Canopy interception of atmospheric chloride ion during precipitation processes in the subalpine Picea asperata plantation in the upper reaches of the Yangtze River
Increasing concentrations of chloride ions (Cl~-) in the atmosphere is one of the most important global environmental factors influencing processes in terrestrial ecosystems. To understand the roles played by plantations in intercepting atmospheric Cl~- in mountainous regions, a one-year field observation of precipitation and throughfall was conducted in a subalpine artificial Picea asperata plantation in western Sichuan and the dynamics of Cl~- concentrations in rainfall, snowfall, and throughfall, and canopy interception on atmospheric Cl~- were investigated from August 2015 to July 2016. During the observational year, 27 rainfalls and 6 snowfalls were observed and sampled. The average concentration of Cl~- in the precipitation was 1.33 mg/L and the average concentrations of Cl~- in rainfall and snowfall were 1.41 mg/L and 0.98 mg/L, respectively. Correspondingly, the total input of Cl~- by the precipitation processes was 7.56 kg/hm~2, which included 6.31 kg/ hm~2 by rainfall and the remainder by snowfall. In one entire year, the total canopy interception of Cl~- was 2.61 kg/hm~2 and the average interception rate was 38.08%. During the rainy season, the canopy interception of Cl~- was 2.20 kg/hm~2 and the average rate was 38.90%, whereas during the snow season, the canopy interception of Cl~- was 0.41 kg/hm~2 and the average rate was 34.39%. The maximum and minimum interception rates occurred in August and September, respectively. Significantly negative correlation was found between the interception rate of Cl~- and precipitation. In summary, the P. asperata plantation in the subalpine forest region of western Sichuan exerts an important role in intercepting atmospheric Cl~-, which is of great significance for maintaining and improving the environment of the water conservation region in the upper reaches of the Yangtze River. Furthermore, changes in the precipitation pattern caused by global changes might affect the role of the artificial forest canopy interception on atmospheric Cl~-.