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Long-Term Monitoring of Atmospheric Nutrient Deposition in Chatham County for Assessment of Potential Effectiveness of Non-Point Source Pollution Mitigation

PI: Richard A. Jahnke (Skidaway Inst of Oceanography, Savannah, Georgia, USA)  

Support: Georgia Coastal Management Program (through a Coastal Incentive Grant)

Timeframe: 2005 -2008 (complete)

Project Objective:

To determine the atmospheric deposition rate of biologically-available nitrogen to Chatham County. Preliminary estimates indicate that atmospheric inputs may rival river and groundwater input rates and thereby significantly affect the effectiveness of non-point source mitigation strategies.

The strategy used for this study involved:

  • Collection of atmospheric deposition samples;
  • Analyses of samples for nitrate plus nitrite, ammonium, total fixed nitrogen and phosphate;
  • Compilation of rainfall at various locations within Chatham County; and
  • Estimate of total fixed-N deposition.


Sample collection and analysis
Beginning January 2006, rain deposition samples were collected weekly at Skidaway Institute of Oceanography and occasionally from the offshore SABSOON towers. Samples were analyzed for phosphorus, nitrate plus nitrite, ammonium, dissolved organic nitrogen and total dissolved nitrogen.

Rainfall data
Available rainfall data (2004-2006) has been compiled from a variety of locations in the Chatham County region, including Savannah International Airport, Hunter Army Airfield, SkIO Priest Landing Facility, UGA Bamboo Farm, The Landings, Halcyon Bluff and Berwick Plantation in West Chatham County.


Average annual fixed-N deposition for 2004 and 2005 is 80.4 mmol/m2, equivalent to 1.12 g N m-2 y-1 or 11.2 kg ha-1. In general, the highest rates of deposition occur in late summer - early fall, following rainfall patterns. However, at present the record is too short and month-to-month variability is too large to statistically constrain a seasonal pattern.

To place the results to-date in a broader context, and to demonstrate the utility of local monitoring, these results were compared to the deposition patterns of nitrate and ammonium reported by the Nat'l Atmospheric Deposition Program for 2005 --Ammonium deposition in the region is estimated from the national data base as 2.5 to 3.0 kg ha-1 while nitrate deposition is estimated to be 8-10 kg ha-1 (1.8 - 2.3 kg ha-1 as N). Using the larger number for both ammonium and nitrate deposition, suggests a total fixed-N deposition for our region of 5.3 kg N ha-1. This is considerably less than the 11.2 kg ha-1 estimated from our direct local collections. Several considerations may account for the observed difference in estimates:

  • the national program does not consider the deposition of organic nitrogen
  • increased fixed-N inputs to the atmosphere through human activities within the urban, Chatham County setting relative to the remote, rural sampling locations of the national program.


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This page was updated September 1, 2009