Spatial and seasonal variations, partitioning and fluxes of dissolved and particulate nutrients in Jiaozhou Bay

The spatial and temporal dynamics of both dissolved and particulate nutrients were studied during 2015-2016 in the Jiaozhou Bay (JZB), a deeply anthropogenic impact ecosystem in China. The dissolved inorganic nutrients was mainly from the wastewater and riverine inputs which is demonstrated from the negative correlation between nutrients with salinity and their higher levels distribution observed in the northeastern and/or northwestern JZB, where mainly received industrial and agricultural source run-off, respectively. The high levels of dissolved and particulate organic pools were also observed in the same area but have autochthonous sources besides terrestrial input, which lead to their higher concentrations in autumn during phytoplankton bloom. The composition of DIN has been changed with the major component from NH4+ to NO3-, which probably due to the controlling load of NH4+ but no limitation of NO3- by human intervention. The average annual DIN/DIP ratio increased by one time but SiO32-/DIN ratio has no obvious variation over the past decade, which indicated that the potential limiting nutrient for phytoplankton growth has been converted from silicon to phosphorus in JZB. Additional, more prone to partition into POC but not DOC pools of organic carbon were found during the phytoplankton bloom in autumn due to the nutrient-rich, diatom dominated condition and both DOP and POP may be the potential P source and can relieve P limitation to some extent during the same time. Nutrient budgets calculation also demonstrated that riverine input and wastewater discharge are major sources of dissolved nitrogen and phosphorus, while silicate were mainly came from submarine fresh groundwater discharge. The mixing flow transported large amounts of nutrients from JZB to the Yellow Sea. Meanwhile, the net ecosystem metabolism and nitrogen metabolism calculation showed the whole ecosystem was heterotrophic and a net nitrogen fixation in JZB.