SEDIMENT PHOSPHORUS ADSORPTION AND FRACTIONATION DIFFERENCE OF IRRIGATION AND DRAINAGE CANALS IN UPPER REACH OF YELLOW RIVER BASIN

Canal sediment is an important chain for phosphorus (P) transport in irrigation and drainage canals. This research investigated P adsorption and fractionation characteristics of sediments in irrigation and drainage canals with isotherm adsorption and selective sequential fractionation of P. The impacts of physico-chemical properties of sediment on P retention characteristics were also analyzed. The total phosphorus (TP) of sediments was about 565.01-1232.06 mg kg(-1) in irrigation canals and 608.10-1109.22 mg kg(-1) in drainage canals. The content of potential bioavailable P, including soluble and loosely bound P, aluminum (Al) bound P, iron (Fe) bound P, and reductant soluble P, was 6.04-16.88% of TP in irrigation canal sediment, and ranged from 12.89 to 33.16% in drainage canal sediments. Maximal adsorption capacity values in irrigation and drainage canal sediments were about 51.68-429.26 mg kg(-1) and 162.42-875.75 mg kg(-1), respectively, which increased from upper reach to lower reach in drainage canal but decreased in irrigation canal. The equilibrium P concentration without net P sorption (EPC0) in sediments of irrigation and drainage canals was 0.093-0.182 mg kg(-1) and 0.029-0.192 mg kg(-1), respectively. As EPC0 was larger than soluble P in overlaying water, the canal sediments can release P into the water, and the release ratio in irrigation canal is higher than in drainage canal. It was found that the adsorption capacity also affected clay and silt percentages of the sediment. Native adsorbed exchangeable P was closely correlated with the potential bioavailable P fractionations. Sediments from drainage have lower P release risk as the higher sediment P adsorption capacity. These findings are helpful for agricultural water management and P pollution prevention.