Characterizing The Effects Of Two Storms On The Coastal Waters Of O'Ahu, Hawai'I, Using Data From The Pacific Islands Ocean Observing System

Pathogens (and other contaminants) associated with urban storm water runoff plumes have long been recognized as adversely affecting the water quality of the coastal ocean. An understanding of the temporal and spatial characteristics of stormwater plumes is a critical first step in protecting the health of people who recreate in coastal waters. Until recently, characterization of stormwater plumes was limited to expensive vessel-based sampling and satellites, which cannot always provide imagery of the nearshore areas, particularly during storms. With the advent of coastal ocean observing systems with their fixed sensor platforms and autonomous underwater vehicles, we have begun to better understand the temporal and spatial characteristics of stormwater plumes in the coastal ocean. The Pacific Islands Ocean Observing System (PacIOOS) provides continuous environmental monitoring of island coastal waters throughout the Pacific Ocean. This network of new ocean-based monitoring stations enabled the authors to study the effects of two storms on coastal water quality. We find that storm runoff from even a relatively small, partially urbanized watershed can profoundly affect the surface waters of the coastal ocean for days to weeks, both inshore and up to hundreds of meters offshore. Even in these coastal waters exposed to the open ocean, the lower salinities and higher turbidity values indicative of stormwater plumes lingered for nearly two days along the southern coast of O'ahu, Hawai'i.