Mercury Methylation and Climate Change in Lake Champlain Jeremy Koslow Nikkohl Luehm Colin Penn Polly Perkins Adam Oliver

Why is Mercury of concern? Increase in industrialization, mercury has become a prominent pollutant Microbial and abiotic processes convert mercury (Hg) into methylmercury (CH3Hg) Methylmercury can be taken up by organisms - bioaccumulates and biomagnifies up the foodweb Shastri and Diwekar, 2008

Mercury in Lake Champlain Contaminant of most concern in Lake Champlain Neurotoxin - especially dangerous to pregnant women and children 2008 LCBP State of the Lake Report

Problem Statement The changing climate will have several effects on the mechanisms controlling the rate of mercury methylation, thereby possibly increasing rates of bioaccumulation and biomagnification in Lake Champlain.

Approach Examine the factors affecting methylation Hg inputs into Lake Champlain Temperature Oxygen Dissolved Organic Matter (DOM) & pH Sulfate Researched what Climate Change trends we expect to see in the N.E. Determined how these trends would affect the above factors, which would affect methylation

Climate Change Assumptions Hayhoe et al. (2007) predicts: General increase in air temperature Increase in total winter precipitation Slight decrease in total summer precipitation, but more frequent intense rainfall events High stream flow rates are predicted to shift from late spring to early spring/late winter Earlier snow melt dates More flooding due to ice jams

NECIA 2006 Under both lower and higher emissions, periods of heavy rainfall may become more common, increasing the risk of flooding.

Number of snow-covered days per month (December – February) NECIA 2006 Number of snow-covered days per month (December – February)

Mercury inputs into Lake Champlain 56.4% of total inputs is from surface run-off and tributary flow – due to watershed to lake surface ratio 18:1 38% comes from deposition onto the lake surface Other minor inputs – wastewater treatment facilities and paper and pulp mill located in Ticonderoga, NY Much of the tributary flow and run-off load is known to originate from atmospheric deposition, therefore it may be concluded that atmospheric deposition accounts for the majority of mercury in Lake Champlain

How Temperature affects Wet Deposition Keeler et al. (2005) studied wet deposition for 11 years (1993-2004) in Underhill, VT Found that mercury wet deposition seemed to increase in the warmer months as a result of temperature Significant relationship between temperature and deposition was found with r2=0.67 Display of monthly average temperatures (line) and average monthly deposition over the 11yr. period for Underhill, VT

Precipitation Type and Wet Deposition Precipitation type is important in the concentration of Hg Rain has a higher capacity to forage and hold different forms of Hg More precipitation has been falling as rain rather than snow in the winter months, a trend expected to continue This suggests that in years to come higher concentrations of Hg will be falling throughout the Lake Champlain Watershed

What does this mean for Hg in Lake Champlain? Balogh et al. (2005) found that streams and rivers can transport large quantities of CH3Hg out of flooded or saturated terrestrial areas in response to intense precipitation events Mississippi River in Minnesota – a is MeHg and b is total Hg. The filled in diamonds are unfiltered samples and the white diamonds are filtered. The solid lines are daily mean discharge and the dotted line is the 95th percentile discharge levels. This is because mercury is bound to particle and sediment. With an increase in high stream flow, flooding, and an increase in intense rainfall events the Lake Champlain Basin can expect to experience an increase in soil erosion, releasing stored mercury from watershed soils, carrying sediment and particulate matter downstream, eventually depositing them into Lake Champlain. Due to the remobilization of Hg from flooded soils as well as an increase in available nutrients and organic matter, which may amplify microbial activity

Temperature Methylation rates increase with increasing water temperatures Most studies show rates of methylation highest in the warmest times of the year, peaking in mid to late summer The relationship between water temperature and methylation is most directly a result in the increased temperature increasing microbial activity.

Callister and Winfrey Greatest Rates at 35ºC

Increased water temperatures have been found to decrease rates of de-methylation. An increase in water temperature decreases the dissolved oxygen, creating a synergistic effect which further increase methylation rates.

Oxygen Methylation of mercury is controlled by anaerobic sulfate reducing bacteria (Watras 1995) DeLaune et al (2004) found that methylation rates decrease when oxygen levels are high, probably because of the reduced activity of sulfate reducing bacteria that prefer anaerobic conditions

Oxygen & Climate Change Increased water temperatures will greatly affect dissolved oxygen concentrations and therefore the methylation of mercury Warmer Temperature = Warmer water = less oxygen = more mercury methylation Warmer water = longer periods of stratification in Lake = less mixing of oxygen to lower layers (Moore et al, 1997).

Dissolved Oxygen and Methylmercury MeHg concentrations vs. DO concentrations (Balogh et al 2006)

DOM and MeHg Hg and MeHg form complexes with DOM in soils and wetlands. Increase in rainfall could increase DOM flushing and MeHg-DOM complexes (Buffman et al. 2001) Expand on first bullet point with literature information 21

DOM and MeHg Possible implications for modeling Hg-DOM-pH in the watershed---small impoundments/development Watras et al. 1995 Greater concentrations of DOC correlated to greater Hg and MeHg concentrations pH implications on [MeHg] in small water impoundments or ponds in the watershed 22

DOM and MeHg Climate change predictions for MeHg Increased [MeHg] in the form of Hg/MeHg-DOM complexes Increased solubility of MeHg to the water column with increases in [DOM] Uncertainties about the biotic uptake of MeHg-DOM complexes and bioaccumulation Periods of inundation followed by flooding could increase MeHg/Hg-DOM flushing from wetland soils (Murdoch et al., 2000) Synergistic effects (Temp, DO, Sulfate, Anaerobic bacteria and Hg complex competition) The possible addition of DOM to the water column may also increase the solubility of methyl mercury by forming DOM-MeHg complexes, although there are still uncertainties about whether or not this would increase or inhibit biotic uptake (Ravichandran, 2004). 23

Sulfate Concentration Methylation of mercury is carried out as a byproduct of sulfate reduction by specialized bacteria. Sulfate deposition has decreased steadily since the 1960’s. Clean Air Act provisions have been passed and updated in 1970, 1977 and 1990 to control emissions Increasing wet deposition could increase bulk deposition

Sulfate concentration (Driscoll et al, 2001)

Sulfate concentration vs. Year (Palmer et al, 2004)

Conclusions Due to the effect Climate Change will have on these factors we will expect to see an increase in mercury methylation rates Increased methylmercury concentrations could lead to more uptake into the foodweb and therefore greater health risk

Recommendations Push legislation for better control of mercury emissions Stormwater management Water impoundment Municipal Treatment Preserve Natural Sinks (Wetlands) Erosion Control Mechanisms Continued monitoring of levels in the lake fish tissue as well as monitoring of the factors influencing methylation will provide better information for management purposes