Effects of freshwater inflows on net ecosystem productivity in the Yellow River Estuary

For sustaining the ecosystem health of estuaries,it is critical to understand how instream flows affect riverine ecosystem health.In this paper,the relationship between freshwater inflows and Net Ecosystem Productivity(NEP) in the Yellow River Estuary was investigated.NEP was calculated by the open-water dissolved oxygen curve method,and correlation analysis was conducted to find out which attribute of the freshwater inflows acts on NEP most.In the Yellow River Estuary as a whole,NEP ranged from-5.32 to 4.84 mg·L-1·d-1 between April and September.Examination of the specific spatiotemporal variation of NEP further revealed that,the up-estuary and the middle-estuary were more heterotrophic than the far-estuary;meanwhile,the whole estuary was relatively highly heterotrophic between August and September(wet period) and but lower between May and June(dry season),and more heterotrophic after water and sediment regulation in the Yellow River.On the whole,the Yellow River estuary was entirely heterotrophic in 2009,and its respiration was greater than its photosynthesis,indicating that it could be a huge source of CO2.Among a variety of variables characterizing the freshwater inflow,turbidity,salinity and COD were identified as significant correlation factors for NEP.These are the significant factors influencing variation of NEP and the turbidity was to a great degree determined by freshwater inflow in Yellow River Estuary.