Groundwater-derived nutrient uptake in coastal ecosystems as driver of reef accretion-erosion balance
PRINCIPAL INVESTIGATOR: Megan Donahue
Co-INVESTIGATORS: Henrietta Dulai, Florence Thomas
Graduate Trainee: Catherine Lubarsky
Coastal coral reefs are subject to freshwater impacts from many sources, including runoff from rivers and streams and discharge of groundwater into the coastal ocean. Although much of the freshwater discharged onto coastal Hawaiian reefs is groundwater, the impacts of groundwater are relatively understudied compared with surface runoff. Groundwater discharged onto Hawai‘i’s reefs has a distinct water chemistry from seawater and from river water and is often high in nutrients, especially in urbanized areas such as the south shore of Oʻahu. These nutrients can directly impact the growth and breakdown of coral reefs by acting as a fertilizer for macroalgae that can outcompete corals or by supplying food for bioeroders that break down the reef structure. Groundwater-derived nutrients can also indirectly affect reef growth and breakdown by increasing rates of photosynthesis and respiration on the reef, driving changes in pH that can hinder coral growth and increase bioerosion rates. Our study characterized groundwater discharge at two sites in Maunalua Bay, Oʻahu and demonstrated that areas of groundwater influence have elevated rates of coral growth and bioerosion.