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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)
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
Sample collection and analysis
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:
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|This page was updated September 1, 2009|