Fuzzy logic for acid sulfate soil mapping: Application to the southern part of the Finnish coastal areas

Acid sulfate (AS) soils constitute a major environmental issue. Leaching considerable amounts of acidity and metals into watercourses, they cause severe ecological damage. Small hot spots may affect large areas of coastal waters and mapping is required in order to carry out an efficient mitigation plan. The primary aim of this study was to assess the use of fuzzy logic for AS soil mapping at reconnaissance scale, applying it to the southern part of the Finnish coastal areas (c. 17,300 km²). Using a limited amount of evidential datalayers (aerogeophysical data, quaternary geology and a Digital Elevation Model), it was possible to create probability maps for AS soil occurrence in the study area. On the most balanced probability map, the combined very high and high probability classes covered 12% of the study area and contained about 70% of the validation points corresponding to known AS soil occurrences. Using only the very high probability class, a conservative extent of AS soils could be assessed for the study area (c. 800 km²), indicating that the extent of AS soil for the whole Finnish coastal areas would be higher than previously estimated. Being systematic and easily transferable, fuzzy logic represents an efficient approach, particularly adapted to carry out large scale preliminary survey in areas offering a limited amount of data.