Using 137Cs and 210Pbex to trace soil erosion rates for a small catchment in the mid-hills of Nepal

Abstract

Purpose Soil erosion is a major threat to agricultural sustainability in the hills of Nepal. However, little is known about the soil erosion rates at a small catchment scale in this region. Materials and methods In this study, the soil redistribution rates in a typical small hilly catchment in the Ramechhap District of Nepal were evaluated using the 137 Cs and 210 Pb ex tracer techniques. Nine representative slopes under three land uses and a reference site from the gentle sloping forest land within the catchment were selected as sample plots. A downhill transect was built in each sample plot, and soil samples were collected at 5-m intervals along the transects. Results and discussion The results showed that the spatial variations in radionuclide inventory and soil erosion rates measured by 137 Cs measurements were highly consistent with equivalent estimates from 210 Pb ex measurements, suggesting the potential for using 137 Cs and 210 Pb ex measurements to estimate soil redistribution rates. All 137 Cs and 210 Pb ex inventories on the slopes were less than the reference values, indicating that net soil loss has occurred at all of the sampling points. The net erosion rates from sloping farmland (37.08 t ha −1 year −1) and shrub land (32.52 t ha −1 year −1) were significantly higher than those from forest land (14.91 t ha −1 year −1). Furthermore, the soil erosion rates obtained from 210 Pb ex measurements were higher than those obtained from 137 Cs measurements, which implies that soil erosion in the catchment was accelerated during the last two decades. The net soil loss from the study catchment was estimated to be 31.29 t ha −1 year −1 , which is mainly contributed by shrub land (55.08%) and sloping farmland (37.68%). Conclusions These results indicate that shrub land and sloping farmland are vulnerable to erosion, which should be specifically considered in the sustainable management of small agricultural catchments in the mid-hills of Nepal, especially in dry valley regions.

Spatial distribution of soil erosion and sediment yield in the Koshi River Basin, Nepal: a case study of Triyuga watershed

“…The gross annual SL of the watershed was estimated to be 2,307,144 t/year with a mean value of 31 t/ha/year. Similar to the current finding, a mean SLR of 31.29 t/ha/year has been reported by Yuan et al (2020), in the mid-hill regions of the Koshi basin, Nepal. However, the rate of our study finding was quite higher than the tolerable SLR (15 t/ha/ year) in the Himalayan region (Ban et al 2016).…”

“…Various research have been conducted in a range of spatial scales in the Koshi River Basin (KRB), related to this thematic area in the last few decades (Santosh et al 2014;Uddin et al 2016;Kafle et al 2017;Mishra et al 2019;Sinha et al 2019;Yuan et al 2020). These studies have mainly focused on the river morphology/landform dynamics, rate of soil loss (SL), sediment connectivity, and the implication of sediment dynamics for flood hazards and their consequences.…”

Effects of fencing project on wind erosion reduction in Alpine grassland and its impact on the development of climbing dunes in southern Tibetan Plateau

“…The 210 Pb ex reference inventories ranging from 3637 to 5983 BqÁm À2 have been reported for an alpine meadow land of the Xinhai Basin in the eastern TP (Hu & Ma, 2022), and values ranged from 2612 to 7377 BqÁm À2 for grassland in the Yangtze, Yellow and Lancang rivers of TP (Li et al, 2019). Yuan et al (2021) reported that the 210 Pb ex reference inventory of 17 876.9 BqÁm À2 in the mid-hills of Nepal, which is higher than the inventory in this study, mainly due to the high mean annual precipitation (1315 mm). The 137 Cs reference value of 385.26 BqÁm À2 is consistent with those reported in adjacent areas when corrected for the sampling year (2020) and the 210 Pb ex reference value in this study falls within the range of adjacent areas, the inventory of 210 Pb ex in this study was tested to be 6485.56 BqÁm À2 .…”

“…The depth distribution of the 137 Cs and 210 Pb ex for the reference site (Figure 2) showed that the surface horizon had the maximum concentrations of both radionuclides, which is typical of an undisturbed site (Gaspar & Navas, 2013;Yuan et al, 2021). The coefficient for the 137 Cs depth distribution shape was calculated to be 0.14 cm À1 , which is a crucial parameter in the profile shape model (Equation ( 2)) for evaluating soil erosion rates on fencing land and grazing land.…”

Modeling and Mapping of Soil Water Erosion Risks in the Srou Basin (Middle Atlas, Morocco) Using the EPM Model, GIS and Magnetic Susceptibility

“…More effective erosion monitoring methods are tracer methods (i.e. 137 Cs, 210 Pb, and 10 Be) (Gaspar et al, 2013;Porto et al, 2014;Yuan et al, 2020), RTK-GPS instruments (Wu & Cheng, 2005;Cheng et al, 2007;Zhang et al, 2011;Castillo et al, 2014), LiDAR and photogrammetry by Drone (Hout et al, 2020;Tak et al, 2020), and 3D laser scanners (Haubrock et al, 2009). In this context, pedometric such as magnetic susceptibility (MS) methods emerged to predict specific soil properties such as soil organic carbon using mass-specific susceptibility at low frequency (Jakšík et al, 2016).…”