Declines in tourism during COVID-19 reduces nitrogen loading of groundwater input to a coral reef in West Maui, Hawaiʻi

The coral reef at Kahekili Beach Park (KBP) in West Maui receives eutrophic submarine groundwater discharge (SGD), of which over half is injected wastewater from the Lahaina Wastewater Reclamation Facility (LWRF). Algal blooms, decreased calcification, calcium carbonate dissolution and bioerosion have been identified as consequences of injected wastewater. During the COVID-19 pandemic, Maui visitor numbers dropped 99 %, which reduced effluent volume and total nitrogen (TN) loading of injected wastewater by 70 % and 60 %, respectively. Water samples were collected at KBP during and after the visitor quarantine to characterize SGD nitrate concentrations ([NO₃⁻]) during changing visitor population and injected wastewater characteristics. These results reveal a > 99 % reduction of SGD [NO₃⁻] at the height of the visitor quarantine and suggest that TN injected at the LWRF should be kept below ∼53 lbs. d⁻¹, which is more than four times the limit outlined in the LWRF National Pollutant Discharge Elimination System draft permit.