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

TOPIC-TITLE Physical Parameters - Ubiquitous Estuaries-Similarities and Differences AUTHOR Roy Brooks Blair Heald Sandra Lopez Belinda Matlock Abigail Resto GRADE SUITABILITY Middle School SCOPE Oceanography, Habitat, and/or Estuaries

Sequence Students should have prior knowledge and understanding of the following: Hypersaline Salinity Hyposaline pH Dissolved oxygen < < go top

Background Summary A unique environment known as an estuary develops where freshwater from rivers meets the sea. Estuaries are among the most productive environments on Earth. Along the shores of many estuaries are often found salt-marsh grasses, seaweed, submerged grass beds, and mangroves. Multitudes of worms, clams, and shrimp reside in the muddy bottom; snails and crabs crawl along the shore; and countless species of fish swim in the often turbid, plankton-rich estuarine waters. Estuaries provide natural nurseries and are also among the environments most affected by humans. This anthropogenic impact has been disastrous to many estuaries. Estuaries are too often filled, dredged, turned into seaports, and used by some humans as sites for garbage disposal. Estuaries are scattered along the shores of the world's oceans and vary greatly in origin, type, and size. Some estuarine environments are called lagoons, such as the Laguna Madre; others are called bays, such as Chesapeake Bay; and some may be referred to as bayous, such as Davis Bayou on the Mississippi Sound. Another example is represented by the mangrove swamps in southern Florida. They all share the mixing of fresh water with the sea in a partially enclosed, shallow section of the coast. Perhaps the most common type of estuary is the drowned river valley or coastal plain estuary. These estuaries were formed when sea level rose at the end of the last "ice age" and the sea invaded lowlands and the mouths of rivers. A good example of this estuary type is the Chesapeake Bay. In a bar-built estuary, an accumulation of sediments along the coast results in sand bars and barrier islands that act as walls between the ocean and the fresh water supply. The Laguna Madre and the Mississippi Sound are examples within the Gulf of Mexico. Tectonic estuaries, such as San Francisco Bay, were created when land sank or subsided as a result of movement in the Earth's crust. The spectacular estuaries known as fjords were created when retreating glaciers cut deep valleys along coasts. The valleys were then flooded by the sea, and rivers formed in the valleys and flowed into the sea. These estuaries are common in southeastern Alaska. Estuaries tend to be broader and more well-developed along coasts with flat plains and wide continental shelves, or passive margins. They are less developed where steep coasts and narrow continental shelves have created narrow river mouths along active margins. Influenced by tides and the mixing fresh and saltwater, estuaries have unique physical and chemical characteristics that impact the lives of the organisms that inhabit them. The characteristics of two estuaries along the Gulf Coast will be compared in this lesson. < < go top Objectives Students will be able to do the following: Define the term estuary. Name, describe, and list examples of different types of estuaries. Compare water parameter data for two estuaries. Determine the differences between estuaries by examining maps, charts, graphs, tables, and other relevant data. < < go top Materials Data tables, location maps (acquired from the U.S. Geological Survey Office), charts, graphs, and other teacher-provided handouts (teacher would need to obtain these materials before this activity). Other classroom resource materials. < < go top Activity Introduce the lesson with background information and a review of the terminology used in measuring physical parameters. Students will be required to take notes. Distribute data tables and other teacher-provided materials and remind students to note details, such as date of data collection. Ask students to compare data tables for their estuaries and to locate each estuary and begin recording observations about the similarities and differences of these estuaries. Discuss results. Then have students prepare hypotheses to account for differences between the two estuaries. < < go top Possible Extension Have students design and conduct a more thorough investigation into the possible causes of differences between the estuaries studied. If possible, conduct field trips to the estuaries studied to enable students to collect and analyze their own data and compare these data with previous results. < < go top Teacher Evaluation Pretest and posttest students on the key concepts. Have students prepare a Venn diagram using the estuarine data. Have students write hypotheses to explain the differences and similarities between the estuaries. < < go top