Application of geographic information system to analyses on heavy metal erosional and depositional rate in the middle part of Songkhla Lake Basin, Southern Thailand

Abstract

The aim of this study is based mainly on the scenario that if the middle pat of Songkhla Lake (SKL) becomes shallow and requires excavation, what the lake sediments would be quantitatively, and whether or not the dug sediments will affect to the environment. Additionally, sources of contamination in the concerned catchment area need to be identified in order to protect and remediate the contamination in the future. The study is divided into two fold – viz. rate and amounts of soil erosion from the SKL catchment area, rate and amounts of sediment deposition in lake, and concentrations and distribution of heavy metals in soils, stream sediments, and lake sediments. All of the data were analyzed with the application of geographic information system (GIS). The results of the analyses were shown as several kinds of maps. The important maps are soil erosion map, maps showing distributions and contaminations of heavy metals both in the Songkhla Lake and its catchment area. Results indicate that the maximum erosion has been found in areas nearby the mountains in the west part of the SKL area with the average rate of 26 tons/ha/yr or 1.64 mm/yr. It is also discovered that contamination of heavy metals varies from places to places. However, comparison was made with the agricultural standard, it is found that none of the heavy metal contents in soils are naturally occurred and do not exceed those of the standards for remediation. Only some elements in stream sediments i.e. As and Pb, which have been distributed naturally in the southern part of western highland and mountains, need to be carefully followed up. For the SKL sedimentation, it is discovered that sediments have been deposited at the average rate of about 0.37 mm/yr. The results of heavy metal analyses on SKL sediments reveal that most sediments contain the heavy metals quantitatively lower than those of the Hong Kong standard for lake excavation. Only the very small amount (<0.05%) shows the values higher than the standard. Therefore it is concluded that the SKL sediments can be excavated without any environmental problem and some specific sediment layers can be extracted for industrial proposes.