水华爆发的突变模型——以巢湖为例

The catastrophic model of water bloom:a case study on Lake Chaohu

面对湖泊水库富营养化的严峻形势,水华防治是当务之急,而根据富营养化现状对水华进行准确的判定和预报更是重中之重.从水生态系统的角度出发,综合考虑TP、T、Chla和DO等4个对巢湖富营养化乃至水华影响最为突出的因子,构建了巢湖水华突变的尖点模型,通过模型来模拟巢湖富营养化引发水华的情势.在对巢湖2000～2003年时间序列的监测数据进行数据拟合的基础上,发现南淝河入湖区断面处逐月TP、T、Chla和DO数据的演变规律符合突变理论的尖点模型特征.经检验,模型的相对误差控制在10%左右,具有较好的拟合精度.根据模型的突变判别,巢湖的水生态系统2003年7月在南淝河入湖区断面处发生了突变,这一模拟结论与该断面2003年8月爆发水华的实际情况相一致.研究表明,水华突变模型的建立,准确地反映了巢湖富营养化引发水华的实际情况,系统地勾勒出富营养化状态下水生态系统各要素间的动态响应模式,揭示了水华爆发的突变机理.通过水华突变模型的构建,不仅能够对巢湖水华的发生进行判断和预报,还可以对各项防治措施的实施效果进行预测和模拟,进而为综合整治方案的优化和统筹提供科学依据.水华的爆发是多诱因的综合作用结果,是营养物质长期累积、由量变到质变的演化过程,作为目前唯一的一种研究由渐变引起突变的系统理论,突变理论满足水华研究的数理要求,为水华现象的数值模拟提供了可行的解决方案.

Along with its rapid economy expanding, China is also facing the increasingly serious problem of cultural eutrophication, especially in aquatic ecosystems of lakes and reservoirs. Water bloom is the worst result of lake or reservoir eutrophication and sometimes leads them to death. To assess and forecast water bloom by studying the extent of eutrophication is crucial to the assurance of people＇ s drinking water and thus it is of great importance. With a ease study of Lake Chaohu, the fifth largest lake in China, as viewed from the whole aquatic ecosystem, this paper synthetically considered TP, T, Chla and DO as a whole, which were the outstanding factors in eutrophication and water bloom of Lake Chaohu, to construct a water bloom cusp model. Using this model, the process that eutrophication brought on water bloom in the lake was simulated. According to the result of data fitting, monthly data of the above four water quality parameters, obtained from a certain sampling site from 2000 to 2003, fitted characteristics of cusp model. The model was tested to be accurate for its relative error was around 10%. What is more convincible, according to the catastrophe discriminant of the cusp model, it could be judged that a discontinuous jump of the aquatic ecosystem had arisen in August, 2003 occurred in July, 2003 in Lake Chaohu, the conclusion was consistent with the fact that water bloom have in the lake. The case study of Lake Chaohu, on the base of data fitting, deduced that some water quality parameters fitted characteristics of cusp model in the process that eutrophication brought on water bloom. The research indicates that water bloom cusp model could reflect the actual state of water bloom caused by eutrophication, describing the dynamic response mode between different factors in the aquatic ecosystem and further revealing the outbreak mechanism of water bloom in the lake. This paper suggests that using catastrophe models to fit water quality data of a time serial would be a constructive approach to forecast and judge the outbreak of water bloom in lakes and reservoirs. In addition, by constructing and studying such catastrophe models, lake or reservoir managers would be able to simulate the effects of different protecting and curing projects and further supply the scientific warrant for the optimization of these projects as well. The outbreak of water bloom is the results of mutual exchange reactions of many inducements and long-term accumulative action of nourishments. As the only system theory studying how gradual change causes catastrophe, catastrophe theory satisfied the mathematical logic of the water bloom and provided us with a feasible solution for the numerical simulation of water bloom. This paper put forward a new idea for the study of the water bloom, which has never reported neither at home nor abroad so far.