Measurement of dry N deposition by physical methods is time-consuming because it is usually difficult to measure directly. In this study, an alternative approach has successfully been proposed by coupling isotopic ratios with tissue N contents of epilithic mosses. The method is to use moss N contents to quantitatively estimate total N (TN) deposition and then to use N-15 natural abundance in mosses to discriminate dry and wet deposition in atmospheric NHy-dominated areas (NHy/TN > 0.75). On the basis of the isotopic balance between atmospheric NHy and moss tissue N and the correlation between atmospheric NHy concentrations and their isotopes, both wet and dry N deposition can be estimated. By the approach, we have estimated rainwater ammonium concentrations and contribution percentage of wet deposition to total N deposition (f(wet)) in some areas of southern China. The results indicated that rainwater ammonium concentrations increased relative to those reported previously in most cities, owing to stronger anthropogenic activity. The f(wet) values estimated in most sites were found to be slightly higher than those reported, because faster transformation rates due to higher SO2 emission later in acid rain areas of southern China favored deposition in the form of wet deposition instead of dry deposition. The largest uncertainty of the approach comes from the influence of NOx in the atmosphere, and thus it cannot be used in areas where NOx deposition is high. The presented isotopic approach represents a new application of moss biomonitoring for estimating atmospheric N deposition in NHy-dominated areas.

 

Publication name	JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES　　Volume: 116　Article Number: D03305　　Published: FEB 15 2011
Author(s)	Xiao, Hua-Yun, Liu, Cong-Qiang
Corresponding author	XIAO Hua-Yun  xiaohuayun@vip.skleg.cn　  Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Peoples R China

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