Isle Royale National Park Air Quality Information
Overview
The air quality related values (AQRVs) of Isle Royale NP are those resources that are potentially sensitive to air pollution, and include vegetation, wildlife, water quality, soils, and visibility.
Although Isle Royale NP is relatively distant from large urban and industrial areas, long-range transport of pollution generated in the Midwest and Ohio River Valley, as well as pollutants emitted by nearby sources, can affect air quality in the park.
A National Atmospheric Deposition Program/National Trends Network (NADP/NTN) wet deposition monitor has been operating at Wallace Lake in Isle Royale NP (site #MI97) since 1985. Because the site can’t be accessed for winter sampling, data don’t meet the completeness criteria required by NADP/NTN for a trend analysis. Trend analyses performed for other NADP/NTN sites in the Great Lakes area show that wet concentration and deposition of sulfate have decreased, while wet concentration and deposition of nitrate and ammonium have increased, decreased, or stayed the same.
Dry deposition data are not collected at Isle Royale NP, and there are no dry deposition monitoring sites nearby.
Surface water chemistry data collected in and near Isle Royale NP were summarized in a 1995 Baseline Water Quality Data Inventory and Analysis report. The summarized data, as well as data collected subsequent to the report, indicate surface waters in the park are not sensitive to acidification from atmospheric deposition.
A portable ozone monitor has been operating in the summer at Isle Royale NP since 2002 (site #26-61-101). Data from this and other ozone monitors in northern Michigan, Wisconsin and Minnesota indicate ozone concentrations are well below the 8-hour National Ambient Air Quality Standard.
Several plant species that occur in Isle Royale NP are known to be sensitive to ozone, e.g., common milkweed (Asclepias syriaca) and quaking aspen (Populus tremuloides), although the specific genotypes found in the park have not been tested under controlled conditions for sensitivity. Ozone concentrations measured at Isle Royale NP and other monitors in northern Michigan, Wisconsin and Minnesota are low enough that ozone-induced foliar injury and/or growth effects are unlikely.
As part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, visual air quality in Isle Royale NP has been monitored using an aerosol sampler (1988 through 1991 and 1999 to the present) and 35mm camera (1987 through 1992). The U.S. Environmental Protection Agency’s new Regional Haze regulations require improving visibility in Class I air quality areas on the days with best visibility and no deterioration on the days with worst visibility. Visibility trend data are not yet available for Isle Royale NP or other IMPROVE sites in the Great Lakes area. 1996 through 1998 IMPROVE data from the Boundary Waters Canoe Area site, 80 miles west of the park, show the major contributors to visibility impairment at the site from November through March were sulfates, followed by nitrates, then organics, then soil, and then light absorbing carbon. In April through October, organics contributed more than nitrates to impairment.
The NPS is particularly concerned about ambient concentrations, deposition, and effects of airborne toxics, such as persistent organic pollutants, and particularly, mercury, at Isle Royale NP.
Isle Royale NP does not have a Mercury Deposition Network (MDN) wet mercury monitoring site, although there are a number of MDN monitors in the Great Lakes area. National wet mercury concentration and deposition maps show that values from MDN monitors in the Great Lakes region are generally higher than those in the Northeast and Western U.S. and comparable to values in Florida and the Gulf Coast. The MDN program has not yet performed trend analyses for their sites.
Preliminary results from a recently completed study showed fish collected in Isle Royale NP had mercury levels which exceeded the Michigan Fish Consumption Advisory level. These findings spurred additional studies to document the mercury levels throughout the food web. Studies are geared toward collecting information on the amount of mercury reaching the park through the atmosphere, and on the amount of mercury found naturally in the bedrock and soils within the park. Scientists are examining mercury levels in the water, sediments, plankton, fish, and common loons of Sargent Lake in the park. The research extends to examining mercury levels in deer mice within the Sargent Lake watershed and in moose teeth across the park. Finally, in an effort to consider mercury at a broader regional level, scientists will assess mercury levels within human baby teeth from children from the Upper Peninsula of Michigan.