Water-soluble nitrogen and phosphorus in aerosols and dry deposition in Jiaozhou Bay, North China: Deposition velocities, origins and biogeochemical implications

To probe the deposition velocities (Vd), fluxes, origins and biogeochemical significance of atmospheric dry deposition (ADD) of nutrients in coastal waters, aerosol and dry deposition samples were collected in Jiaozhou Bay (JZB) from June 2015 to May 2016. We measured water-soluble inorganic nitrogen (WSIN; including ammonium (NH4N), nitrate (NO3N) and nitrite (NO2N)), organic nitrogen (WSON), inorganic phosphorus (WSIP; including reactive phosphate (PO4P)) and organic phosphorus (WSOP) for all samples. The concentrations of aerosol N species were comparatively higher than those in other aquatic ecosystems worldwide. Although WSIN and WSIP represented relatively large percentages of species, WSON (~16%) and WSOP (~35%) cannot be ignored in aerosols. The dry deposition fluxes for NH4N, NO3N, NO2N, WSON, PO4P and WSOP were 29.4, 29.9, 0.058, 15.4, 0.099 and 0.165 mmol m−2 yr−1, respectively, with apparent seasonal variations. The average annual Vd values of NH4N, NO3N, NO2N, WSON, PO4P and WSOP were indirectly calculated as 0.17 ± 0.11, 0.35 ± 0.20, 0.34 ± 0.25, 0.30 ± 0.22, 0.43 ± 0.28 and 0.91 ± 0.60 cm s−1, respectively. The considerable differences between the percentages of corresponding nutrient concentrations and ADD fluxes were mainly attributed to Vd variations. Anthropogenic emissions were the most common source of WSON and WSIN based on a correlation analysis. WSIP was highly correlated with WSOP, suggesting that they may share similar sources. Additionally, the long-range transport of natural and anthropogenic pollutants, especially the air-masses originating from the northwest direction, exerted greater effects than local emissions on aerosol N and P species in JZB based on an air mass backward trajectory analysis. The increasing ADD flux may have non-negligible biogeochemical effects on JZB by increasing primary productivity and altering the nutrient structure due to the high WSIN/WSIP ratio.