Organic Acids and Aldehydes in Throughfall and Dew in a Japanese Pine Forest

Abstract

We analyzed low molecular weight organic acids and aldehydes in throughfall under pine forest, and organic acids in dew on chemically inert surfaces and pine needle surfaces at urban- and mountain-facing sites of pine forest in western Japan. Low molecular weight organic acids and aldehydes accounted for less than 5% of the dissolved organic carbon in throughfall at both sites. Formaldehyde at both sites and formate at the mountain-facing site were found at significantly lower concentrations in throughfall than in rainfall, which may be explained by the degradation and/or retention of these components by the pine canopy as the incident precipitation passed through it. The oxalate concentration in throughfall was significantly higher than those in rainfall at both sites, suggesting that oxalate was derived from leaching from the pine foliage. At both sites, organic acid concentrations were higher in dew on the pine needles than in throughfall or dew on chemically inert surfaces. This could be due to the long contact time of dew on pine needles, during which leached substances from pine needles and dry deposits accumulated on their surfaces can dissolve into the small volume of dew. The role of enhanced concentrations of oxalate in an aqueous phase on the plant surfaces (e.g., dew) is discussed in relation to hydroxyl radical formation via the photo-Fenton reaction.

Molecular Insights into Dissolved Organic Matter in Natural Dew Water: Biogrime Films on Leaf Surfaces

“…Biogrime’s role in an ecosystem will depend on its chemical composition. Biogrime films on leaf surfaces in forests have been investigated in throughfall experiments where rainwater that has washed through the canopy is collected and analyzed. − Complex organic mixtures were observed in these samples, with some evidence for longer range transport and deposition of anthropogenic organic aerosol particles . Other studies imaged deposited particles on clean substrates and show large biological particles including fungi and bacteria. , Throughfall experiments provide a good perspective on biogrime as they target tree leaf surfaces, but a more complete picture of the composition of natural biogrime across different ecosystems is needed, as well as a comparison between dry surface films and wet surface films such as dew water.…”

Evaluation of the Contribution of Deposited Precipitation

“…Polluting substances present in the atmospheric boundary layer are deposited during precipitation events. Beysens et al [6][7][8], Chiwa et al [9], Clus et al [10][11][12], and Galek et al [13] have measured precipitation levels and assessed chemical pollution content. Chemical attributes of deposited precipitation in India are presented in Muselli et al [14] and Sharan et al [15], for example.…”