1. Estuary Definition and Orientation
5 slides

2. What is an estuary? An estuary is formed where rivers meet the sea.
An estuary is a semi-enclosed river mouth or bay where salty seawater is diluted by freshwater from rivers and creeks.
An estuary is made up of tidal marshes, tidal flats, and open water channels.
An estuary is flooded by the tides.
These descriptions of an estuary help us to understand the physical place and the forces that shape an estuary. We will learn more about these special environments and the rich diversity of life they support as we study estuaries in the classroom and the field.

3. What does an estuary look like from the air?
These aerial photos of the Coos estuary show how different parts of the same estuary can look quite different.

4. What is South Slough National Estuarine Research Reserve?
South Slough NERR
Pacific Ocean
Coos Bay
a 4,771 acre protected natural area
A place to investigate and conduct studies (research)
A place for people to learn about estuaries and their watersheds (education)
A place to restore and protect estuaries and their watersheds (stewardship)
Established in 1974, the South Slough National Estuarine Research Reserve (formerly named Sanctuary) provides a natural laboratory for scientists and students of all ages to learn how estuaries work. The lessons learned at South Slough are then applied to other similar estuaries and their watersheds to improve overall ecosystem management in our region.

5. Is this still the estuary?
Estuary wetlands have been filled and altered for many different uses. Along the Oregon coast, mountains leave few flat areas where tidal wetlands can form. These areas have also attracted human settlement and the resulting filling, diking, and dredging have changed the way the estuary functions. The city of Coos Bay was once called Marshfield, tribute to the fact that much of the city is built on filled former marshes.

6. Is this still the estuary?
Areas up rivers where the tides once flooded over the edge of the land have been drained and levees have been built. These areas are often used for agriculture and livestock grazing. However, over time the former marsh land settles and sinks as plants decay and soil is compacted. The low areas flood with winter rains and may eventually become part of the estuary once again. The ridges of the coastal mountains in the distance define and divide the upper watershed. Precipitation that falls on these slopes may eventually reach the river and the estuary or if it falls on the backside of the ridge, it may drain into a different watershed.

7. The Physical Estuary
7 slides (two multi-part)

8. The flooding and ebbing of the tides is one of the most important forces shaping and influencing the estuary.
Tidal waters flood the estuary twice each day bringing nutrients, sediment, and oxygen rich waters from the ocean. Tidal currents also transport flora such as algae and fauna such as fish, crabs, and shrimp into the estuary. The tides shape the shoreline as they flood and ebb, moving tons of sediment and water each day.

9. The flooding and ebbing of the tides is one of the most important forces shaping and influencing the estuary.
Tides image at low tide photopoint – South Slough NERR mid-estuary

10. High tides and low tides can make the same place look very different.
The tidal habitat of the estuary is defined by three zones – tidal marshes, tide flats, and the open water channel. Each of these zones has special characteristics. Specially adapted rooted, flowering plants able to tolerate flooding with salty water are found on tidal marshes. These places are called salt marshes. Some tidal marshes are only flooded by fresh water that backs up as the tide slows the river. These places are called tidal fresh marshes.

11. High tides and low tides can make the same place look very different.
Where rooted, flowering plants can not withstand the strong currents and salty, murky tidewater, the mudflats are found. These areas are more properly called tide flats since they may be muddy, sandy, or even rocky. At the lowest tides, the only visible water is contained in the open water channel.

12. The gravitational forces of the moon and the sun drive the tides.
Spring tide
Tugging the waters of the ocean, the pull of the moons gravity as it orbits around the earth is the primary cause of the tides. The much more distant sun may slightly reinforce or offset this pull, depending on the location of the moon. The most extreme high tides and low tides are called “spring tides”, not because of the season, but rather because they seem to “spring up”. They occur at full moon and new moon. The more average tides are called “neap tides” and these occur when the moon is at a right angle to the sun relative to earth during the first and third quarters.
Neap tide

13. Sediment and other particles are common in the estuary’s waters, yet too much sediment can cause damage to habitat and the flora and fauna.
Turbidity is a measure of the amount of sediment and other particles suspended in water. High turbidity caused soil erosion and dredging reduces water clarity limiting the depth reached by sunlight. Low light levels impact plant growth and may clog the gills of aquatic animals that depend on dissolved oxygen in the water to breathe.

