Effects of agricultural land use on the transport of cadmium in Mae Tao Creek, Thailand

Abstract

At the Mae Tao subcatchment high cadmium concentrations in environmental samples have been found i.e. soil in paddy fields absorbing water from the Mae Tao Creek, sediment in the Mae Tao Creek and rice. So, the government has established an implementation plan to solve the problems of cadmium contamination such as collecting and purchasing the contaminated rice and destroy it, establishment of the sugarcane plantation for ethanol production, construction of dams for development of water resources. This research concentrated on the effects of the change of agricultural land usage and the hydraulic structure on cadmium transport via suspended sediment and bed load in the Mae Tao Creek. The cadmium concentrations of suspended sediment, bed load and grain size distribution of bed load along the Mae Tao Creek were gathered from field observations conducted from the dry and wet seasons. MIKE SHE coupled with MIKE 11 was applied to determine the time series of hydrodynamics (water depth and water discharge), which was calibrated with the measured water depth. Sediment transport was consequently computed by inputting the simulated hydrodynamics into the sediment transport module in MIKE 11. Eventually, the sediment transport data was simulated by the model and observed cadmium concentrations were used to obtain the cadmium transport in the Mae Tao Creek. From the results, cadmium contaminated via sediment transport in the Mae Tao Creek is mainly generated in the wet season, and was dominated by suspended sediment transport. From May 2011 to February 2012, the amount of cadmium transported out of the Mae Tao Creek was approximately 16.33 kg in the wet season with 16.20 kg and in the dry season with 0.13 kg. As substitution of rice in current agricultural land use to sugarcane plantation leaded to a decrease of accumulated sediment both suspended sediment and bed load. However, the small change sediment slightly affected the cadmium; the land use change was a small area when compared to the whole study area. The assessment of hydraulic structure responses on cadmium transport in the Mae Tao Creek indicated that the cadmium transport through weir location for case without weir and with weir in the period May 2011 to February 2012 are 18.06 kg and 12.86 kg, respectively.