Electromagnetic Induction (EMI) Measurement of Apparent Soil Electrical Conductivity (ECa) to Characterize Soils and Stratigraphy for Wetland Restoration.
Karen Davis, NCSU, Box 7619, Raleigh, NC 27695
Apparent soil electrical conductivity (ECa) might prove useful in characterizing soils for wetland restoration. Juniper Bay is a 300 ha CarolinaBay wetland in Robeson County, NC drained for agriculture in the 1970’s and 1980’s. The bay is being restored to a wetland by the North Carolina Department of Transportation. The Geonics EM38 single-frequency and the Geophex GEM-2 multiple-frequency sensors determine ECa via electromagnetic induction. We used them to survey >20 km of transects in JuniperBay prior to restoration. Interpolated ECa maps were made by kriging in ArcMap 9.1. The ECa maps derived from the different frequencies had different ranges of ECa. The largest range was from the GEM-2 and the smallest from the EM38. Soil cores were taken to ~6 m and soil pits dug to ~1 m at 17 locations on a triangular grid spanning the bay. Horizons were sampled for particle size and chemical analyses and depth-weighted averages were calculated. Relationships were found between soil ECa and core clay content range; as the clay content range increased, the correlation weakened. A relationship was also noted for pit organic C and ECa; when correlations were significant, the correlation strengthened as mean organic C increased. Correlations were strongest with GEM-2 frequencies in both relationships. When pit data were separated by soil type, ECa was not related with particle size distribution in organic soils. Clay content was best predicted in histic soils with vertical GEM-2 frequencies. In both pits and cores, P had few correlations with ECa. When soil map units were considered together, soil ECa was not correlated with depth to the first clay layer (aquitard) determined from 174 ground-truth cores across the bay. Data analysis continues in our efforts to determine if soil ECa can help characterize soils for wetland restoration.