Effect of fire on runoff quality in forest watersheds (Case study: Kheyrud educational and research forest)

Forest fires can have a significant impact on water quality, especially in basins that provide drinking water. To investigate the effects of low, medium and high intensities of prescribed fire on runoff quality, 12 runoff plots were established in Kheyrud educational and research forest, north of Iran. In the first rainfall event after fire, six and 12 months after the fire, runoff samples were collected and transferred to the laboratory. Qualitative characteristics of the runoff were pH, electrical conductivity (EC), total suspended solids (TSS), total soluble solids (TDS) and total hardness (TH). The results showed that all the quality characteristics of the runoff after the fire increased compared to the control plots, but the differences among them were not significant. Most of these characteristics were in the high fire intensity, but as time passed after the fire, they had had a declining trend. The time elapsed after the fire had a significant effect only on TSS and TH. TSS values after six months and pH values after one year at low and medium fire intensities reached the level of control plots. TDS values immediately in the first event of precipitation in control, low, medium and high intensities were 22, 46, 53 and 78 mg/l, respectively. After one year, the values were 25, 36, 41 and 44 mg, respectively. Fire causes changes in the quality characteristics of runoff, element loss and reduced soil fertility. In order to reduce soil degradation, forest soil management measures after fire are necessary.