Measuring Salinity in Buzzards Bay
How do we measure salinity, and what impact does it have on the health of our ecosystem? Our Baywatchers can tell you all about it.
Buzzards Bay is where fresh water from rivers, streams and rainfall collides with the salt water of the Atlantic Ocean. The meeting of the two makes for diverse levels of salt content, or salinity, in its waters.
How do we measure that salinity, and what impact does it have on the health of our ecosystem? Our Baywatchers can tell you all about it.
How do we measure salinity?
Salinity is the measurement of the amount of dissolved salts in a volume of water. It is actually determined by referring to a salinity table, based upon the density and temperature of the water.
Cold water is more “dense,” or heavier, than warm water, and seawater is more dense than freshwater. Because this relationship exists between salinity, temperature, and density, we can predict any one from the other two. Baywatchers will measure density using a hydrometer and temperature with a thermometer to predict salinity.
Usually made from glass, hydrometers have an unmistakable shape and easily float in liquid- a long, skinny tube connects to a thicker, heavy base. Along the tube is a graduated marking with a density scale, whose unit of measure is known as Specific Gravity, or SG.
To measure density with the hydrometer, it must be placed in a container of water - in this case, we use a graduated cylinder.
Why does it matter?
Because Buzzards Bay and its estuaries contain a mixture of seawater and freshwater, its salinity is constantly varied along the coast. Our Baywatchers data shows us when and where salt and freshwater levels are different, which leads to stratification of the water column - where more dense, higher salinity water forms a wedge under the lighter freshwater entering from a watershed.
Stratification has important ecological effects on nutrient rich coastal environments like ours. In a well mixed system, oxygen at all levels of the water can be replenished and exchanged with the atmosphere; but in a stratified water column, bottom waters may become isolated and oxygen concentrations decline, negatively affecting the plants and animals that dwell in bottom waters. Baywatchers monitor water salinity, along with temperature and oxygen concentrations, all around the Bay.
How can I help?
Join the Baywatchers and help us test water quality in your community! Please email Tony Williams, Director of Monitoring Programs, at williams@savebuzzardsbay.org to learn more.
