| In order to investigate the effect of submerged macrophyte on phosphorus transformations between sediment and water, Hydrilla verticillata, Vallisneria natans and Potamogeton crispus was used in this research. Phosphorus concentrations in sediment and water of the inside and outside of community were investigated, and environmental factors temperature, pH, DO, Eh were also studied during different growth period of submerged macrophyte. The main results are summarized as follows:(1) Phosphorus concentrations increased in the day and decreased at night which was affected by environmental factors caused by V. natans photosynthesis. The maximum difference of TP, DTP and SRP were 0.016 mg/L,0.015 mg/L,9.240?g/L. Environmental factors pH, DO and Eh changed contrarily with phosphorus in water, and the maximum difference were 0.94,5.68 mg/L,21 mV, respectively.(2) Submerged macrophyte affect phosphorus transferring through absorbing phosphorus and increasing pH, DO and Eh in the water. Compared with the control the maximum difference of TP in water of H. verticillata, V. natans and P. crispus were 0.17,0.10 and 0.11 mg/L, the maximum difference of DTP in pore water were 0.23,0.37 and 0.77 mg/L, the maximum difference of TP in sediment were 35.34, 60.67 and 25.92 mg/kg. Submerged macrophyte H. verticillata, V. natans and P. crispus absorbed 4.25%,6.66% and 3.08% of phosphorus of sediment and water in the growth period. DO, Eh and pH were increased also (DO,10.0—14.0 mg/L; Eh, 185—240 mV; pH,8.0—11.0).(3) Submerged macrophyte affect phosphorus transferring through releasing phosphorus and decreasing pH, DO and Eh in the water. Phosphorus in system 'sediment-plant-water'transferred to sediment. The maximum decreased difference of pH, DO and Eh in group H. verticillata, V. natans and P. crispus were 1.14,3.33 mg/L,44.29 mV; 0.81,1.91 mg/L,20.44 mV; 0.94,2.63 mg/L,103.33mV.The maximum increased difference of TP in water of H. verticillata, V. natans and P. crispus were 0.56,0.03 and 0.54 mg/L, the maximum increased difference of TP in sediment were 33.92,14.69 and 29.51 mg/kg. The percentage of phosphorus in H. verticillata, V. natans and P. crispus of the "sediment-water-plant" system were increased from 91.69%,94.36% and 93.36% at the beginning to 98.48%,95.55% and 97.91% at the end.(4) Submerged macrophyte affect phosphorus transferring through absorbing phosphorus from plant in the decomposition period, increasing DO and Eh in water. Compared with group H. verticillata, the maximum value of TP, DTP, PP, SRP and DOP in group H. verticillata+P. crispus were reduced 0.30,0.24,0.01,0.18 and 0.11 mg/L, the maximum value of TP in sediment were reduced 35.92mg/kg. However, there was no significant difference of all phosphorus concentrations in water between group V. natans and group V. natans+P. crispus, and phosphorus concentrations in water were maintained in a low level (TP,0.04—0.06 mg/L). The maximum difference of TP in water between group V. natans and group V. natans+ P. crispus was 0.01 mg/L. Compared with group V. natans, TP in sediment of group V. natans+ P. crispus was reduced 26.94mg/kg. Compared with group P. crispus, the maximum value of TP, DTP, PP, SRP and DOP in group P. crispus+ H. verticillata and P. crispus+ V. natans were reduced 0.29,0.24,0.05,0.14,0.10 mg/L; 0.32, 0.23,0.02,0.11,0.10 mg/L, the maximum value of TP in sediment were reduced 8.25,2.42mg/kg.Compared with group single plant, the maximum difference of DO and Eh in water of H. verticillata+ P. crispus and V. natans+ P. crispus were 6.92 mg/L,43.85 mV; 7.44 mg/L,50.00mV. Compared with group single plant, The maximum difference of DO and Eh in water of P. crispus+ H. verticillata and P. crispus+ V. natans were 3.08 mg/L,64.58 mV; 3.81 mg/L,123.13mV.(5) Submerged macrophyte absorbed phosphorus from sediment and water in the growth period and released phosphorus to sediment and water in the decomposition period under different phosphorus load, phosphorus transferred to sediment in the sediment-water system.In the growth period of submerged macrophyte, the maximum percentage of phosphorus in plant of H. verticillata, V. natans amd P. crispus in 'sediemnt-plant-water'system under low, middle and heavy phosphorus load were 2.01%,7.66%,4.08%; 2.44%,11.48%,7.89%; 2.07%,6.53%,3.53%. In the decomposition period of submerged macrophyte, the maximum percentage of phosphorus in plant of H. verticillata, V. natans amd P. crispus in 'sediemnt-plant-water'system under low, middle and heavy phosphorus load were 99.62%,98.70%,98.89%; 99.26%,90.69%,93.33%; 99.07%,98.87%,99.01%.(6) The amount of phosphorus decreased with the density of V. natans increased. There was no significant effect on phosphorus concentrations during the disturbance course when the density of V. natans was more than 100 individuals/m2. |
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