Uptake of groundwater nitrogen by a near-shore coral reef community on Bermuda
Abstract
Nutrient enrichment can slow growth, enhance bioerosion rates, and intensify algal competition for reef-building corals. In areas of high human population density and/or limited waste management, submarine groundwater discharge can transfer anthropogenic nutrients from polluted groundwater to coastal reefs. In this case study, we investigate the impact of submarine groundwater discharge on a near-shore reef in Bermuda, where over 60% of sewage generated by the island's 64,000 residents enters the groundwater through untreated cesspits. Temperature, salinity, pH, and alkalinity were monitored at a groundwater discharge vent, three locations across the adjacent coral reef (0–30 m from shore), and a comparison patch reef site 2 km from shore. Groundwater discharge was characterized by low salinity, low aragonite saturation state (Ω_(ar)), high alkalinity, elevated nitrate + nitrite (NO₃₋ + NO₂₋; hereafter, "NO₃₋") concentrations (> 400 µM), and an elevated ¹⁵N/¹⁴N ratio of NO₃₋ (δ¹⁵N = 10.9 ± 0.02‰ vs. air, mean ± SD). Rainfall and tidal cycles strongly impacted groundwater discharge, with maximum discharge during low tide. NO₃₋ concentrations on the near-shore reef averaged 4 µM, ten times higher than that found at the control site 2 km away, and elevated NO₃₋ δ¹⁵N at the near-shore reef indicated sewage-contaminated groundwater as a significant nitrogen source. Tissue δ¹⁵N of Porites astreoides, a dominant reef-building coral, was elevated by ~ 3‰ on the near-shore reef compared to the control site, indicating that corals across the near-shore reef were assimilating groundwater-derived nitrogen. In addition, coral skeletal density and calcification rates across the near-shore reef were inversely correlated with NO₃₋ concentration and δ¹⁵N, indicating a negative coral health response to groundwater-borne nutrient inputs. P. astreoides bioerosion rates, in contrast, did not show an effect from the groundwater input.
Additional Information
© 2019 Springer-Verlag GmbH Germany, part of Springer Nature. Received 19 February 2019; Accepted 24 November 2019; First Online 04 December 2019. We sincerely thank H. Rivera, J. Middleton, H. Barkley, S. de Putron, K. Pietro, M. A. Weigand, P. Barbosa, T. deCarlo, V. Yao, S. Bellamy, T. Phelps, K. Wong, A. Ratteray, C. Emerson, A. Finkelstein, H. Reich, R. Bier, A. Schmidt, I. Salvaterra, C. Walsh, V. Schmidt, S. Kennedy, D. Becker, A. Hunter, K. Hollis, D. Ward, S. Cramer, D. Wellwood, P. Henderson, and the Bermuda Institute of Ocean Sciences staff for fieldwork and analysis assistance. We also thank S. Pacala, S. R. Smith, J. Thomson, and G. Smith for insightful discussion and three anonymous reviewers for their constructive feedback on the manuscript. This work was funded by the Princeton Environmental Institute through the Smith–Newton Scholars Program and Colvin Memorial Award to Z.C.S. and through the Grand Challenges Program to D.M.S., a grant from the Princeton University Ecology and Evolutionary Biology Department to Z.C.S., BIOS Grants-in-Aid to Z.C.S. and A.L.C, a Link Foundation award to A.L.C., a U.S. NSF Graduate Research Fellowship to V.H.L., and U.S. NSF grants OCE-1536547, OCE-1536368, and OCE-1537338 to S. de Putron, D.M.S., and A.L.C, respectively.Attached Files
Supplemental Material - 338_2019_1879_MOESM1_ESM.pdf
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Additional details
- Eprint ID
- 100177
- Resolver ID
- CaltechAUTHORS:20191204-090854275
- Princeton University
- Bermuda Institute of Ocean Sciences
- Link Foundation
- NSF Graduate Research Fellowship
- OCE-1536547
- NSF
- OCE-1536368
- NSF
- OCE-1537338
- NSF
- Created
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2019-12-04Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field