Study On Assessment And Forecast Of Eutrophication In Fen He Reservoir

Fenhe reservoir is located in Loufan County. As the largest reservoir in Shanxi province, Fenhe reservoir has a storage capacity of350million cubic meters and is one of the sources of drinking water which comes from surface water in Taiyuan city and also a provider for part of its industrial and agricultural water. The water quality in Fenhe reservoir, especially the problem of eutrophication, can have serious impact on industry, agriculture and people’s life. With the mechanism for water quality eutrophication as theoretical basis, this thesis has made a dynamic analysis on water quality eutrophication(Chla、TN、TP、COD) in Fenhe reservoir (including four sections:inlet area of reservoir, inflow area of Jianhe River, center of Fenhe reservoir and the outlet area of Fenhe reservoir) from2006to2012. It has made forecast on the indicators of water quality eutrophication in Fenhe reservoir from2013to2017by applying improved grey GM(1,1) model. Based on these, it has made assessment of eutrophication level for four monitoring sections in Fenhe reservoir to rate eutrophication in the reservoir. In addition, in order to find the pollution sources of the reservoir and its prevention and control measurement, material collection and surveys have been made around the reservoir and its upper reaches, analyses on point source pollution and non-point source have been made and prevention and control measures have been reached. This thesis has provided theoretical basis for the improvement of water quality in Fenhe and prevention and control measures for eutrophication in Fenhe reservoir. Main conclusions in this thesis are as following:1、The result of dynamic analysis on water quality eutrophication in Fenhe reservoir shows that the content of chlorophyll a (chlorophyll-a) fluctuates bigger with time while the other three water quality indicators are relatively stable in the monitoring sections of the inlets of Fenhe and Jianhe Rivers. In the center section of the reservoir, the fluctuation of TN content is bigger in2008and2012with a minimum of about0.015mg/L, and it is relatively stable in other years. The content of TN reached a peak of around0.85mg/L in2009and keeps stable in other years. The content of chlorophyll (chl-a) is larger in2009,2010and2012with a peak of6.95mg/m3in2012and remains at a lower level about2mg/m3in other years. The content of CODmn is stable all the time. In the outlet monitoring section of Fenhe river, the content of chlorophyll (chl-a) keeps at a relatively lower level in the first five years. However, it has rocketed to18.6mg/L in2012, while the other three indicators remains stable.2、Improved GM(1,1) model has been used to forecast four index values of four monitoring sections in Fenhe reservoir in the following five years and the accuracy of these values are tested by methods of salvage value deviation. The deviation between the predicted and actual values in the previous five years shows that the deviation of improved GM(1,1) is relatively small, hence it is suitable for forecasting the index values for water quality eutrophication in Fenhe reservoir.3、It has made assessment on water quality eutrophication in Fenhe reservoir by applying BP neutral network and T-S fuzzy neural network. By comparing the accuracy and precision of these two neutral networks, it has concluded that T-S fuzzy neural network is better than BP neutral network, hence the rating model of assessing water quality eutrophication in Fenhe reservoir.4、The results for water quality eutrophication assessment of four monitoring sections in Fenhe reservoir by training completed T-s fuzzy neural network shows that the ratings of water quality eutrophication in the center sections are generally higher than those in the other three monitoring sections such as the inlet area of the reservoir, the inflow area of Jianhe River and the outlet area of Fenhe reservoir. The ratings of water quality eutrophication in the inlet area of the reservoir, the inflow area of Jianhe River and the center of Fenhe reservoir are generally lower than III, which means small occurence of eutrophication while those around the outlet area of Fenhe reservoir are IV, which belong to large occurrence of eutrophication. In addition, judging from water quality status of the sections over the years, the ratings of eutrophication in May are generally higher than those in September.5、The analysis of pollutants to water quality in Fenhe reservoir shows that industrial pollution source is distributed in the upper reaches of incoming streams of Fenhe reservoir; main industries are ironworks, ore treatment plant, coal washing and coking plant, etc. Agricultural non-point source pollution is mainly distributed in the surroundings of Fenhe reservoir; the failure of reasonable control of livestock and poultry industry in the surroundings of the reservoir results in excessive use of breeding area and pesticide, then the pollutants of agricultural production flow into the reservoir through surface runoff and underground water. Ultimately, it leads to the fact that water quality indicators in Fenhe reservoir such as TP, TN, etc. exceed the normal range.6、Based on analyses of the trend of water quality eutrophication, pollution assessment and pollutants sources in Fenhe reservoir, prevention and control measures for water quality eutrophication in reservoirs have been offered in this thesis, including controls of point source and non-point source pollution to water quality in Fenhe reservoir from the upper reaches of Fenhe River, Jianhe River and the surroundings of the reservoir and the corresponding countermeasures.