Study On Aquatic Plant Community Purification Technology For Stagnant Reach Of Secondary River In Mountainous City

After the impoundment of Three Gorges Reservoir Region, many secondary riveroccurred the following changes: the flow velocity of backwater section, waterself-purification ability and pollutant carrying capacity is reduced, water quality andbottom sediment of backwater section is locally deteriorated, phenomenon ofeutrophication is frequentlyoccurred. FuNiu creek is located in dadukoudistrict,chongqing municipality, which is a typical secondary river in mountain city, hasthe characteristics of fast influx and fast discharge. As the river built many hydraulicstructures, in addition to many continuous curve, so there is multiple stagnant reach.Thedownstream river has been heavy disrupted, riverbank has been reclaimed to farmland,water loss and soil erosion is serious. There is less aquatic plants in the river,waterself-purification ability is poor,basic ecological function has been lost. Most of theindexes of the water has surpassed the five kinds standards of the national groundwaterenvironmental quality, which belongs to the five bad water quality.The screening test of emergent plant, floating-leaved plant and submerged plantprovided the basis for pioneer screening, which considered river structure, hydrology,water quality, riverside.The screening test of aquatic plant growth substrate material,which can not only adapt to the aquatic plant growth but also purify matrix, provide thebasis for the construction of floating bed heavy bed. Putting forward variousconfiguration scheme for different reaches made Funiu Creek become a self-purificationability of aquatic species-rich river landscape. The main contents and conclusions are asfollows:①The water purification effect test of emergent plant, floating-leaved plant wasdone in stagnant reach,FuNiu creek.The results show that:Cyperusalternifolius,Pontederia cordata and Iris pseudacorus adapt to changes of water quality and waterlevel. Canna generalis couldn’t adapt to the change of water level and high temperature,Myriophyllumspicatum and Nymphaeutetragona were not suitable to plante in theflowing river, the three plants should avoid to plant in flood season and fixing thefloating-leaved plan.Purifying effects of NH4+-N, TN, CODMnwere not obvious,whilethe TP had some purifying effect and its maximum removal rate reached to25.97%,butChlorophyll a concentration was increased.②The water purification effect test of submerged plants was donein indoor laboratory, the concentration of NH4+-N、TN、TP、CODMnwere1.44mg/L、2.16mg/L、0.6mg/L、13.2mg/L respectively.The results show that: The submerged plants,includingCeratophyllum demersum, Myriophyllum spicatum,Hydrilla verticillata and Vallisnerianatans, could adapt to the water quality. The biomass growth rate, the average heightincrease, total nitrogen, ammonia nitrogen and total phosphorus removal ability and theincreasing oxygen of Ceratophyllum demersum and Hydrilla verticillata were superiorto Vallisneria natans and Myriophyllum spicatum. Myriophyllum spicatum subductionof nitrogen and phosphorus is not strong, initially only have a purifying effect test.③The water purification effect test ofsubstrate materialwas donein indoorlaboratory,which was divided into two phases.The first concentration of NH4+-N、TN、TP、CODMnwere2.0mg/L、2.51mg/L、0.49mg/L、6.7mg/L,the second concentration ofNH4+-N、TN、TP、CODMnwere2.78mg/L、2.95mg/L、0.75mg/L、6.82mg/L.The resultsshow that: the best removal effect of ammonia nitrogen was zeolite,whose highestremoval rate up to92.45%. The best removal effect of nitrate nitrogen, total nitrogenand total phosphorus was sponge iron,and the highest removal rate was92.20%,85.37%,96.00%respectively. Mixed substrate had good purification effect of ammonia nitrogen,nitrate nitrogen, total nitrogen and total phosphorus,and the highest removal rate was74.50%,58.21%,74.50%and54.23%respectively.④The common purification effect of submerged plants and substrate materialwasdonein outdoor laboratory.The results show that:Mixed substrate consist of Zeolite,ceramic ring and sponge ironcould be used as a submerged plant growth substrate,whichhad good removal effect in ammonia nitrogen, total nitrogen and total phosphorus.Thedifferencein water purification effect between mixedsubstrate plants and mixedsubstratewas not obvious.The purification effect of soil plant group was poor.⑤Through FuNiu Creek water quality monitoring, founding that various waterquality indicators of the wind and rain covered Bridges (B02) were higher thanlandscape bridge (B01).The main pollutants of FuNiu are ammonia nitrogen, totalnitrogen, total phosphorus.Water quality was gradually deteriorated from upstream todownstream. According to the hypothesis test of various pollutants among low waterperiod,normal water period and high water period, founding the rainfall had a littleeffects on water quality.On the basis of the experiment and investigation, differentaquatic plant community configuration scheme were put forward in different types ofFuNiu creek reach.When the river is narrow, aquatic plants can been planted directly.When the river is wide, the river edge grows aquatic plants directly, shallow deep water plants emergent plant and floating-leaved plant by floating-bed,and submerged plant bysubmerging bed.The optimum time toplantaquatic plants is March, April, October. Themaintenance of aquatic plant community is very important for the growth of aquaticplants. we should strictly control the discharge of the pollutants from the river coast,salvage the duckweed and organic pollution floater, rameting and harvesting Aquaticplants timely.The researchs of aquatic plant community purification technology for stagnantreach of secondary river in mountainous cityhave important realistic meanings.It willoffer technological support foraquatic plant community purification technology, willprovide theoretical basis foraquatic plant community purificationengineering design,andwill lay a foundation of further study onaquatic plantpurificationtechnology.