Spatial distribution patterns of nitrogen and phosphorus in water and bed sediment of the Three Gorges Reservoir

Nutrient state in the Three Gorges Reservoir has long been concerned. Mainstream of the reservoir however has received relatively less researchers' attention compared to tributaries. In 2015-2017, we sampled 40 cross-sections along mainstream and 10 tributaries in flood and dry seasons in order to reveal lateral, vertical, and longitudinal distribution patterns of total nitrogen (TN) and phosphorus (TP) in water and sediment. Concentrations of waterborne TN and TP ranged from 1.48 to 2.33 mg/L and 0.09 to 0.16 mg/L respectively. Laterally, nutrients were well mixed and homogeneously distributed. Vertically, nutrients concentrations in surface water were higher than in bottom water. Longitudinally, TN concentration increased from tail to head of the reservoir due to accumulation of nitrogen imported from riparian zone and tributaries, whereas TP concentration decreased from tail to head because of sediment deposition. TN and TP concentrations in channel bed sediment were 622-949 and 916-950 mg/kg respectively. Neither of them had significant longitudinal trends nor correlations with waterborne nutrient concentrations. This work will help to understand nutrient dynamics in the Three Gorges Reservoir.