Role of underground leakage in soil, water and nutrient loss from a rock-mantled slope in the karst rocky desertification area

Leakage loss of soil and water is the main reason for karst rocky desertification, and the concomitant nutrient loss/leakage carried by soil and sediment is an important factor that affects groundwater quality. Due to the difficulty in measuring the underground leakage of soil water, the amount of nutrient loss/leakage on a karst slope is currently unknown. A karst slope farmland is simulated in a laboratory based on field investigations in slope farmlands in a karst plateau region in Guizhou Province, China. Rainfall experiments were conducted to determine the surface losses and underground leakages of soil, water, nitrogen, phosphorus, and potassium, as well as the effects of rainfall intensity and slope on these factors in karst slope farmlands. Surface runoff occurs only at rainfall intensities greater than 30 mm/h, but underground runoff occurs under all rainfall intensity conditions. Moreover, underground leakage loss is the main mode of water loss. Soil loss on a karst slope farmland is a process that transitions from underground leakage to surface erosion as the rainfall intensity increases. The concentrations of total nitrogen (TN), total phosphorus (TP), and total potassium (TIC) in surface runoff increase with increasing rainfall intensity and decrease with increasing slope gradient. The total loss loads of TN and TK in runoff and sediment increase with increasing rainfall intensity or slope gradient. The total nutrient loss loads of TN and TP are dominated by runoff losses, but the TK loss load is dominated by sediment losses.