【作者】 刘俊杰；

【导师】 钱忠东； 董斌；

【作者基本信息】 武汉大学 ， 水利水电工程， 2023， 博士

【摘要】 近年来,我国政府陆续出台了多项农业面源污染治理的计划和方案,表明了我国农业面源污染防治工作仍任重道远。采用沟渠湿地治理面源污染时应有持续、稳定、良好的去除效果才可提升水质,然而不同时间尺度下环境因素的变化导致沟渠湿地氮磷去除效果发生大范围变化。沟渠湿地溶解氧既对环境变化反应灵敏,又与氮磷去除效果关系密切。故以溶解氧为媒介,研究不同时间尺度下沟渠湿地氮磷去除效果的变化特征及其机理。本文以两处沟渠湿地(澳大利亚西澳大利亚州珀斯市Anvil沟渠湿地和中国巢湖流域东湾圩沟渠湿地)为研究对象,长期监测环境因素、溶解氧浓度(高频)和氮磷浓度,识别多时间尺度下溶解氧和氮磷去除效果的主要影响因素;构建模型阐明溶解氧和氮磷去除效果的变化机理;在此基础上调控溶解氧以提高沟渠湿地氮磷去除效果,并应用于巢湖典型圩区。本文主要研究内容和结论如下:(1)基于长系列高频溶解氧浓度,研究日尺度、降雨时间尺度、季节尺度和年尺度下溶解氧变化特征和影响因素,分析溶解氧浓度、产耗氧过程和环境因素之间的相互关系,揭示环境因素对溶解氧浓度的影响途径。研究结果表明,日尺度下Anvil沟渠湿地和东湾圩沟渠湿地溶解氧浓度昼夜变化明显,主要影响因素为光合有效辐射。降雨时间尺度下溶解氧浓度昼夜变化特征消失,主要影响因素为流量。季节上Anvil沟渠湿地溶解氧浓度夏季低,冬季高,主要影响因素为水温;东湾圩沟渠湿地溶解氧浓度夏季高,冬季低,主要影响因素为流量。年际变化上沟渠湿地溶解氧浓度差异较小。溶解氧浓度、产耗氧和环境因素之间的两两关系表明光合有效辐射通过湿地总产氧影响溶解氧浓度。(2)建立适用于沟渠湿地的水动力水生态模型,模拟了降雨引起的产耗氧过程变化,比较了非降雨期和降雨期主要产耗氧过程,揭示了降雨对溶解氧的影响机理。非降雨期Anvil沟渠湿地和东湾圩沟渠湿地溶解氧主要来源分别为底栖植物产氧(34%)和浮游植物产氧(60%),揭示了日尺度下溶解氧昼夜变化的原因,两处沟渠湿地溶解氧主要消耗均为底泥耗氧(90%和55%);降雨期两处沟渠湿地溶解氧主要来源和消耗为溶解氧流入(94%和99%)和流出(68%和94%),揭示了降雨时间尺度下溶解氧浓度主要影响因素为流量的原因。(3)基于长系列的氮磷浓度,比较日尺度、降雨时间尺度、季节尺度和年尺度下氮磷去除效果,发现氮磷去除效果的变化主要表现在日尺度和降雨时间尺度上。Anvil沟渠湿地日尺度下氮磷浓度去除率大于降雨时间尺度,东湾圩沟渠湿地日尺度下氮磷浓度去除率与降雨时间尺度无显著性差异,两处沟渠湿地的差异是因为两者的功能略微不同。日尺度下氮去除效果的影响因素排序为:氮浓度和质量负荷>化学环境因素>水力因素,磷去除效果主要影响因素为化学环境因素;降雨时间尺度下氮去除效果的影响因素排序为氮浓度和质量负荷>水力因素>化学环境因素,磷去除效果的主要影响因素为进口磷浓度。(4)现有水生态模型因模拟步长大和模型过于简化,忽略了降雨引起的氮磷转化过程变化,难以在机理上说明降雨对氮磷去除效果的影响。因此,基于高频率溶解氧数据,构建溶解氧与氮磷转化过程联动的水生态模型,模拟降雨引起的氮磷转化过程变化,比较非降雨期和降雨期氮磷主要转化过程,揭示降雨对氮磷去除效果的影响机理。非降雨期Anvil沟渠湿地氮主要转化过程为底泥释放氨氮、硝化和反硝化,磷主要转化过程为颗粒磷沉降;东湾圩沟渠湿地氮主要转化过程为氨氮和有机氮的流入和反硝化,磷主要转化过程为颗粒磷沉降。降雨期两处沟渠湿地氮磷主要转化过程为各种形态氮磷的流入和流出。非降雨期和降雨期两处沟渠湿地氮磷主要转化过程的差异是降雨引起的氮磷去除效果变化的原因。(5)在东湾圩沟渠湿地上采用模型模拟和试验验证的方法优选了溶解氧调控模式。研究结果表明:溶解氧最佳调控模式是溶解氧浓度为8.00 mg/L,增氧时间与非增氧时间之比约为1:1,调控周期须等于湿地停留时间;在此模式下,总氮浓度去除率从3.9%提高到23.2%。调控溶解氧使氮去除效果达到最佳的关键是硝化通量与反硝化通量接近。调控溶解氧不能提高总磷去除效果。(6)目前圩区利用水循环治理面源污染的方案仅强调沟和塘的重复使用,未考虑沟或塘本身去除能力有限和两者的协同运用,可能会导致面源污染治理效果不佳。结合本文上述研究成果,提出了调控溶解氧-沟塘协同治理面源污染的技术方案。针对东湾圩具体地形,首先研究水塘增氧/不增氧、沟渠和水塘连接流量和支沟选择对氮去除效果的影响规律;然后确定调控溶解氧-沟塘协同治理面源污染的具体应用方案。研究结果表明,水塘增氧后沟渠湿地在长度方向上形成了溶解氧浓度梯度分布;流量为0.04-0.20 m~3/s时水塘增氧后总氮浓度去除率从19.5%增至33.7%。支沟进口距泵站的距离越长,总氮浓度去除率越大。巢湖典型圩区治理面源污染的技术方案为:利用水稻烤田期处理水塘存储的水,流量为0.124 m~3/s,选择东十一支沟、东十支沟、西十一支沟或西十支沟承接水塘出水,水塘增氧后沟渠总氮浓度去除率从18.0%提升至28.8%。更多还原

【Abstract】 In recent years,Chinese Government have issued multiple plans for the control of agricultural non-point source pollution,indicating that there is still a long way to go for control of agricultural non-point source pollution in China.When ditch wetlands are used to treat non-point source pollution,continuous,stable,and good removal performance is needed to improve water quality.However,changes in environmental factors at different time scales lead to large-scale changes in removal performance of nitrogen and phosphorus in ditch wetlands.Dissolved oxygen(DO)in ditch wetlands is not only sensitive to changes in environmental factors and is also closely related to removal performance of nitrogen and phosphorus.Therefore,DO is used as a medium to reveval variation features and mechanism of removal performance of nitrogen and phosphorus in ditch wetlands at different time scales.This paper take two ditch wetlands as examples(the Anvil ditch wetland located in Perth,Western Australia,Australia and the Dongwanwei Ditch Wetland located in Dongwan Polder,Chaohu Lake Basin,China),monitor environmental factors,DO(high frequency),nitrogen and phosphorus concentration for long period,select factors affecting DO and removal performance of nitrogen and phosphorus at multi-time scales;construct an ecological model to elucidate the mechanism of change in DO and nitrogen and phosphorus removal,and regulate DO to improve removal performance of nitrogen and phosphorus in ditch wetlands,finally apply it to polders in