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Webinar: Nutrient Biogeochemistry of Vatia Bay, American Samoa: Variability, Sources and Effects

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Wednesday, 02 May 2018, 12:00

Wednesday, May 2, 2018. 12:00PM. Webinar: Nutrient Biogeochemistry of Vatia Bay, American Samoa: Variability, Sources and Effects. David Whitall, NOAA/NOS/National Centers for Coastal Ocean Science. Sponsored by Center for Satellite Applications and Research. More information here.


Over the past ten years field observations have noted a decrease in healthy coral cover in Vatia Bay, on the island of Tutuila, American Samoa.  The cause for this is unknown, but one hypothesis is that nutrient pollution from the local village may be driving the decline. Excess nutrients (nitrogen and phosphorus) can impact corals directly by lowering fertilization success, and reducing both photosynthesis and calcification rates, or indirectly such as through stimulation of the grown of benthic algae. Declining coral health adversely affects the biodiversity of the Bay and likely decreases ecosystem services.  Water samples were collected monthly at sites selected from a stratified random design for analysis for nitrate, nitrite, ammonium, urea, total nitrogen, orthophosphoric, total phosphorus, silica and salinity. Biological surveys found that reef habitat was more degraded in the inner portion of the Bay, which coincides with elevated levels of nitrogen and phosphorus. However, other stressors (sedimentation and increased turbidity) may also be driving this pattern. Land based contributions of phosphorus and reactive nitrogen can enter the environment from a variety of sources, but in Vatia the most likely sources are piggeries and septic systems.  Analysis of water samples for tracers of human waste (caffeine and sucralose) confirmed that human derived nutrients are contributing to the nutrient budget of the Bay. These data are useful not only to enhance our understanding of the role that anthropogenic nutrients play in the biodiversity and ecosystem health of the Bay, but also serve as an important “baseline” against which to measure future change. Current ongoing research will attempt to model the nutrient budget of the watershed that drains the Bay, as well as focus on event sampling to better capture precipitation events.

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