14. Estuaries are flooded by the tides twice daily
Estuaries are flooded by the tides twice daily. Winter rains increase the depth of the flooding waters expanding the reach of the floodplain.
Seasonal weather patterns and storms in the winter months may deliver more fresh water to the estuary than the available area of the floodplain can hold. Historically, marshes in these area reduced flooding, acting like giant sponges. The loss of floodplains through filling and construction of levees and the conversion of marshes to pastures has reduced the estuary’s ability to absorb and gradually release flood waters. (Coquille River valley during winter.)

15. Upwelling occurs during the late spring and summer when strong, continuous winds from the north bring cold, nutrient rich ocean water to the surface.
Summer coastal weather is often dominated by strong winds blowing off the ocean from the northwest. If these winds persist over a period of a week or more, upwelling begins to bring cold, nutrient rich, oxygen poor ocean water to the surface near the shore. Here the action of the surf mixes oxygen into the water and creates an excellent environment for plankton growth. As the tides force these waters into the estuary, they are warmed and growth occurs more rapidly, feeding the base of the food web.

16. The Life Zones of the Estuary
6 slides (two multi-part)

17. Estuary zones – upper estuary
Depending on where you are at in the estuary, the various life zones may look quite different.

18. Estuary zones – upper estuary
Tidal marsh
Depending on where you are at in the estuary, the various life zones may look quite different.

19. Estuary zones – upper estuary
Tidal marsh
Tidal flat
Depending on where you are at in the estuary, the various life zones may look quite different.

20. Estuary zones – upper estuary
Tidal marsh
Tidal flat
Open water channel
Depending on where you are at in the estuary, the various life zones may look quite different.

21. Estuary zones – lower estuary
Depending on where you are at in the estuary, the various life zones may look quite different.

22. Estuary zones – lower estuary
Open water channel
Depending on where you are at in the estuary, the various life zones may look quite different.

23. Estuary zones – lower estuary
Open water channel
Tidal flat
Depending on where you are at in the estuary, the various life zones may look quite different.

24. Estuary zones – lower estuary
Open water channel
Tidal flat
Depending on where you are at in the estuary, the various life zones may look quite different.
Tidal marsh

25. Salt marshes and tidal fresh marshes are some of the most productive environments on earth!
The mass of the plants produced in a single season of growth on the salt marsh (biomass) is greater than any comparable area of land any where else on earth. This is because the marshes are flooded with nutrient rich waters twice daily and have adapted to life in a salty environment.

26. Tidal flats of the estuary are usually made of sand, mud, or cobble.
Holes at the surface indicate the burrows of clams, shrimp, and worms that live below. These benthic creatures depend upon the tides daily flooding to bring cool, oxygen rich seawater rich in food to their homes in the sediment.

27. Tidal flats may be made of exposed bedrock where strong currents prevent sediment from accumulating.
At low tide, eelgrass beds are exposed where they grow in mud settled between exposed rock reefs. Rocky shores are uncommon in most estuaries along the Oregon coast because of the large amounts of sediment that are deposited as the flow of the river is slowed by the rising tide. Eelgrass is a valuable type of habitat in the estuary. This rooted, flowering plant is an important food source for certain migratory ducks and geese, a place where snails and sea slugs lay their eggs, and the dense grass provides cover from predators for young fish and crabs.

28. Low tide exposes the flats to predators such as herons, shorebirds, and raccoons.
At low tide, the mudflats and marshes are exposed to the air. A narrow channel of open water remains and aquatic creatures such as fish are concentrated in these areas. Here they may seek the cover of eelgrass meadows as they try to evade larger fish or even larger seals and sea lions.

29. Life of the Estuary
6 slides

30. The producers of the estuary are the plants
The producers of the estuary are the plants. They capture the sun’s energy and convert it to a food source for millions of animals.
Whether they are microscopic phytoplankton or dense meadows of marsh grass, the flora of the estuary is the base of the food web. Some plants like eelgrass (lower right) are adapted to use low light levels in later winter and early spring to get a head start on the growing season. The blades of this amazing plant will become coated with algae, diatoms, and the eggs of many invertebrates. Microscopic phytoplankton (upper right) grow rapidly in the shallow estuary waters where warmer temperatures and an abundance of nutrients support their growth. These same waters flood over the marshes (photo at left) fertilizing and water the specially adapted plants that live there.

