Characterization of the isotopic composition and bulk ion deposition of precipitation from Central to West Hawaiʻi Island between 2017 and 2019

Abstract

Study regionThe current study evaluates the isotopic and chemical compositions of rainfall from central to leeward Hawaiʻi Island, an area characterized by the interactions of Pacific trade wind flow with two 4,000-meter high mountains as well as one of the largest natural emitters of sulfur dioxide on the planet. Study focusOur study collected cumulative rainfall samples at regular intervals over a 28-month period from 20 stations spanning a range of elevations across this region and determined average isotopic and dissolved ion compositions in those samples. The study period included an extreme weather event (Hurricane Lane), a major volcanic eruption at Kīlauea in 2018, and the nearly complete cessation of long-term volcanic emissions following that eruptive event. New hydrological insightsto the Region Consistent with previous literature, results show long-term variability through our establishment of an enhanced local meteoric water line (LMWL) for West Hawaiʻi. We hypothesize the two LMWL represent ends of a spectrum, due to the variability in atmospheric and climate processes in this region. Additionally, results of stable isotope compositions and bulk ion deposition highlight how extreme events, such as volcanic eruptions and hurricanes, can affect the chemistry of precipitation. Sulfate concentrations in bulk precipitation decreased by a mean of 70 % (p = 0.032) after the 2018 Kīlauea eruption ceased. The results from this study can be used to better quantify and characterize precipitation, which is the ultimate source of Hawai‘i’s groundwater.