Sieved Transport and Redistribution of Bioavailable Phosphorus from Watershed with Complex River Networks to Lake

An innovative approach was developed to reveal phosphorus (P) transport and redistribution in large and complex river networks in the Lake Taihu basin by establishing the relations between sediment P spatial distribution and P sorption behavior on particles with different grain size, sorted by hydrodynamics. The sediment P fractionation composition changed greatly across the basin, where 69% consisted of acid-soluble fractions (HCl-P) in upstream rivers while 70% was in fractions associated with reducible metal hydroxides (BD-P) and amorphous hydroxides (NaOH25-P) in downstream rivers. Fine particles enriched in BD-P and NaOH25-P fractions tended to sorb liberated P during the resuspension process, and fine particles were more easily delivered downstream toward the lake, forming a sieved transport of P in the river networks. This will lead to a great potential for sediment P release when environmental anoxia develops in the sediments or high pH occurs in the sediment surface during intensive algal blooms in the shallow lake. Reduction of external P from point sources from urbanized areas is an important requirement at the basin scale; however, long-term efforts are needed to restore aquatic macrophytes in the lake, which would decrease P recycling rates at the water-sediment interface.