Integration Research Of Ecological Restoration Technology In Shanghai Rural Eutrophication River

This article is in the foundation which the predecessor studies, has profited fromthe numerous disciplines, the massive scholars to the eutrophication waterecology.Considering the features of heavy polluted rural river environment inShanghai，the research focus on how floating net-bed made by submerged plantworking and also study how the submerged plant working with Hyriopsis Cumingiiand Daphnia magna. Some conclusions were summed up through many indoor andoutdoor experiments as following：(1)Water quality of16rivers in Shanghai was analy sized and evaluated based onmain parameters such as Chla，TN，TP，CODMnand NH4-N, from September2009to May2010．Comprehensive trophicstate index TLI(Σ) was used to value the watertrophic state.The conclusion showed that all of the investigated river channels inshanghai were eutrophicated.In fall and winter, the total nitrogen content in morethan90%of the rivers are worse than class Ⅴ and83.33%of the rivers in the summer;The ratio of the rivers channels which showed inferior category V water qualityaccording to the total phosphorus content was81.25%in winter,58.33%in summerand about56.25%of the rivers in fall are at class Ⅲ. Ammonia content in the springand winter were respectively56.25%and62.5%of the rivers at the inferior class Ⅴstate, but75%of the rivers in summer were in the class Ⅲ or class Ⅱ; The annualCODMnindex in these rivers were at the water status class Ⅳ. The survey also foundthat the salinity in the same river changed through the year, in which the salinityreached to maximum1.6‰in winter.It has become a huge urgency to analysis thewater polution scientifically,take appropriate measures to strengthen the managementof rural river channles,and avoid further water deterioration. (2)Laboratory tests and enclosure tests show us that submerged Myriophyllum andElodea have strong ability of removal of nitrogen and phosphorus. The trend ofremoval of nitrogen and phosphorus of these two kinds of experiments are similar,however the results are not same. The planting density of Myriophyllum should not betoo high, if doing that Myriophyllum would be corrupt and release of eutrophicationsubstances, they can make the water worse. In the poor mobility the water appropriateMyriophyllum density is200g/m2. The Elodea are light, they are easy to survive andmore convenient to be used in ecological restoration. The enclosure tests showed thatthe positive correlation between the number of submerged plants and water columnnitrogen and phosphorus removal. Due to the limitations of enclosure size and withthe passage of time, the submerged plants growth rate are decreased; Hyriopsiscumingii could remove suspended substance and chla in the water well.(3)From March2010, a bioremediation experiment was conducted in Litang riverShanghai. The ecological restoration area is500m long,20m wide and3.5m deep.Daphnia magna (4Kg) was first introduced to filter the high biomass ofphytoplankton and other particulate organic matter. Then,2kinds of submerged plantsVallisneria spiralis(30,000in south side) and Elodea Canadensis (400Kg) weretransplanted，their density are100/m2and135g/m2respectively. Water samples werecollected monthly to monitor the water quality and to investigate the bioremediationefficiency. One year monitoring data showed that water quality was improvedsignificantly after two months of cultivation and operation in the remediation area.Compared with the water in January,the mean concentrations of chemical oxygendemand（CODMn), total nitrogen (TN) and total phosphoru（sTP）in November reducedby60.67%、85.36%and88.74%respectively. The mean concentrations of ammoniumnitrogen (NH4-N,nitrite nitrogen (NO2-N)and Chla were0.088mg/L,0.024mg/L and5.31mg/m3, respectively. In the remediation area, the water body’sTN, TP, NO2-N,NH4+N and COD were significantly lower than the water which was in the controlarea. The average Secchi depth (SD) was reached in the range between 150cm-180cm.Overall, the water quality had been up to gradesⅡor Ⅲ of state waterquality standards for surface water. The results indicated that it was efficient toimprove river ecosystems with the engineering measures, biological purificationmethods-using Vallisnerianatans and Elodea nattalii. The implementation of thisproject provides technical supports for other similar river restoration constructions.Alternanthera philoxeroides has well ability of intercepting the sediment. Thetechnology that submerged plants combine with Alternanthera philoxeroides forreducing the nutrient runoffs in high sediment river can bringing good results.(4)Aquatic plants as one of the primary producers of aquatic ecosystems, byadjusting the depth of the net-bed or by alternanthera philoxeroides to interceptsediment to make the submerged plants survival easy and the technology beeconomical.By doing that the DO of the water body will be higher than before,restoring water ecological balance. Adjustable submerged plant net-bed can improvedwater quality significantly. In the early period of the experiment, the concentration ofnitrogen and phosphorus show a sharp downward trend,a more gentle decline in themedium-term experiments, the removal rate is relatively low; the end of experimentsthe concentration of nitrogen and phosphorus show downward trend no longer, theconcentration keep stable. It can be seen from the removal rate that the nitrogenremoval rate related to how much nitrogen the water column itself contains.The morenitrogen and phosphorus in the water, the faster the reaction rate, the higher theremoval rate.