Estuaries Where Rivers Meet the Sea. Origins And Types of Estuaries Estuaries are semi-enclosed areas where fresh water and seawater meet and mix

EstuariesEstuaries

Where Rivers Meet the SeaWhere Rivers Meet the Sea

Origins And Types of EstuariesOrigins And Types of Estuaries

EstuariesEstuaries are semi-enclosed areas where are semi-enclosed areas where fresh water and seawater meet and mixfresh water and seawater meet and mix

They therefore represent a close They therefore represent a close interaction between land and seainteraction between land and sea

EstuariesEstuaries are among the most productive are among the most productive environments on earth.environments on earth.

EstuariesEstuaries also rank among the also rank among the environments most affected by humansenvironments most affected by humans

Estuaries are scattered along the shores Estuaries are scattered along the shores of all the oceans and vary widely in origin, of all the oceans and vary widely in origin, type, and sizetype, and size

They may be called They may be called lagoonslagoons, , sloughssloughs, or , or baysbays – – such as Florida Baysuch as Florida Bay

Some oceanographers classify enclosed Some oceanographers classify enclosed seas with restricted circulation, such as seas with restricted circulation, such as the Baltic and Black seas, as estuariesthe Baltic and Black seas, as estuaries


Many estuaries were formed when sea level Many estuaries were formed when sea level rose because of the melting of ice at the end of rose because of the melting of ice at the end of the last ice age (the last ice age (18,000 years ago18,000 years ago))

The sea invaded lowlands and river mouths in The sea invaded lowlands and river mouths in the processthe process

These estuaries are called These estuaries are called drowned river drowned river valleysvalleys or or coastal plain estuariescoastal plain estuaries

They are the most common type of estuaryThey are the most common type of estuary


Another type of estuary is the Another type of estuary is the bar built estuarybar built estuary The accumilation of sediments along the coast builds The accumilation of sediments along the coast builds

up sand bars and barrier islands (up sand bars and barrier islands (found along coasts found along coasts in the Gulf of Mexicoin the Gulf of Mexico))

Other estuaries, such as San Francisco Bay in Other estuaries, such as San Francisco Bay in California, were created not because sea level California, were created not because sea level rose but because the land sank – rose but because the land sank – tectonic tectonic estuariesestuaries

Fjords Fjords are estuaries where retreating glaciers are estuaries where retreating glaciers cut deep, often spectacular, valleys alond the cut deep, often spectacular, valleys alond the coast. The valleys were partially submerged coast. The valleys were partially submerged when sea level rose, and rivers flowed into themwhen sea level rose, and rivers flowed into them


estuariesestuaries

Physical Characteristics of Physical Characteristics of EstuariesEstuaries

Influenced by the tides and mixing of fresh Influenced by the tides and mixing of fresh and salt water, estuaries have a unique and salt water, estuaries have a unique combination of physical and chemical combination of physical and chemical characteristicscharacteristics

These factors govern the lives of the These factors govern the lives of the organisms that live there.organisms that live there.

The salinity of estuaries fluctuates The salinity of estuaries fluctuates dramatically both from place to place and dramatically both from place to place and from time to timefrom time to time

Salinity varies with depth as wellSalinity varies with depth as well Salt water being more dense sinks to the Salt water being more dense sinks to the

bottom and creates bottom and creates salt wedgessalt wedges Salt wedgesSalt wedges move back and forth with the move back and forth with the

daily tidesdaily tides


Salt WedgeSalt Wedge

In regions of little freshwater runoff and In regions of little freshwater runoff and high evaporation the salinity of the water high evaporation the salinity of the water increasesincreases

The average salinity for some locations The average salinity for some locations like this – Laguna Madre, Texas coast – is like this – Laguna Madre, Texas coast – is over 50% in some areas, and may reach over 50% in some areas, and may reach 100% in dry spells. These high salinity 100% in dry spells. These high salinity estuaries are called estuaries are called negative estuariesnegative estuaries


Living in EstuariesLiving in EstuariesCoping with Salinity FluctuationsCoping with Salinity Fluctuations

Living in an estuary is not easy, so few Living in an estuary is not easy, so few species have adapted to these conditionsspecies have adapted to these conditions

Maintaining the proper salt and water Maintaining the proper salt and water balance in cells and body fluids is one of balance in cells and body fluids is one of the greatest challenges of organisms living the greatest challenges of organisms living in estuariesin estuaries

Most estuary organisms are marine Most estuary organisms are marine organisms that can tolerate low salinity.organisms that can tolerate low salinity.

