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SWAT建模过程的改进及对韩江流域面源污染的模拟研究

Improvements of SWAT Model-Building Procedure and the Simulation of Non-Point Source Pollution in Hanjiang River Basin

【作者】 郑宇

【导师】 程香菊;

【作者基本信息】 华南理工大学 , 水利工程, 2019, 硕士

【摘要】 面源污染难以监测和评估,采用流域水文模型进行模拟是一种重要的研究手段,因此探索如何提高模型的精度是一个有价值的研究课题。面源污染的形成受景观格局等多种因素影响,研究景观格局对面源污染的贡献有助于深入了解面源污染的产生发展机理,从而设计和评估控制流域面源污染的最佳管理措施,对于水环境保护具有重要意义。本文以韩江流域为研究对象,收集气象地理资料,统计污染情况,基于SWAT(Soil and Water Assessment Tool)建立面源污染模型,并探索改进建模流程的方法;利用校准好的模型对流域污染情况进行模拟,并研究景观格局与面源污染的关系;结合成果设计最佳管理措施并进行模拟评估,为流域面源污染治理提供依据。主要成果如下:1.建立了韩江流域的SWAT模型,并在此过程中提出了一种在数据缺乏地区构建土壤属性数据库的方法,能同时计算土壤基质和完整土体的湿容重、饱和导水率、有效含水量等参数。在校准过程中推广了基流分割的滤波方程并提出了一种改进的基流退水指数校准方式。2.针对研究区提出了一种基于SWAT-CUP的多目标多站点的校准和验证流程,结果表明径流、泥沙、氨氮的决定系数R2和纳什效率系数ENS基本都超过0.7,相对误差ER基本都小于8.5%,说明模型的拟合效果良好。3.采用桑基图代替传统的土地利用转移矩阵,更直观地表达了不同时期的土地利用组成格局以及它们的转换过程,结果表明流域的城镇化进程呈现出从下游向上游蔓延的趋势。4.利用多元统计分析方法,建立景观指标与不同污染物浓度增量之间的线性回归方程和冗余分析模型。结果表明,景观指标能解释81.7%的面源污染变化。景观组成格局指标的贡献比景观空间格局指标更大。林地面积百分比与面源污染呈现负相关。城镇或农田的斑块密度、形状指数等空间格局指标与污染物浓度具有较强的负相关性。旱地相比水田对面源污染的贡献更大。5.模拟结果表明,在当前土地利用策略和人类活动影响下,研究区水质呈恶化趋势。研究区西部的宁江流域地区是总氮污染的关键区,总氮浓度达到3.91mg/L;东部龙岩市永定区地区的总磷浓度较高,达到2.15mg/L。采用植被过滤带、植草水道、退耕退草还林、旱地改水田等措施能够削减流域内4.63%-8.95%的总氮和0.91%-42.41%的总磷。

【Abstract】 As non-point source pollution is difficult to monitor and control,numerical modeling has become an important way to study on it,and it is valuable to investigate approaches to improve the accuracy of non-point source pollution modeling.The mechanism of non-point source pollution to take shape and transfer is affected by multiple factors including landscape pattern,so investigating the contribution of landscape pattern to non-point source pollution leads to a better understanding of the mechanism of non-point source pollution.Besides,designing and assessing best management practices for controlling watershed non-point source pollution is helpful for water environment protection.In this study,geographical and meteorology data in Hanjiang River Basin were collected to build a non-point source pollution model based on SWAT(Soil and Water Assessment Tool).Approaches to improve modelling procedure were investigated.The calibrated model was used for simulating the pollution of Hanjiang River Basin and studying the relationship between landscape pattern and non-point source pollution.Best management practices were proposed and assessed based on the results of the simulation.Main results are as follows:1.A SWAT model for Hanjiang River Basin was built,with an improved approach for constructing SWAT soil parameters database of regions in China proposed.The approach allows modeller to calculate the bulk density,saturated hydraulic conductivity and available water of both soil matric and total soil.An improved approach for the calibration of baseflow recession constant was proposed,based on a generalized digital filter equation for baseflow separation introduced by this study.2.A multiple-objective-and-multiple-station calibration and validation procedure based on SWAT-CUP program was put forward.According to the modelling results,the coefficients of determination and Nash-Sutcliffe coefficients of streamflow,sediment and ammonia nitrogen were basically over 0.7 with relative error basically less than 8.5%.3.Sankey diagram was used instead of land use transition matrix to express the status and dynamics of landscape pattern,and it was revealed that the urbanization progress in Hanjiang River Basin presented a trend that the urban area was spreading from lower stream to upstream.4.By means of multivariate statistics,regression equations and redundancy analysis were conduct to investigate the relationship between landscape metrics and water quality indicators.The results showed that landscape metrics accounted for 81.7% variation in changing of nonpoint source pollution,where the contribution of landscape configuration metrics were greater than landscape composition metrics.The percentage of forest area was negatively related to non-point source pollution.The patch density and shape index of urban and agricultural land were strongly negatively related to non-point source pollution.Uplands contributed more pollutant than paddy fields.5.The simulation results also showed that the water quality in the Hanjiang River Basin presented a downtrend in the context of current land use management strategies and human activities.The western subbasins were key areas of total nitrogen pollution,with a total nitrogen concentration of 3.91 mg/L.The eastern subbasins were key area of total phosphorous pollution,with a total phosphorous concentration of 2.15 mg/L.Best management practices,such as vegetated filter strips,riparian buffer zones,reforestation and adjusting agrotypes can reduce nitrogen pollution by 4.63%-8.95% and phosphorous pollution by 0.91%-42.41%.

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