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

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 delta N-15 values in cities and forests were found in distinctly different ranges of approximately -10 parts per thousand to -6 parts per thousand and approximately -2 parts per thousand to 2 parts per thousand, 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 delta N-15 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 delta N-15 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.