Fluxes, seasonal patterns and sources of various nutrient species (nitrogen, phosphorus and silicon) in atmospheric wet deposition and their ecological effects on Jiaozhou Bay, North China.

Atmospheric wet deposition (AWD) is an important pathway for anthropogenic and natural pollutants entering aquatic ecosystems. However, the study on the magnitudes and ecological effects of AWD of various nutrient species (nitrogen, phosphorus and silicon) on Jiaozhou Bay is scarce. To address these issues, in this study, wet deposition samples were collected at a coastline site along Jiaozhou Bay from June 2015 to May 2016. Dissolved inorganic nitrogen (DIN, including NH4-N, NO3-N and NO2-N), dissolved organic nitrogen (DON), dissolved inorganic phosphorus (DIP, i.e. PO4-P), dissolved organic phosphorus (DOP) and reactive silicate (SiO3-Si) were analyzed. The volume-weighted mean (VWM) concentrations of NH4-N, NO3-N and DON in AWD were higher compared with those of NO2-N, PO4-P, DOP and SiO3-Si. The annual influxes of NH4-N, NO3-N, NO2-N, DON, DIP, DOP, and SiO3-Si via AWD were 92.8, 54.5, 0.427, 47.5, 0.274, 0.448 and 1.73mmol·m-2·yr-1 respectively; NH4-N and DOP were the dominant species for N and P, and the roles of DON and DOP in AWD could not be neglected. Significant seasonal variations were observed in concentrations and fluxes of all nutrient species owing to the effects of rainfall, the intensities of local emission sources and the long-distance transports of natural and anthropogenic pollutants. The major sources of N, Si and P in AWD were agricultural activities, soil dust and a mixing one involving both anthropogenic and natural sources, respectively. Though AWD represents relatively low percentages of external inputs for nutrients and low contribution to primary productivity (PP) of Jiaozhou Bay, large amounts of nutrient inputs originating from sudden heavy rains may enhance PP prominently, as well as aggravate P-limitation and Si-limitation and further affect phytoplankton community structures and size-fractioned structures with the quite high DIN:DIP ratios and extremely low Si:DIN ratios in AWD.