Sediment Flow and Importance Within an Estuary

SEDIMENT FLOW AND IMPORTANCE WITHIN AN ESTUARY NOVA SCOTIA – SECONDARY

Sediment Flow and Importance Within an Estuary

Lesson Overview:

Estuaries are one of the most productive, yet under appreciated, ecosystems in the world. The sediments in and around the estuary play a critical role in the physical and biological processes in this environment. This lesson looks at the origin and transportation of the sediments within the estuary, and relates this to its biological productivity.

Grade Level:

High School. The lesson can be adapted to middle school.

Time Required:

One 50-minute class should cover the main elements, but two classes could be used if some of the lesson extensions are done.

Curriculum Connection (Province and course):

The lesson is applicable for any province in Canada, but might be more meaningful in Atlantic Canada. The lesson content could apply to any high school Geography course or to Oceans 11. There is certainly material here that could also fit into Agricultural Science and Biology courses.

Atlantic Provinces Education Foundation Curriculum for Social Studies:

General Curriculum Outcomes and Processes:

§  Individuals, Societies, and Economic Decisions

§  Interdependence; People, Place, and Environment

This lesson stresses the need to make educated, responsible decisions regarding the value of estuaries, human impacts on this ecosystem and the long term implications of interfering with it proper functioning.

§  Communication,

§  Inquiry

§  Participation

Students are encouraged to gather “ the facts” regarding natural and human impacts on the estuary environment, make an informed decision regarding a possible development (like golf course), debate the pros and cons of that development in a civilized and respectful manner.

Link to Canadian National Geography Standards:

Essential Element #2: Places and Regions

§  Interdependence of places and regions

§  Physical and human processes shape places and regions

Oceans Scope & Sequence Standard #2: Places and Regions

§  Interdependence of land areas and the ocean

§  Physical and human processes that shape the ocean and coasts

Essential Element #3: Physical Systems

§  Components of Earth’s physical system (atmosphere, lithosphere, biosphere and hydrosphere)

§  Global ocean and atmospheric systems

Oceans Scope & Sequence Standard #3: Physical Systems

§  Processes of ocean physical system

§  Ecosystem processes

Essential Element #5: Environment and Society

§  Global effects of human modification of the physical environment

Oceans Scope & Sequence Standard #5: Environment and Society

§  Ocean policy and regulations

Geographic Skill #1: Asking Geographic Questions

§  Identify geographic issues, define geographic problems and pose geographic questions.

Geographic Skill 3: Organizing Geographic Information

§  Select and organize appropriate forms of maps to organize geographic information.

Additional Resources, Materials and Equipment Required:

§  Map

§  Attached puzzle, graphic organizers, question sheet, teacher information sheet and vocabulary list.

Main Objective:

To have students understand the many processes that contribute to sediment flow within the estuary, and to have students appreciate how these sediments affect life within the estuary.

Learning Outcomes:

By the end of this lesson, students should be able to:

§  Know what an estuary is

§  Locate estuaries on a map (generally)

§  Locate specific estuaries (Fraser River Estuary, Mackenzie River Estuary, St. Lawrence River Estuary, Bay of Fundy Estuary)

§  Know that the sediments in the estuary are both terrestrial and oceanic

§  Know how these sediments are transported to the estuary

§  Understand the role of tidal action, and be able to understand a tide chart

§  Know what is meant by a salt wedge and understand its role (along with the tides) in distributing sediments

§  Understand the role of the eelgrass within the estuary

§  Appreciate the value of estuaries

§  Understand factors that can harm estuaries

The Lesson:

Teacher Activity / Student Activity
Introduction /

The teacher could begin this lesson by asking students why the oceans are salty. Where does this salt come from?

The teacher should define the word estuary, and point out where the estuary is in terms of the following: Mackenzie River, Fraser River, St. Lawrence River and the Bay of Fundy.

