Research Of Water Environmental System Models Based On Complexity Theory

This dissertation first reviews the research progresses on complexity theory and its applications to the models of water environmental system, and accounts for the current problems on complex environmental models. Then from the respective of the mathematic theories, methodologies and applications and based on complexity theory, the focus is given on the development of new theory and new methodology for the water environmental modeling establishment. This dissertation systematically studies the modeling problems in such areas as follows: water quality model, calculation of water environmental capacity, risk analysis of water environment, mechanism discussion of water environmental time series, lake eutrophication model and temporal distribution simulation of acid precipitation. By means of complexity theory, we hope to found some environmental system models which are more accorded with the objective rules and facts.The main work and novel results of this dissertation includes the following elements. (1) Under the condition of unclear water environment, inexact cognition of parameters, without the detailed monitoring flow field and to avoid full dependence of practical monitoring data of river, an interval two-dimensional water quality model, its numerical algorithm and interval risk (denoted by"degree"of interval number) have been proposed, the availability and reliability of which were calibrated by numerical experiment of the ideal regular river reach. The results of a case study indicated that the interval water quality model offered a realistic approach for dealing with uncertainties in real-world problems compared with traditional stochastic or fuzzy methods. (2) Based on the non-linear relationship between Chlorophyll-a and environmental parameters as well as biological parameters in the lake eutrophication, the Bayesian regularized BP neural network (BRBPNN) and the least squares support vector machine within Baysiean evidence framework (BEFLSSVM) were proposed to predict Chlorophyll-a concentration. The results showed that BRBPNN and BEFLSSVM models were capable of automated selection of regularization and kernel parameters, and thus it may ensure the excellent generation ability and robustness. (3) Based on the pollutant concentration distribution in lake effluent (the risk of exceeding standard was lower than 10%, which was considered as the control goal of water quality), with the unascertained mathematics theory and Monte-Carlo method by the Pearson-III distribution curve, a new model for the calculation of water environmental capacity in eutrophic lake under unascertained information was proposed. This modeling could offer the feasible and reliable capacity of the water environment. (4) Three statistical methods were used to examine the self-organized criticality (SOC) of weekly dissolved oxygen (DO) series: empirical probability distribution function, power spectrum analysis and detrended fluctuation analysis (DFA). We found evidence that DO events were analogous to avalanches of granular piles exhibiting SOC properties. The weekly DO events complied with double power-law in two different regimes separated by a characteristic scale, X c, and could be described as 1 /fβnoise with long-range persistence. Then additionally, we argued that the critical state of DO events referred to the concentration of the saturated dissolved oxygen ( O s). Therefore, DO evolution was consistent with the three criteria of complex SOC systems. We thus suggested that SOC might be a possible mechanism underlying weekly DO evolution. (5) On the basis of Streeter-Phelps and Shastry's water quality model, the concept of stochastic force was introduced to develop the stochastic differential equation of water environment. The probability density distribution function was deduced by numerically solving the multi-dimensional stochastic partial differential equation. Accordingly, the relationship between the risk and duration of pollution exceeding standard could be obtained. The calculation of case study showed that a very small stochastic vibration maybe changed the"fate"of water environment and thus the managers and planners should fully attach importance to the non-linear and uncertain effect in the environment. (6) Based on the nonlinear and uncertain characteristics of acid precipitation, the BRBPNN and BEFLSSVM models of Chapter 3 were applied to the trend analysis, acidity and chemical composition of precipitation. And the simulation results were obviously better than those of multiple linear regression (MLR), which proved that the environmental system modeling based on complexity theory had the excellent applicability and practicality and was helpful to explain the mechanism of trend analysis of precipitation.Due to the complexity characteristics of environmental system, this dissertation systematically and further developed the theory and methodology in prediction, simulation and assessment of the water environmental system models. To sum up, on one hand, this dissertation has been helpful to develop a set of environmental system modeling based on complexity theory and essentially deepen to recognize the objective rules. On the other hand, the results of the typical case study, such as Three-Gorge Reservoir and Dongting Lake, proved that the models based on complexity theory could more accurately and effectively account for the complex behaviors of water environment. And these offered theoretical and technical bases for environmental management and planning, and thus would more effectively boost the sustainable development of environmental system.