Effects of rainfall intensity and slope gradients on total carbon, nitrogen, and phosphorus lateral transport under simulated extraordinary rainstorm

Abstract

The aim of this research was to study the characteristics and influence of the lateral transport of total carbon (TC), total nitrogen (TN), and total phosphorus (TP) under different slope gradients (5°, 8°, 15°, 25°) caused by extraordinary rainstorms (90 mm h⁻¹, 120 mm h⁻¹, 150 mm h⁻¹) on a decomposed granite soil in the Zhejiang-Fujian hilly region. Rainfall induced runoff (RIR) contains overland flow (OF) and interflow (IF). Results show that with the increase of runoff time and runoff volume, TN and TP mass concentrations decrease rapidly; however, TC mass concentration increases with the increase of runoff volume in IF. TC mass concentrations greater than 55 mg L⁻¹ are distributed in areas with IF volume more than 5,100 mL. Meanwhile, a marginal effect of TC, TN, and TP increments appeared when examining TC, TN, and TP cumulative loss amounts in RIR; the inflection points appeared at the end of rainfall event. A simple stoichiometry was applied. Simulated rainfall reduced the C: N ratio with a range from 6.68 to 5.98 while increasing the C:P and N:P ratios when rainfall intensity was 120 or 150 mm h⁻¹. Sediment is the main carrier for C lateral transport. We also noted that the gross amount of TC loss in RIR accounted for more than 10%. The loss of TC with runoff cannot be ignored. Our research enriches slope land hydrology research under extraordinary rainstorm conditions and provides a basis for the effective control of TC, TN, and TP loss in the decomposed granite soil area of China and globally.