Sequence | Background | Objectives | Materials | Activity | Extensions | Evaluations

TOPIC-TITLE Physical Parameters - Creating and Comparing Various Saline Environments Within the Gulf of Mexico AUTHOR Haidee Anthony GRADE SUITABILITY Middle School SCOPE Life Science, Marine Science, Ecology, and Environmental Science

Sequence Students should have an understanding of the following: How to use a hydrometer The relationship of density and salinity < < go top

Background Summary The average salinity of the ocean is 35 parts per thousand (ppt); most of the Gulf of Mexico averages 28 to 32 ppt. However, some areas of the Gulf of Mexico average 36 ppt. There are many influences on the salinity within the Gulf of Mexico. More than 30 rivers contribute freshwater to the Gulf. The Mississippi River makes the greatest contribution, but rivers are not the only contributors of freshwater to the Gulf. Freshwater vents on the southwest shelf of Florida are also notable sources of freshwater to this semi-enclosed body of water. The fact some areas of the Gulf of Mexico have a slightly higher salinity than the open ocean is a surprising peculiarity. This peculiarity may be attributed to many things, but perhaps the most interesting is the existence of brine seeps. Brine seeps are often associated with oil pockets and are located in at least two areas of the Gulf of Mexico. One well known brine seep is located near the East Flower Garden Banks, and an even larger one is located at the Orca Basin. These seeps have a salinity of 200 ppt and 250 ppt, respectively. The variation of salinity will influence the ecosystems around them. North of the barrier islands, the freshwater is prevented from completely mixing with the Gulf water, so the salinity is lower from Florida to the upper Texas coast. The mid-Texas coast through much of Mexico has a high salinity north of the barrier islands. The freshwater influx through riverine input and precipitation is less than the evaporation rate. The Laguna Madre is an example of a bay that has a hyper-saline environment. Ecosystems and the life forms that exist in high salinity environments are very different from those found elsewhere. It is interesting to investigate those life forms and their adaptations for survival in such hostile environments. < < go top Objectives Students will be able to do the following: Predict the amount of salt required to bring a given amount of water to the average salinity level of the Gulf of Mexico. Design and write a testing method to determine whether their hypotheses are correct or incorrect. Perform the testing procedure designed by students and determine how much salt is needed to achieve the desired salinity. < < go top Materials Salt Five-gallon bucket Hydrometer Graduated beaker Any other material the students may decide they need for testing < < go top Activity Present the problem of the investigation to the students--"How many milliliters of salt are needed to make 5 gallons of water read 1.020 on the hydrometer?" Allow the students to work in cooperative learning groups to develop the results of their laboratory proposals. Students are required to present their proposals and develop and submit a request for materials to the teacher for approval. (This should take one day of class time.) Each group will begin the experiment using its proposed testing procedure. Students will record the salinity changes during the experiment on a self-designed data table. Students will then graph the results from the data table in a bar graph. Students will develop and write conclusions for their laboratory investigations using a grammatically correct format (minimum of five sentences in the conclusion). They will predict the amount of salt required to prepare a 20-gallon aquarium for living marine organisms. < < go top Possible Extension Discuss how much salt is needed for the closest coastal waters and why the salinity of these waters is so much lower than the Gulf of Mexico. Discuss how much salt is needed for the hypersaline environments and the causes for such conditions. Contrast and compare the differences in a coastal, hypersaline body of water and Gulf of Mexico salinities. < < go top Teacher Evaluation Have student groups develop a hypothesis for the problem. Have student groups design a testing procedure to determine whether their hypotheses are correct. Have student groups make a bar graph to show the increased salinity from their test results. Have student groups complete a written laboratory report (from problem to conclusion). Teachers should evaluate the content, accuracy, and conceptual understanding of the graphs and laboratory reports. < < go top