Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 8
Biogeosciences, 15, 2467-2480, 2018
https://doi.org/10.5194/bg-15-2467-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 2467-2480, 2018
https://doi.org/10.5194/bg-15-2467-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Apr 2018

Research article | 23 Apr 2018

Carbonate system parameters of an algal-dominated reef along West Maui

Nancy G. Prouty1, Kimberly K. Yates2, Nathan Smiley2, Chris Gallagher3, Olivia Cheriton1, and Curt D. Storlazzi1 Nancy G. Prouty et al.
  • 1U.S. Geological Survey, Coastal and Marine Geology, Pacific Coastal and Marine Science Center, Santa Cruz, CA 95060, USA
  • 2U.S. Geological Survey, Coastal and Marine Geology, St. Petersburg Coastal and Marine Science Center, 600 4th Street South, St. Petersburg, FL 33701, USA
  • 3University of California, Santa Cruz, Santa Cruz, CA 95060, USA

Abstract. Constraining coral reef metabolism and carbon chemistry dynamics are fundamental for understanding and predicting reef vulnerability to rising coastal CO2 concentrations and decreasing seawater pH. However, few studies exist along reefs occupying densely inhabited shorelines with known input from land-based sources of pollution. The shallow coral reefs off Kahekili, West Maui, are exposed to nutrient-enriched, low-pH submarine groundwater discharge (SGD) and are particularly vulnerable to the compounding stressors from land-based sources of pollution and lower seawater pH. To constrain the carbonate chemistry system, nutrients and carbonate chemistry were measured along the Kahekili reef flat every 4h over a 6-day sampling period in March 2016. Abiotic process – primarily SGD fluxes – controlled the carbonate chemistry adjacent to the primary SGD vent site, with nutrient-laden freshwater decreasing pH levels and favoring undersaturated aragonite saturation (Ωarag) conditions. In contrast, diurnal variability in the carbonate chemistry at other sites along the reef flat was driven by reef community metabolism. Superimposed on the diurnal signal was a transition during the second sampling period to a surplus of total alkalinity (TA) and dissolved inorganic carbon (DIC) compared to ocean endmember TA and DIC measurements. A shift from positive net community production and positive net community calcification to negative net community production and negative net community calcification was identified. This transition occurred during a period of increased SGD-driven nutrient loading, lower wave height, and reduced current speeds. This detailed study of carbon chemistry dynamics highlights the need to incorporate local effects of nearshore oceanographic processes into predictions of coral reef vulnerability and resilience.

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Coral reefs provide critical shoreline protection and important services, such as marine habitat, tourism, fishing, and recreation. However, coral reefs are being threatened by global climate change. If we are to understand how reefs will response to climate change, we must also understand how local conditions may impact the reefs. Our study offers a first glimpse into how human inputs of nutrients might add an additional stressor to reef health.
Coral reefs provide critical shoreline protection and important services, such as marine...
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