Eleven of the fourteen PRIMENet park sites have had National Atmospheric Deposition Program/National Trends Network (NADP/NTN) precipitation collectors since 1984. These parks include; Acadia, Big Bend, Denali, Everglades, Glacier, Great Smoky Mountains, Olympic, Rocky Mountain (Beaver Meadows - BM), Rocky Mountain (Loch Vale - LV), Shenandoah, Sequoia/Kings Canyon and Theodore Roosevelt NPs. Canyonlands and Virgin Islands NPs were added to the network in 1998, and Hawaii Volcanoes NP is expected to join in July 1999.
NADP/NTN Site Information. Data available HERE.
*Canyonlands and Virgin Islands NPs were not presented in Figure 4 due to insufficient years of data.
The following graph shows a summary of the precipitation data for concentrations of nitrate and sulfate averaged over a 14-year period. It is organized to show the parks with the lowest to highest concentrations of nitrate in wetfall, with paired bars indicating sulfate concentrations. The error bars indicate standard deviations of the means. The lowest volume-weighted mean concentrations of nitrate were recorded at Olympic and Denali NPs. High concentrations of nitrate (values above 15 m eq l-1) were measured in Rocky Mountain-BM, Great Smoky Mountains, Theodore Roosevelt, Shenandoah, Acadia and Big Bend NPs. Concentrations of sulfate had a wider range in values than nitrate. Again, the lowest concentrations of sulfate were recorded in samples collected at Olympic and Denali NPs, with very high concentrations (values above 30 m eq l-1) for Acadia, Shenandoah and Great Smoky Mountains NPs. The sulfate to nitrate ratios approach one at the two sites in Rocky Mountain and at Glacier NP. Only Sequoia/Kings Canyon and Rocky Mountain (BM) NPs showed nitrate in excess of sulfate.
Average Annual Concentrations of Nitrate and Sulfate in Precipitation from 1984 to 1997.
These spatial patterns in deposition among the park sites reflect the influence of sulfur emissions in the eastern part of the United States, and the ubiquitous nature of nitrogen emissions throughout the U.S., except at purported "background" sites as Olympic and Denali NPs. However, it is important to note that the trend analysis for Olympic NP indicates a significant increase in nitrate concentrations over the period 1985-1993.
The data summarized in the previous graph are expressed as volume-weighted concentrations of nitrate and sulfate. This convention was used because it allows the comparison of sites with different amounts of annual precipitation. However, from the ecosystem perspective, it is most important to determine the amount of solutes (sulfate, inorganic nitrogen, base cations or acidity) that are "loaded" into the sensitive systems of interest. These sensitive ecosystems include low-acid neutralizing capacity (ANC) surface waters, acidic soils, small watersheds, and nitrogen-limited estuaries. The NADP/NTN data summaries include an estimate of the loading of nitrogen and sulfur in wet deposition, based on the amount of rain or snow that fell at that point. For many park ecosystems, such as high elevation watersheds, where snow and cloudwater inputs are an important part of the hydrologic budget, or in aridlands, where dry deposition is most important, these point estimates are inadequate to characterize loading. Other, alternate methods to estimate deposition inputs are needed to calculate total chemical inputs. In the snow zone we have used snowpack sampling at maximum accumulation to estimate winter chemical and hydrological inputs.
To obtain complete data sets for these sites, including both concentrations and loading, refer to the NADP/NTN web site.
For more background information on the USGS Acid Rain Program link to bqs.usgs.gov/acidrain.