Impact of submarine groundwater discharge on phytoplankton and coral reef productivity using 3D plume models from drone thermal infrared imagery
Presentation Type
Poster
Presentation Type
Submission
Department
Biology
Abstract
In oligotrophic coral reef ecosystems, nutrient concentrations are a major driver for productivity and ecosystem stability. While moderate nutrient levels support coral growth, excess nutrients can cause phytoplankton blooms and algal overgrowth, which in turn leads to competition over resources such as space and light. Maunalua Bay (O‘ahu, HI) has experienced dramatic urban development and increase in population over the last 100 years, which has affected the water quality in the nearshore coral reefs of the bay. The main source of land-based inorganic nutrients in Maunalua Bay is submarine groundwater discharge (SGD), which is a chronic freshwater vector for nutrients. SGD increases productivity of the algae that can withstand high nutrients and low salinity, leads to increases in biomass for some species, and decreases biodiversity. Our goal is to assess the effects of land-based nutrient loading on coral reefs via SDG. We are utilizing drones equipped with thermal infrared cameras to map the SGD, which is colder than surrounding coastal water, on a reef at night. To validate our thermal imagery, we collected water samples for inorganic nutrient analysis and water quality data (i.e., salinity, temperature, pH, Oxidation-Reduction Potential, Total Dissolved Solids) at the surface of the water column. From our nutrient data, we have found that increased nutrients from SGD, such as nitrate (p = 5.92*10-8; R2 = 0.423), phosphate (p = 6.12*10-6; R2 = 0.318), and silicate (p = 1.46*10-8; R2 = 0.451) have a statistically significant correlation with temperature. At lower nitrate/nutrient levels, increasing nitrate boosts productivity. At higher nitrate/nutrient levels, increasing nitrate reduces productivity of Bryopsis pennata, Pterocladiella sp. and Acanthophora spicifera. These conditions favor particular algal species which can lead to shifts in composition of the macroalgal community. Utilizing this data and 3D plume models of the SGD, we will be able to quantify the magnitude of its effects on benthic and water column phytoplankton productivity of coral reefs. Understanding the impact of nutrient-loading from SGD is vital for predicting ecosystem shifts, mitigating harmful algal overgrowth, and preserving biodiversity in the face of coastal development and climate change.
Faculty Mentor
Dr. La Valle
Funding Source or Research Program
Academic Year Undergraduate Research Initiative
Location
Waves Cafeteria
Start Date
11-4-2025 1:00 PM
End Date
11-4-2025 2:00 PM
Impact of submarine groundwater discharge on phytoplankton and coral reef productivity using 3D plume models from drone thermal infrared imagery
Waves Cafeteria
In oligotrophic coral reef ecosystems, nutrient concentrations are a major driver for productivity and ecosystem stability. While moderate nutrient levels support coral growth, excess nutrients can cause phytoplankton blooms and algal overgrowth, which in turn leads to competition over resources such as space and light. Maunalua Bay (O‘ahu, HI) has experienced dramatic urban development and increase in population over the last 100 years, which has affected the water quality in the nearshore coral reefs of the bay. The main source of land-based inorganic nutrients in Maunalua Bay is submarine groundwater discharge (SGD), which is a chronic freshwater vector for nutrients. SGD increases productivity of the algae that can withstand high nutrients and low salinity, leads to increases in biomass for some species, and decreases biodiversity. Our goal is to assess the effects of land-based nutrient loading on coral reefs via SDG. We are utilizing drones equipped with thermal infrared cameras to map the SGD, which is colder than surrounding coastal water, on a reef at night. To validate our thermal imagery, we collected water samples for inorganic nutrient analysis and water quality data (i.e., salinity, temperature, pH, Oxidation-Reduction Potential, Total Dissolved Solids) at the surface of the water column. From our nutrient data, we have found that increased nutrients from SGD, such as nitrate (p = 5.92*10-8; R2 = 0.423), phosphate (p = 6.12*10-6; R2 = 0.318), and silicate (p = 1.46*10-8; R2 = 0.451) have a statistically significant correlation with temperature. At lower nitrate/nutrient levels, increasing nitrate boosts productivity. At higher nitrate/nutrient levels, increasing nitrate reduces productivity of Bryopsis pennata, Pterocladiella sp. and Acanthophora spicifera. These conditions favor particular algal species which can lead to shifts in composition of the macroalgal community. Utilizing this data and 3D plume models of the SGD, we will be able to quantify the magnitude of its effects on benthic and water column phytoplankton productivity of coral reefs. Understanding the impact of nutrient-loading from SGD is vital for predicting ecosystem shifts, mitigating harmful algal overgrowth, and preserving biodiversity in the face of coastal development and climate change.
