Urea-nitrogen (N) is commonly applied to crop fields, yet it is not routinely monitored despite its association with reduced water quality and ability to increase toxicity of certain phytoplankton species. The purpose of this work was to characterize temporal fluctuations in urea-N concentrations and associated environmental conditions to infer sources of urea-N in agricultural drainage ditches. Physicochemical properties and N forms in ditch waters were measured weekly during the growing seasons of 2015 - 2018. Fertilizer application was only associated with spring peaks of urea-N concentrations in ditches next to cornfields; whereas, summer peaks in ditches adjacent to corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields were not associated with fertilizer applications. Environmental conditions of warmer temperatures, lower dissolved oxygen concentrations, and lower redox potentials were correlated with higher urea-N concentrations. In 2018, peaks of urea-N and ammonium-N during the summer co-occurred with peaks of dissolved organic N (DON) and total dissolved N (TDN), suggesting they might be associated with the breakdown of organic matter and turnover of the organic N pool. Although the highest urea-N concentrations occurred when ditch surface waters were hydrologically disconnected from nearby streams, heavy rainfalls can potentially flush accumulated urea-N into coastal waters where it may affect algal bloom toxicity. Therefore, implementation of available drainage ditch management practices is recommended, but these strategies need to be optimized for targeting periods with high rainfall that coincide with fertilizer additions, as well as for periods with low rainfall that promote stagnant water conditions. This article is protected by copyright. All rights reserved.

中文翻译：

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导致农业排水沟地表水中尿素氮积累的季节和时间因素

尿素氮 (N) 通常用于农田，尽管它与水质降低和增加某些浮游植物物种毒性的能力有关，但并未对其进行常规监测。这项工作的目的是表征尿素氮浓度和相关环境条件的时间波动，以推断农业排水沟中尿素氮的来源。在 2015 年至 2018 年的生长季节，每周测量沟水中的理化性质和氮形式。施肥仅与玉米田附近沟渠中尿素氮浓度的春季峰值有关；而玉米 (Zea mays L.) 和大豆 [Glycine max (L.) Merr.] 田附近沟渠的夏季高峰与施肥无关。温度较高的环境条件，较低的溶解氧浓度和较低的氧化还原电位与较高的尿素氮浓度相关。2018 年夏季尿素氮和铵态氮的峰值与溶解有机氮 (DON) 和总溶解氮 (TDN) 的峰值同时出现，表明它们可能与有机质分解和土壤周转有关。有机氮池。尽管当沟渠地表水与附近溪流在水文上断开时，尿素氮浓度最高，但强降雨可能会将积累的尿素氮冲入沿海水域，从而可能影响藻华毒性。因此，建议实施可用的排水沟管理实践，但这些策略需要针对与肥料添加同时出现的高降雨量的目标时段进行优化，以及降雨量低的时期，导致积水条件。本文受版权保护。版权所有。