Retention And Loss Of Phosphorus In Soils And Its Effect On Eutrophication Of Reservoirs In South China

Phosphorus transfer from soil to water and its sedimentation plays a critical role in eutrophication of freshwater. A column leaching experiment was conducted for comparing sorption and release of phosphorus in three typical soils(red soil, black soil and loess) in China. We also tested the effect of acid rain and rainfall intensity on phosphorus elution from soils. Meanwhile, elements(P, Al, Ca, Fe and Mn) content or concentration in hydro-fluctuation belt soils, surface sediments and water columns were investigated and measured in 31 large reservoirs(>108 m3) in Guangdong province. Main results were showed as follows:1. Red soil showed much higher sorption capacity for phosphorus than the two other soils. Phosphorus sorption capacity of the soils is affected by phosphorus concentration in added solution. Phosphorus is mainly sorbed by iron and aluminium in red soil, and the sorption by iron contributed up to 50%.2. Phosphorus release is related to p H and flow rate. Acidification would promote phosphorus release from the three soils; Otherwise, high flow rate would be adverse to phosphorus release under the same flux. A portion of phosphorus sorbed by red soil can still be fixed in various eluting conditions.3. Content of TP significantly and positively correlated to that of Fe in hydro-fluctuation belt soils and surface sediments in reservoirs. While TP content was up to 0.6 mg/g and Fe/P mass ratio was below 70 in the sediments, phosphorus sorption by iron might approach to saturation. Phosphorus concentration in overlying water was negatively correlated to Fe/P ratio in the surface sediments when Fe/P mass ratio was below 70.4. Migration of iron and manganese from catchment to waterbodies and sediments could be a critical casue for the concentration of the two elements usually exceeding the standard of water quality in reservoirs of South China.