Measuring & Comparing Salinity in Different Aquatic Environments

Most of you have learned in life science or through experience that there are two main types of aquatic environments - saltwater and freshwater. Oceans, bays, gulfs, and seas are examples of saltwater habitats, while lakes, ponds, rivers, streams, etc. are bodies of freshwater.

There is, however, a third type of water habitat - a mixture of both salt and fresh water - found where rivers meet, or flow into, the ocean. These aquatic environments are known as estuaries. The distinguishing characteristic in each of these water habitats is the amount of dissolved salt found in the water, known as the salinity. In this fun science fair project, designed by Dr. Sara Agee of Science Buddies, students will collect and test several water samples from various fresh water and salt water aquatic environments to determine the difference in salinity.

Materials You'll Need

• Glass canning jars with lids (12 oz.)
• Metric scale (weight in grams, g)
• Metric measuring cup (volume in liters and milliliters, L and mL)
• Cookie sheet
• Oven

Project Overview

1. Create a data table like the one shown above (or to download a copy). (NOTE: Accurately recording all pertinent data throughout the experiment is very important. When in doubt - write it down! You can sift through the information later when you compile your findings.)
2. Brainstorm aquatic locations in your vicinity. Include both fresh water and salt water environments. (If you live near the coast, don't forget any estuaries!) Making a prediction as to their salinity, rank the locations from least salty to most salty. Choose five or more environments to visit and collect samples.
3. Collect your water samples. Make sure to follow the correct procedure. (NOTE: For accuracy, each sample will need to have the same volume of water. Use a metric measuring cup to collect 300mL of water from each location. This will be more precise than 'eyeballing' the water levels in each jar.) Don't forget to create a negative control with distilled water!
4. Measure and record pre-evaporation and control weights.
5. Evaporate the water in each sample. Measure and record the post-evaporation weights.
6. Use the following formulas to compute the amount of salt (in grams), and finally the salinity of each sample:

1. Evaluate findings and report significant relationships, conclusions, etc.