Exchange and deposition fluxes of nitrogen and phosphorus across sediment-water interface in lower Yellow River

This paper studies the exchange and deposition fluxes of nitrogen(N) and phosphorus(P) across the sediment-water interface in the lower Yellow River to estimate the impacts of these two processes on the budget of N and P during river transportation.The results show that the concentrations of total nitrogen(TN)and total phosphorus(TP) in surface water ranged between 2.67 and 5.49mg/L(mean 4.18±0.98mg/L),0.02 and 0.94mg/L(mean 0.39±0.29mg/L) during the study period,respectively,indicating the river water quality was not optimistic.Exchange fluxes of NO-3-N,NH+4-N and PO43--P across the sediment-water interface ranged between- 0.31 and 0.52g /(m2·d),- 0.06 and 0.06g/(m2·d),-1.52 and 0.50mg/(m2·d),with the average values of 0.11±0.24g/(m2·d),-0.01±0.03g/(m2·d),-0.26 ±0.65 mg/(m2·d),respectively.This suggestes that the river sediment acted as a sink of NO-3-N while a source of PO43--P and NH+4-N.Deposition fluxes of TN and TP ranged between 0.57 and 706.55g /(m2·d),2.54 and 1 180.60g /(m2·d),with the average values of 108.72±191.12g/(m2·d) and 256.34±359.39g/(m2·d),respectively.Taking the external loads of N and P into consideration,it is estimated that the impact of exchange process on the riverine budgets of N and P can be neglected.However,about 2.25% of N and3 6.90% of P could be reduced by the process of deposition,which indicates that deposition was the main retention process of P in the lower Yellow River.