Studies On The Eutrophication In The River With Dam

With the building of the cascade hydropower stations in the north Jiulong River, many hydropower stations reservoirs areas came into being and the "being lakes and reservoirs" is very serious. The eutrophication of the water in the reservoir areas is becoming serious in recent two years and in 2009, blooms of the dinoflagellate hydration occurred. Therefore, it is an urgent issue to study the reasons and the mechanism of the eutrophication of river with dam, which has important theoretical and practical significance.The objectives of this study gives an overall evaluation to the waters of Nord Stream reservoir areas of Jinlong River on the basis of related testing data, and analyses the characteristics of the water nutrition salt,chla and phytoplankton from quantitative and qualitative perspective. Finally, it offers the measures to prevent the waters from eutrophication. The main conclusions of this paper as follows:(1) In dry period, the water in Nord Stream is mesotrophic-eutrophic,Some waters is more eutrophic(the waters in Mayang River and Longjin River). There are spatial differences in the level of eutrophication in Nord main stream.(2) The concentration of TP and TN in the waters of Nord main stream reservoirs areas is higher than that in the branch stream reservoirs areas. The contract is much more prominent in dry period. From the analysis of the characteristics of the concentration ratio of TN and TP and the 2009 "dinoflagellate " event, It can be asserted that TP is the main limit nutrient salts in the waters of the Nord main Stream reservoir areas; TN may be the main limit nutrient salts in the waters of xinqiao River reservoir areas; TP is the limit nutrient salts in the waters of Longtan Lake reservoir areas. There may be also uncertain factors, like TN and TP limit, which can be seen from the following phenomenon:the nearer to the upstream waters in the main stream, the stronger of the control of TN; the nearer to the downstream waters in the main stream, the weaker of the control of TN. This phenomenon means that the reasons for the eutrophication in the waters of the Nord Stream are complicated.(3) In spatial and temporal distribution, the concentration of Chla in the waters of Jiangdong reservoir areas(including Mayang River and Longjin River backwater area) and Longtan Lake is in a very high level while the concentration of chlorophyll a in the waters of other main and branch streams reservoir areas is generally low with an annual average of below 10mg/m3. The concentration of Chla is higher in dry period than that in the wet and level period. From the waters of the whole basin, the relation between the TP and Chla is very obvious:they are positively related and their relations are:ρ=56.482×ρ(TP)+2.3589 (r=0.251 p=0.009). In dry months, the temperature and the increase of Chla is closely related and there are certain relations among PH, DO and CODmn.(4) Diatom-chlorophyta is the main phytoplankton in the waters of Nord Stream reservoir areas. The alga cells in the mouth of Mayang River, Longjin River and Longtan Lake are denser than that of other reservoir areas. The algae cell density of every reservoir area is relatively bigger in dry seasons. The number of the alga cell which are diatom in all the reservoir areas are very close in winter, summer and autumn while the number increases and the dominant species are changing in winter. The dominant species are changed into the mixture of diatom, chlorophyta and cyanothece or the diatom is changed into chlorophyta or cyanothece in October. The number of the alga, the permanganate index, the temperature of water, and the DO correlate well and the temperature of water is the main factor that cause alga to grow in dry season.(5) According to analysis of eutrophication, the source and load of the nutrient salt of the waters in the Nord Stream, this thesis gives control measures from the perspective of the control of the pollution source, the ecological management of the power stations, the perfection of the detection system in the river basin and the ecological and environmental protection of the rivers to reduce the eutrophication of waters.