Vegetation Effects on Total Atmospheric Chloride Deposition and Its Variability in Small Islands: Insights From South Pacific's Norfolk Island

ABSTRACT Chloride is a natural ion and widely used tracer in hydrological and ecological studies. Tree canopies possess a natural filtration capacity that enables them to effectively capture aerosols, leading to potentially higher rates of ion deposition beneath the canopies compared to open areas. Therefore, understanding the spatial and temporal variability of chloride deposition in throughfall is crucial, particularly in coastal areas where chloride deposition exhibits significant variation. This study aims to estimate chloride throughfall deposition and analyze its distribution among different vegetation types on a small island, while concurrently comparing deposition rates in vegetated sites and open areas. The monitoring network consisted of 17 throughfall collectors positioned beneath the primary vegetation types. The findings demonstrate that vegetation plays a substantial role in enhancing chloride deposition by effectively intercepting marine aerosols, resulting in total deposition values among throughfall sites ranging from 8% to 3742% higher than nearby open sites over a ~ 2‐year period. Norfolk pines, white oak, and hardwood forest exhibit significantly elevated chloride deposition in throughfall compared to a shrub stand (Hawaiian holly) and a mixed palm forest. Notably, isolated Norfolk pine sites exhibit exceptionally high chloride deposition. Key factors contributing to the spatial variation of chloride deposition in throughfall include vegetation type, leaf area index (LAI), and exposure to wind and marine aerosols. Additionally, temporal analysis using multiple regression reveals the considerable influence of rainfall depth and wind gust speed on the temporal distribution of chloride deposition in throughfall. The relatively high chloride deposition recorded on Norfolk Island highlights the significant role of vegetation in shaping total chloride deposition in small islands or coastal environments with extensive canopy cover. These findings add to the limited global evidence that neglecting vegetation effects in hydrological studies can underestimate chloride inputs, with implications for chloride mass balance and related methods.