亚热带农业小流域塘库水体氮磷化学计量特征的时空变异及其环境效应

A watershed is an effective geographic unit to control agricultural non-point source pollutions. Ponds and reservoirs are important water nodes for water storage and drainage in agricultural production process in subtropical regions of China. They are also sources and sinks for N and P pollutants, and hot zones which are are easily affected by human disturbance and environmental changes at the watershed scale. From the perspective of ecological stoichiometry, the spatio-temporal variability of stoichiometric characteristics of N and P and its driving mechanism are studied in the pond-reservoir systems in a subtropical agricultural watershed. .150 ponds and reservoirs are investigated under five different landscape types (woodland, tea plantation, cropland, settlement and the mixed) in the watershed. With long-run field observation and indoor cultivation experiments, the contents of N and P are determined for water body, suspended particulate matter and sediment in the ponds and reservoirs. The different chemical forms of N and P to be determined are dissolved, particulate, organic and inorganic forms in water body. The other water quality indexes, such as chlorophyll contents, dissolved oxygen contents, pH values are also observed with portable water quality analysis instruments. In order to explore the source of nitrogen, the abundances of nitrogen isotopes are analyzed in water, particles and sediment in pond-reservoir systems with 15N isotope tracing technology. The structures and diversity of microbial communities in samplers of water body, suspended particulate matter and sediment are explored across the different stoichiometric gradients of nitrogen and phosphorus with microbial 16S high flux sequencing. .With the above observed datasets from the pond-reservoir ecological systems, our goals include:.(1) Spatio-temporal variability of the contents of N and P and their stoichiometric characteristics in water bodies under different landscape features .(2) Effects of the changes of N and P stoichiometry on primary productivity and microbial community structure in water bodies ..(3) Do exogenous or endogenous factors affect the imbalance of N and P stoichiometry in water bodies?.(4) What are the key factors driving the variability of N and P contents and their stoichiometry in water bodies?.Our works will not only reveal environmental effects and the mechanism of N and P pollution in the watershed from the perspective of N and P circulation imbalance, but also provide scientific and technical support for the prevention and control of nitrogen and phosphorus pollution in subtropical agricultural watersheds, China.

作为我国亚热带农业生产中蓄水和供水的重要水利节点，池塘和水库（塘库）是容纳流域氮磷污染物的源/汇，也是易受流域人为扰动和环境变化影响的热区。本项目拟以亚热带典型农业小流域塘库为对象，通过野外定位观测、室内培养试验及微生物16S高通量测序等技术，研究不同景观环境下塘库生态系统水体氮磷化学计量特征的时空变化规律，研究塘库水体初级生产力和微生物群落结构对氮磷化学计量特征变化的响应机理；结合塘库水体氮磷收支和15N同位素示踪研究，探明是外源还是内源因子影响塘库氮磷化学计量特征变化；最后用空间关联、CCA及结构方程等统计技术分析塘库氮磷化学计量特征与景观类型、降雨事件、人为扰动、初级生产力及微生物群落结构和氮磷转化功能基因丰度等因子的关联性，提取引发塘库水体氮磷计量比失衡的主控因子。研究结果利于从氮磷化学计量比失衡的角度诠释流域氮磷污染的发生机理，也为亚热带流域氮磷污染防控提供可参考的技术理论。

池塘和水库（塘库）是易受人为扰动和环境变化影响的热区，理解塘库氮磷计量比变异规律利于塘库水体氮磷污染管控。本研究主要以亚热带典型农业源头流域塘库为研究对象，通过野外全生态观测试验、15N同位素溯源、微生物16S 高通量测序等技术手段，研究了塘库水体氮磷组份含量及其计量比的时空变异规律，探讨了塘库水体氮磷失衡的关键驱动因素及其环境效应，主要研究结果如下： . 1、从城市和农业小流域两个尺度上建立了野外塘库水质长期监测试验，近6年间（2017-2022）布设了213个塘库长期/短期定位监测点，监测了塘库水体/底泥氮磷组份、溶氧、pH、Chla、15N同位素、微生物群落和氮磷功能基因及温室气体等31个指标；构建了融合智能手机、无人机和视频监控为一体的塘库信息智能监管模型，可应用于村级小水体的全覆盖管理。. 2、探明了养鱼和农业土地利用是驱动塘库氮磷计量比失衡、影响塘库生态功能的关键因素。研究区2016年塘库面积比1990年增加22.2%，且80%以上塘库用于养鱼；塘库面积占比增加（>4.0%）抑制流域径流输出。受塘库养鱼和农业土地利用影响，受扰塘库水体氮磷积累失衡严重，TN:TP (24.6)显著低于未扰动塘库（72.1）；超过93%的受扰动塘库发生氮磷污染，且TN和TP含量分别超过下游把水口的24.2%、41.6%，塘库水体正成为流域下游氮磷污染的输出源。受扰动塘库水体中与疫病/寄生虫类相关的微生物群落、硝化和脱氮微生物功能基因和15N同位素丰度以及温室气体（CH4、N2O）排放通量增加，水体偏碱化，氨挥发加剧。 . 3、研究区塘库水体氮磷污染防控，控磷重于控氮；加强塘库周边农用地和生活污水的氮磷污染治理，开展塘库养鱼退出或生态治理，有望提升塘库水质的同时，实现温室气体CH4和N2O年减排分别达4.98 kg C ha−1和 0.42 kg N ha−1，减少年氨挥发1.77 kg N ha−1。

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