Effects of woodland slope on heavy metal migration via surface runoff, interflow, and sediments and associated potential ecological risks following the application of sewage sludge

Abstract

Abstract The application of sewage sludge (SS) to woodland is an effective approach for the disposal and utilization of SS. However, the woodland slope may determine the risk of heavy metal (HM) migration via runoff. We conducted indoor rainfall simulations and natural rainfall experiments to clarify the effect of slope on the migration of HMs via runoff (including surface and interflow) and sediments. In the simulated rainfall experiment, HMs lost via sediments increased by 9.79–27.28% when the slope increased from 5° to 25°. However, in the natural rainfall experiment, when the slope of forested land increased from 7° to 23°, HMs lost via surface runoff increased by 2.38% to 6.13%. It revealed that the surface runoff water on a high slope (25°) posed high water quality pollution risks. The migration of HMs via surface runoff water or interflow increased as the steepness of the slope increased. The total migration of Cu, Zn, Pb, Ni, Cr and Cd via sediment greatly exceeded that via surface runoff and interflow. Particles ≤0.05 mm contributed the most to the ecological risks posed by sediments. Cd was the main source of potential ecological risks in sediments under both experimental conditions.