Most estuary organisms are Most estuary organisms are euryhalineeuryhaline species, species, that is, they tolerate a wide range of salinities.that is, they tolerate a wide range of salinities.

The relatively few The relatively few stenohalinestenohaline species, those species, those that tolerate only a narrow range of salinities, that tolerate only a narrow range of salinities, are limited to the upper or lower ends of the are limited to the upper or lower ends of the estuary and rarely penetrate in the estuary estuary and rarely penetrate in the estuary properproper

Some live in brackish water, or water of Some live in brackish water, or water of intermediate salinityintermediate salinity


Soft-bodied estuarine animals, such as many molluscs Soft-bodied estuarine animals, such as many molluscs and polychaete worms, often maintain osmotic balance and polychaete worms, often maintain osmotic balance simply by allowing their body fluids to change with the simply by allowing their body fluids to change with the salinity of the water. These are called salinity of the water. These are called osmoconformersosmoconformers..

Many fish, crabs, molluscs, and plochaete worms are Many fish, crabs, molluscs, and plochaete worms are instead instead osmoregulatorsosmoregulators. They keep the salt . They keep the salt concentration of body fluids more or less the same concentration of body fluids more or less the same regardless of the salinity of the water.regardless of the salinity of the water.

When salinity of water is lower than that of their blood, they get When salinity of water is lower than that of their blood, they get rid of excess water and take-up solutes via active transport by rid of excess water and take-up solutes via active transport by the gills, kidneys, and other structuresthe gills, kidneys, and other structures

AnadromousAnadromous fish: migrate from sea to spawn in freshwater fish: migrate from sea to spawn in freshwater CatadromousCatadromous fish: migrate from fresh water to spawn in the sea fish: migrate from fresh water to spawn in the sea


Types of Estuarine CommunitiesTypes of Estuarine Communities

Several distinct communities are Several distinct communities are associated with estuariesassociated with estuaries

One consists of the plankton, fishes, and One consists of the plankton, fishes, and other open water organisms that come in other open water organisms that come in and leave with the tideand leave with the tide

Several other communities are permanent Several other communities are permanent parts of the ecosystemparts of the ecosystem

Open WaterOpen Water MudflatsMudflats Salt MarshesSalt Marshes Mangrove ForestsMangrove Forests

Types of Estuarine CommunitiesTypes of Estuarine Communities

One of the reasons many of the world’s great One of the reasons many of the world’s great cities developed around estuaries is the rich cities developed around estuaries is the rich supply of fish and shellfish in or near estuariessupply of fish and shellfish in or near estuaries

Many species of commercially important fishes Many species of commercially important fishes and shrimps use estuaries as nurseriesand shrimps use estuaries as nurseries

90% of the marine commercial catch in the 90% of the marine commercial catch in the northern Gulf of Mexico, for example, is of northern Gulf of Mexico, for example, is of species that depend on estuaries at some point species that depend on estuaries at some point in their livesin their lives

Types of Estuarine Communities:Types of Estuarine Communities:Open WaterOpen Water

The bottoms of estuaries that becaome exposed during The bottoms of estuaries that becaome exposed during low tide often form mudflatslow tide often form mudflats

Organisms exposed to desiccation, wide variations in Organisms exposed to desiccation, wide variations in temperature, predation, and variations in salinity.temperature, predation, and variations in salinity.

