Extending electromagnetic methods to map coastal pore water salinities

Area of Science:

• Geophysics
• Environmental Science
• Coastal Ecology

Background:

• Mapping pore water salinity is crucial for understanding coastal wetland dynamics.
• Surface electromagnetic (EM) methods offer a non-invasive approach for subsurface characterization.
• Previous studies have explored EM methods for groundwater and soil salinity assessments.

Purpose of the Study:

• To assess the feasibility of using surface electromagnetic (EM) methods for mapping pore water salinity in a coastal wetland.
• To evaluate the performance of EM-31 and EM-34 instruments in shallow marine and land environments.
• To develop an effective technique for predicting pore water conductivity using EM data.

Main Methods:

• Utilized EM-31 and EM-34 instruments for surface geophysical surveys in a coastal wetland.
• Conducted resistivity soundings and collected pore water samples for ground-truthing.
• Developed a method combining formation factors from resistivity data with EM-31 readings.

Main Results:

• The EM-31 instrument provided valuable data, correlating well with resistivity soundings and pore water samples.
• EM-34 experiments in marine water did not match theoretical responses.
• The combined method successfully imaged zones of elevated pore water salinity adjacent to mangrove forests.

Conclusions:

• Surface EM methods, particularly the EM-31, are feasible for mapping pore water salinity anomalies in coastal wetlands.
• The developed technique is effective for identifying high-contrast salinity zones in challenging terrains.
• Further research is needed to assess EM-31 resolution for detecting subtle salinity variations like freshwater discharge.