Spatial variations of groundwater salinity in a mangrove-salt flat system, Cocoa Creek, Australia

In this work the average groundwater salt concentration in a mangrove swamp and tropical salt flat system adjacent to Cocoa Creek near Townsville in North Queensland was measured with ground conductivity probes based on low frequency EMI (Electromagnetic Induction) and V-I (Resistivity) Methods. Transects of conductivity were measured with the conductivity probes and the spatial variations in the average groundwater salt concentration were determined from conductivity measurement with both probes. Lower concentrations occurred within mangrove forest as well as near the edges of the salt flats. Comparison of the results above 0.8 m and below 0.8 m showed that as depth increases, the concentrations become more homogeneous. For example at 0.4 m, salt concentrations across the salt flat vary from 75 g/l to 175 g/l where at 2 m the variation is only from about 75 g/l to 125 g/l. High lateral groundwater salt concentration gradients occured at the boundary between the mangroves and salt flat and also at the edges of the salt flat. Typical gradients were about 6 g/l/m and 2 g/l/m respectively.