Understanding Salinity in Northwest Florida’s Waters with a Family Activity

Dana Stephens, 4-H Agent

Salinity is the amount of total dissolved salts in water. This includes all salts not just sodium chloride, or table salt. Salinity is important in aquatic environments as many flora and fauna depend on salt and the level of dissolved salts in the water for survival. People interested in the composition of water frequently measure chemical and physical components of water.  Salinity is one of the vital chemical components measured and often measured by a device determining how readily electrical conductance passes between two metal plates or electrodes. These units of electrical conductance, the estimate of total dissolved salts in water, is described in units of measurement of parts per thousand (PPT).

At the large scale, Earth processes, such as weathering of rocks, evaporation of ocean waters, and ice formation in the ocean, add salt to the aquatic environment. Earth processes, such as freshwater input from rivers, rain and snow precipitation, and ice melting, decrease the concentration of salt in the aquatic environment. Anthropogenic (human-induced) activities, such as urbanization or atmospheric deposition, can also contribute to changes in salinity.

Salinity and changes in salinity affect how water moves on Earth due to contrasts in the density of water. Water containing no dissolved salts is less dense than water containing dissolved salts. Density is weight per volume, so water with no dissolved salts (less dense) will float on top of water with dissolved salts (denser). This is why swimming in the ocean may feel easier than swimming in a lake because the denser water provides increased buoyancy.

Northwest Florida is a unique place because we have a variety of surface waters that range in salinity. There are ponds, lakes, streams, rivers, and springs, which have no to low salinity levels (0 to 0.5 PPT), and commonly referred to as freshwater systems. We house six estuaries—Perdido Bay, Pensacola/Escambia Bay, Choctawhatchee Bay, St. Andrews Bay, St. Joseph Bay, and Apalachicola Bay. Estuaries are bodies of water with freshwater input(s) (e.g., rivers) and a permanent opening to the ocean (e.g., Destin Pass in the Choctawhatchee Bay). Estuarine waters are termed brackish water (0.5 to 30 PPT) due to the dynamic changes in salinity at spatial and temporal scales. Waterbodies with an even more dynamic change in salinity are the coastal dune lakes Northwest Florida’s Walton and Bay Counties. Coastal dune lakes are waterbodies perched on sand dunes that intermittently open and close to the Gulf of Mexico. Sometimes these waterbodies are fresh and sometimes they have the same salinity as the Gulf of Mexico, like after a large storm event. Finally, the Gulf of Mexico, or ocean, has the highest salinity (> 30 PPT) among the waterbodies of Northwest Florida.

Here is an educational activity for the family to explore salinity and how salinity differs among Northwest Florida waters.

Understanding Salinity Activity--Join in this family activity to explore understanding salinity in water. Here is what you will need for the activity. Three containers for mixing. Four, clear glasses. Salt. Food coloring. Measuring cups. Spoons.

Salinity Activity for Families. Step 1: Prepare Water. Set three mixing containers on hard surface. Measure 1/2 cup of salt and 1/4 cup of salt. Pour 1/2 cup of salt into one container. Pour 1/4 cup of salt into another container. Add 1 cup of hot tap water to all three containers. Add different food coloring to containers with salt. Mix salt, water, and food coloring until completely dissolved in each container using separate spoons.Salinity Activity for Families-Step 2: Explore Salinity Densities. Pour contents of three containers into three clear glasses separately. Pour 1/2 cup from the clear water glass into the fourth, empty glass. Add water with a spoon from the lower salinity glass to the glass with clear water. Do this slowly along the side of the glass. Do not stir/share this glass. Add water with a spoon from the higher salinity glass to the same glass. Do this slowly along side of the glass. Do not stir or share the glass. Observe changes when adding the waters with different salinity levels.Salinity Activity for Families-Step 3: Questions to Consider and Discuss. What happened when the first colored water was added? What happened when the second color water was added? Why do you think this happened? How may salinity levels affect the density of water?Broad Questions for Consideration--Name some waterbodies in Northwest Florida where salinity may be the same and where salinity may differ. Why id density of water important in our waters in Northwest Florida?Salinity Changes Everything--thanks for participating. Please contact Dana Stephens at dlbigham@ufl.edu or 850-826-1316 for more discussion questions or family activities.