Sediment Phosphorus Migration Feature In Aquatic Plant Community Under Different Hydrodynamic Conditions

There are many shallow lakes in the middle or lower reaches of the Yangtze river, own more than 1km2 lakes 651, accounting for 60% of the total freshwater lakes. A mass of researches indicated that sediment in shallow lakes were vulnerable to waves and lake flows joint with action and frequent suspension, the alternate process caused water pollutant concentration rised abruptly. Meanwhile, aquatic plants plays an important role in the biological epitomizes, cycle of nutrient, migration and inmigration of lakes. Therefore, the research on phosphorus of sediments by aquatic plants to environmental effects under dynamic actions of important theoretical and practical significance.This paper take Tai Lake as the research object, through field sampling and indoor simulation experiments, using the method that combining sediments suspended device simulate large aquatic plants in Tai Lake against sediment suspension and phosphorus environmental effects. A series of cylindrical suspended analogue devices developed for indoor simulation, designed 0.2～0.5 N·m-2 shear and 60～1800s oscillations duration condition, to study the sediment suspension characteristics of original core samples from Tai Lake, from a water resuspension caused by sediments, based on dynamic mechanism of constructing water bottom shear stress level and duration and sediment resuspension the quantitative relation flux, and reveals sediments-water process of sediment suspension again interface phosphorus release features.The experiment of aquatic plants on population distribution according to the characteristics of Tai Lake, choosing waterweeed and reed from Tai Lake, submerged plant and quite as representatives of water plants, and through the hydroponic experiments, each aquatic plant set up different population density contrast (waterweeed coverage 90%,60%,30%, reed planting density 150 trees/m2,80 trees/m2,50 trees/m2), including no plants as constrast, totally seven groups, The effects on phosphorus content of different aquatic vegetations density to sediment resuspension and overlying water.This study found that suspended sediment concentration rised slowly with disturbing time, remarkbally rise with shear stress increased; The concentration of a plant controls over time SPM rises obviously less than no plant controls. Tai Lake suspended sediment characteristics shows, static settlement after static SPM is disturbed presents on the settlement of the overall process of falling fast, medium-term slow drop and later basically stable three stages. No plants comparison, relative to a plant controls the duration of slow drop process shorten, somewhat 5h concentration achieve namely in basically stable.Again in sediment suspension and settlement changes with time characteristics on the basis of study of aquatic plants, analyzes the population density distribution characteristics of the mechanism of the effect of material. Results show that:waterweeed growing algae coverage, the shear stress overlying water corresponding SPM a trend of gradual decrease concentration; Along with the shear stress overlying water increased, with aquatic plants SPM concentration of population density decreases gradually increased the range; And quite water plants of sediment suspension again reed strong inhibition submerged plant waterweeed better than them. Aquatic plants SPM concentration of the vertical distribution characteristics of aquatic plants study shows that the concentration of SPM vertical distribution has certain inhibition and aquatic plants exists interfere with external disturbance energy produced downward transmission, makes the overlying water and tends to reduce SPM concentration homogenization. Along with the further strengthen external disturbance, various control situation are not obvious vertical gradient.The total phosphorus, phosphate, BAP without plants, have no relevant with shear stress and external disturbances time. Compared with different forms of phosphorus concentration, overlying water total phosphorus significantly higher than phosphates, BAP phosphate of general prep above also. BAP and phosphate decreased with plant density ratio increasing and increased with of shear stress enhance.