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Groundwater-derived Nutrient Uptake in Coastal Ecosystems as Driver of Reef Accretion-Erosion Balance

Principal Investigator: Megan Donahue

The last century of human activity has dramatically affected coral reefs. Global changes, due to increased atmospheric carbon dioxide, and local changes, like coastal development and overfishing, have altered the community composition on coral reefs and jeopardized the accretion-erosion balance of natural reefs. Our study looks at interactions between groundwater runoff and these local and global threats. Inputs of anthropogenic nutrients onto coral reefs have some well-known deleterious effects, often causing algal overgrowth of coral reefs. However, anthropogenic nutrients also have more complex effects on reef chemistry that may add to the impacts. High nutrients can make the day/night photosynthesis/respiration cycle more extreme, leading to high variability in pH. The variability in pH may shift the accretion-erosion toward reef degradation. In this study, we plan to measure the input of groundwater into Maunalua Bay and track the nutrients to see how much is taken up by reef organisms and how much is diluted away. We will also measure the changes in the photosynthesis/respiration cycle as a result of those nutrient inputs. Finally, we will measure the effect of nutrient inputs on rates of erosion and accretion on the reef. Together, these experiments will help us understand the many ways that anthropogenic nutrients may impact the coral reef ecosystem.