多重干湿交替下雨水生物滤池氮素迁移转化特性与淋失机理研究

One of the most promising urban stormwater management practices is biofilters, a technology that has demonstrated good performance for controlling polluted stormwater discharges and improving watershed hydrologic characteristics by reducing peak flows towards predevelopment conditions. But under multiple drying-rewetting alternation caused by climatic change, nitrogen is prone to leaching. As a result, it can bring a serious threat to water ecological sensitive area of urban river systems. Unfortunately, recent studies, focusing on optimization of nitrogen removal performance in biofilters, are mainly on the base of single alternation of drying and rewetting, the results of which can lead to the failure of expected functions and lack of resilience in adapting to the challenges of changing climatic condition. Meanwhile, nitrogen leaching mechanism and its characteristics of transport and transformation in biofilters under multiple drying-rewetting cycles remain unclear. Based on this fact, nitrogen in multimedia consisting of plants, soil, and microbes is chosen as a research object. Firstly, the contribution of multimedia to the fate and transport of nitrogen is quantitatively identified with isotope tracer technique, and then coupling response relationship between nitrogen process and environmental factors is analyzed. Secondly, migration pathways and flux of nitrogen in functional microbial communities are determined with the aid of stable isotope probing (DNA-SIP). Based on above discussions, the project maps the flux diagram for fate and transport path of nitrogen, assesses the potentiality of nitrogen leaching flux, and establishes the mechanism for nitrogen leaching. This research has great scientific guiding significance of improving the adaptability of biofilters to the change of climatic condition as well as practical significance for realizing the sustainable management of urban stormwater in China.

雨水生物滤池已广泛应用于城市雨水管理实践中，具有水文削峰和污染物控制双重效应。但在气候变化形成的多重干湿交替条件下，雨水生物滤池易出现氮素淋失问题，对城市水生态敏感区造成严重威胁。目前对除氮性能方面的优化研究主要基于单一干湿交替条件，可能导致雨水生物滤池无法达到预期功能，且在适应气候变化上缺乏弹性。关于多重干湿交替下氮素迁移转化特性与淋失机理尚不明确。本项目拟以雨水生物滤池多介质（植物-土壤-微生物）中的氮素为研究对象，利用同位素示踪技术量化多介质对氮素转化与归趋的贡献，并揭示氮素过程与环境因素的耦合响应关系；借助稳定同位素探针（DNA-SIP）技术探明氮素在功能微生物中的运移路径与通量；在此基础上，绘制氮素转化路径与归趋通量图，评估氮素淋失潜势，并阐释氮素淋失机理。研究成果不仅对于提高雨水生物滤池适应气候变化能力具有重要的科学指导意义，对于实现我国城市雨水可持续管理也具有重要的现实意义。

雨水生物滤池（SWBF），亦称生物滞留系统，是一种集水文削峰和污染物控制双重效应的城市雨水管理措施，但关于多重干湿交替下氮素迁移转化特性与淋失机理尚不明确。项目以明确不同干湿交替下氮素过程为目标，系统考察了不同前期干旱天数（ADD）下SWBF除氮性能，探讨了含氮污染物在空间和时间尺度上的迁移、转化与赋存累积特性，并借助于宏基因组学等技术探明环境因素对微生物种群结构及氮代谢通路的影响规律，得到如下结论：.（1）SWBF对氨氮的去除受ADD影响不显著，而主要受填料水力渗透性能和植物生长状况的影响，其平均去除率均能达到70%以上。系统对硝氮和TN的去除受ADD影响较大，较长的ADD（7、12和22d）不利于硝氮和TN的去除。系统对TN的去除能力取决于硝氮的去除，且除氮过程受淹没层含水率所调控，而硝氮可通过淹没层中NaR、NiR和HyR的次第催化还原作用发生DNRA，进而影响系统对氨氮的去除能力。.（2）输入性氮素主要被表层土（0-10cm）部分截留，但过长ADD（12d和22d）将促进氮的氨化作用。氮素主要累积于茎部位，其累积量受ADD影响，植物对氮的吸收固持能力受根系体积控制。氮素在土壤介质中的累积主要发生在种植层，并随ADD增加而呈递减趋势。同位素示踪表明，不同形态氮在多介质中的即时转化路径和分配比例受ADD影响而存在较大差异，且长时间干旱易发生硝态氮淋失。.（3）干湿交替改变了SWBF细菌的多样性，且细菌群落结构受季节、土壤空间和ADD而呈现较大差异；同时，AOB、nirK和 nirS基因丰度受季节和土壤空间影响，并随ADD增加呈现降低的趋势。代谢通路分析表明，变化干湿交替时由于反硝化占比较低，使得大部分硝氮随水流流出系统，发生淋失现象。.研究成果识别了氮素发生淋失的环境条件，阐明了淋洗机理，并提出了基于干旱期含水率调控的氮素淋失防控理念，为提高SWBF适应气候变化的能力提供了理论支撑。