【作者】 沈晔娜；

【导师】 吕军；

【作者基本信息】 浙江大学 ， 农业资源利用， 2010， 博士

【摘要】 水污染,是全人类在经济高速发展过程中所面临的共同问题。随着点源污染控制能力的提高,非点源问题日益凸显。如何实现流域非点源污染过程的定量并明确其定量控制目标是开展非点源污染控制实践的基础和关键,也是当前本领域研究的热点和难点问题。本文针对非点源污染的多源性、复合性、污染发生的时空不确定性、污染物迁移的高度非线性、实测困难等特点,选择分布式的SWAT (Soil and Water Assessment Tool)模型为工具,以我国东南沿海经济相对发达地区典型非点源污染流域——长乐江流域为研究对象,通过长期连续(2003年7月至2007年12月)的按月水文水质监测,协同流域土壤、气象、地形、地貌等自然条件排污状况资料分析,运用土壤学、环境科学、水文学等理论,应用模型模拟、统计分析、质量守恒等方法和原理,完成了SWAT模型数据库构建、非点源与模型耦合、参数敏感性分析、率定和验证,实现了流域非点源污染过程的动态模拟；估算了流域背景和人为投排放引起的污染物入河量,定量分析了分区、分源、分类、分期的非点源污染特征,给出了各污染源入河系数和各土地利用类型的输出系数；以此为基础,定量分析了河流中污染物的自净能力及其时空演化规律,明确了不同自净能力表达指标的差异性和应用的限制性；最后,根据段末水质控制目标,建立了流域污染物投排放量控制方案,并提出了结合提高河流自净能力进一步提高水质的方法。基于以上研究,较为完整地建立了流域非点源污染过程动态模拟与定量控制的方法体系,为我国东南沿海地区的流域非点源污染控制提供了重要参考。本文的主要结果与结论如下：1)针对我国东南经济发达地区典型小流域的特征,建立了SWAT模型的建模方法体系,包括模型基础信息数据库构建、流域内非点源污染和模型之间有效耦合、模型参数的敏感性分析、率定和验证,为模型在其它类似区域的应用提供了借鉴。2)在长乐江流域所建立的SWAT模型,其径流(地表径流—基流—总径流)、泥沙、养分(TN和TP)率定和验证的模拟精度系数Ens和R2基本上都大于0.6,取得了较为理想的结果,可以满足流域非点源污染过程动态模拟的需要。3)长乐江流域内氮、磷的主要来源包括农业生产、生活污染和畜禽养殖。农地、生活污染、畜禽养殖的TN投排放量分别为3596.00 t yr-1、1394.47 t yr-1、1563.23 t yr-1,TP的投排放量分别为1770.51 t yr-1、348.62 t yr-1、554.50 t yr-1。4)流域TN和TP入河量分别为1972.20-2843.99 t yr-1和71.54-132.07 t yr-1,其中来自农地(水田、园地、旱地)的TN入河量为全流域TN入河量的76.69%-79.14%,TP的入河量为全流域TP入河量的88.13%-90.69%；农业生产是流域内最大的污染源。干流河段MS I所在集水区内TN和TP入河量分别为974.86-1349.05 t yr-1和33.59-57.37 t yr-1,占全流域TN和TP入河量的57.84%-63.37%和50.28%-57.05%,其次是支流崇仁江所在集水区,TN和TP的入河量分别为527.01-848.73 t yr-1和20.20-36.16 t yr-1,占整个流域TN和TP入河量的26.72%-30.27%和27.37%-28.99%。TN和TP的入河量均随流量的增加而增加。5)长乐江流域各土地利用类型TN的背景输出系数为5.03±0.98kg ha-1yr-1 23.26±4.24 kg ha-1yr-1,且旱地>其他用地>水田>林地>园地>人居地,TP的背景输出系数为0.018±0.008kg ha-1yr-1-1.404±0.422 kg ha-1yr-1,且旱地>水田>其他用地>园地>人居地>林地。流域内TN.TP的背景入河量分别占TN.TP总入河量的26.76%-34.74%,TP为14.87%-24.44%。TN和TP的背景输出系数和流量呈极显著的正相关关系。6)长乐江流域内人为投排放至旱地、水田、园地、人居地的TN入河系数分别为0.3793-0.4367、0.1491-0.2140、0.2730-0.4727和0.2134-0.2942,TP入河系数分别为0.0854-0.1754、0.0197-0.0293、0.0171-0.517、0.0256-0.0619。7)长乐江水系全年TN和TP自净量分别为962.58-1186.23 t yr-1和49.68-79.36t yr-1,自净率分别为38.68%-46.35%和48.8%-74.80%。其中两个干流河段TN和TP的自净量超过整个水系自净量的50%,但是自净率却小于三条支流。丰水期的TN和TP的自净量最大,枯水期的自净量则最小。8)现有的自净能力表达指标可以分为三类,第一类包括RL、RA,主要表达了“量”的概念；第二类包括Kx、SL、RE、RLW、Kt,主要表达了“率”的概念；第三类是Vf,其主要表达了河流的自净潜能。第一类“量”的指标表达的自净能力随着流量(包括水深和流速)等水文变量、河宽、河长等河流形态特征参数以及污染物负荷量的增加而增加,第二类“率”的指标表达的自净能力则相反；而Vf与以上因素都无相关关系,只随着水温的增加而增加。Vf和RA两个自净指标适合进行空间尺度的比较,其余只适合时间尺度的比较。9)长乐江TN和TP水环境容量(最大允许污染物入河量)分别为1068.78-2023.90tyr-1和88.97-143.35 tyr-1。与现状相比,需削减656.60-1540.16tyr-1TN入河量才能达到该流域河段水质不再进一步恶化的目标,这占了现状入河量的27.35%-54.15%；相应地,流域TN投排放量共需削减2688.94-4483.46 t yr-1,其中水田的削减量最大。相反,TP尚有10.22-35.24 t yr-1的剩余水环境容量,为当前该流域TP入河量的8.54%-42.48%；相应地,TP全年剩余投排放量为244.89-1463.85 t yr-1。10)长乐江在现状TN投排放量下,当流速人为减小30%时,流域出口处的TN浓度将下降30%,通过人为减少流速以提高河流污染物自净能力的方法为推进流域非点源污染的有效控制提供了新途径。本文主要创新点和特色如下：1)针对我国农村人居地人口集中且产生的污染物处理率低的特征,在SWAT模型中引入了农村生活产生的污染物每日均匀输入到人居地中的处理方法,取得较为理想的校正和验证结果(养分模拟精度系数Ens和R2均大于0.6)。这对于推进SWAT模型在我国农村和农业为主流域的应用提供了借鉴。2)应用SWAT模型,首次提出了不同土地利用类型在无人类活动情况下的背景氮、磷输出系数计算方法,明确了背景输出对河流水污染的贡献,定量解释了流域污染物投排放量削减后河流水质提高不显著的原因,为进一步科学制定流域水污染控制措施和对策提供了重要依据。3)率先系统总结了现有表达河流污染物自净能力的定量指标的物理意义及其计算方法,对定量指标进行了科学分类,明确了河流自净能力对水文、气象、地质等条件的响应关系,给出了各自的关系和差异及其适用范围,推进了河流自净能力的定量研究。4)针对削减流域污染物投排放量的经济成本较高的实际,提出了削减陆域的污染物投排放量与提高河流污染物自净能力相结合的水污染控制方案,缓解了陆域污染物投排放量削减的压力,有利于水污染控制方案的实施,也为推进流域非点源污染的有效控制提供了新途径。更多还原

【Abstract】 Recently, water pollution and its resulting harms on the human health has been a common problem worldwide. Non-point source (NPS) pollution has been a main cause for water quality impairment in many countries and regions. The quantitative information of NPS pollution in watershed scale, which is the basis for NPS pollution control in practice, is one of the most focuses in current studies. This study selected the ChangLe River watershed as the study area, which was a representative NPS pollution dominative watershed in southeastern China. The SWAT (Soil and Water Assessment Tool) model was adopted to quantitatively analyze the NPS pollution. Water quality and hydrological parameters were monitored along the ChangLe River system monthly during 2003-2007. The watershed natural condition (including soil, climate, land use, etc) and