Acid sulfate soils decrease surface water quality in coastal area of West Malaysia: Quo Vadis?

To satiate the surging world food demand, agricultural activities have been attempted on marginal land such as acid sulfate soils (ASS) which are distinguished by their low pH and presence of oxidized sulfidic material. However, the spatial distribution of chemical characteristics in ASS areas has received little attention; thus, this study was carried out with the goal of investigating an actual ASS area from a geochemical perspective and its effects on the quality of a nearby waterbody. ASS samples were collected from Kampung Sungai Raya, an agricultural area located at the west coast of Peninsular Malaysia. The study site is mostly covered with silty soil with a pH of 3.6 ± 0.9 throughout the 1-m soil profile. Soil content of aluminum, iron and soluble sulfate were found to be significantly different between the sampling locations (p < 0.05). Iron hydroxysulfate jarosite was identified at most of the sampling points, confirming the presence of oxidative dissolution processes of iron sulfide. The Sungai Raya river that flows in the vicinity of the ASS study area displayed comparable results with respect to low pH as well as soluble sulfate, aluminum, and iron concentrations. There is a possibility of intensification of sulfate and aluminum concentration as the river water flows downstream. Study on this site indicates that sustainable amelioration of the ASS area for growing crops requires an appropriate soil amendment practice. Alternatively, restoration of the land to its natural ecology and practicing silviculture or agroforestry could be a solution for ASS, both at this site and potentially at other active ASS sites all over the world.