Physical Features of Estuaries

Basic Information

Estuaries vary in origin, size and type Also called: lagoons, bays and sloughs 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 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

Chesapeake Bay

Coastal Plain Estuaries

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

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

This type of estuary occurs along major fault lines

Fjords or Glacier- carved Estuaries

Retreating glaciers cut deep valleys along a coastline

The valleys then filled with ocean water and rivers now empty into them

Found in those areas with long histories of glaciers

Fjord Estuary

Salinity

Differs from estuary to estuary and during different times of day

Varies with depth Salt water sinks due

to its increased density

Freshwater is less dense so it floats on top of a saline layer

This phenomenon is called a salt wedge

Salt Wedges move with the diurnal tides

Tidal Bore

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

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 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 Most of the estuary

ecosystems have a muddy bottom

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