pollution sources information were also investigated and analyzed. Under the guidance of such theories as soil, ecology, environment, hydrology science, etc, SWAT model for nitrogen and phosphorus dynamic simulations in the watershed was calibrated and validated effectively. Then, the watershed nutrient exports from background and human activities to the river were both estimated to reveal the NPS pollution characteristics in different regions, pollution sources, and periods. The nutrient export coefficients for different pollution sources were obtained. Further more, in-stream nutrient removal capacity and its spatial and temporal variations were both fully addressed using different metrics. According to the river water quality control target, the water pollution control scheme that focused on the watershed nutrient input quantity in different pollution sources was founded. To further improve the river water quality, the approaches that can enhance in-stream nutrient removal capacity were also discussed. The developed theories and methods system on NPS pollution dynamic simulation and its quantitative control in this study provide a demonstration for watershed NPS pollution control in southeastern China.The main research results and conclusions of the dissertation are included:1) Aimed at the characteristics of the typical small watershed in developed area of southeastern China, the SWAT modeling approach system for NPS pollution simulation was established, which included the methods for model databases establishment, the NPS pollution combined in the model, the sensitivity analysis for model parameters, calibration and validation. It provides a referential experience for SWAT model application in similar watershed.2) Established SWAT model in ChangLe River watershed provided satisfactory modeling results on runoff (surface runoff, base flow and total flow), sediment, and nutrients (total nitrogen and total phosphorus) in both calibration and validation procedures, since the Ens and R2 for their modeled and measured values were both higher than 0.6.3) The inputs from fertilizer application, domestic and animal waste were the main sources for nitrogen and phosphorus in the watershed. The TN input quantity from these three sources was 3596.00 t yr-1,1394.47 t yr-1,1563.23 t yr-1, respectively, and for TP was 1770.51 t yr-1,348.62 t yr-1,554.50 t yr-1, respectively.4) Watershed TN and TP export load to the river was 1972.20-2843.99 t TN yr-1 and 71.54-132.07 t TP yr-1, respectively. The TN and TP export load from farm land contributed 76.69%-79% and 88.13%-90.69% of total TN and TP load for the watershed, respectively. The TN and TP export load from sub-watershed MS I occupied 57.84%-63.37% and 50.28%-57.05% of total TN and TP load for the watershed, respectively. However, TN and TP export loads were both increased with river water flow.5) Background TN export coefficients for different land uses ranged from 5.03±0.98 kg ha-1 yr-1-23.26±4.24 kg ha-1 yr-1, with the order as following:dry land > other land> paddy field> forest> garden> residence land. Background TP export coefficients ranged from 0.018±0.008 kg ha-1 yr-1-1.404±0.422 kg ha-1 yr-1, with the order as following:dry land> paddy field> other land> garden> residence land> forest. The background TN and TP export loads accounted 26.76%-34.74% and 14.87%-24.44% for their total export loads for the watershed, respectively. Background TN and TP export loads were also significantly increased with river water flow. 6) The TN export ratio (the ratio between the nutrient export load derived from anthropogenic input and the anthropogenic input quantity) in dry land, paddy field, garden, and residence land was 0.3793-0.4367,0.1491-0.2140,0.2730-0.4727 and 0.2134-0.2942, respectively. For TP, it was 0.0854-0.1754,0.0197-0.0293, 0.0171-0.517, and 0.0256-0.0619, respectively.7) The in-stream removal amounts for TN and TP was 962.58-1186.23 t yr-1 and. 49.68-79.36t yr-1, respectively. More than 50% removal amounts were occurred in the