In agricultural areas with poorly drained soils, subsurface tile drains are commonly installed to improve drainage but also serve as conduits that deliver excess nutrients to adjacent streams. Our goal was to understand the transport of phosphorus (P) along these flow paths by applying a novel mixture of tracers (including 866 g of conservative chloride (Cl), 3.4 g of potassium phosphate, and approximately 3.6 × 10 fluorescent micrometer-sized particles, or 49.5 g) to a farm field and sampling their breakthrough curves at the outlet to a stream, approximately 30 m away. Simultaneously, we performed a 26-h time-lapse electrical resistivity tomography (ERT) survey to monitor the saline tracer migration in three dimensions every 0.5 to 1 h. The initial pulse of tracers had a mean arrival time of 21 min and transported 262 g of added Cl (28 %), 0.65 g of dissolved P (17 %), and 1.4 × 10 particles (4 %) to the tile drain outlet. A stochastic mobile-immobile model fit the anomalous (non-Fickian) solute breakthrough curves, where the mobile zone represents the macropore and tile drain network, and the immobile zone represents the soil matrix. Residence times in the immobile zone exhibited a heavy (power-law) tail. ERT images confirmed the retention of tracer mixture in soils after concentrations were no longer measurable at the tile drain outlet. Core samples suggest that 96 % of particles and 21 % of dissolved P were retained within 10.5 cm of the application location. Solutes and particles were remobilized over longer timescales during three successive storms. Exported masses of Cl and dissolved P at the tile drain outlet ranged from 1,490–12,300 g and 25.7–65.2 g, respectively, indicating flushing of older Cl and P stored in soils before the tracer experiment. Less than 0.01 % of the added fluorescent particles were flushed during these storm events. This study indicates the wide range of P travel times through the subsurface in tile drained landscapes and the need to incorporate non-Fickian transport behavior in models.

中文翻译：

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在瓷砖排水景观中地下磷从田地到溪流的大范围时间尺度迁移

在土壤排水不良的农业地区，通常安装地下瓷砖排水沟以改善排水，但也可作为将多余养分输送到邻近溪流的管道。我们的目标是通过应用新型示踪剂混合物（包括 866 克保守氯化物 (Cl)、3.4 克磷酸钾和大约 3.6 × 10 荧光微米尺寸颗粒）来了解磷 (P) 沿着这些流动路径的传输，或 49.5 g）到农田，并在大约 30 m 外的溪流出口处对其突破曲线进行采样。同时，我们进行了一次 26 小时的延时电阻率断层扫描 (ERT) 调查，每 0.5 至 1 小时监测一次盐水示踪剂的三维迁移。示踪剂的初始脉冲的平均到达时间为 21 分钟，并将 262 克添加的 Cl (28%)、0.65 克溶解的磷 (17%) 和 1.4 × 10 颗粒 (4%) 输送到瓷砖排水口。随机移动-固定模型拟合异常（非菲克）溶质突破曲线，其中移动区域代表大孔和瓦排水网络，固定区域代表土壤基质。不动区的停留时间呈现出沉重的（幂律）尾部。 ERT 图像证实了示踪剂混合物在瓷砖排水口不再可测量浓度后保留在土壤中。岩心样本表明，96% 的颗粒和 21% 的溶解磷保留在施药位置 10.5 厘米范围内。在连续三场风暴中，溶质和颗粒在较长的时间尺度内重新流动。瓷砖排水口输出的 Cl 和溶解 P 质量分别为 1,490-12,300 g 和 25.7-65.2 g，表明示踪剂实验前土壤中储存的旧 Cl 和 P 被冲刷掉。在这些风暴事件中，只有不到 0.01% 的添加荧光颗粒被冲走。这项研究表明，在瓦片排水景观中，P 通过地下的传播时间范围很广，并且需要在模型中纳入非菲克传输行为。