LAUSR

Improvement of water quality has frequently been delayed due to high recycling rates of nutrients across the sediment–water interface in a reservoir. Diffusive fluxes and annual loads of ammonia nitrogen (NH 4 + -N) and phosphate (PO 4 3− -P) in sediments from Guanting Reservoir (GTR) were estimated according to their vertical distribution. The average contents of NH 4 + -N and PO 4 3− -P in surface pore water were higher by factors of 6.9 – 11.7 and 1.3 – 6.4 than those in overlying water, respectively. The ranges of fluxes were 1.59 – 13.0 (mg m 2  d −1 ) for NH 4 + -N, and 0.002 – 0.196 (mg m 2  d −1 ) for PO 4 3− -P. The annual load contributions from sediments of GTR were 659 t a −1 for NH 4 + -N and 4.83 t a −1 for PO 4 3− -P. Notably, the upstream of GTR accounted for 50.7% annual loads for NH 4 + -N, while the downstream contributed 71.2% loads to PO 4 3− -P. This study will better inform future environmental management for the reservoir.