Distribution of Nitrogen and Phosphorus in Pore Water Profiles and Estimation of Their Diffusive Fluxes and Annual Loads in Guanting Reservoir (GTR), Northern China

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 (NH4+-N) and phosphate (PO43−-P) in sediments from Guanting Reservoir (GTR) were estimated according to their vertical distribution. The average contents of NH4+-N and PO43−-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 m2 d−1) for NH4+-N, and 0.002 – 0.196 (mg m2 d−1) for PO43−-P. The annual load contributions from sediments of GTR were 659 t a−1 for NH4+-N and 4.83 t a−1 for PO43−-P. Notably, the upstream of GTR accounted for 50.7% annual loads for NH4+-N, while the downstream contributed 71.2% loads to PO43−-P. This study will better inform future environmental management for the reservoir.