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

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.

San Carlos Park

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.

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

Winged Foot/Oriole

Delta N 15 Duckweed (March) 0.86,

3.67 Duckweed (Sept) 3.13 2.83 Extract flock (Sept) 1.87

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

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

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

Laurel Valley/New Jersey

Delta N 15 (Sept)Flock 5.07Lettuce leaves 0.93Lettuce roots -0.98Extract flock 5.62

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

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

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

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

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

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

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

Golf Course Effluent

Delta N 15 Sediment Flock March 17.84Sept 17.80 19.46 17.68

16.79

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

Golf Course- Lake

Delta N 15March Sediment Flock 9.96Sept scraping off leaves 6.98

5.05Sediment flock 7.81Extract flock 7.69