QUANTIFYING DISSOLVED SILICATE FLUXES ACROSS HEEIA SHORELINE IN HAWAII VIA INTEGRATED HYDROLOGICAL MODELING APPROACH

Dissolved silicate (DSi) is one of the essential elements of biogeochemical cycles in the coastal zones. It plays a vital role in the preservation of endangered and endemic diverse organisms’ structure like plankton groups. DSi estimation and distribution within aquifer and its fluxes into the coastal ocean has been getting great attention among researchers, managers, and policymakers especially who focus on the coastal environmental health. Estimating DSi is very challenging due to the fact that the nutrient fluxes magnitude can vary spatially and temporally, which in turn depends on the groundwater flow as the main source of DSi. In Hawaii, the main sources of DSi are the weathering products of basaltic rock and volcanic ashes. An integrated groundwater modeling approach is considered as a robust way to estimate DSi fluxes both for temporal and spatial scales. In this study, the SWAT, MODFLOW, and SEAWAT models were applied to estimate DSi fluxes under different scenarios that consist of wetland restoration, climate change, and sea level rise. The results illustrated that the average DSi flux was about 49 mole per day that increased by 15% during the wet season but decreased by16% during the dry season. The DSi fluxes were a function of fresh submarine groundwater discharge (FSGD). Climate change has a more negative impact on DSi fluxes than sea level rise (SLR) resulting in a decrease in FSGD of 5% more than that due to a SLR of 1.1 meter. Wetland restoration did not have a significant effect on DSi fluxes. The decrease in DSi fluxes under SLR and climate change had a positive effect on the accumulative storing of DSi within coastal wetland. Overall, the integrated hydrological modeling approach has drawn a comprehensive picture of DSi fluxes and silicate behavior under various conditions within the Heeia coastal zone.