mainstreams. However, removal efficiencies that compared with the total input nutrient load in mainstream were lower than that of three tributaries. The largest removal amounts for TN and TP were appeared in flood season, and the lowest values appeared in dry season.8) There were three groups for current in-stream nutrient removal metrics. RL and RA formed first group, which reflected the amount properties about removal process. The second group included Kx, SL, RE, RLW and Kt, which indicated the efficiency properties about removal process. The third group was Vf, which expressed the inherent removal potential. Metrics in the first group were increased with river water flow, water depth, widths and lengths, while metrics in the second group were in opposite. The Vf, which was the only metric that influenced by water temperature, was increased with water temperature. Both Vf and RA can be used to compare the nutrient removal capacities among different streams or reaches, while others were only suitable for temporal comparisons.9) The water environmental capacity (the largest output loads permitted) for TN and TP was 1068.78-2023.9 t TN yr-1 and 88.97-143.35 t TN yr-1, respectively. To maintain the current water quality,656.60-1540.16 t yr-1 of TN export loads should be reduced, which occupied 27.35%-54.15% of current TN export load. Accordingly, the TN input quantity in the watershed should be reduced 2688.94-4483.46 t yr-1, with TN input quantity in the paddy fields accounting for the largest amount. Contrary, TP still had 10.22-35.24 t yr-1 residual water environmental capacity, which accounted for 8.54%-42.48% of the current TP export load. Thus there was 244.89-1463.85 t yr-1 residual TP input quantity in the watershed. 10) If maintain the current TN input quantity in the watershed, the average TN concentration at the watershed outlet can be decreased 30% of current TN concentration through slowing down 30% of river flow velocity. This provided a simple but efficient approach to improve the river water quality and control NPS pollution.The innovative and distinctive points about the dissertation were:1) The population was centralized in rural habitation area and its domestic wastes were treated inefficiently in China. Thus the daily rural domestic wastes was treated as a nutrient input into the habitation land in this study, which obtained the satisfying modeling results (the coefficients En and R2 were both more than 0.6 for nutrient simulations). This method provided a useful reference to take the rural human living influence into consideration in the SWAT model application at the similar watersheds.2) Background nitrogen and phosphorus export coefficients for different land uses were firstly estimated, which quantitatively explained the results that river water quality could not be improved rapidly and significantly after reducing the watershed nutrient input quantity in a certain proportion. This provided the important information to establish more scientific practices and strategies that aimed at water quality improvement.3) The study systemically explored the physical mechanisms and calculation methods for current in-stream nutrient removal metrics. The metrics were classified by statistical method and clarifies their differences in the responses to the hydrological condition, climate and geological characteristics. The relationships and differences among all metrics were fully addressed and their application limitations were distinguished. These efforts advanced the quantitative methods on in-stream nutrient removal capacity.4) The water pollution control scheme, which combined the watershed nutrient input reduction with river removal capacity enhancement, was founded. It was in favor of mitigating contradictions between water pollution control and economy development, and benefited the implement of the water quality control scheme in practice. This combined water pollution control scheme offered an improved approach to combat the NPS pollution control in watershed scale.更多还原