Assessment of soil erosion and deposition using fallout radionuclide technique under different land uses and its relationship with soil chemical properties in the Gregory Lake catchment, Nuwara Eliya

Abstract

Removal of the topsoil layer reduces soil health, water retention capacity, and carbon sequestration ability while contaminating reservoirs and increasing runoff and flooding. Therefore, accurate assessment of soil erosion is very important for sustainable land management and building aclimate-resilient environment. This study was conducted to quantify soil erosion rates using the Fallout Radio Nucleotide (FRN) technique in the Gregory Lake Catchment. The study further investigated the relationship between soil chemical properties and soil erosion under selected land uses including natural forest, tea land, vegetable land, grassland and municipal area. Sediment samples from Gregory Lake were also analyzed. Three soil samples (0 – 40cm) were collected from each land use and analyzed for radioisotopes of 137Cs and 210Pb activities using High Purity Germanium Gamma detector. These radioactivity values were converted to soil erosion/deposition rates using the mass balance model. Soil samples were also tested for chemical properties such as pH, EC, available phosphorus, exchangeable potassium and organic matter content. Using Turkey’s mean separation, differences (p<0.05) in erosion estimates and chemical properties among land uses were identified. The study revealed that soil erosion rates vary significantly with land use type. The highest soil erosion was observed under vegetable cultivation (43.56t/ha/yr), which is highly influenced by human activities and a high rate of sediment deposition was observed in Gregory Lake (16.53t/ha/yr). There was a significant negative correlation between soil erosion and soil organic matter percentage. Since there was a strong correlation between soil erosion rates measured using 137Cs and 210Pb methods both Cs and Pb radioisotopes can be used to measure soil erosion rates with comparable accuracy. This method aids long-term erosion assessment in highland catchments by quantifying soil erosion rates, identifying suitable conservation methods, locating critical erosion-prone areas and preventing degradation of agricultural lands, tea plantations and forests.