Application of Magnetic Susceptibility for Wetlands Delineation

摘要

Wetlands are natural resources that are protected under federal regulations; therefore, the delineation of wetlands is necessary to ensure their protection. Standard methods used for delineating wetlands can be time consuming, or a wetland could be problematic, i.e., lacking hydrophytic vegetation or hydric soil indicators, or periodically lacking hydrologic indicators. A magnetic susceptibility study could be an additional technique used to aid in the delineation process. A study using magnetic susceptibility was undertaken in central Mississippi to identify the transitional zone or boundary between non-hydric (uplands) and hydric (wetlands) soils. The soils were silt loam with a minor percentage of sand. A survey line that traversed the transitional zone between wetland and upland on each end of the transect was revisited four times during a single year and once two years later. One survey was conducted a few weeks after the winter inundation (moderately wet soil conditions), one was conducted several months after inundation but immediately after some heavy rainfall (moderately wet soil conditions), and two were conducted several weeks or months after inundation or significant rainfall (dry soil conditions). There were measurable differences between the magnetic susceptibility values collected in the upland and wetland regions during each survey. 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, transition, and wetland regions, and the characteristics of the curves were similar for all time-periods. Overall, magnetic susceptibility proved to be a successful method for delineating a wetland in this area.