about 50% less organic matter and mercury than unburned soils collected adjacent to the burned samples.  In aqueous release experiments from historically burned soils, there was half the amount of carbon and mercury as unburned soils.

In contrast to the Mesa Verde field results, laboratory heating increased the release of organic matter and major ions from soils.  Mercury release was linked to organic matter release, though losses from volatilization during heating reduced the total release into solution.  Soil subjected to heating contained more oxidized sulfur and less sulfur of intermediate oxidation states, while sulfur oxidation states in ash-laden sediments shifted toward reduced forms following deposition in a reservoir.  Laboratory experiments simulating each of these shifts resulted in increased mercury binding capacity. Following heating, a 50% increase in strong mercury binding sites was measured.  Following simulated reservoir deposition, there was a 10-fold increase in the number of strong binding sites in the ash-laden sediments.  Overall, this study characterizes the underlying processes influencing mercury behavior in soils and sediments following wildfire.

Last Modified: 01/06/2016
Modified by: Joseph N Ryan

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