Characteristics of surface flow and interflow and nitrogen loss in Quercus acutissima forest land under simulated rainfall

To explore the mechanism of runoff and loss of nitrogen in artificial forest surface flow and interflow, the typical Quercus acutissima forest in a hilly area of middle southern Shandong Province was evaluated as the research object. Simulated artificial rainfall experiments were carried out to examine the characteristics of runoff and nitrogen loss in Q. acutissima forest land and grassland. The results showed the following:(1) The total flow, surface flow, and interflow in the Q. acutissima forest land were 80.5%, 61.4%, and 162.2% of that in grassland, respectively. The surface flow process tended to increase and then were stable. The interflow generation time clearly lagged behind the surface flow, and the runoff fluctuation of interflow was relatively smaller and more stable than that of surface flow. The relationship between the logarithm function and polynomial function was determined from the surface flow and interflow and rainfall time.(2) The total nitrogen output density, total nitrogen output density of surface flow, and total nitrogen output density of interflow in the Q. acutissima forest land were 11.5, 13.1, and 8.9 mg/L, which were 19.0%, 13.8%, and 8.2% lower than those of grassland, respectively. The output density of nitrogen through surface flow was high at the initial time but was generally stable as simulated rainfall continued. The output density of nitrogen through interflow remained relatively stable throughout the runoff process. The concentration of runoff and total nitrogen loss in surface flow and interflow revealed a relationship between the power function and polynomial function.(3) Throughout the simulated rainfall process, the surface flow in Q. acutissima forest land and grassland accounted for 61.8% and 81.1% of the total runoff, respectively. Total nitrogen loss from the surface flow in Q. acutissima forest land and grassland accounted for 70.4% and 87.0% of the total nitrogen loss, respectively, and the runoff and nitrogen losses from the surface flow accounted for a high proportion. Compared to grassland, the Q. acutissima forest land showed significantly increased interflow and decreased surface flow and nitrogen loss.