Interflow pattern govern nitrogen loss from tea orchard slopes in response to rainfall pattern in Three Gorges Reservoir Area

Nitrogen loss from tea orchards in the Three Gorges Reservoir Area (TGRA) will increase the risk of eutrophication in reservoir surrounding bodies of water. However, runoff and nitrogen loss from tea orchard slopes in response to rainstorm patterns have been rarely reported，especially on the interflow process. The study was conducted using simulated slopes containing soil collected from the slopes of tea orchards in the Lanlingxi watershed of the TGRA. Rainfall runoff processes were then monitored and recorded for three typical rainstorms (similar total rainfall volumes) in 2019 rainy season: rainfall concentrated towards the middle stage(MR), latter stage(LR) and early stage(ER) of the rainstorm. Results revealed that: (1) runoff and soil nitrogen loss characteristics differed significantly among these three rainstorm patterns, among which the ER rainstorm had the greatest runoff amount (58.45 L，83.06% and 54.38% higher than MR and LR, respectively), the greatest nitrogen loss load (623.99 kg·km−2，92.92% and 95.71% higher than MR and LR, respectively) and the greatest interflow proportion to total runoff (76.00%); (2) interflow is the primary process governing nitrogen loss in tea orchard slopes during rainstorms, more than 90% of the total nitrogen (TN) was lost with the interflow, and the nitrate nitrogen loss in the interflow accounted for more than 50% of the TN. (3) the nitrogen loss process differed significantly among the three rainfall patterns under rainstorm events, but the nitrogen loss load was mainly concentrated in the first half of the interflow. As such, reducing or delaying interflow generation or intercepting and collecting it during the interflow generation stage may better cope with the loss of soil nutrients under rainstorm or even extreme rainstorm events, lowering the risk of eutrophication for surrounding bodies of water.