Chaohu Lake Basin.The main content and results of this paper are as follows:(1)Based on high-frequency DO concentrations for long period,the characteristics and influencing factors of DO at daily scale,rainfall time scale,seasonal scale and annual scale are studied.The relationship among DO concentration,oxygen production and consumption and environmental factors is studied to reveal influence path of environmental factors on DO concentration.The results show that at the diurnal scale,DO concentration in the two ditch wetlands had a typical diurnal variation,and the main influencing factor was photosynthetically active radiation(PAR).At the rainfall time scale,diurnal variation of DO concentration in the Anvil and Dongwanwei Ditch Wetlands disappeared,and the main influencing factor was flow.At a seasonal scale,the DO concentration in the Anvil Ditch Wetland is low in summer and high in winter and the main influencing factor is water temperature;the DO concentration in the Dongwanwei Ditch Wetland is high in summer and low in winter and the main influencing factor is flow.The interannual difference in DO concentration in the two ditch wetlands is small.The mutual relationship between DO concentration,oxygen production and consumption,and environmental factors shows that PAR affects DO concentration through the oxygen production of wetlands.(2)An ecological model suitable for ditch wetlands was established to model changes in the oxygen production and consumption caused by rainfall.The oxygen production and consumption between non-rainfall and rainfall periods were compared to study the effect mechanism of rainfall on DO concentration.During the non-rainfall period,the main process of DO in the Anvil Ditch Wetland and Dongwanwei Ditch Wetland was the oxygen production by benthic plants(34%)and by phytoplankton(60%),respectively,which explains the diurnal variation of DO.The main consumption process is sediment oxygen demand(90%and 55%).During the rainfall period,the main production and consumption processes of DO in the two ditch wetlands were the inflow(94%and 99%)and outflow(68%and 94%)of DO,which explain the high correlation between DO concentration and flow at the corresponding time scale.(3)Based on meansured nitrogen and phosphorus concentrations for long time,removal performance of nitrogen and phosphorus and its influencing factors in ditch wetlands were analyzed at multiple time scales.The comparison of removal performance of nitrogen and phosphorus at daily,rainfall time,seasonal and annual scales showed that changes in removal performance of nitrogen and phosphorus mainly occurred at the daily scale and rainfall time scale.In Anvil Ditch Wetland,the removal performance of nitrogen and phosphorus at the daily scale is greater than that at the rainfall time scale.In Dongwanwei Ditch Wetland,there was no significant difference in removal performance of nitrogen and phosphorus between the daily scale and rainfall time scale.The difference between the two ditch wetlands is due to their slightly different functions.At the daily scale,the order of factors influencing nitrogen removal performance is nitrogen concentration and mass loading>chemical environmental factors>hydraulic factors;The main factors influencing phosphorus removal performance are chemical environmental factors.At rainfall time scale,the order of factors influencing nitrogen removal performance is nitrogen concentration and mass loading>hydraulic factors>Chemical environmental factors;the main factor influencing phosphorus removal performance is phosphorus concentration.