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Nutrient transformations between rainfall and stormwater runoff in an urbanized coastal environment: Sarasota Bay, Florida
Author(s) -
Dillon Kevin S.,
Chanton Jeffrey P.
Publication year - 2005
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2005.50.1.0062
Subject(s) - rainwater harvesting , stormwater , surface runoff , environmental science , nitrate , ammonium , hydrology (agriculture) , environmental chemistry , bay , nutrient , chemistry , ecology , geology , oceanography , biology , organic chemistry , geotechnical engineering
To determine the relative importance of atmospheric deposition and stormwater runoff as nitrogen sources to Sarasota Bay, Florida, we examined dissolved inorganic nitrogen (DIN) concentrations and d15N compositions of rainwater and stormwater runoff. Rainwater collected in Sarasota, Florida, had ammonium concentrations of 2.1–29.0 µmol L −1 in the summers of 1999 and 2000. Corresponding rainwater nitrate concentrations were 3.7–56.0 µmol L −1 . Rainwater ammonium Δ 15 N values were −11.6‰ to −0.3‰, and nitrate Δ 15 N values were −5.1 to +3.8 over the 2‐yr period. Decreases on the order of 50% in ammonium concentration and Δ 15 N enrichments as great as 124‰ relative to rainwater ammonium were typically observed in the evolution of rainwater into stormwater. Stormwater Δ 15 NH 4 values were +7 to +18‰. Nitrate (NO 3 ) concentrations were typically elevated in stormwater relative to rainwater, although this trend was not statistically significant, and Δ 15 N values were generally slightly enriched in stormwater. Rainfall phosphate (PO 4 ) concentrations were always low (≪2.1 µmol L −1 ), whereas stormwater consistently had elevated PO 4 concentrations (up to 13.8 µmol L −1 ). 15 N‐enriched N in the environment has generally been interpreted as an anthropogenic signal (wastewater and agricultural runoff). Our results will require the broadening of that interpretation to include stormwater DIN.