McNabs Island Estuary EarthCache
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McNabs Island is about 5 km long and up to 1.5 km wide, its 400 ha (1000 acres) present a combination of historical, natural resources and outstanding recreational and educational opportunities.
An estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries are often associated with high rates of biological productivity.
Estuaries are typically the tidal mouths of rivers (aestus is Latin for tide), and they are often characterized by sedimentation or silt carried in from terrestrial runoff and, frequently, from offshore. They are made up of brackish water. Estuaries are often given names like bay, sound, fjord, etc. The terms are not mutually exclusive.
Estuary circulation:
Estuaries are marine environments whose pH, salinity, and water levels vary, depending on the river that feeds the estuary and the ocean from which it derives its salinity (oceans and seas have different salinity levels). The time it takes an estuary to completely cycle is called its flushing time.
• Estuarine circulation is common in estuaries; this occurs when fresh or brackish water flows out near the surface, while denser saline water flows inward near the bottom.
• Anti-estuarine flow is its opposite, in which dense water flows out near the bottom and less dense water circulates inward at the surface.
These two terms, however, have a broader oceanographic application that extends beyond estuaries proper, such as in describing the circulation of nearly-closed ocean basins.
Estuaries are more likely to occur on submerged coast, where the sea level has risen in relation to the land; this process floods valleys to form rias and fjords. These can become estuaries if there is a stream or river flowing into them.
McNab's Island has a few
Coastal marshes, Coastal marshes may be associated with estuaries and along waterways between coastal barrier islands and the inner coast. Below water decomposition processes often produce marsh gas, which may through self-ignition manifest as Will o' the wisps (aka. Jack-a-lanterns or spirites). Marshes are critically important wildlife habitat, often serving as breeding grounds for a wide variety of animal life. Constructed wetlands featuring surface-flow design are usually in the form of a marsh.
In order to register to this earthcache, you must answer 2 questions:
1- Send me a picture of you with your GPS in front of the river?
2- After reading this text and looking the landscape around you, why there are river in this place?
3-Email us the type of bottom found in this marsh (this may be done by taking a handfull of material from the edge of the Marsh, and squeezing the water out. Sand will fall apart, mud will stick together. Photograph and upload your results with your log entry.
Additional Hints
(Decrypt)
oevat n pnzren
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