Characterizing the Atmospheric Mn Cycle and Its Impact on Terrestrial Biogeochemistry
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AbstractThe role of manganese (Mn) in ecosystem carbon (C) biogeochemical cycling is gaining increasing attention. While soil Mn is mainly derived from bedrock, atmospheric deposition could be a major source of Mn to surface soils, with implications for soil C cycling. However, quantification of the atmospheric Mn cycle, which comprises emissions from natural (desert dust, sea salts, volcanoes, primary biogenic particles, and wildfires) and anthropogenic sources (e.g., industrialization and landuse change due to agriculture), transport, and deposition, remains uncertain. Here, we use compiled emission data sets for each identified source to model and quantify the atmospheric Mn cycle by combining an atmospheric model and in situ atmospheric concentration measurements. We estimated global emissions of atmospheric Mn in aerosols (<10m in aerodynamic diameter) to be 1,400Gg Mn year1. Approximately 31% of the emissions come from anthropogenic sources. Deposition of the anthropogenic Mn shortened Mn pseudo turnover times in 1mthick surface soils (ranging from 1,000 to over 10,000,000years) by 12 orders of magnitude in industrialized regions. Such anthropogenic Mn inputs boosted the MntoN ratio of the atmospheric deposition in nondesert dominated regions (between 5105 and 0.02) across industrialized areas, but that was still lower than soil MntoN ratio by 13 orders of magnitude. Correlation analysis revealed a negative relationship between Mn deposition and topsoil C density across temperate and (sub)tropical forests, consisting with atmospheric Mn deposition enhancing carbon respiration as seen in in situ biogeochemical studies.
