TY - JOUR
T1 - Tracing the fate of seabird-derived nitrogen in a coral reef using nitrate and coral skeleton nitrogen isotopes
AU - Choisnard, Noémie
AU - Duprey, Nicolas Noel
AU - Wald, Tanja
AU - Thibault, Martin
AU - Houlbrèque, Fanny
AU - Foreman, Alan D.
AU - Cuet, Pascale
AU - Guillaume, Mireille M.M.
AU - Vonhof, Hubert
AU - Sigman, Daniel M.
AU - Haug, Gerald H.
AU - Maguer, Jean François
AU - L'Helguen, Stéphane
AU - Martínez-García, Alfredo
AU - Lorrain, Anne
N1 - Publisher Copyright:
© 2024 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.
PY - 2024/2
Y1 - 2024/2
N2 - Seabirds transfer nutrients from the ocean to their nesting island, potentially altering nitrogen (N) cycling within adjacent terrestrial and marine ecosystems. Yet, the processes involved in seabird-N transfer along the land–sea continuum remain elusive. Using δ15N and δ18O measurements of groundwater nitrate, we demonstrate the role of brackish groundwater located within a coral island's landmass as a major reservoir of nitrate (at millimolar levels). Nearly all of the total dissolved seabird-derived N leaching into the groundwater (mostly ammonium and uric acid) is converted to nitrate by nitrification, as supported by the relatively low δ18O of the groundwater nitrate (3.97‰ ± 0.30‰). Comparison of nitrate δ15N and δ18O suggests that little denitrification takes place within the groundwater lens, implying that the high δ15N of groundwater nitrate (13.73‰ ± 0.05‰) derives from the high trophic position of seabirds and postdepositional processes that increase the δ15N of seabird excreta. Seawater and coral skeleton samples from a reef flat exposed to groundwater had higher δ15N values than at sites devoid of groundwater influence, indicating that the main source of N at the latter site was the Subtropical Upper Water, while the groundwater nitrate dominated the exposed reef flat N pool up to 200 m from shore. In addition, these results indicate that coral-bound δ15N can detect seabird-derived nitrate δ15N, raising opportunities to reconstruct historical seabird-N inputs to coral reefs in relation to climatic and other changes, such as the introduction of invasive species.
AB - Seabirds transfer nutrients from the ocean to their nesting island, potentially altering nitrogen (N) cycling within adjacent terrestrial and marine ecosystems. Yet, the processes involved in seabird-N transfer along the land–sea continuum remain elusive. Using δ15N and δ18O measurements of groundwater nitrate, we demonstrate the role of brackish groundwater located within a coral island's landmass as a major reservoir of nitrate (at millimolar levels). Nearly all of the total dissolved seabird-derived N leaching into the groundwater (mostly ammonium and uric acid) is converted to nitrate by nitrification, as supported by the relatively low δ18O of the groundwater nitrate (3.97‰ ± 0.30‰). Comparison of nitrate δ15N and δ18O suggests that little denitrification takes place within the groundwater lens, implying that the high δ15N of groundwater nitrate (13.73‰ ± 0.05‰) derives from the high trophic position of seabirds and postdepositional processes that increase the δ15N of seabird excreta. Seawater and coral skeleton samples from a reef flat exposed to groundwater had higher δ15N values than at sites devoid of groundwater influence, indicating that the main source of N at the latter site was the Subtropical Upper Water, while the groundwater nitrate dominated the exposed reef flat N pool up to 200 m from shore. In addition, these results indicate that coral-bound δ15N can detect seabird-derived nitrate δ15N, raising opportunities to reconstruct historical seabird-N inputs to coral reefs in relation to climatic and other changes, such as the introduction of invasive species.
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U2 - 10.1002/lno.12485
DO - 10.1002/lno.12485
M3 - Article
AN - SCOPUS:85181252657
SN - 0024-3590
VL - 69
SP - 309
EP - 324
JO - Limnology and Oceanography
JF - Limnology and Oceanography
IS - 2
ER -