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 δ 15 N 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 δ 15 N values and the ratios of NH 4 -N/NO 3 -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 δ 15 N values in this study strongly indicate that NH y -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.Copyright 2010 by the American Geophysical Union.