Bacteria are abundant in mudflats as decomposers of Bacteria are abundant in mudflats as decomposers of organic matter.organic matter.

Chemosynthetic bacteriaChemosynthetic bacteria (hydrogen sulfide) (hydrogen sulfide) InfaunaInfauna: Dominant animals in mudflats that burrow: Dominant animals in mudflats that burrow EpifaunaEpifauna: aniamls that live on the surface or as sessil : aniamls that live on the surface or as sessil

formsforms These include detritivores, deposit, suspension, and filter These include detritivores, deposit, suspension, and filter

feedersfeeders

Types of Estuarine Communities:Types of Estuarine Communities:MudflatsMudflats

Estuaries in temperate and subtropic Estuaries in temperate and subtropic regions are usually bordered by extensive regions are usually bordered by extensive grassy areas that extend inland from the grassy areas that extend inland from the mudflatsmudflats

Sometimes they are grouped with coastal Sometimes they are grouped with coastal environments flooded at high tide and with environments flooded at high tide and with freshwater marshes and collectively called freshwater marshes and collectively called wetlandswetlands

Types of Estuarine Communities:Types of Estuarine Communities:Salt MarshesSalt Marshes

Salt Marsh Salt Marsh and Mudflatand Mudflat

Some Some Inhabitants Inhabitants of mud flatsof mud flats

Mangrove forests (mangals)Mangrove forests (mangals) are not limited to are not limited to estuaries, but in some ways they are the tropical estuaries, but in some ways they are the tropical equivalents of equivalents of salt marshessalt marshes, though the two , though the two coexist in many placescoexist in many places

MangrovesMangroves are flowering land plants adapted to are flowering land plants adapted to live in the intertidallive in the intertidal

75% of all sheltered tropical shores were at one 75% of all sheltered tropical shores were at one time fringed with mangrovestime fringed with mangroves

Mangrove forests, however, are being rapidly Mangrove forests, however, are being rapidly destroyed by humansdestroyed by humans

Types of Estuarine Communities:Types of Estuarine Communities:Mangrove ForestsMangrove Forests

World Distribution of Salt World Distribution of Salt Marshes and Mangrove ForestsMarshes and Mangrove Forests

Human Impact on Estuarine Human Impact on Estuarine CommunitiesCommunities

The environmental consequences of human intrusion in estuarine The environmental consequences of human intrusion in estuarine communities, particularly in highly productive salt marshes and communities, particularly in highly productive salt marshes and mangrove forests, have been disastrousmangrove forests, have been disastrous

Countless have been obliterated, and many surviving ones are Countless have been obliterated, and many surviving ones are endangeredendangered

All around the world estuaries are being dredged to make marinas, All around the world estuaries are being dredged to make marinas, artificial harbors, and seaportsartificial harbors, and seaports

Others are filled to create everything from industrial parks and urban Others are filled to create everything from industrial parks and urban development to garbage dumpsdevelopment to garbage dumps

Dredging navigational channels increases the exposure to wave action Dredging navigational channels increases the exposure to wave action and therefore the destruction of salt marshesand therefore the destruction of salt marshes

70% of those in California have been lost70% of those in California have been lost Similar affects are being and have been felt by mangrove forestsSimilar affects are being and have been felt by mangrove forests There is evidence that the 2004 tsunami would have been less severe in There is evidence that the 2004 tsunami would have been less severe in

some areas if the mangroves would have still been present.some areas if the mangroves would have still been present. Mangrove forests also help with shoreline erosion and protects against Mangrove forests also help with shoreline erosion and protects against

storm surges generated by hurricanes.storm surges generated by hurricanes.

Florida EstuariesFlorida Estuaries

Florida Estuary, Gulf CoastFlorida Estuary, Gulf Coast

Generalized Food Web in an EstuaryGeneralized Food Web in an Estuary

The endThe end

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Estuaries Where Rivers Meet the Sea. Origins And Types of Estuaries Estuaries are semi-enclosed areas where fresh water and seawater meet and mix