Using Radionuclides 7Be, 210Pb and 137 Cs to Estimate Soil Erosion in the Khlong U-Tapao Catchment and Accumlated Sedimentation Rate in the Outer Songkhla Lagoon

Abstract

Nowadays, the pollution problems in the Songkhla watershed and the Songkhla lagoon have continuously become worse as evidenced by several factors: high soil erosion affected from changing the land use, overall low water quality, contamination by toxic pollutants/nutrients, and rapid sedimentation in some areas. The study of soil erosion in the Songkhla watershed, sedimentation rates and its dynamic patterns in the Songkhla lagoon will provide understanding of these problems. Moreover, the obtained results will be used to manage sustainable land use area, and to protect the ecosystem of the Songkhla lagoon. In this research, we present the atmospheric concentration and deposition fluxes of 'Be at three sites in the U-Tapao watershed, Songkhla province. The atmospheric depositional fluxes of 'Be were positively related to the event rainfall, monthly rainfall, and event rainfall separated by NE, SW, and summer seasons. These relationships were used to understand the behavior of deposition of 'Be in our study area where is in tropical monsoonal environment. Second, the reference inventory and relaxation mass depth of 'Be in undisturbed and flat areas were reported and these parameters were used to calculate short-term erosion. Third, the vertical distribution and the maximum penetration depths of 'Be in lagoon sediment were determined to estimate recent sedimentation patterns. Fourth, the sediment mixing rates to indicate the particle exchanged processes at the sediment-water interface derived by the 210Pb, and 'Be depth profiles and the spatial distribution of sediment mixing coefficients in the outer Songkhla lagoon were presented. Finally, we present the determination of sediment accumulation rate by using the vertical profiles of excess 210Pb and 137Cs in the outer Songkhla lagoon located at southern Thailand. The Constant Initial Concentration (CIC) and the constant rate of 210Pb supply (CRS) models were used to calculate sediment accumulation by the use of unsupported 210Pb. Moreover, two-marker events technique based on 137Cs activity was used to validate age of sediment layers obtained using 210Pbx method.