Program

River-estuary interface is the location of major transformations of nitrogen, controlling how much nitrogen is delivered to the estuary and coastal zones. Our understanding of these transformations across this interface is still limited. To investigate nitrogen dynamics and tranformations across the river-estuary interface, high spatial and temporal resolution observations were conducted for the Jiulong River estuary in southeast China in 2015. Non-conservative behaviors (addtion or removal) of nitrogen in water column were obviously observed, especially through the turbidity maximum zone (TMZ). In most cases, ammonium N exhibited removal along the upper river-estuary, probably due to strong nitrification or bioassimilation during the interaction of fresh water and seawater. Ammonium released from suspended particles or sediment core-water by resuspension might be an important source to ammonium additon in spring. Nitrite N peaked in the upper estuary (salinity 4-5 psu) across seasons. We speculated that ammonium oxidation was far active than nitrite oxidation during nitrification and nitrite accumulated as a result. Regulated by strong biogeochemical processes, riverine ammonium could be removed by 12%-60%, while nitrite added by 124%-342% before export into lower estuary. Current results highlighted the vital filtration of river-estuary interface on regulating N export from watershed to coast.