外源输入对湖泊疏浚新生表层界面回复过程及氮平衡的影响

The control effect of sediment dredging on internal nitrogen loading in lakes is still unclear, and the influence of the external input on the interface recovery process and the nitrogen balance at the interface of the new born surface after sediment dredging is also unclear. In view of the relatively complex problems of transfer process and the trend of nitrogen in water environment, the estuary area and non estuary area in Meiliang Bay, an eutrophied bay in Taihu Lake, are selected as our research object. We use both simulation study in the laboratory and track monitoring in the field, and also utilize various experimental techniques such as continuous flow incubation, high resolution interface micro probe, N-15 tracer, membrane-inlet mass spectrometry analysis (MIMS), and Rhizon pore-water active sampling, to study the effect of lake dredging on nitrogen mineraliztion and nitrogen fixation, denitrification and anaerobic ammonium oxidation at the sediment-water interface with or without external particle sedimentation and sewage input, and to identify the influence of external source input on the recovery process and nitrogen balance at the sediment-water interface of new born sediment layer. The purpose of this project is to give comprehensive evaluation of the effect of sediment dredging on internal nitrogen loading according to the rough budgets constructed for the nitrogen balance, and further to provide scientific basis for the decision making of the dredging project of eutrophic lakes and the external source control on the river basin.

底泥疏浚对内源氮负荷的控制效应仍不明确，底泥疏浚后外源输入对疏浚新生表层界面回复过程及氮平衡产生何种影响还不清楚。针对氮在水环境中界面过程及归趋相对复杂的问题，本项目选择富营养化湖区-太湖梅梁湾河口区及非河口区为研究对象，采用室内疏浚模拟及疏浚湖区原位跟踪试验方法，应用连续流动培养、高精度界面微探针、N-15示踪、膜接口质谱（MIMS）分析及间隙水Rhizon法主动获取等技术，研究有无外源颗粒物沉降或污水输入情况下，湖泊疏浚对沉积物-水界面氮的矿化、氮固定、反硝化及厌氧氨氧化过程的影响，揭示外源输入对疏浚后新生表层界面回复过程及氮平衡的影响，并根据构建的沉积物-水界面氮收支综合评价底泥疏浚对内源氮负荷的控制效应，为富营养化湖泊疏浚工程的决策及疏浚后流域尺度上外源控制提供科学理论依据。

底泥环保疏浚是控制内源氮污染的重要途径之一，但由于外源颗粒物的不断沉降，疏浚对内源氮负荷的控制效果尚不明确，当前尚缺乏基于沉积物-水界面氮收支的新视角系统综合地评估底泥疏浚对内源氮负荷的控制效应。本项目选取富营养化湖区-太湖梅梁湾重污染沉积物为研究对象，采用模拟疏浚及湖泊原位培养试验方法，应用连续流动培养、高精度界面微探针、N-15示踪、膜接口质谱（MIMS）分析及间隙水HR-Peeper被动获取等技术，研究有无外源颗粒物沉降或污水输入情况下，湖泊疏浚对沉积物-水界面氮的矿化、氮固定、反硝化及厌氧氨氧化过程的影响，揭示外源输入对疏浚后新生表层界面回复过程及氮平衡的影响，并根据构建的沉积物-水界面氮收支模型综合评价底泥疏浚对内源氮负荷的控制效应。.研究结果表明：疏浚后表层沉积物中有机质（LOI）、TN、NH4+-N和NO3—-N都有所降低，在SP的作用下疏浚后表层沉积物的TN、NH4+-N和NO3—-N逐渐回复甚至会超过未疏浚前的状态。疏浚后沉积物微生物活性及功能多样性降低，颗粒物的沉降能够促使沉积物微生物性质的回复。疏浚后NH4+-N全年保持较低的释放速率，疏浚后在SP的作用下NH4+-N释放速率逐渐回复。疏浚后沉积物-水界面（SWI）处反硝化、厌氧氨氧化及固定速率显著降低（p<0.05），而颗粒物的不断沉降能够导致这些氮循环过程的逐渐回复。沉积物-水界面氮损失主要来源于无机氮扩散，占比68.5%；其次是反硝化脱氮过程，占比25.5%；厌氧氨氧化过程仅占6.0%。疏浚使得沉积物-水界面无机氮扩散速率降低，而微生物脱氮过程造成的沉积物氮损失占比升高。对整个太湖梅梁湾而言，无SP沉降时疏浚后较未疏浚沉积物氮损失减少了1304.1t，有SP沉降时疏浚后较未疏浚沉积物氮损失减少了3272.6t。疏浚可以减少沉积物的内源释放，表现为正向效应；另一方面疏浚导致微生物脱氮速率下降，从而潜在地增加了沉积物氮负荷，表现为负效应。本项目研究结果能够为富营养化湖泊疏浚工程的决策及疏浚后流域尺度上外源控制提供科学理论依据。