Utilizing δ15N of biomonitors to assess N emission sources and deposition chemistry?

Abstract

Anthropogenic nitrogen (N) emissions and subsequent deposition can cause harm to ecosystem function and processes. Identifying emission sources of atmospheric N deposition (Ndep) is critical for land management and policy development to understand what N species are impacting an area and where action can be taken to reduce loading. Measuring and monitoring deposition is time intensive and expensive, but biomonitors, such as mosses and lichens, can be used to evaluate finer-scale deposition patterns and source attribution using stable isotope analysis. The N stable isotope composition (δ15N) of Ndep provides unique insight into emission sources and chemistry at different temporal and spatial scales because it is determined in part by the δ15N of contributing N emission sources that vary at a local, regional, and global level. The δ15N of biomonitor organisms can be used to monitor Ndep at these diverse scales capturing the spatial and temporal heterogeneity of Ndep rates and source chemistries. However, the δ15N of biomonitors integrates not only source effects, but also isotopic effects associated with canopy dynamics and organism biology, thus interpretation of biomonitor δ15N needs to consider multiple factors including emission source, atmospheric transformations, and canopy and physiological effects. Despite local scale and organism specific responses, lichens and mosses from herbaria collections document coherent anthropogenically driven shifts in Ndep δ15N signals over the last century consistent with observations from lake sediments and ice cores.

Keywords

• Stable isotope
• Nitrogen
• Anthropogenic emissions
• Lichen
• Moss