Home Methods of Study Bathymetry Freshwater Flow Specific Conductance Summary & References

Specific Conductance

Figure 11. (above) Specific conductance at 10 feet below the surface or near the bottom if depth is less than 10 feet, wet season of August 8, 1984. [larger image]		Figure 12. (above) Specific conductance at 10 feet below the surface or near the bottom if depth is less than 10 feet, dry season of May 11, 1984. [larger image]

Salinity distribution in Matlacha Pass based on specific conductance is characterized as well mixed. Salinity gradients change daily with tides and seasonally with the quantity of freshwater flow. Specific conductance ranged from less than 1,000 to 57,000 µS/cm throughout Matlacha Pass. Specific conductance at Matlacha ranged from 9,000 to 53,000 µS/cm 2 ft below the water surface (averaging 36,000 µS/cm) and from 19,000 to 57,000 µS/cm 2 ft above the bottom (averaging 40,000 µS/cm) for February to September 1992. Specific conductance 2 ft below the water surface and 2 ft above the bottom at Matlacha Pass and daily mean discharge from the north Cape Coral spreader canal system are shown in figure 13. Freshwater inflow from Cape Coral is minimal and specific conductance remains high during the dry season. Freshwater inflow increases and specific conductance decreases during the wet season (fig. 13).

Specific conductance for the northern part of Matlacha Pass during wet-season conditions (August 8, 1984) is shown in figure 11. Specific conductance ranged from 4,000 to 15,500 µS/cm at two breaks in the north Cape Coral spreader canal system near Matlacha where freshwater enters the pass. Specific conductance ranged from 15,000 to 20,800 µS/cm over a relatively large area of the north-central pass. Similar specific conductance patterns were detected for waters measured within the top 2 ft of water surface and waters measured at 10 ft below the surface or total depth if less than 10 ft. An area of canals between the Shadroe and Hermosa Canals does not receive sufficient freshwater inflow to flush the saline waters near the bottom (fig. 11). Specific conductance near the bottom of the canals remained between 1,300 and 4,000 µS/cm, even though waters near the surface were less than 1,300 µS/cm.

Specific conductance for the northern part of Matlacha Pass during dry-season conditions (May 11, 1984) is shown in figure 12. Specific conductance was greater than 28,000 µS/cm throughout the estuary, indicating well-mixed tidal waters. Freshwater flow into the estuary was minimal during the dry season. Specific conductance measurements within the brackish range were evident in the spreader canal systems and canals downstream of the control structures, indicating tidal overtopping of the north Cape Coral spreader canal system during the dry season.

Figure 13. Specific conductance 2 feet below the surface and 2 feet above the bottom at Matlacha and daily mean discharge from the north Cape Coral Spreader canal system. [larger image]