31. Salmon and many other kinds of fish use the estuary as a zone of transition, a place where young fish grow, safe from predators they will face in the ocean.
For salmon, the estuary is an essential part of a journey that will take them from the streams where they hatch to the ocean and back. They will feed and grow while hiding from predators as they make the change from living in fresh water to living in the salty ocean. In the ocean, they will grow larger and then return through the estuary to reach the headwaters of the rivers and creeks where they were born so that they may spawn and die, returning nutrients to the ecosystem.

32. Many forms of life in the estuary live beneath the surface of the mud or sand.
Creatures living beneath the surface of the tidal flats are known as benthic dwellers. Living below or on the bottom, they often feed on decaying plant and animal material called detritus. Some are filter feeders like clams and worms which draw the estuary waters into their burrows and strain the nutrient rich “soup” for food such as microscopic plankton. These animals depend on the dissolved oxygen in the tidewater and use their burrows for protection from predators. Ghost shrimp are called detritivores because they sift through decaying plant and animal material for food.

33. Migratory birds depend on the wetlands of the estuary for resting and feeding as they travel between nesting and wintering grounds.
Many shorebirds, seabirds, and waterfowl depend on the estuary as travel distances as great as 11,000 miles from nesting grounds to over-wintering areas and back. The fuel provided by the food they eat along the way is essential as they follow seasonal weather patterns to reach safe nesting habitat. Their young must be healthy and fit for the return to places with a milder climate during the winter. Along Oregon’s coast, Black brant (on the left) migrate northward in the spring and some spend the winter here. The Greater yellowlegs (on the right) are found here throughout the year.

34. Crabs live in many different types of habitat in the estuary.
The Red rock crab (on the left) may be found throughout the lower estuary, but as the name implies, it prefers rocky shores. Dungeness crabs (upper right) ocassionally use the cover of eelgrass beds, while the Lined shore crab (lower right) is typically found in burrows between rocky rubble or dug into the bank beneath the marsh.

35. Many animals begin their lives in the protective waters of the estuary.
The complex and diverse habitat found in the estuary is well suited to rearing young animals. A kind of nursery, the unique conditions caused by the mixing of salty seawater and freshwater from rivers that occurs in the estuary limits adult predators from the ocean and rivers from entering. The wide variety and abundance of food available means that young animals will grow rapidly and be more fit as adults.
A larval crab
A juvenile English sole

36. Estuary Functions and Impacts
4 slides

37. Healthy estuaries can provide many different values and perform many important functions.
Flood control
Nursery areas
Migratory stopovers
Recreation
Production of biomass
Safe harbor
Feeding grounds
The marshes, tidal flats, and open waters of the estuary are part of one of the most productive ecosystems on earth. In the calm, shallow waters, billions of microscopic plants called phytoplankton trap the sun’s energy and convert it to food. Rapidly growing marshes do this as well. These producers in turn become the food for millions of animals from microscopic creatures called zooplankton to filter feeding clams and worms. As the web of life grows, larger animals feed upon the smaller ones and so forth until the mighty Chinook salmon and the Dungeness crab in turn become food for orcas, eagles, seals, and people. All of this requires that we care for the estuary and restore the functions and habitat wherever possible.

38. Timber harvest is a regulated activity in the watershed that must be properly conducted to reduce impacts to streams, rivers, and estuaries.
Forest practices have improved significantly over the past 100 years. Sediment that once reached the streams from unplanted clearcut slopes is now buffered by trees left along the edges of the stream. However, science continues to help us understand what can be done to reduce the impacts of our actions while still benefiting from the natural resources the ecosystem provides.

39. Waste that is not properly treated pollutes the waters of the estuary with excess nutrients.
When the estuary’s waters are used to dilute sewage and other wastes, the results can cause damage to many of the estuary’s inhabitants. Excess nutrients cause bacteria and algae to grow rapidly which uses up available dissolved oxygen in the water. As the oxygen is depleted, other types of bacteria begin to take over causing dangerous conditions toxic to fish and wildlife. Proper treatment of waste can reduce this problem.

40. Research has improved our understanding of what is necessary to restore estuary functions and habitat.
Research contributes to our understanding of the estuary and can identify better ways to manage our activities so that the ecosystem remains healthy. In many cases, habitat restoration is the only way to improve conditions.

41. Welcome to the Estuary!