The Chesapeake Bay Program estimates that air deposition accounts for between 25 and 31 percent of the total controllable nitrogen load to the Bay’s tidal waters. However, both research and available models suggests that these estimates are low, particularly for the dry deposition of nitrogen.

There is far less monitoring of dry deposition than wet deposition. Only five stations monitor dry deposition in the Chesapeake Bay Watershed, and three of these are clustered in Delaware and on Maryland’s eastern shore. Consequently, estimates of dry deposition across the watershed are based on a percentage of measured wet deposition. In addition to spatial limitations, dry deposition monitoring does not measure all of the components that can be deposited--NO, NO2, and ammonia gas being of primary concern. Current calculations methods further misconstrued actual percentages as these are measured using depositional velocities for flat terrain. Deposition onto complex terrain is, as a result, likely underestimated.

The fate of atmospheric deposition onto the landscape remains somewhat unclear as well. Forests, key nutrient sinks, may be reaching their saturation points across the watershed. There is evidence that some forests are not able to retain as much nutrients as accounted for in the models. Additionally, growing amounts of impervious surface may be increasing the amount of nutrients loading to the Bay.

The workshop, held May 30, 2007, brought together key experts to document the current state of knowledge and identify priorities and recommendations for advancing scientific knowledge, and improving monitoring and modeling efforts for atmospheric deposition of nitrogen. With a better understanding of atmospheric deposition, scientists can more appropriately advise future management actions. A workshop proceedings report is in progress.