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Using stable δN15 ratios to help differentiate nitrogen sources within a residential community- another tool for the TMDL toolbox.
Nora Egan Demers Associate Professor of Biology and Interdisciplinary StudiesFlorida Gulf Coast UniversityFt. Myers, Florida
Report to the Watershed Council January 17, 2008
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stable δN15 ratios help differentiate nitrogen sources
Ratio is based on heavy and light form of N
In general – according to the literature
δN15 between 2.00 and 8 is from atmospheric
δN15 between -4.00 and 4.00 is from fertilizer
δN15 between 18.00 and 22.00 is from humans
δ15N =[R(sample)-R(standard)/R(standard)]*1000
where R= ratio of 15N/14N and R standard is the atmospheric standard.
Generally, Nitrogen from fertilizers has an δ15N around 0+- 4 0/00 (parts per thousand) (Heaton, 1986), while Nitrogen from septic systems and animal waste has a δ15N from +8 to +22 0/00. (Heaton, 1986). Levels of δ 15N in atmospheric depositions are about +2 to +8.00 0/00 (Kreitler et al, 1978).
This is because the lighter 14N isotope is preferentially fractionated during bacterial nitrification, resulting in higher δ15N ratios as you move toward meat-eating consumers in the food web.
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San Carlos Park
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Lee County Utilities overlayshowing sewer and
water infrastructure for San Carlos Park, Lee County, Florida. Areas in green are served by municipal sewer and water, in blue by water, (with septic) and in red have well-water and septic systems.
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Winged Foot/Oriole
(mg/L) 3/07 9/07 Ammonia 0.871 0.453 Nitrite 0.008 0.01 Nitrate 0.01 0.01 PO4 0.09 0.09 TKN 62 5.9 TN 62 5.9 Total PO4 8.3 .59
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Winged Foot/Oriole
Delta N 15 Duckweed (March) 0.86,
3.67 Duckweed (Sept) 3.13 2.83 Extract flock (Sept) 1.87
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Kakareka
(mg/L) March Sept Ammonia 0.222 0.049 Nitrite 0.008
0.004 Nitrate 0.01 0.02 PO4 0 0 TKN 1.1 0.94 TN 1.12 0.96 Total PO4 0.046 0.027
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Kakareka
Delta N 15 Sediments leafy (March) 1.70 Algae (March) 2.66 Sediment flock (March) 2.50
2.38 Roots (Sept) -0.90 -1.82 Scrapings from leaves (Sept) -
0.35
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Laurel Valley/New Jersey
(mg/L) Sept Ammonia 0.348 Nitrite 0.007 Nitrate 0.04 PO4 0 TKN 1.1 TN 1.1 Total PO4 0.022
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Laurel Valley/New Jersey
Delta N 15 (Sept)Flock 5.07Lettuce leaves 0.93Lettuce roots -0.98Extract flock 5.62
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Demers
(mg/L) March Sept Ammonia 0.042 0.315 Nitrite 0.007 0.014
Nitrate 0.02 0.06 PO4 0.02 0 TKN 1.8 0.94 TN 1.83 1 Total PO4 0.17 .0033
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Demers
Delta N 15Marchfloaty algae 4.08
leafy 4.15 Sediment 6.49
5.9
Sept.Floating blob: 4.68 6.02Lettuce leaf 2.92 3.82Lettuce roots 4.47 Sediment flock 5.79Extract flock 4.34 4.95 2.92
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Constitution
(mg/L) March Sept Ammonia 0.087 0.052 Nitrite 0.008 0.006 Nitrate 0.15 0.21 PO4 0.01 0 TKN 0.81 0.58 TN 0.97 0.8 Total PO4 0.084 0.018
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Constitution
Delta N 15Macroalgae (March) 8.72Sediment flock (March) 6.39
Rinsed roots (Sept) 9.27Sediment flock (Sept) 4.24Extract flock (Sept) 5.37
5.32
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Outfall: 46B-9GR
( mg/L) March Sept. Ammonia 0.067 0.017
Nitrite 0.008 0.004 Nitrate 0.2 0.22 PO4 0.01 0 TKN 0.57 0.83 TN 0.78 1.1 Total PO4 0.026 .009
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Outfall: 46B-9GRDelta N 15
Green algae (March) 11.05Brown macro algae (March) 8.51Sediment flock (March) 10.65Sept:Root ball rinsed 6.03Algae 7.43Sediment flock 5.77Extract flock 7.35
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Golf Course Effluent
(mg/L) March Sept Ammonia 0.414 0.213 Nitrite 0.178
0.098 Nitrate 0.44 2.48 PO4 0.67 .73 TKN 2.4 2.3 TN 3.02 4.8 Total PO4 1.00 0.89
Average of 200,000 gallons per day of reclaimed water delivered to this lake
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Golf Course Effluent
Delta N 15 Sediment Flock March 17.84Sept 17.80 19.46 17.68
16.79
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Golf Course- Lake
(mg/L) March Sept Ammonia 0.2 0.105 Nitrite 0.009 0.006 Nitrate 0.01 0.09 PO4 0.02 0 TKN 1.8 2 TN 1.82 2.1 Total PO4 0.13 0.13
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Golf Course- Lake
Delta N 15March Sediment Flock 9.96Sept scraping off leaves 6.98
5.05Sediment flock 7.81Extract flock 7.69
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