Impacts of oak deforestation and rainfed cultivation on soil redistribution processes across hillslopes using 137Cs techniques

Abstract

Background As one of the main components of land-use change, deforestation is considered the greatest threat to global environmental diversity with possible irreversible environmental consequences. Specifically, one example could be the impacts of land-use changes from oak forests into agricultural ecosystems, which may have detrimental impacts on soil mobilization across hillslopes. However, to date, scarce studies are assessing these impacts at different slope positions and soil depths, shedding light on key geomorphological processes. Methods In this research, the Caesium-137 ( 137 Cs) technique was applied to evaluate soil redistribution and soil erosion rates due to the effects of these above-mentioned land-use changes. To achieve this goal, we select a representative area in the Lordegan district, central Iran. 137 Cs depth distribution profiles were established in four different hillslope positions after converting natural oak forests to rainfed farming. In each hillslope, soil samples from three depths (0–10, 10–20, and 20–50\u2009cm) and in four different slope positions (summit, shoulder, backslope, and footslope) were taken in three transects of about 20\u2009m away from each other. The activity of 137 Cs was determined in all the soil samples (72 soil samples) by a gamma spectrometer. In addition, some physicochemical properties and the magnetic susceptibility (MS) of soil samples were measured. Results Erosion rates reached 51.1\u2009t·ha −\u20091 ·yr −\u20091 in rainfed farming, whereas in the natural forest, the erosion rate was 9.3\u2009t·ha −\u20091 ·yr −\u20091 . Magnetic susceptibility was considerably lower in the cultivated land ( χ hf = 43.5\u2009×\u200910 −\u20098 \u2009m 3 ·kg −\u20091 ) than in the natural forest ( χ hf = 55.1\u2009×\u200910 −\u20098 \u2009m 3 ·kg −\u20091 ). The lower soil erosion rate in the natural forest land indicated significantly higher MS in all landform positions except at the summit one, compared to that in the rainfed farming land. The shoulder and summit positions were the most erodible hillslope positions in the natural forest and rainfed farming, respectively. Conclusions We concluded that land-use change and hillslope positions played a key role in eroding the surface soils in this area. Moreover, land management can influence soil erosion intensity and may both mitigate and amplify soil loss.