Chemical Composition and Deposition Characteristics of Precipitation into a Typical Temperate Forest in Northeastern China

The chemical compositions and deposition characteristics of atmospheric precipitation affect the structure and function of forest ecosystems and reflect regional air quality. Although northeastern China constitutes a vital forested area, few relevant studies reveal the chemical composition and the nitrogen (N) and sulphur (S) deposition characteristics within precipitation. In this study, we monitor precipitation chemistry during 2018-2020 at a rural forested site in northeastern China (the Qingyuan site) and compare it with those from background sites (Mondy in Russia and Ochiishi in Japan) and highly anthropogenically influenced areas (Beijing). The precipitation pH range was 4.7-8.0 (volume-weighted average 6.2). The average concentration of total ions in precipitation was 459 mu mol L-1, representing a moderate pollution level. Nitrate (NO3-, 73 mu mol L-1) and ammonium (NH4+, 133 mu mol L-1) were the major anions and cations in the precipitation. Total inorganic nitrogen (TIN) deposition was 12.3-15.9 kg N ha(-1) year(-1) (NH4+-N deposition accounted for 54-67%), lower than the average level in China (19.4 kg N ha(-1) year(-1)). Annual precipitation sulphate (SO42-) deposition was 4.9-6.7 kg S ha(-1) year(-1). Seventy-two percent of the precipitation ions at our site originated from human activities. This work has revealed that N and S deposition is an important ion deposition component in atmospheric precipitation in the study of temperate forests in northeastern China. Nitrogen deposition, as a source of vital nutrients in the forest ecosystem, may promote forest growth and, thereby, forest carbon sequestration.