| Eutrophication of surface waters is a serious problem in many parts of the world. Internal load of nitrogen and phosphorus especially P play a major role in eutrophication. Phosphorus release in sediment is very important to support algae during eutrophication. But, release and sorption of phosphorus was controlled by many factors, including physico-Chemical characteristics of sediment and other environmental conditions, such as redo condition, pH, temperature and so on. As represent of purple soil, Long-shui Lake is selected. The means is about field research, sample analyse and simulation of study in lab. The study on character of sediment and phosphorus release is primary. At the same time, evaluation of water quality will be done. The aim is open out the characteristic of sediment and law of phosphorus release and sorption. The study should benefit the precaution of eutrophication in this area.Research and analyse indicated, water quality in this lake changed evidence in different seasons, and, water quality in spring was better than in summer that effected by temperature and pH. In summer, lake water was alkalescence with the value of pH 9.11 caused by algae. According to Chinese and foreign criterion about lake, Long-shui lake was in mesotrophication.Iron (Fe) ranged from 28717.87mg.kg-1 to 44650.00 mg.kg-1 sediment, averaged 39493.04 mg.kg-1.Mg had a high level (5004.95-8957.45 mg.kg-1 sediment), averaged 6538.83 mg.kg-1.Ca and Mn had few but more than the values of soil background. From the analyse of phosphorus fraction, we found sediment total P ranged from 304.71 mg.kg-1 to 571.00 mg.kg-1 (mean=442.04 mg.kg-1). Fe-P and O-P (Occluded P) represented major fraction in inorganic phosphorus. Fe-P averaged 89.75 mg.kg-1 (20% of TP). The contents of Ca-P (mean=29.50 mg.kg-1) and Al-P (mean=5.21 mg.kg-1) were rather low. The correlation between TP, Fe-P and organic matter contents, the amount of Fe and Mg, was very significant.The experiment of thermodynamics showed, P sorption capacity of fresh sediment was higher than dry sediment. P sorption maxima (Smax) ranged from 454.00 mg.kg-1 to 1667.00 mg.kg-1 sediment (mean=1042.00 mg.kg-1). While phosphorus retention was only 72% of P adsorbed. Organic matter content, Fe, Mg and clay could play a significant role in determining Smax.The P sorption speed in first phase showed very fast. In general, the more sediment absorbed, the faster sorption speed is, and then the fewer balanceable time will be. The factors affecting sediment sorption speed included OM, Fe, Ca, Mg and Mn. Clay content also play significant role. Elovich equation was the best among the fitted model equations.Biologically available phosphorus (BAP) averaged 138.53 mg.kg-1 sediment (31.34% of TP).Phosphorus sorption index (PSI) and phosphorus sorption capacity in sediment were wellcorrelated (r=0.991...) suggesting that PSI could be an effective means to rapidly screen sediments for their phosphorus sorption capacity. While the degree of P saturation (DPS) in sediment showed low level (mean=15.17%) and suggested to have a lower susceptibility to P losses than those with higher DPS values. Sediment available phosphorus (Olsen extracted P) averaged 9.76 mg.kg-1 and explained the level of supplying P from sediment was very low.Under anaerobic conditions, the values of pH both in overlying water and sediment indicated fluctuate but with downside. Redox potential (Eh) in sediment changed a little and showed it was stabilization from the end of spring to the beginning of summer. Phosphorus should release from sediment under anaerobic conditions with a progress from raise to descend. The equilibrium P concentrations in overlying water were higher than total P in first phase.Microbe can make organic P into inorganic P by its catabolism, and returned to overlying water again. The effect to sediment P release of microbe was complex and tremendous. Total P in water sometimes raised and sometimes descended in different conditions because of the effect of microbe. In this experiment, t...
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