Study On Eutrophication Assessment Of An Artificial Lake In Chongqing And Aquatic Plants Repair Ability

Landscape water can improve the natural environment of urban residential area, cater to people close to nature and the pursuit of health, but also are the indispensable component of upscale ecological residential community. Due to the high land costs, it is difficult to create a massive water body, so mostly are stationary or illiquid closed system. Currently, many the urban landscape water appeared pollution of different degrees, eutrophication is serious. Aquatic plants has obvious effect on transfer nitrogen and phosphorus or allelopathic effect, can be used for the purifying eutrophic water. Although the purifying ability of rational aquatic plants combination better than a single plant, always overlooked the ecological habits and aesthetic value of aquatic plants. As people’s living standards improve, the people to aesthetic and ecological demand gradually increased, ecological waterscape emerged. Ecological waterscape design require native aquatic plants as the main material whith better adaptability and ornamental value,formed the effective water purification ability and harmonious water environment through the rational allocation. Therefore, strengthen the research on native aquatic plants about screening and optimizing configuration, has important significance in the purification ability of aquatic plants in eutrophic water.This study based on monitored an artificial Jing Lake of Chongqing area in dry season and wet period during 2014~2015, 6 points of water quality was analysized, finally confirmed the eutrophication level. Refered to improved Hoagland nutrient solution, the experimental nutrient solution of low concentration, concentration, high concentration have been prepared, simulated mild, moderate and severe eutrophic water, through screening test detected the purification ability of aquatic plants whith ornamental value, looking for aquatic plant combination suitable for grow in polluted environmental of different degrees and has good repairing effect, and the conclusion as follows.① The 5 basic indicators(SD, CODMn, Chl-a, TN and TP) tested by artificially sampled to 6 points in Jing Lake, were analyzed and evaluated by single factor index, nemerow index method, trophic state index method and Arc GIS spatial method for winter dry season water quality conditions of Jing Lake. The results showed that the sites of the Chl-a and CODMn exceed 83% and 17%, while TN and TP met the GB3838-2002 water quality standards, TN even up to class III. The water quality of inlet region(1#, 2#) and the main lake area(4#, 5#, 6#) were poor, 3# regional water quality was better.②Adopted the eutrophication assessment method published by environmental protection department office file([2011] No. 22), the results showed that the content of Chl-a and TN, TP has a significant linear correlation(the R2 were 0.9233、0.8754), and the order of each factor contribute to the eutrophication were Chl-a, TP, SD and CODMn, and TN. During dry season showed that the community landscape water eutrophication level of different monitoring points achieved moderate eutrophication, the range of TLI(∑) between 64.37 ~ 67.60, most points were close to its limit, to easily break through the moderate eutrophication to severe eutrophication. After people’s governance, the monitoring points of wet period was still in moderate eutrophication, but TLI(∑) down to the lower limit values(60.6 ~ 63.1). The result shown that early people’s governance has a certain effect, but the effect is not particularly evident, so looking for environmentally friendly ecological restoration method is necessary.③ Ecological restoration experiment was been artificial simulated, first screened out aquatic plants whith ornamental value, good purification effect and can adapt to the growth in Chongqing. Removed the Philodendron’con-go’ can not adapt to the environment lead to leaves yellowing among emergent plants, screened out the Chamaedorea Elegans(TN 53%, TP 59%), Rohdea japonica(NH4+-N 81%, NO3--N 65%), and the Dracaena reflexa affect dissolved oxygen minimal. Screened out the Cabomba caroliniana Gray(TN 42%), Vallisneria natans(Lour.) Hara(TP 92%) and Echinodorus quadricostatus xinguensis(NO3--N 38%, NH4+-N 89%), they have better purification ability among the submerged plants. Lemna minor L were been screened out have obvious advantage(TN 78%, NO3--N 84%, TP 92%), and the Salvinia natans(L.) All. NH4+-N removal rate reached 90%.④Seven different combinations have been set up to investigate purify effect in low, medium and high concentrations eutrophic water, and screened out nutrient removal high and stable aquatic plant combinations,which has a good effect in purification capacity, growth characteristics, landscape effects, ecological effects and other integration. The results showed that 7 kinds of plant combinations can grow normally in the eutrophic water, has better removal efficiency to nitrogen and phosphorus, while the purification ability of different plants combinations represented significant difference.In eutrophication of low concentration stage, T5 combination( 3 Rohdea japonicas + 3 Chamaedorea Eleganses + 2 Echinodorus quadricostatus xinguensises + 1 plexus Vallisneria natans(Lour.) Hara + A third of the floating area Salvinia natans(L.) All., Lemna minor L) was the best plant nutrition combination for purifying mild eutrophic, the pollution factors removal rate were TN 91%, NH4+-N 72%, NO3--N 97%, TP 85%; In eutrophication of medium concentration stage, T7 combination(3 Dracaena reflexas + 3 Rohdea japonicas + 2 Echinodorus quadricostatus xinguensises +1 plexus Vallisneria natans(Lour.) Hara + A third of the floating area Salvinia natans(L.) All., Lemna minor L) was the best plant nutrition combination for purifying moderate eutrophic, the pollution factors removal rate were TN 60%、NH4+-N 88%、NO3--N 55%、TP 74%. In eutrophication of high concentration stage, T1 combination( 3 Rohdea japonicas + 1 Dracaena reflexa + 2 Chamaedorea Eleganses + 2 Echinodorus quadricostatus xinguensises +1 plexus Vallisneria natans(Lour.) Hara + A third of the floating area Salvinia natans(L.) All., Lemna minor L) was the best plant nutrition combination for purifying severe eutrophic, the pollution factors removal rate were TN 60%、NH4+-N 88%、NO3--N 55%、TP 74%. Though applied T1, T5 and T7 combination to actual water purification experiment confirmed its repair ability, the pollution factors removal rate were TN(T1 63%, T5 77%, T7 66%)、NH4+-N(T1 66%, T5 62%, T7 65%)、TP(T1 90%, T5 90%, T7 88%)、CODMn(T1 32%, T5 19%, T7 26%)、Chl-a(T1 83%, T5 90%, T7 82%).This experiment will provide a theoretical basis and technical support for create ecological waterscape of ornamental value and self-purification capacity, made a preliminary exploration to construct the ecological model in Chongqing city area, at the same time, promoted the construction of real estate towards the comfort,health, ecological direction. Research results have important theoretical and practical value.