Mosses Indicating Atmospheric Nitrogen Deposition and Sources in the Yangtze River Drainage Basin, China

Abstract

Characterizing the level and sources of atmospheric N deposition in a large‐scale area is not easy when using physical monitoring. In this study, we attempted to use epilithic mosses (Haplocladium microphyllum (Hedw.)) as a bioindicator. A gradient of atmospheric N deposition from 13.8 kg N ha−1 yr−1 to 47.7 kg N ha−1 yr−1 was estimated on the basis of moss tissue N concentrations and the linear equation between them. The estimated results are reliable because the highest atmospheric N deposition occurred in the middle parts of the Yangtze River, where the highest TN concentrations were also observed. Moss δ15N values in cities and forests were found in distinctly different ranges of approximately −10‰ to −6‰ and approximately −2‰ to 2‰, respectively, indicating that the main N sources in most of these cities were excretory wastes and those in forests were soil emissions. A negative correlation between moss δ15N values and the ratios of NH4‐N/NO3‐N in deposition (y = −1.53 x + 1.78) has been established when the ratio increased from 1.6 to 6.5. On the basis of the source information, the negative moss δ15N values in this study strongly indicate that NHy‐N is the dominant N form in N deposition in the whole drainage basin. These findings are supported by the existing data of chemical composition of local N deposition.