| To explore the the annual variation of water ecology and investigate the water environmental quality of the urban landscape water in Xian,three typical landscape waters were chosen for this study and water samples from selected position were grasped once every two months from April 2016 to February 2017.Based on the analysis results of the physical and chemical indicators,such as pH,COD,WT,COND,TN,NH4-N,NO3-N,TP,Chl-a etc.,daily variation and seasonal variation of the water environment in these landscape waters were investigated.At the same time,the composition and variation of planktonic algae in these landscape waters in May and August,2016 were analyzed.In addition,the water environmental quality and the degree of eutrophication were evaluated.In order to restore the ecological system and improve the water environment of these landscape waters,suggetions and actions from six aspects have been taken into consideration.These include water source protection,ecological revetment construction,reasonable construction of aquatic vegetation,introduction of edible protozoa and filter-feeding fish,and strengthening the management mechanism.The main results were as follows:(1)The analysis of the daily variation of water environment showed that the metabolism activity of aquatic plants has an important influence on the landscape water ecosystem.It is shown that diurnal variations of pH and DO were different in different growing areas of aquatic plants.The seasonal variation of water environment showed that the variation of physical and chemical indexes is affected not only by the ecological factors in the system,but also by the external pollution sources.(2)The nitrogen and phosphorus pollution were serious in all the waters of Fengqing Lake?Lianhu Lake and Geming Lake,while concentrations of nitrogen in most landscape waters were much higher than the IV class standard in the Surface Water Environment Quality Standard(GB3838-2002).In contrast,phosphorus pollution is relatively light.According to the TN/TP ratios of the landscape waters,waters in all Lakes were in phosphorus-limited status.(3)There are a number of kinds of planktonic algae in the three landscape waters.Among them,Chlorophyta and Cyanophyta were in absolute advantage in the cell density.During the phytoplankton investigation in May and August 2016,respectively,7 phyla with 70 species and 4 phyla with 30 species were found in Fengqing Lake;6 phyla with 89 species and 6 phyla with 43 species were identified in Lianhu Lake;while 5 phyla with 26 species and phyla with 12 species of phytoplankton were discovered in Geming Lake,respectively.The dominant species in the three landscape waters were Limnothrix planctonica,Glaucospira,Cosmarium depressum,Microcystis sp.,Pseudanabaena mucicola,Microcystis sp.,Anabaenopsis circularis and Aphanocapsa sp.(4)Based on the single factor evaluation method,the water quality of the landscape waters was assessed.It met V class standard while the main contaminants were chemical oxygen demand and total nitrogen(TN).Based on Nemerow Index evaluation method,the water qualities of Fengqing Lake and Lianhu Lake were in a status of “pollution” while the water quality in Geming Lake is “heavy pollution”.Moreover,the index of biologic diversity of phytoplankton also showed that the water qualities of the three landscape waters exhibited a trend of moving from mid-contaminated to severe pollution.(5)According to the standard of the single factor of eutrophication in OECD(Chl-a),Fengqing Lake belonged to the eutrophication level while the other landscape waters belonged to the serious eutrophication level.From the result of the comprehensive trophic state index(TLI)and the dominant species in the three landscape waters,it can be concluded that the landscape waters studied were in a status of eutrophication on the whole. |
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