Study On Nitrogen And Phosphorus Purification Capacity Of Dominant Plants In Ziqi River

Ziqi River flows into Danjiangkou Reservoir through Madeng Town,Xichuan County.Domestic sewage from Madeng Town and non-point source pollutants from farmland in Ziqi River Basin flow into Danjiangkou Reservoir.According to the investigation of water quality in the river about 3 kilomerters from Madeng Town to the reservoir inlet,it showed that the content of nitrogen and phosphorus pollutants in the water from upstream to downstream is getting lower and lower.These results proved that Ziqi River has strong self-purification ability.According to the investigation,the water flow speed in Ziqi River is slow,and there is little material exchange with other water bodies,which shows that aquatic organisms in Ziqi River waters have strong ecological restoration function.Based on the investigation of aquatic plants in the waters of Ziqi River,13 dominant aquatic and wet plants were selected: Alternanthera philoxeroides,Eichhornia crassipes,Paspalum paspaloides,Typha orientalis Presl orientalis,Potamogeton crispus,Mentha haplocalyx Briq,Lycopus lucidus Turcz,Ranunculus chinensis,Ranunculus sceleratus,Acorus calamus,Veronica undulata Wall,Alisma plantago-aquatica,Polygonum hydropiper.The ability of different plants to remove nitrogen and phosphorus pollutants in water was studied.The results showed that the total nitrogen removal ability of plants was as follows: Potamogeton crispus > Typha orientalis Presl orientalis > Eichhornia crassipes >Paspalum paspaloides > Alternanthera philoxeroides > Lycopus lucidus > Mentha haplocalyx Briq.The highest removal rate of TP was Mentha haplocalyx Briq and Typha orientalis Presl latifolia,and the lowest was Potamogeton crispus and Alternanthera philoxeroides.Their average removal rate of ammonia nitrogen is as follows: Eichhornia crassipes > Typha orientalis Presl latifolia > Paspalum bicolor > Lycopus lucidus Turcz >Potamogeton crispus > Alternanthera philoxeroides > Mentha haplocalyx Briq.Their average removal rate of phosphate is as follows: Lycopus lucidus Turcz > Typha orientalis Presl latifolia > Paspalum bicolor > Mentha haplocalyx Briq > Alternanthera philoxeroides > Potamogeton crispus > Eichhornia crassipes.Their average removal rate of COD is as follows: Typha orientalis Presl latifolia > Lycopus lucidus Turcz > Alternanthera philoxeroides > Potamogeton crispus > Eichhornia crassipes > Alternanthera philoxeroides > Paspalum bicolor.The experimental process mentioned above is completed in summer.In spring,plants in the waters of Ziqi River are flourishing and metabolized vigorously.The dominant aquatic plants in Ziqi River were selected: Typha orientalis Presl latifolia,Alternanthera philoxeroides,Lycopus lucidus Turcz and the combination of Lycopus lucidus Turcz +Acorus calamus + Alternanthera philoxeroides,Euphorbia chinensis + Alisma orientalis and Euphorbia chinensis,their degradation ability of nitrogen and phosphorus was studied.The results showed that the total nitrogen and ammonia nitrogen removal rate of Typha orientalis Presl latifolia,Alternanthera philoxeroides and Lycopus lucidus Turcz were much higher than its removal rate in summer,while their removal rate of TP and COD were just the opposite.The results of spring experiment showed that the plant with the strongest total nitrogen removal ability was Lycopus lucidus Turcz,the plant combination was Acorus calamus and Alternanthera philoxeroides,the plant with the strongest TP removal ability was Alternanthera philoxeroides,the plant with the strongest COD removal ability was Ranunculus chinensis,the combination was Polygonum multiflorum and Alternanthera philoxeroides,and the plant with the strongest ammonia nitrogen removal ability was Polygonum multiflorum.This study found that Typha orientalis Presl angustifolia and Potamogeton crispus in the dominant aquatic plants in summer of Ziqi River had better nitrogen removal effect.Mentha haplocalyx Briq and Typha orientalis Presl angustifolia have the best phosphorus removal effect.Lycopus lucidus Turcz and Typha orientalis Presl latifolia have the best removal effect on ammonia nitrogen.Eichhornia crassipes and Typha orientalis Presl angustifolia have the highest removal rate of phosphate.The highest average removal rate of COD was Typha orientalis Presl latifolia and Lycopus lucidus Turcz.In spring,the plants and plant combinations with the best nitrogen and phosphorus removal efficiency are Alternanthera philoxeroides,Typha orientalis Presl latifolia,Euphorbia chinensis,and Lycopus lucidus Turcz + Acorus calamus + Alternanthera philoxeroides,among which Lycopus lucidus Turcz + Acorus calamus + Alternanthera philoxeroides is the best combination in aquatic plant combination test.Alternanthera philoxeroides,Typha orientalis Presl latifolia and ground Lycopus lucidus Turcz have good purification effects in both spring and summer,which can be combined with other aquatic plants to purify water quality,in order to overcome the defects of annual cycle of remediation of polluted water by aquatic plants with alternating seasons.By monitoring the removal of nitrogen and phosphorus from water by dominant indigenous aquatic plant communities and combinations,the best plants and combinations for water purification were selected,which provided a theoretical basis for the construction of aquatic and wetland plant water purification system in Danjiangkou reservoir area.