Nitrogen Isotopic Records of Terrestrial Pollution Encoded in Floridian and Bahamian Gorgonian Corals

• Published in: Environmental science & technology 2010-02, Vol.44 (3), p.874-880
• Main Authors: Sherwood, Owen A, Lapointe, Brian E, Risk, Michael J, Jamieson, Robyn E
• Format: Article
• Language: English
• Subjects: Animals; Anthozoa - physiology; Applied sciences; Bahamas; Characterization of Natural and Affected Environments; Chelonia mydas; Coral reefs; Environmental Monitoring - methods; Environmental Pollutants - chemistry; Environmental Pollutants - metabolism; Environmental Pollution; Environmental science; Exact sciences and technology; Florida; General purification processes; Gorgonacea; Isotopes; Natural water pollution; Nitrogen; Nitrogen - chemistry; Nitrogen - metabolism; Pollution; Seawaters, estuaries; Sewage disposal; Wastewaters; Water Pollution, Chemical; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es9018404

Stable nitrogen isotope (δ15N) analysis has proven an effective “fingerprint” of sewage contamination in coral reef environments; however, short-term variability in nitrogen cycling and isotopic fractionation may obscure long-term trends. Here, we examine δ15N signatures in the organic endoskeletons of long-lived (20−40 years) gorgonian corals. Specimens were collected from relatively pristine reefs off Green Turtle Cay, Bahamas, and from reefs off southeast Florida heavily impacted by multiple sources of anthropogenic nitrogen. The δ15N of the most recently grown skeleton (branch tips) ranged from +2 to +3 ‰ at Green Turtle Cay, and +4.5 to +10 ‰ off Florida. These values closely match the δ15N of macroalgae collected from the same locations, indicating that gorgonian corals are isotopically similar to primary producers, and therefore suitable for assessing sources of dissolved inorganic nitrogen. Differences in the δ15N between younger and older skeleton indicated an overall decline of −0.34 ± 0.06 ‰ (1 s.e) over the last 20 − 40 years at Green Turtle Cay, reflecting a possible increase in nitrogen fixation and/or atmospheric deposition of anthropogenic nitrogen. Off southeast Florida, there was an overall increase in δ15N over the same time period, reflecting increasing wastewater discharges from the rapidly growing population. These results highlight the usefulness of δ15N recorded in gorgonians and other long-lived organisms in assessing spatiotemporal patterns of nitrogen sources to coastal marine environments.