SEASONALITY OF GROUNDWATER INPUTS AND ASSOCIATED ANTHROPOGENIC FLUXES IN THE KAHALUʻU STREAM COMPLEX, OʻAHU

Kāneʻohe Bay, a reef-dominated embayment located on the windward side of Oʻahu, has been subject to persistent water pollution issues. Recent water quality issues in northwestern Kāneʻohe Bay have emerged forcing the Hawaiʻi State Department of Health to close beaches near Kahaluʻu Lagoon. Contamination transport from the Kahaluʻu watershed is suspected to not only be stream-based, but also via groundwater pathways. Previous research has indicated that there is a strong seasonal difference between surface runoff and groundwater discharge regime dominance in Kāneʻohe Bay. Seasonality, as well as spatial and temporal variations of discharge, will be captured by a series of snapshot studies using natural isotopes of radon and radium as tracers for groundwater inflows. We present results from dry and wet seasons and examine the influence of both ground and surface water discharge on coastal water quality, focusing on nutrient and contaminant of emerging concern fluxes across the land-ocean interface. Investigating the roles that surface and groundwater inputs play in driving water quality in the Kahaluʻu watershed is instrumental to understanding the bigger picture on how surface and groundwater inputs can impact pollutant pathways.