Effect of soil surface disturbance on overland flow, sediment yield, and nutrient loss in a hyrcanian deciduous forest stand in Iran

Abstract

Disturbance of forest watersheds has numerous effects on up and downstream environments, including erosion and reduction in productivity in disturbed areas, removal of nutrients, and deposition of pollutants on the land surface by runoff contamination of water resources. Little research has been conducted on forest ecosystems despite the environmental problems induced by nutrient transport. Therefore, the present study was conducted to quantitatively compare sediment yield, surface runoff, and nutrient and organic matter (OM) loss from undisturbed and disturbed forest areas during rain events in the Research and Educational Forest Watershed of Tarbiat Modares University in northern Iran. The study involved two treatments with three replications using 6-m2 plots. Results verified the significant effects of forest degradation (P < 0.05) on hydrological components and nutrient and OM loss. The surface runoff volume, runoff coefficient, sediment concentration, and sediment yield from plots located in the disturbed forest area were 5, 7, 5.5, and 18 times more, respectively than those measured in the undisturbed area. Also, the loss of carbon, nitrogen, phosphorus, and potassium in the disturbed area was more than in the undisturbed forest by 5, 10, 16, and 19 times. The maximum rate of loss of nutrients was 25 kg.ha−1. Enrichment ratios for carbon, nitrogen, phosphorus and potassium in the undisturbed area were 1.38 ± 0.33, 1.13 ± 0.11, 0.25 ± 1.86 and 1.24 ± 0.20, respectively, and 0.36 ± 1.59, 0.37 ± 1.57, 0.22 ± 1.98 and 0.29 ± 1.008, respectively, in the disturbed area. The study results should be applied to improve the management of Iranian forest ecosystems.