Ask students to speculate on the percent of salt in the water within an estuary. Introduce the term brackish. / Have students look at a map of Canada, find the following, and trace their route to the ocean.
-Canada’s longest river, and important calving area for belugas – Mackenzie River
-Canada’s fifth longest river (it has the largest population of wintering shorebirds and eagles in Canada) – Fraser River
-Eastern Canada’s busiest seaway (home to many whales)- St. Lawrence River
-The bay with the highest tides and an important feeding ground for many whales, including the endangered right whale - Bay of Fundy
Lesson Development / We know that the rivers carry tiny amounts of salt to the oceans, but what other sediments do they transport? Ask students to suggest the origin of the sediments in this river to ocean journey.
Ask students how flooding affects this sediment transport system.
Point out to students that the sediments carried by the rivers come in many sizes and types
Point out the settling rates for each of these particles.
Ask students what sediments they think the oceans bring to the estuary.
Introduce the words: terrigeneous, biogenic.
Ask students what they think is the main physical force that transports and circulates the sediments in the estuary. ( Winds, waves and especially the tides) Introduce the words: flood tide and ebb tide.
Students can be provided with a tide chart, and learn how some basic information can be obtained from it - tidal range, tidal periods.
Introduce the terms salt wedge and upwelling.
This section of the lesson could begin by asking students if they know what a “snow fence” is, and why it is effective.
Ask students if they know what the main “snow fence” of the estuary is.
Introduce the word detritus.
Discuss further the importance of eelgrass. / Ask students to look at the Northumberland Strait region in Atlantic Canada, and locate estuaries along this coastline. Locate Antigonish Harbour, and point out that in the 1930's large boats used to make their way 12 to 15 kilometres inland, where now, only a canoe can travel.
Provide students with a diagram (A) and ask them to label the type of sediment in the appropriate place. (Boulders, sand, silt, clay).
Ask students to:
- Calculate the tidal range for certain days
-Have them figure out the average tidal range for this area.
-Calculate the time differences between flood and ebb tide
- Calculate how much later is the high or low tide each day
-Label freshwater and ocean water on the given diagram. (B) (Salt water is denser)
Given this generalized diagram, ask students to place the terms in the appropriate spots. (This can act as a summary of some the ideas in the lesson).
Give students a copy of the incomplete bubble diagram on the importance of estuaries, and ask them, either in groups of whatever, to fill in as many bubbles as possible.
Conclusion / A summary of the importance of an estuary:
- It helps to control coastal erosion by acting as a buffer against strong ocean waves and currents
- It helps to filter harmful chemicals that may enter the estuary from either direction
- It is one of the most biologically production environments in the world and as such sustains a great number of food webs. Many organisms found offshore spend part of their life cycle in the estuary and are therefore, dependent on it. Many of these species used the estuary as a nursery or spawning ground. The mechanisms of the estuary distribute these organisms.
- Estuaries are important feeding grounds for migratory birds. The exposed surfaces at low tide are like a buffet table, providing birds with protein rich amphipods and worms. / 1. A golf course developer wishes to purchase a large parcel of property, much of it bordering on an estuary. The land in question is forested, but the soil quality is poor. He proposes to clear most of this land and he suggests that he needs to use extensive fertilizers (and likely some herbicides) in order to construct an appealing golf course. What are the possible implications of this development on the estuary, on the life within the estuary, and on the offshore fishery?
2. Why are forest harvesters required to leave a buffer zone of vegetation on either side of a river?
3. A farmer keeps his cattle in a low-lying area of his field so they are more protected from bad weather. There is a river running through this section of his field, a river that empties into a nearby estuary. The cattle are allowed to drink from and generally wander through the river at will. Discuss the implications of this situation on the cattle and on the environment. What suggestions would you make to the farmer to help him deal with the issues raised in this scenario?
4. You are a commercial fisher earning your living from what you catch offshore, kilometres removed from the estuary. There is a town meeting planned to discuss the health of the local estuary. What personal interest do you have for attending this meeting?
5. A recent invasive species into Atlantic Canada waters is the green crab. Green crabs, which can be present in huge numbers, are mainly scavengers. They like to dig in the mud of estuaries attempting to find food. How is the green crab a threat to the estuary? (By digging in the sediment, they disturb the roots of the eelgrass, dislodging the plant. They can wipe out large sections of eelgrass, and with it all the benefits of eelgrass)

Lesson Extension:

1. Indicate to students that several other terms are used in defining an estuary. These terms include: bay, delta, sound, inlet and harbour. Ask students to locate some estuaries with these terms.
2. Have students investigate some of the animals that call the estuary home, either on a temporary or permanent basis.
3. Migratory birds like: great blue heron, Canada goose, mergansers, brant or kingfishers.

b.  Oysters and mussels - year round residents.

