Research Projects 2014-2016

Groundwater-derived nutrient uptake in coastal ecosystems as driver of reef accretion-erosion balance

Graduate Trainee: Christina Richardson

A peninsula with houses and palm trees sticks out into the waves of a blue ocean
Black Point, Oʻahu, proves an important location for studying the effects of groundwater input on coral reef health.

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 looked at interactions between groundwater runoff and inputs of anthropogenic nutrients onto coral reefs. Our study has been able to identify septic systems as a major nitrogen pollutant in the Black Point region of the bay. Nutrients have some well-known deleterious effects, often causing algal overgrowth of coral reefs. However, anthropogenic nutrients also have more complex effects on coastal water quality. We found that SGD directly affects coastal pH, causing local ocean acidification, and offsets the expected marine nitrogen-to-phosphorus ratios. In addition, excess nutrient delivery by SGD amplifies the photosynthesis respiration cycle in coastal ecosystems and we can link large variations in coastal dissolved oxygen, pH, and nutrients to groundwater fluxes.