Linking Transpiration to Reef Nitrogen Supply on a Tropical Coral Island

Dirk V. Erler; Christine L. Dudgeon; Asia O. Armstrong; Eddie W. Banks; Orlando Ramirez-Valle; Hugo A. Gutiérrez-Jurado; Ben L. Gilby; Kathy A. Townsend

doi:10.1029/2023JG007413

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Linking Transpiration to Reef Nitrogen Supply on a Tropical Coral Island

Journal article

Open access

Peer reviewed

Linking Transpiration to Reef Nitrogen Supply on a Tropical Coral Island

Dirk V. Erler, Christine L. Dudgeon, Asia O. Armstrong, Eddie W. Banks, Orlando Ramirez-Valle, Hugo A. Gutiérrez-Jurado, Ben L. Gilby and Kathy A. Townsend

Journal of Geophysical Research: Biogeosciences, Vol.129(2), pp.1-16

2024

DOI: https://doi.org/10.1029/2023JG007413

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Abstract

coral reef

groundwater

nitrate

stable isotope

transpiration

Coral reef islands are biodiversity hotspots with high conservation value, but we have a poor understanding of how island vegetation, through transpiration, influences groundwater nutrient supply to adjacent reef systems. Here we combine stable isotope tracing, geophysical surveys, and satellite analysis to unravel the links between transpiration and the discharge of groundwater nitrate to the waters surrounding a coral reef island (Lady Elliot Island in the Great Barrier Reef). Over a 2-year study period (2020–2021) there was a net loss of freshwater from the island, that is, evapotranspiration (ET) exceeded rainfall, largely caused by high rates of transpiration (73% of ET). Transpiration was higher in forested areas, and groundwater salinity appeared to be higher there. By tracing the nitrogen stable isotope signature of groundwater nitrate into reef organism tissue we were able to map groundwater nitrogen discharge spatially and temporally. Groundwater nitrogen discharge was focussed on one side of the island and did not vary seasonally as expected, despite reduced rainfall and seabird guano inputs over the austral winter/spring. Based on our results, we propose that transpiration by island vegetation slows groundwater flow and concentrates nitrate in the groundwater being released to the surrounding reef system. High concentrations of nitrate in groundwater (up to 27 mmol L−) were observed on Lady Elliot Island and these seem to have increased since 2014, but further work is required to understand if this is a normal scenario for tropical coral islands or the result of the islands' revegetation program.

Details

Title: Linking Transpiration to Reef Nitrogen Supply on a Tropical Coral Island
Authors: Dirk V. Erler (Corresponding Author) - Southern Cross University
Christine L. Dudgeon (Author) - University of the Sunshine Coast, Queensland, School of Science, Technology and Engineering
Asia O. Armstrong (Author) - University of the Sunshine Coast, Queensland, School of Science, Technology and Engineering
Eddie W. Banks (Author) - National Centre for Groundwater Research and Training
Orlando Ramirez-Valle (Author) - The University of Texas at El Paso
Hugo A. Gutiérrez-Jurado (Author) - The University of Texas at El Paso
Ben L. Gilby (Author) - University of the Sunshine Coast, Queensland, School of Science, Technology and Engineering
Kathy A. Townsend (Author) - University of the Sunshine Coast, Queensland, School of Science, Technology and Engineering
Publication details: Journal of Geophysical Research: Biogeosciences, Vol.129(2), pp.1-16
Publisher: Wiley-Blackwell Publishing, Inc.
Date published: 2024
DOI: 10.1029/2023JG007413
ISSN: 2169-8961; 2169-8953
Copyright note: © 2024 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Data Availability: All relevant borehole data is provided in Supporting Information S1. The nitrogen stable isotope data for the reef organisms is available at https://doi.org/10.25918/data.331.
Organisation Unit: School of Science, Technology and Engineering
Language: English
Record Identifier: 991002031502621
Output Type: Journal article

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