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Title
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Transitional Habitats
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Type
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Primary: Mission Briefing Article
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Operation
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Resilient Planet
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Mission:
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Mission 3: Paradise Lost
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Print Page
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56
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Subjects
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Science | Earth and space science | Earths water | Freshwater | Oceans | Life science | BioDiversity | Physical science | Properties of materials | Chemical properties | Physical properties
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Grades
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5 | 6 | 7 | 8
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Keywords
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Transitional, habitat, brackish, halocline, thermocline, intertidal zone, fresh, water, salt, Atlantic, ocean, estuary, river, stream, ocean tide, salinity, abiotic, factor, Susquehanna River, density, estuarine, region, Chesapeake, Bay, wind, turbulence, biodiversity, immersion, exposure, organism, environmental, change
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Duration
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00:15:00 (HH:MM:SS)
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Audience
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Teachers | Elementary Grades | Junior High
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Created On
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4/20/2008
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Copyright
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NOAA Photo Library
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From: Resilient Planet Mission 3: Paradise Lost (pp: 56) |
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Transitional Habitats This article discusses the transition that occurs in water due to either changes in salinity, called haloclines, or temperature, called thermoclines. |
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Fresh water from land mixes with salt water from the Atlantic Ocean to create brackish water. Nutrients wash into the estuary from rivers, streams, and ocean tides. The combination of nutrients and brackish water makes estuaries one of the most productive habitats on the planet. Salinity is the amount of dissolved salts in the water and is an important abiotic factor in determining what plants and animals can exist in any part of the estuary. Where the Susquehanna River empties fresh water into the northern part of the Bay, the salinity is low. It is higher closer to the Atlantic Ocean.
However, when conditions are right, salt water may not mix with the fresh water. Because salt water has a higher density, it settles to the bottom under the lower density fresh water. That is why, in estuarine regions, the water near the surface may be fresher than the water near the bottom. The salinity increases as you go deeper into the water. A zone where salinity changes rapidly with depth is called a halocline ("halo" means salt and "cline" means slope or change). The halocline illustration shows how different the salinity can be from the top to the bottom of a body of water. These layers are not permanent features. For example, wind can move and mix the water.
Temperature is another important abiotic factor in the Chesapeake Bay. In the spring and summer, water temperature at the surface is warmer than the denser and colder deep water. At these times, a zone can form where temperature rapidly changes with depth, called a thermocline. In the fall, the surface water cools quickly and drops to the bottom causing the thermal layers to mix. Wind and water turbulence can also mix water of different temperatures. This movement of water is important for mixing the nutrients in the water to support the Bay's large biodiversity.
Another factor that affects organisms living along the shoreline is changes in sea level. When the tide is high, large expanses of sand and mud may be covered by water. When the tide goes out, that land becomes exposed to air. This pattern of immersion and exposure creates a very stressful environment. Known as the intertidal zone, the land between high and low tides is home to only organisms that are adapted to its severe changes.
 Along the shore is one of the harshest habitats. It is an area between the lowest tide level and the highest tide level called the intertidal zone. Organisms that live here are adapted for sudden environmental changes.
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