Estuaries: Introduction

ESTUARIES:

Where Rivers Meet the Sea

By: Ezel Anne Benitez

Jhulien DizonMark Adrian Bernardino

Estuaries:

Origins and Types of Estuaries

Physical Characteristics of Estuaries (Salinity, Substrate, Other Physical Factors)

Estuaries as Ecosystem (Types of Communities, Feeding Interactions)

Human Impact on Estuarine Communities

http://www.earthgauge.net/wp-content/images/Estuaries_Low.jpg

Estuaries are partially closed bodies of water where freshwater rivers and streams meet and mix with the salt water of the ocean.

Over 60% of coastal rivers and bays in the continental U.S. are degraded by nutrient pollution from things like fertilizers and pet waste

75% of commercial aquatic species – like salmon, oysters and horseshoe crabs – depend on estuaries for their primary habitat, spawning grounds and nursery areas.

Estuaries come in all shapes and sizes. They can be called bays, lagoons and inlets.

• Drowned River Valleys / Coastal Plain Estuaries

Melting of ice rose sea level = sea invaded lowlands and river mouths

Most common

Ex. Chesapeake Bay, mouth of Delaware River, St. Lawrence River, mouth of River Thames

Origin and Types of Estuaries

←Delaware River

Chesapeake Bay

← Cape Hatteras

• Bar-built Estuaries

Accumulation of sediments along the coast =sand bars & barrier islands

acts as walls between fresh water and ocean.

Ex. Cape Hatteras , Texas Coast of Gulf Mexico


←Delaware River

Chesapeake Bay

← Cape Hatteras

• Tectonic Estuaries

Land sank or subsided,

Result of movements of crust


• Fjords

Retreating glaciers cut deep valleys along the coast.

Submerged when sea level rose and rivers flow

Common in Southeastern Alaska, British Columbia, Norway, New Zealand


Physical Characteristics of Estuaries

• SALINITY

Seawater 35% salinity + Freshwater 0% salinity

↑ Salinity = ↑ Depth 35% 25% 15% 5% 0%

• SALINITY

Diurnal tide – organisms are subjected to 2 shifts in salinity

Semidiurnal Tide- 4 shifts in salinity

35% 25% 15% 5% 0%

25% 15% 5% 0%

35%


• SALINITY

Distribution of Salinity is influenced by:

the shape of estuary & its bottom, wind, evaporation of water, and tide

Seasonal variations in freshwater runoff from rivers by rainfall patterns or snowmelt

Little freshwater runoff + high evaporation = high salinity estuaries

May reach 50% -100% during dry spells = negative estuaries


• SALINITYCurrent – tide rushes in creating strong tidal currentsIn few places tide comes in a nearly vertical wall of water tidal bore - as high as 6m in Qiantang River, ChinaGreatly affects salinity


• SALINITYCoriolis Effect

Northern hemisphere– fresh water toward the sea is deflected to the right

Southern hemisphere– the flow is to the left


• SUBSTRATELarge amount of sediments & other materials are from river


• SUBSTRATESand & Coarse material settle out in upper reaches

Fine, muddy particles are carried down the estuary in quiet waters

Substrate of most estuaries is sand or soft mud


• SUBSTRATE

Mud

Combination of silt and clay , rich in organic material

Decay bacteria uses up oxygen in interstitial water

Water cannot easily flow through fine sediments to replenish oxygen

As result, sediments in estuaries are devoid of oxygen = anoxic


• SUBSTRATE

Mud

Black color and rotten-egg smell

Accumulation of Hydrogen sulfide H2S → toxic to most organisms

Anaerobic bacteria thrive under these conditions


• SUBSTRATE

There is plenty of oxygen in unimpeded tidal flow

Sill restricts water circulation

Stagnant deep water may become depleted in oxygen ↔ decomposition of organic matter


• OTHER PHYSICAL FACTORS

Water temperature is affected by depths and surface area

Organisms exposed at low tide face drastic temperature fluctuations

Suspended sediments reduces water clarity

Can clog surfaces of filter feeders → death


Estuaries as Ecosystems

Estuaries are tremendously productive and are home to large numbers of organisms

Provide breeding & feeding grounds for birds, fishes, shrimps, etc.

Estuarine ecosystems consist of several distinct communities


Need to adapt to extremes in salinity, temperature, and other physical factors.

No other marine environments changes so rapidly in many ways as an estuary.

Few species have adapted to estuarine conditions

• LIVING IN AN ESTUARY


Coping with Salinity Fluctuations

Euryhaline species tolerate wide range of salinities

Stenohaline species are limited to upper/lower ends of estuary

Rarely penetrate estuary proper

Can be marine or freshwater origin




Brackishwater – water of intermediate salinity

Brakishwater, stenohaline, and freshwater marine species.




Some undergo osmosis

Some animals adapt by hiding in mud burrows, close their shells, or swim away

Most organism rely on other mechanism




Osmoconformers – maintain osmotic balance by changing salinity of body fluids.

Soft-bodied estuarine animals, mollusks, polychaetes worms.




Osmoregulators – keep the salinity of body fluids constant.

Via Active transport

Accomplished by gills, kidneys & other structures

Bony fishes osmoregulate - lower salinity of body fluid

Salmon & freshwater eel - active transport in gills and kidney




Perfect Osmoconformers or Perfect Osmoregulators –

Invertebrates

Osmoregulate = low salinities

Osmoconform =high salinities




Estuarine Plants

Grasses & some Salt-marsh plants have high salt tolerance

Absorb salts & concentrate sugars to prevent water from leaving tissues

Opposite to marine organisms in estuaries



Coping with Salinity FluctuationsCordgrasses, other Salt-marsh plants, and Mangroves

Excrete excess salts by salt glands in their leaves


Cordgrass (Spartina)

Black Mangrove leaf


Coping with Salinity FluctuationsPickleweed (Salicornia) – succulents

Absorb water to dilute salts


Estuaries as Ecosystems• LIVING IN AN ESTUARY

Adapting to the MudProblem:

Nothing to hold on to → most animals burrow or live in permanent tubes

Clams extend their siphons for food and oxygen

Difficult to move on mud → inhabitants tend to be stationary/ slow-moving

Depletion of oxygen → burrowers pump oxygen-rich water into their burrows

→ Some have blood with hemoglobin

Estuaries as Ecosystems• LIVING IN AN ESTUARY

Adapting to the MudBenefit:

Salinity fluctuation is less drastic

Environment

Estuaries: Introduction