Estuaries: Introduction
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This document discusses estuaries, including their physical characteristics and ecosystems. Estuaries are bodies of water where freshwater rivers meet and mix with saltwater oceans. They can have varying salinity levels depending on their location and tidal influences. Estuaries provide important habitat for many species but are also impacted by human activities like pollution. Organisms living in estuaries have developed ways of coping with the ever-changing conditions, such as maintaining constant internal salt levels or burrowing in the mud.
Estuaries: Introduction
- 2. Estuaries: Origins and Types of Estuaries Physical Characteristics of Estuaries (Salinity, Substrate, Other Physical Factors) Estuaries as Ecosystem (Types of Communities, Feeding Interactions) Human Impact on Estuarine Communities
- 3. http://www.earthgauge.net/wp-content/images/Estuaries_Low.jpg Estuaries are partially closed bodies of water where freshwater rivers and streams meet and mix with the salt water of the ocean. Over 60% of coastal rivers and bays in the continental U.S. are degraded by nutrient pollution from things like fertilizers and pet waste 75% of commercial aquatic species – like salmon, oysters and horseshoe crabs – depend on estuaries for their primary habitat, spawning grounds and nursery areas. Estuaries come in all shapes and sizes. They can be called bays, lagoons and inlets.
- 4. • Drowned River Valleys / Coastal Plain Estuaries Melting of ice rose sea level = sea invaded lowlands and river mouths Most common Ex. Chesapeake Bay, mouth of Delaware River, St. Lawrence River, mouth of River Thames ←Delaware River Chesapeake Bay ← Cape Hatteras
- 5. • Bar-built Estuaries Accumulation of sediments along the coast =sand bars & barrier islands acts as walls between fresh water and ocean. Ex. Cape Hatteras , Texas Coast of Gulf Mexico ←Delaware River Chesapeake Bay ← Cape Hatteras
- 6. • Tectonic Estuaries Land sank or subsided, Result of movements of crust
- 7. • Fjords Retreating glaciers cut deep valleys along the coast. Submerged when sea level rose and rivers flow Common in Southeastern Alaska, British Columbia, Norway, New Zealand
- 8. • SALINITY Seawater 35% salinity + Freshwater 0% salinity ↑ Salinity = ↑ Depth 35% 25% 15% 5% 0%
- 9. • SALINITY Diurnal tide – organisms are subjected to 2 shifts in salinity Semidiurnal Tide- 4 shifts in salinity 35% 25% 15% 5% 0% 25% 15% 5% 0% 35%
- 10. • SALINITY Distribution of Salinity is influenced by: the shape of estuary & its bottom, wind, evaporation of water, and tide Seasonal variations in freshwater runoff from rivers by rainfall patterns or snowmelt Little freshwater runoff + high evaporation = high salinity estuaries May reach 50% -100% during dry spells = negative estuaries
- 11. • SALINITY Current – tide rushes in creating strong tidal currents In few places tide comes in a nearly vertical wall of water tidal bore - as high as 6m in Qiantang River, China Greatly affects salinity
- 12. • SALINITY Coriolis Effect Northern hemisphere– fresh water toward the sea is deflected to the right Southern hemisphere– the flow is to the left
- 13. • SUBSTRATE Large amount of sediments & other materials are from river
- 14. • SUBSTRATE Sand & Coarse material settle out in upper reaches Fine, muddy particles are carried down the estuary in quiet waters Substrate of most estuaries is sand or soft mud
- 15. • SUBSTRATE Mud Combination of silt and clay , rich in organic material Decay bacteria uses up oxygen in interstitial water Water cannot easily flow through fine sediments to replenish oxygen As result, sediments in estuaries are devoid of oxygen = anoxic
- 16. • SUBSTRATE Mud Black color and rotten-egg smell Accumulation of Hydrogen sulfide H2S → toxic to most organisms Anaerobic bacteria thrive under these conditions
- 17. • SUBSTRATE There is plenty of oxygen in unimpeded tidal flow Sill restricts water circulation Stagnant deep water may become depleted in oxygen ↔ decomposition of organic matter
- 18. • OTHER PHYSICAL FACTORS Water temperature is affected by depths and surface area Organisms exposed at low tide face drastic temperature fluctuations Suspended sediments reduces water clarity Can clog surfaces of filter feeders → death
- 19. Estuaries are tremendously productive and are home to large numbers of organisms Provide breeding & feeding grounds for birds, fishes, shrimps, etc. Estuarine ecosystems consist of several distinct communities
- 20. Need to adapt to extremes in salinity, temperature, and other physical factors. No other marine environments changes so rapidly in many ways as an estuary. Few species have adapted to estuarine conditions • LIVING IN AN ESTUARY
- 21. Coping with Salinity Fluctuations Euryhaline species tolerate wide range of salinities Stenohaline species are limited to upper/lower ends of estuary Rarely penetrate estuary proper Can be marine or freshwater origin • LIVING IN AN ESTUARY
- 22. Coping with Salinity Fluctuations Brackishwater – water of intermediate salinity Brakishwater, stenohaline, and freshwater marine species. • LIVING IN AN ESTUARY
- 23. Coping with Salinity Fluctuations Some undergo osmosis Some animals adapt by hiding in mud burrows, close their shells, or swim away Most organism rely on other mechanism • LIVING IN AN ESTUARY
- 24. Coping with Salinity Fluctuations Osmoconformers – maintain osmotic balance by changing salinity of body fluids. Soft-bodied estuarine animals, mollusks, polychaetes worms. • LIVING IN AN ESTUARY
- 25. Coping with Salinity Fluctuations Osmoregulators – keep the salinity of body fluids constant. Via Active transport Accomplished by gills, kidneys & other structures Bony fishes osmoregulate - lower salinity of body fluid Salmon & freshwater eel - active transport in gills and kidney • LIVING IN AN ESTUARY
- 26. Coping with Salinity Fluctuations Perfect Osmoconformers or Perfect Osmoregulators – Invertebrates Osmoregulate = low salinities Osmoconform =high salinities • LIVING IN AN ESTUARY
- 27. Coping with Salinity Fluctuations Estuarine Plants Grasses & some Salt-marsh plants have high salt tolerance Absorb salts & concentrate sugars to prevent water from leaving tissues Opposite to marine organisms in estuaries • LIVING IN AN ESTUARY
- 28. Coping with Salinity Fluctuations Cordgrasses, other Salt-marsh plants, and Mangroves Excrete excess salts by salt glands in their leaves • LIVING IN AN ESTUARY Cordgrass (Spartina) Black Mangrove leaf
- 29. Coping with Salinity Fluctuations Pickleweed (Salicornia) – succulents Absorb water to dilute salts • LIVING IN AN ESTUARY
- 30. • LIVING IN AN ESTUARY Adapting to the Mud Problem: Nothing to hold on to → most animals burrow or live in permanent tubes Clams extend their siphons for food and oxygen Difficult to move on mud → inhabitants tend to be stationary/ slow-moving Depletion of oxygen → burrowers pump oxygen-rich water into their burrows → Some have blood with hemoglobin
- 31. • LIVING IN AN ESTUARY Adapting to the Mud Benefit: Salinity fluctuation is less drastic