Atmospheric nitrogen deposition from a remote source enriches macroalgae in coral reef ecosystems near Green Turtle Cay, Abacos, Bahamas

Abstract

Over the past several decades, the fixation of “new” nitrogen to the biosphere has doubled. For the early 21st century, the most significant rate increases in atmospheric nitrogen deposition are predicted for developing nations. Wet nitrogen deposition was assessed on the remote island of Green Turtle Cay, Bahamas in a dry and wet season from January to July 2000. Episodic deposition of nitrate (∼1–137 μM) and ammonia (∼2–122 μM) represented a mean deposition rate of ∼0.2 mg DIN m −2 yr −1. Wet deposition of nitrogen to the climatologically-linked east coast of Florida is ∼4 times greater than the estimated annual wet nitrogen deposition value at Green Turtle Cay, suggesting the continental US as a principal airshed for this loading source. Short-term bioassays of macroalgal productivity with a 5% rainfall solution caused depressed net productivity and increased dark respiration, well known “transient metabolic” responses by nutrient-limited tropical macroalgae. Wet deposition of inorganic nitrogen from episodic rainfall events may provide up to 20% of the “new” nitrogen necessary to meet growth demands of macroalgae on coral reefs near Green Turtle Cay.