Agricultural runoff recycling systems are manmade aquatic ecosystems of growing significance to global water sustainability, crop health, and production. This study investigated the seasonal dynamics of microbial community in a three-reservoir recycling irrigation system with a stepwise water flow and compared with that of an adjacent runoff-free stream. Runoff water from all production areas was captured in a sedimentation reservoir which overflowed to a transition reservoir then retention reservoir through a culvert. Stream water was pumped to replenish the reservoirs as needed during growing seasons. 16S rDNA PCR clone libraries of quarterly water samples from three reservoirs and one stream were sequenced, and 575 operational taxonomic units (OTUs) were identified and assigned to cyanobacteria, eukaryotic phytoplankton, and other bacteria. When compared to the stream, three reservoirs consistently had low microbial diversity. A distinct seasonal pattern of microbial community structure was observed for each reservoir and the stream. Stream was consistently dominated by other bacteria. Retention reservoir was dominated by cyanobacteria during the summer and fall and eukaryotic phytoplankton during the winter and spring. Sedimentation reservoir was dominated by cyanobacteria beginning in the spring but that dominance was altered when water was pumped from the stream from early spring to fall seasons. Transition reservoir had the greatest shift of microbial community structure, being dominated by other bacteria in the summer, cyanobacteria in the fall, and eukaryotic phytoplankton in the winter and spring. Water temperature and ammonium level were the two most important contributing factors to the seasonality of microbial community in these reservoirs. The three recycling irrigation reservoirs consistently had lower microbial diversity and distinct community structure when compared to the stream. These reservoirs were typically dominated by cyanobacteria during warm seasons and eukaryotic phytoplankton during cool seasons. This seasonal pattern was altered when water was pumped from the stream. The cyanobacteria dominance was associated with rising water temperature and ammonium level. These results highlight the importance of preventing agricultural runoff from entering natural waterways and water resources and provide a useful framework for further investigations into the ecological processes of this emerging ecosystem.

中文翻译：

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多水库循环灌溉系统中蓝细菌和真核浮游植物的季节性动态

农业径流回收系统是人造水生生态系统，对全球水的可持续性，作物健康和生产具有日益重要的意义。这项研究调查了三水库循环灌溉系统中微生物群落的季节性动态，该系统具有逐步的水流，并与相邻的无径流水流进行了比较。来自所有生产区的径流水被收集到一个沉淀池中，该溢流溢流到过渡池，然后通过涵洞保留池。在生长季节，根据需要泵送溪流水以补充水库。对来自三个水库和一个水流的季度水样的16S rDNA PCR克隆文库进行了测序，并鉴定了575个操作分类单位（OTU），并将其分配给蓝细菌，真核浮游植物和其他细菌。与河流相比，三个水库始终具有较低的微生物多样性。对于每个水库和河流，微生物群落结构都有明显的季节性变化。流始终被其他细菌所控制。在夏季和秋季，留存库以蓝细菌为主，而在冬季和春季，则以真核浮游植物为主。从春季开始，沉淀池就以蓝细菌为主导，但是从早春到秋季从溪流中抽水时，优势度发生了变化。过渡水库的微生物群落结构变化最大，夏季以其他细菌为主，秋季以蓝细菌为主，冬季和春季以真核浮游植物为主。水温和铵水平是影响这些水库微生物群落季节性的两个最重要的因素。与溪流相比，三个循环灌溉水库始终具有较低的微生物多样性和独特的群落结构。这些水库通常在温暖季节主要由蓝细菌控制，而在寒冷季节主要由真核浮游植物控制。当从溪流中抽水时，这种季节性模式发生了变化。蓝细菌的优势与水温升高和铵水平升高有关。这些结果凸显了防止农业径流进入天然水道和水资源的重要性，并为进一步研究这一新兴生态系统的生态过程提供了有用的框架。