Comparative Study On Water Quality Effects Of Inflated Aeration On Different Aquatic Plants During Decomposition Process

Eutrophication of water bodies has become one of the important environmental problems in the world today.As an effective and commonly used means of ecological restoration,the restoration technology of aquatic vegetation play an important role in the control of eutrophication.Aquatic plant is an important primary producer of aquatic ecosystem,and is the foundation to support the whole aquatic ecosystem structure integrity and function.The environmental effects of life cycle of aquatic plant is important to improve the water environment.The aquatic plants absorb nutrients in water and sediment during the growth stage,but the decomposition of the residues is easy to cause the water pollution.It is important to study the effect of water quality and its influencing factors in the process of plant decomposition.The effect of decomposition of aquatic plants on water quality is closely related to the decomposition conditions and plant species.In this study,the effect of litter decomposition on water quality of 3 aquatic plants Vallisneria natans,Nymphoides peltatum,and Phragmites australis,which represent 3 life forms of submerged plants,floating-leaf plants and emergent plants,were compared by laboratory simulation experiment under non-inflated aeration and inflated aeration conditions,and the experiment lasted 80 days.Results showed that:?1?In the process of aquatic plants decomposition,water quality indices had significant stage change,among them,ammonia nitrogen?NH₄⁺-N?,nitrite nitrogen?NO₂^--N?,nitrate nitrogen?NO₃^--N?concentration of water rapid rise to the peak value after decreased slightly in the initial stage and then continued to decline,while total phosphorus?TP?,chemical oxygen demand?COD?concentration gradually increased to the peak value at the beginning of decomposition,and then decreased gradually in the late,however,pH and oxidation-reduction potential?ORP?value showed different trends in different dissolved oxygen levels in plants decomposition.Although the relative changes and peak value of the main water quality indices among different species occurred in different time,but to the end of the experiment,the water quality indices of different plant species decreased corresponding to the low level,and relatively consistent with the blank control group.On the whole,the stage characteristics are obvious,and the differences of water quality indices are larger in the early and middle stages of decomposition,while the latter tend to be consistent.?2?The effect of decay of Vallisneria natans and Nymphoides peltatum on water quality was relatively large,ammonia nitrogen?NH₄⁺-N?,nitrite nitrogen?NO₂^--N?,nitrate nitrogen?NO₃^--N?concentration of water in Vallisneria natans group was higher then other groups,and total phosphorus?TP?,chemical oxygen demand?COD?concentration of water in Nymphoides peltatum was relatively high,while the main water quality indices in Phragmites australis group were lower and had little difference with the blank control group.In the process of decomposition,the change trend and relative value of the main water quality indices are often different because of the different water quality indices and plant species.?3?The peak concentrations of ammonia nitrogen?NH₄⁺-N?,nitrite nitrogen?NO₂^-N?,nitrate nitrogen?NO₃^--N?,chemical oxygen demand?COD?and total phosphorus?TP?in the water under inflated aeration condition were lower than those in non-inflated aeration group,but the peak time was much earlier than that in non-inflated aeration group.Effect of aeration condition or not on the changes of water quality indices from high to low is Vallisneria natans,Nymphoides peltatum,Phragmites australis.The faster the relatively decomposition rate of the species,the more significant the effect of aeration conditions on the water quality.On the whole,the water quality effects of aquatic plants in the process of decomposition are species diversity.Different life forms of aquatic plants have different effects on water,and the decomposition of submerged plants and floating-leaf plants have greater effect on water quality,while the emergent plants have relatively small effects.Inflation conditions to increase dissolved oxygen content of water have a certain impact on the plant decomposition process and water quality effect.Compared with the change of dissolved oxygen level in the water environment,the plant species should be the more important factors that affect the water quality in the process of plant decomposition.