(4)Due to large simulation step and the oversimplification of previous ecological model,the change of nitrogen and phosphorus transformation caused by rainfall is ignored,and therefore the effect mechanism of rainfall on removal performance of nitrogen and phosphorus remain unsolved.Therefore,based on the high-frequency DO data,an ecological model with the linkage between DO and nitrogen and phosphorus transformation processes were established to model changes in the nitrogen and phosphorus transformation caused by rainfall.The main nitrogen and phosphorus transformation pathways between non-rainfall and rainfall periods are compared to reveal the effect mechanism of rainfall on removal performance of nitrogen and phosphorus.During the non-rainfall period,the main transformation pathways of nitrogen in Anvil Ditch Wetland are the release of ammonia nitrogen from sediment,nitrification,and denitrification;and the main transformation pathway of phosphorus is the sedimentation of particulate phosphorus.In Dongwanwei Ditch Wetland,the main transformation pathways of nitrogen are the inflow of ammonia and organic nitrogen,and denitrification;the main transformation pathway of phosphorus is the sedimentation of particulate phosphorus.During the rainfall period,the main transformation process of nitrogen and phosphorus in the two ditch wetlands is the inflow and outflow of various forms of nitrogen and phosphorus.The changes in the main transformation pathways of nitrogen and phosphorus in the two ditch wetlands explained the change in removal performance of nitrogen and phosphorus between the non-rainfall and rainfall period.(5)In Dongwanwei Ditch Wetland,Model simulation and experimental verification are used to optimize the DO regulation pattern.The optimal DO regulation pattern is that the DO concentration is 8.00 mg/L;the ratio of oxygenation time to non-oxygenation time is about 1:1,and aeration cycle period is equal to residence time of wetlands.Under this pattern,nitrogen removal performance increased from 3.9%to23.2%.The key to regulating DO to achieve optimal nitrogen removal performance is that nitrification flux is close to denitrification flux.DO regulation can not improve total phosphorus removal performance.(6)The previous approach of polder water cycle to treating non-point source pollution emphasizes the repeated use of ditches and ponds,and ignore the insufficient removal capacity of ditches and ponds and their synergistic use,which may lead to poor performance of non-point source pollution control.Based on previous research results in this paper,the scheme of regulating DO to make ditches and ponds synergistically treat drainage is proposed.Based on the specific topography of Dongwanwei Polder,first study the influence of pond aeration/non-aeration,ditches and pond connection flow,and branch ditch selection on nitrogen removal performance,and then determine the specific application plan.The results showed that when the pond is aerated,the gradient distribution of DO concentration is formed longitudinally in ditch wetlands.Nitrogen removal performance increased from 19.5%to 33.7%when the flow rate was0.04-0.20 m~3/s.The longer the distance between branch ditch inlet and pump station,the greater nitrogen removal performance.The specific plan for regulation of DO to make ditches and ponds synergistically treat non-point pollution in Chaohu Lake polder area is as follows.The drainage stored in the pond is treated during the drying period of paddy and the flow rate is 0.124 m~3/s.Choose branch ditches symbolled as D11,D10,X11,and X10 to receive water from the pond.Under this scheme,the nitrogen removal performance of ditch wetlands increased from 18.0%to 28.8%when ponds are aerated.更多还原