Atmospheric Deposition and Stress

Importance / Issues

Atmospheric deposition is a stressor to terrestrial and aquatic systems throughout the NETN and has been implicated in the decline or degradation of many ecological systems in the region. Estimates of atmospheric deposition are critical for understanding water chemistry and stress (Likens and Bormann 1974). Swain et al. (1992) estimated that 90% of the mercury entering remote lakes in Voyageurs National Park (Minnesota) was derived from atmospheric deposition. Acidic deposition stresses terrestrial vegetation and alters system functioning and biogeochemical cycles. Compiling acidic deposition data is important for any long-term monitoring program because this stressor has demonstrated negative effects on aquatic systems and can alter wetland function and biogeochemical processes. The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) is a nationwide network of precipitation monitoring sites. We will work closely with the NPS Air Resources Division to acquire and summarize these existing data to interpret changes at the park level. 

Protocol Development & Status

At this time the NETN is not developing a protocol for this vital sign. The data collected by the National Park Service Air Resources Division (ARD) will be utilized by the network. The ARD has developed a Wet Deposition Monitoring Protocol. More information is also available on their website: Air Resources Division.

Potential Measures

Wet and dry deposition rates, soil nitrification, soil base cation availability, soil Ca:Al ratio, streamwater ANC, streamwater nitrate concentration 

Preliminary Monitoring Objective

ARD is developing strategies for estimating the amount of deposition that causes harm to ecosystems. This "critical load" is defined as the amount of pollutant deposition below which significant harmful effects to sensitive resources do not occur. Deposition monitoring and research on ecosystem effects will facilitate the identification of critical loads for park resources. Deposition monitoring will enable managers to evaluate whether deposition is below or above critical or target loads.

Contact Information

NPS lead: Brian R. Mitchell

Email: Brian R. Mitchell

802-457-3368 ext. 37

References

Likens, G. E., and F. H. Bormann. 1974. Acid rain - A serious regional environmental problem. Science 184:1176-1179.

Swain, E.B., D.R. Engstrom, M.E. Brighan, T.A. Henning, and P.L. Brezonik. 1992. Increasing Rates of Atmospheric Mercury Deposition. Science 257: 748-787.