Atmospheric nitrogen deposition in Yangtze River Delta: insights gained from the nitrogen content and isotopic composition of the moss Haplocladium microphyllum

Abstract

Simple and inexpensive estimation of the rates and sources of atmospheric nitrogen (N) deposition is critical for its effective mitigation in a region with different land-use types. In this study, the N content and N isotopic composition (δ15N) of moss (Haplocladium microphyllum) tissues and precipitation at six sites with three land-use types (urban, suburban, and rural) were measured in the Yangtze River Delta. A significant linear relationship between moss N content and wet N deposition, and a consistent decrease trend for moss N content and wet N deposition from urban to suburban to rural areas were observed. More negative δ15N of suburban and rural mosses indicated N mainly released from agriculture and effluent, while the less negative δ15N of urban mosses were mainly influenced by fossil fuel combustion and traffic emissions. Although the negative moss δ15N indicates that reduced N dominates wet N deposition, there was no significant correlation between moss δ15N and the ratio of ammonium to nitrate (NH4+/NO3−). These results reveal that the moss N content and δ15N can be used as a complementary tool for estimating the rates and sources of wet N deposition in a region with different land-use types.

Keywords

• epilithic mosses
• nitrogen content
• nitrogen isotope
• atmospheric wet nitrogen deposition
• sources