Mercury Deposition & It's Effects on the San Juans

Why Mercury?

In 2007, MSI began studying mercury in rain and snow, lakes, and forest soils. Mercury is an emerging environmental health concern in the Four Corners. It is neurotoxin to humans and wildlife and becomes more concentrated as it is passed up the food web from plants to herbivores to predators. Mercury is a naturally occurring element in rocks and soil, but it also is emitted into the air by burning mercury-containing coal and waste products. Precipitation falling in Mesa Verde National Park has some of the highest mercury concentrations measured across the United States. Many reservoirs in SW Colorado and NW New Mexico are listed for fish consumption advisories due to bioaccumulation of mercury in game fish.

Back Trajectory Modeling of Mercury Deposition Events at Molas Pass, San Juan County CO.

Since 2009 the national Mercury Deposition Network has been monitoring mercury deposition at Molas Pass. This site is adjacent to the Wemenuchi Wilderness and is within a Class I clean air area. In 2011 MSI in collaboration with the San Juan Public Lands Center conducted a back trajectory modeling exercise to examine the storm tracks that deposited mercury at Molas Pass. The results of this modeling effort determined that storms that produced the greates mercury in precipitation came out of the southwest, where there are a number of coal fired powerplants. 

Mercury in Forest Soils

In 2008 MSI’s Nydick, along with Fort Lewis College student Anya Angst, began looking at mercury in forest soils from burned and unburned areas in Missionary Ridge. “We really want to understand how fire affects mercury bound to forest soils and the transport of this mercury into water bodies” remarked Nydick. MSI is collaborating with researchers from the University of Colorado and the US Geological Survey to study this question.
Preliminary results indicate that low intensity prescribed burning had no effect on the amount of mercury or organic matter in soil, but high intensity wildfire dramatically decreased both organic matter and mercury concentrations. In both cases, mercury and organic matter were highly correlated, indicating the importance of organic material to bind the mercury in these soils.

Sources of Atmospheric Mercury Concentrations and Wet Deposition at Mesa Verde National Park, Southwestern Colorado, 2002-2008

The purpose of this study was to better understand the sources of atmospheric mercury deposited by precipitation events at Mesa Verde National Park. The method of investigation was to conduct various data analyses to determine trends in mercury concentrations in precipitation over time, compare trends in mercury concentrations to other major-ion concentrations, track movement of air parcels involved with precipitation events at Mesa Verde and estimate below vs. above background mercury concentrations. Precipitation, mercury concentrations in precipitation and major-ion concentrations in precipitation data from the National Atmospheric Deposition Program (NADP), National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA) was used. This study concluded that the coal-fired power plants south of Mesa Verde National Park are likely an important source of mercury to the Park. The study also showed a decreasing trend in concentrations of sulfate, nitrate, chloride and hydrogen following implementation of emission reductions at two coal-fired power plants. This suggests that similar measures implementing mercury emissions reductions may have a beneficial effect.

Pilot Study of the Ecological Effects of Mercury Deposition in Mesa Verde National Park, Colorado

When atmospheric mercury is deposited by precipitation, it may be converted to methyl mercury, a form that can be taken up by organisms and consequently becomes biomagnified in the food chain. Mercury is most easily converted to methyl mercury in wet environments with low oxygen, so mercury bioaccumulation studies are often focused on aquatic ecosystems. The purpose of this pilot study was to determine if mercury bioaccumulation occurs in wildlife at Mesa Verde National Park and if a full study would be justified. Groups of species examined were wetland songbirds, invertebrates, stream fish and crayfish. The organisms examined did not show toxic levels of mercury, however sub-lethal effects of mercury on wildlife are not well studied and should not be discounted. The scope of this study was limited, and further investigation is recommended.

Mercury in Lakes and Precipitation of Southwestern Colorado

This study provides greater insight into the patterns and processes that affect mercury in the environment of southwestern Colorado. One objective was to determine the amount and concentration of mercury in precipitation falling at high altitude in SW Colorado. “We’ve found rather elevated concentrations of mercury in rain collected at Molas Pass” reported Dr. Koren Nydick, MSI’s chief scientist. As a result, the San Juan National Forest will be installing a long-term precipitation collector on Molas Pass to track mercury deposition for years to come.

MSI also measured mercury in zooplankton from 28 lakes and reservoirs. Zooplankton are small invertebrates that are consumed by fish. “Mercury concentrations in zooplankton varied a lot among lakes from low to quite high”, says Nydick. Six lakes had methyl mercury levels in zooplankton that were higher than the levels measured from two reservoirs with fish consumption advisories. Zooplankton from three lakes had methyl mercury concentrations above the level of concern for fish-eating mammals. Nydick noted, “The variability among lakes was not that surprising because bioaccumulation of mercury depends on a lot of factors in addition to the amount of airborne mercury deposition. However, it was surprising how high mercury concentrations were in a few of the lakes”. MSI plans to use water quality and watershed measurements to identify what makes lakes and reservoirs in our region more or less susceptible to bioaccumulation of mercury.

Lake sediments record a history of mercury accumulation as material is deposited on the lake bottom over time. MSI collected sediment cores from four mountain lakes and Vallecito Reservoir. The cores from the lakes show that mercury input increased since pre-industrial times, peaked between 1960 and 1990, and then decreased or remained constant in the past two decades. “The peak (in mercury input) is pretty consistent with when many coal-fired power plants came online in the western US”, says Nydick. “Recent declines are probably due to regulations that were enacted in the 1990’s on mercury emissions from waste incinerators”. Coal-fired power plants are the largest source of human-caused mercury emissions in the USA, according to the Environmental Protection Agency.

Project Partners

  • Mountain Studies Institute
  • University of Colorado at Boulder
  • Mesa Verde National Park
  • BioDiversity Research Institute
  • Win Wright - Southwest HydroLogic

Thanks to the Project Supporters!

Major Funders

  • US Environmental Protection Agency
  • US Forest Service - San Juan National Forest
  • National Park Service

Other Funders

  • San Miguel County
  • US Forest Service - Grand Mesa, Uncompahgre, and Gunnison NFs
  • Telluride Institute