SIGNIFICANT CONTRIBUTION ASSESSMENT OF HEAVY METAL CONTAMINATED RIVER SEDIMENT DUE TO HEAVY METAL MIGRATION BY SOIL EROSION IN A REMOTE WATERSHED

Abstract

The Mae Tao Basin is a small basin located in Mae Sot, Thailand. The Mae Tao Creeks is a main branch belongs to the basin, originates at Doi Mae Tao and Doi Rei Pha. The Creeks has the flow direction pass through the mining production area and residential area. The Creeks has been claimed as a cadmium contamination site, which is certified to be higher than the acceptable level at 5.0 mg/L in water. Due to the geological characteristic of the area that is the deposition area of zinc-composite mineral, there are some possibilities that the natural erosion by the flood during the wet season can wash down the small particles with high concentration of zinc and cadmium into the Mae Tao Creeks. According to this information, the study has been set up and aimed to clarify the possibility that geological characteristic of the basin can contribute to the concentration of cadmium. The study has been set up by applying the combination between empirical study based on Revised Universal Soil Loss Equation (RUSLE) and a hypothetical estimation using hydrological model name as MIKE which has a capability to simulate the phenomena of the water especially overland flow in basin scale and the remote sensing technique. In order to evaluate the potential of geological characteristic of the area as a contributor for contaminated particles and sediments, new external modules named as Overland flow Sediment Transport module (OfSET) was developed. This development can enhance the capability of the program from simulating only the sediment transport via channel flow, to be capable to simulation the migration of cohesive contaminated particles through the overland flow over the surface area of the Mae Tao Basin. The model input, applied in this study come from both primary and secondary sources. Direct field observations were conduct in the available area of the basin, while some in the remote area were represented by the secondary value from literatures review. As a result of empirical estimation, mining production area demonstrates the highest potential in releasing cadmium contamination flux due to erosion at 1.854 ± 0.088 t/ha/y. For the hypothetical estimation, total cadmium flux in stream sediment, transported by the Mae Tao Creeks, is equal to 21.93 kg and 0.51 kg during wet and dry season of 2012-2013 respectively. Additionally, cadmium transported via overland sediment are equal to 8.36 kg and 0.08 kg in wet and dry season. These simulated values indicate that the natural zinc- cadmium deposition in the Mae Tao Basin is one of the contributions of cadmium contamination in the Mae Tao Creeks with the highest contribution at 38.12% in wet season.