Application of Magnetic Susceptibility for Wetlands Delineation

Abstract

Wetlands are a natural resource that are protected under federal regulations, therefore the delineation of wetlands is necessary to ensure their protection. A study using magnetic susceptibility was undertaken in central Mississippi to identify the transitional zone between non-hydric (uplands) and hydric (wetlands) soils. The soils were clayey with a minor percentage of sand. A survey line that traversed an upland, transitional zone, and wetland on each end of a transect was revisited four times during a single year. The first survey occurred in the spring three weeks after the winter flood inundation (moderately wet soil conditions), and the other three were in the summer (one, dry soil conditions) and fall (two, dry and moderately wet soil conditions). There were measurable differences between the magnetic susceptibility values collected in the upland and wetland regions during each survey period. One transitional zone was easily identified using magnetic susceptibility, exhibiting a sharp decrease in susceptibility values between the upland and wetland. The other transitional zone contained an intermediate ridge, which made demarcation of the zone less obvious. The measured magnetic susceptibility values were comparable for the respective upland, transitional, and wetland regions, and the characteristics of the curves were similar for all time periods. A general increase in magnetic susceptibility values was observed in all regions as the site dried throughout the year. Overall, magnetic susceptibility proved to be a successful method for delineating a wetland in this area.