Acidic deposition of sulfates and nitrogen compounds from anthropogenic sources can negatively impact sensitive ecosystems. These compounds can acidify soil and surface waters, affect nutrient cycling and impact the ecosystem services provided by forests. Sulfates and nitrogen compounds are deposited in precipitation (known as wet deposition), as well as particulates and aerosols (know as dry deposition), or directly from clouds/fog vapor. Click here to learn more about how acidic deposition impacts ecosystems.
In the United States, there are many locations where measurements are taken of wet deposition, as opposed to dry or cloud deposition. However, not all National Forests or wildernesses are monitored directly. For this reason, staticstical models, using monitored wet acidic deposition, precipitation amounts, and topographic data are being used to provide a spatial estimate of wet acidic deposition for the eastern United States (Grimm and Lynch, 2004).
The purpose of this webpage is to provide summaries of the amount acidic deposition and how it changes overtime for an individual wilderness or National Forest in the eastern United States. By selecting the State and Forest or Wilderness, a time series of the annual distribution of wet sulfate (top), wet total nitrogen (middle) deposition, and precipitation (bottom) will be displayed. The influence of aspect and elevation in mountainous locations has a profound effect on both annual precipitation, and hence annual wet acidic deposition, which result in large annual distributions (estimated by the standard deviation) across forests. Mean annual trends in acidic deposition and precipitation are represented by the red line in each of the graphs as determined by linear regression. The historical mean (blue line) and 95% confidence interval are shown when no significant trend are present in the data.
Since 1983, the following has occured:
Wet Sulfate: Deposition has decreased on average about 0.6286 kilograms per hectare (kg/ha) each year. The model is highly significant with less than 1 in 1000 cases where there is actually no relationship between the mean of the annual wet sulfate deposition as predicted by the years since 1983 and the mean of the annual precipitation. Overall, 77% of the variation in the estimated mean of the annual wet sulfate deposition can be accounted for with the two predictors. The multiple regression model and graphic for wet sulfate deposition is: Wet Sulfate = 23.11  0.6286*Year + 0.0718*Precipitation 
Convert Instructions Enter a value into one of the boxes and then use your enter key or select (click) on a different box to see the equivalent amount expressed in a different unit of measure. Graph Instructions The X and Y axes can be adjusted. Click and Drag your mouse along the axes to scroll through the values. To adjust the scale of the axes, Click and Drag your mouse along the axes while holding the shift key and left mouse button. The Xaxis adjusts on each graph in unison with other graphs. Both the Yaxes (English and Metric) adjust together in each graph to remain accurate, but each graph's Yaxes adjust independent of other graphs.
Please note: the results will not display properly in Internet Explorer version 8.0 or earlier. 
Sulfate (kg/ha): Sulfur (kg/ha): Sulfur (meq/m^{2}): Please note: The calculated value for Sulfate (meq/m^{2}) is the same as Sulfur (meq/m^{2}) shown above. 

Wet Total Nitrogen: Deposition has decreased on average about 0.0656 kg/ha each year. The model is highly significant with less than 1 in 1000 cases where there is actually no relationship between the mean of the annual wet total nitrogen deposition as predicted by the years since 1983 and the mean of the annual precipitation. Overall, 40% of the variation in the estimated mean of the annual wet total nitrogen deposition can be accounted for with the two predictors. The multiple regression model and graphic for wet total nitrogen is: 

Total Nitrogen (kg/ha): Nitrate (kg/ha): Nitrate (meq/m^{2}): Please note: The calculated value for Total Nitrogen (meq/m^{2}) and Ammonia (meq/m^{2}) is the same as Nitrate (meq/m^{2}) shown above. 

Precipitation: The precipitation trend could not be determined because one or more linear regression assumptions were not met, or the coefficient for the year predictor was not significant. Therefore, the graphic below shows the historical mean annual precipitation of 56.2 inches with the true mean between 51.88 and 60.6 inches for 95% the time.  
Right click on one of the following links to download the data used to produce the graphics:  
Grimm, J. W. and Lynch, J. A. 2004. Enhanced wet deposition estimates using modeled precipitation inputs. Environmental Monitoring and Assessment 90: 243268.