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Hydrology 2019, 6(1), 18; https://doi.org/10.3390/hydrology6010018

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

1
Department of Earth Sciences, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
2
Water Resources Research Center, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
3
Botany, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
4
Department of Microbiology, Cornell University, Ithaca, NY 14850, USA
5
Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of at Hawaiʻi Mānoa, Honolulu, HI 96822, USA
6
Department of Oceanography, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
7
Sea Grant College Program, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
*
Author to whom correspondence should be addressed.
Received: 9 January 2019 / Revised: 10 February 2019 / Accepted: 12 February 2019 / Published: 16 February 2019
(This article belongs to the Special Issue Submarine Groundwater Discharge and Its Effects)
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Abstract

Anthropogenic nutrient loading is well recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This study examines connections between land use and nutrient loading through comparison of four watersheds and embayments spanning a gradient of human use impact on Tutuila, a high tropical oceanic island in American Samoa. In each study location, coastal radon-222 measurements, dissolved nutrient concentrations, and nitrogen isotope values (δ15N) in water and in situ macroalgal tissue were used to explore SGD and baseflow derived nutrient impacts, and to determine probable nutrient sources. In addition to sampling in situ macroalgae, pre-treated macroalgal specimens were deployed throughout each embayment to uptake ambient nutrients and provide a standardized assessment of differences between locations. Results show SGD-derived nutrient flux was more significant than baseflow nutrient flux in all watersheds, and δ15N values in water and algae suggested wastewater or manure are likely sources of elevated nutrient levels. While nutrient loading correlated well with expected anthropogenic impact, other factors such as differences in hydrogeology, distribution of development, and wastewater infrastructure also likely play a role in the visibility of impacts in each watershed. View Full-Text
Keywords: submarine groundwater discharge; nutrients; nitrogen isotopes; macroalgae; non-point source pollution; American Samoa submarine groundwater discharge; nutrients; nitrogen isotopes; macroalgae; non-point source pollution; American Samoa
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Shuler, C.K.; Amato, D.W.; Gibson, V.; Baker, L.; Olguin, A.N.; Dulai, H.; Smith, C.M.; Alegado, R.A. Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa. Hydrology 2019, 6, 18.

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