Groundwater-derived nutrient and trace element transport to a nearshore Kona coral ecosystem: Experimental mixing model results

Abstract

Study region The groundwater influenced coastal waters along the arid Kona coast ofthe Big Island, Hawai'i. Study focus A salinity-and phase partitioning-based mixing experiment was constructed using contrasting groundwater endmembers along the arid Konacoast of the Big Island, Hawai'i and local open seawater to better understand biogeochemical and physicochemical processes that influence the fate of submarine groundwater discharge (SGD)-derived nutrients and trace elements. New Hydrological Insights for the Region Treated wastewater effluent was the main source for nutrient enrichment downstream at the Honokōhau Harbor site. Conservative mixing for some constituents, such as nitrate + nitrite, illustrate the effectiveness of physical mixing to maintain oceanic concentrations in the colloid (0.02–0.45 μm) and truly dissolved (<0.02 μm) forms. In contrast, the nonconservative behavior of phosphate highlights the importance of surface complexation reactions that can lead to higher concentrations based on conservative mixing alone. Results from this physiochemical mixing experiment demonstrate how relative availability of P can shift with adsorption behavior, affecting the mobility of phosphate in the environment. With a proposed 8-hectare wastewater treatment facility (WWTF) to be constructed upslope of the Kaloko-Honokōhau National Historical Park (NHP), treated effluent is projected to add additional nutrients. Combined with high permeability, rapid discharge, and increased nutrient loading SGD will likely continue to serve as a persistent source of nutrients and potential contaminant to coral ecosystems.