The soil displacement measurement of mercury emission flux of the sewage irrigation farmlands in Northern China

Mercury fate of sewage irrigation in farmlands deserves attention with increasing scarcity of freshwater resources for agriculture in the worldwide. Soil-air total gaseous mercury (TGM) fluxes from four-sewage and one-fresh water irrigated farmlands were determined simultaneously. During maize-wheat rotation, soil-air TGM fluxes showed patterns of both emission and deposition during different growth stages. It enhanced one-order of magnitude emission with increased Hg contamination from historical sewage irrigation. A linear response relationship of TGM fluxes with soil Hg concentration was found, which showed greater TGM emission potential comparing with those from forest and urban soils. However, the ratio of soil-air TGM flux in daytime to nighttime were 3.94 in maize-season and 3.41 in wheat-season, respectively, which were little related to the change in soil Hg concentration. Furthermore, soil temperature and moisture, ambient-air TGM concentration all effected TGM evasion from sewage-irrigated soils. The data presented here suggest that evasion of TGM from historical sewage irrigation farmlands with high Hg concentrations may be potential hotspots for Hg emission in atmosphere, and it was likely to underestimate Hg emissions from farmlands in existing emissions inventory. Additional regional-investigations and process-level researches are needed to better understand role of sewage irrigation farmlands in local-global Hg-biogeochemical-cycles.