Shallow Landslide Accelerates Soil Carbon and Nitrogen Loss by Facilitating Sediment Production in Steep Gully‐Slope Under Extreme Rainfall

Abstract To mitigate the nutrient loss driven by shallow landslides under extreme rainfall, it is imperative to study the primary pathways of nutrient loss associated with runoff and sediment. Reducing such nutrient loss is critical to maintain gully‐slope soil fertility and prevent downstream water eutrophication. We conducted seven simulations of extreme rainfall where 270 mm of cumulative rain was applied at a constant 60 mm·h −1 intensity over seven 20 × 2.5 m plots on a gully‐slope in China's Loess Plateau with an approximate gradient of 35° and over 70% grass coverage. The impacts of landslides on runoff, sediment, soil carbon and nitrogen loss were explored in three plots with landslides (SL), using three plots without landslides as controls (CK). Landslides elevated runoff, sediment, organic carbon (OC) and total nitrogen (TN) losses by factors of 2.4, 21.3, 14.1 and 14.1 compared to CK plots, respectively. Landslides caused discontinuity and abruptness in the runoff‐sediment relationship, impacting sediment transport rates more than runoff rates. Landslides reduced the contribution of dissolved organic carbon in runoff to OC and dissolved total nitrogen in runoff to TN losses. 98% of OC and 93% of TN losses were attributed to sediment‐bound forms. Landslides weakened the correlation between the runoff rate and the loss rates of OC and TN, but the correlation between the sediment transport rate and the loss rates of OC and TN remained relatively unaffected. Our study established nutrient loss equations based on runoff and sediment ( P < 0.01). Landslides enhance soil carbon and nitrogen loss through increased sediment production. The results offer a scientific basis for soil and water conservation, and carbon‐nitrogen source‐sink management in gully‐slope of ecologically sensitive regions.