A Comparison between Wet-only and Bulk Deposition at Two Forest Sites in Japan

Abstract

To investigate the effects of forest and the surrounding natural and anthropogenic sources on the bulk depositions on forested land, this study examined differences in ion concentrations between wet-only and bulk samples at two forested sites in Japan. The surrounding natural and anthropogenic sources at each site were different; Shirasaka is in a rural area and Tanashi is an urban environment. The volume weighted (vw) mean concentrations of K+ and Ca2+ in the bulk samples were significantly (p<0.05) higher than those in the wet-only samples at both sites. The forest canopy and a nearby incineration plant were hypothesized to be the main sources of K+ contaminants at Shirasaka and Tanashi, respectively. The transport of sea salt and urban dust may explain the presence of enriched Ca2+ concentrations in the bulk samples at Shirasaka and Tanashi, respectively. The NH4+ concentrations in the Shirasaka bulk samples were significantly (p<0.05) lower than those in the wet-only samples. The vw mean SO42- and NO3- concentrations in both sample types were not significantly different at either site. This study demonstrated that the ion concentration differences between wet-only and bulk samples were affected by nearby natural and anthropogenic sources even at forest sites, similar to previous findings for non-forested locations. However, the K+ concentration differences between wet-only and bulk samples may be higher owing to forest sources, even in the absence of anthropogenic sources.

Keywords

• atmospheric deposition
• dry deposition
• forests
• urban areas
• rural areas