Physical Features of Estuaries
Basic Information Estuaries vary in origin, size and type Estuaries vary in origin, size and type Also called: lagoons, bays and sloughs Also called: lagoons, bays and sloughs Defined by being an area where fresh and salt water mix Defined by being an area where fresh and salt water mix It is the transition from land to sea and from fresh water to salt water It is the transition from land to sea and from fresh water to salt water Transport and trap nutrients and sediment to provide a rich ecosystem Transport and trap nutrients and sediment to provide a rich ecosystem
Drowned River Valley Formed when the ice melted during the last ice age and flooded the river mouths Formed when the ice melted during the last ice age and flooded the river mouths Chesapeake Bay
Coastal Plain Estuaries Formed when low areas around rivers were flooded due to the ice melting after the last ice age Formed when low areas around rivers were flooded due to the ice melting after the last ice age
Coastal Plain Estuary
Barrier Built Estuary Formed by an accumulation of sediments Formed by an accumulation of sediments The sand bars that form create a barrier between a shallow lagoon and the ocean The sand bars that form create a barrier between a shallow lagoon and the ocean
Barrier Built Estuary
Tectonic Estuaries Created when the land around a river sank as a result of tectonic action Created when the land around a river sank as a result of tectonic action This type of estuary occurs along major fault lines This type of estuary occurs along major fault lines
Fjords or Glacier- carved Estuaries Retreating glaciers cut deep valleys along a coastline Retreating glaciers cut deep valleys along a coastline The valleys then filled with ocean water and rivers now empty into them The valleys then filled with ocean water and rivers now empty into them Found in those areas with long histories of glaciers Found in those areas with long histories of glaciers
Fjord Estuary
Salinity Differs from estuary to estuary and during different times of day Differs from estuary to estuary and during different times of day Varies with depth Varies with depth Salt water sinks due to its increased density Salt water sinks due to its increased density Freshwater is less dense so it floats on top of a saline layer Freshwater is less dense so it floats on top of a saline layer This phenomenon is called a salt wedge This phenomenon is called a salt wedge Salt Wedges move with the diurnal tides Salt Wedges move with the diurnal tides
Tidal Bore Nearly vertical wall of water that develops as the tide comes into an estuary Nearly vertical wall of water that develops as the tide comes into an estuary
Tidal Currents Caused because of the narrow opening of the estuary – the water moves in fast and strong Caused because of the narrow opening of the estuary – the water moves in fast and strong Due to the Coriolis effect the tide is less on the left side of a river in the northern hemisphere – tide is deflected to the right Due to the Coriolis effect the tide is less on the left side of a river in the northern hemisphere – tide is deflected to the right
Substrates Particles settle out of the river at different locations due to their grain size Particles settle out of the river at different locations due to their grain size Sand and coarse materials settle out in the upper reaches of the estuary Sand and coarse materials settle out in the upper reaches of the estuary Mud and fine particles settle out closer to the ocean and may even be carried out to sea Mud and fine particles settle out closer to the ocean and may even be carried out to sea
Mud Most of the estuary ecosystems have a muddy bottom Most of the estuary ecosystems have a muddy bottom Mud is a combination of silt and clay Mud is a combination of silt and clay Because mud does not allow water to flow through it easily and mix with the water column – it becomes anoxic quickly Because mud does not allow water to flow through it easily and mix with the water column – it becomes anoxic quickly