1. Amphipods (important as a food source)
2. Investigate the difference between anadromous and catadromous species. Students could trace the life cycle of one of these, namely, the salmon or eel.
3. Physical factors can vary a great deal within the estuary. Along with constantly shifting sediments, there is a wide variation in salinity and temperature. Students could research how plants and animals adapt to these changing conditions. Suggested species to study are: eelgrass, crabs, mussels, snails and worms.
4. Students could research how the estuaries of the Bay of Fundy differ from those of the Northumberland Strait.
5. Students could investigate the importance of mud flats, with particular reference to migratory birds.

Assessment of Student Learning:

1. The teacher could select one of the situations or issues given above and assess their understanding of the concepts involved.
2. Students could fill in the given puzzle as a way of assessing their knowledge of the terms used in the lesson.
3. Have students complete questions on the lesson.

Sediment Flow and Importance Within an Estuary

1. Distinguish between biogenic and terrigeneous sediments. As it refers to their origin, list several sources of the sediments found within the estuary and for each one tell which of the two types it is.
2. Sediment transportation and deposition in the estuary is determined by many factors. Comment on the role of each of these in these processes: Tides, wind, eelgrass, salt wedge.
3. An estuary is a place where physical factors, like salinity, change a great deal. A researcher takes salinity readings by dropping a probe into the water at a certain point in the estuary. The probe records a reading of 29 ppt near the bottom and 0.8 ppt near the surface. What might explain the difference?
4. Many different interest groups have a role to play in the health of the estuary. Some of these groups include: fishers, loggers, developers, tourist operators and farmers. For each of these, briefly discuss how they may affect, or are affected by, the balance within this environment.
5. Sediments are important in building estuaries and marshes, yet a delicate balance has to be achieved to have a healthy ecosystem. Comment.

6.  Why are upwellings so critical in the estuary ecosystem?

Sediment Flow and Importance Within an Estuary

Teacher Information

§  Students are often surprised to learn that the salt comes from the rivers that drain into the ocean. Point out that this occurs over a long period of time as the weathering action on the rocks occurs within the rivers. It could be pointed out that the average salt content of the world’s oceans is 35ppt or 3.5%.

§  Estuary waters vary in salinity, but the average is about 17 parts per thousand, ppt or 1.7%.

§  The origin of the sediment in an estuary is from erosion along river banks, weathering within the river as rocks grind over rocks, wind drift into the river, weathering due to ice, glacier material, runoff from adjacent lands, etc.)

§  Increased erosion along the banks, greater volume of water and greater velocity of water speed up erosion and speed up the transport of sediments, etc. As an illustration, students can fill a sink with dirty water, pull the drain plug and see what remains in the sink afterwards. Repeat the procedure, but this time, have the sink semi-clogged so the water does not rush down as quickly. Students should see the difference in the amount of “sediment” left in the sink.

§  Point out the settling rates for each of these particles. (Settling order: pebbles, sand, silt and clay particles. Settling rates: clay particles - several years, silt - several months, sand - day or so). Point out that suspended sediment causes turbidity, which can clog respiratory systems of many organisms, suffocating others and inhibiting photosynthesis.

§  The ocean brings many things to an estuary. (Sand from nearby headlands, phytoplankton and zooplankton, shell fragments from the continental shelf offshore). Point out that the continental shelf off Nova Scotia and Newfoundland are some of the richest fishing grounds in the world, i.e., there is a great deal of life in the water.