Water Quality Notes-Estuary

Estuary

Area of water and shoreline where freshwater from a stream/river merges with the ocean.

Partially enclosed estuary body

Bays, lagoons, sounds, or sloughs where two different bodies of water meet and mix.

Salt marsh

Coastal wetland regularly flooded and drained by salty ocean tides.

Intertidal mudflat

Coastal wetland formed in protected areas such as bays and estuaries when tides and rivers deposit fine silt and clay.

Common precursor to salt marshes

Intertidal mudflats.

Salt marsh vegetation

High; densely covered with salt-tolerant plants such as cordgrass and rushes.

Intertidal mudflat vegetation

Low to none; mostly bare mud with microscopic algae or occasional eelgrass.

Salt marsh tidal elevation

Upper intertidal zone; flooded only during high or spring tides.

Intertidal mudflat tidal elevation

Lower intertidal zone; completely submerged and exposed twice daily.

Salt marsh soil composition

Peat and root mats mixed with mud; highly structured and stable.

Intertidal mudflat soil composition

Soft silt and clay; loose, waterlogged, and easily shifted by currents.

Salt marsh primary wildlife

Nesting birds, crabs, small mammals, and juvenile fish.

Intertidal mudflat primary wildlife

Benthic invertebrates such as burrowing worms and clams, plus feeding wading birds.

Salt marsh ecological role

Carbon sink and buffer; traps sediment, builds land, and absorbs massive wave energy.

Intertidal mudflat ecological role

Foraging ground with massive nutrient cycling and a primary feeding zone for shorebirds.

Estuary salinity

Varies from near-freshwater to ocean water and changes daily because of tides.

Why estuaries are productive

Nutrients are brought in by rivers.

Why estuaries have many habitats

Various brackish-water combinations create different habitats for plants and animals.

Major estuary producers

Salt marsh grasses, algae, and phytoplankton.

Common estuary organisms

Annelids, oysters, crabs, and fish.

How marine invertebrates and fish use estuaries

They breed in estuaries or migrate through them to freshwater habitats upstream, such as salmon.

How waterfowl use estuaries

They use estuaries as feeding areas.

Human impacts on estuaries

Pollution from feeder streams and rivers, residential/commercial development, land filling, and eutrophication.

Freshwater estuary

Freshwater from rivers mixing with large freshwater bodies such as the Great Lakes, creating an ecosystem that functions like a typical brackish estuary.

Estuary classification by water circulation

Classifies estuaries based on the amount of water circulation, which affects salt distribution and salinity concentrations.

Salt wedge estuary

Estuary where a river flows directly into saltwater and river flow pushes back seawater.

Salt wedge estuary examples

Mouths of the Mississippi, Columbia, and Hudson Rivers.

Salt wedge circulation

River flow pushes back seawater, creating a sharp boundary between a less-salty upper layer and a wedge-shaped saltwater bottom layer.

Fjord

Deep, elongated, U-shaped basin with a ledge or barrier separating it from the sea, formed by glacial erosion.

Where fjords are found

Glaciated coasts such as British Columbia, Alaska, Chile, New Zealand, and Scandinavian countries.

Fjord river input and tidal mixing

Moderately high river input and little tidal mixing.

Fjord water layers

A shallow brackish top layer moves outward and pulls denser ocean water into the deep fjord to replace it.

Shallow sill in a fjord

Blocks deep-water exchange, causing stagnant and low-oxygen lower layers.

Deep sill in a fjord

Allows better flushing and renewal of deep layers.

Slightly stratified/partially mixed estuary

Tidal flows erase the clear boundaries of a salt wedge.

Partially mixed estuary examples

Puget Sound and San Francisco Bay.

Water movement in partially mixed estuaries

Saltwater is mixed upward and freshwater is mixed downward.

Salinity in partially mixed estuaries

Lower layers typically remain saltier than upper layers.

Well-mixed estuary

Strong tidal mixing and low river flow mix seawater throughout a shallow estuary.

Why well-mixed estuaries are usually shallow

If too deep, currents cannot reach the bottom effectively.

Well-mixed estuary example

Delaware Bay.

Salinity in a well-mixed estuary

Salinity is approximately the same at the top and bottom and decreases from the ocean toward the river.

Freshwater estuary formation

Occurs when large freshwater systems such as the Great Lakes are diluted by rivers or streams draining adjacent lands.

Do freshwater estuaries contain saltwater?

No.

Freshwater estuary water sources

River water and lake water.

Lotic

River water; rivers are lotic systems.

Lentic

Lake water; lakes are lentic systems.

Chemical difference between rivers and lakes

Lakes usually have more nutrients, while rivers usually have more dissolved oxygen.

Freshwater estuary driving force

Storms.

Brackish estuary driving force

Tides.

Seiche

Vertical oscillation or sloshing of lake water caused by high winds, rapid atmospheric-pressure changes, seismic activity, and storms.

Role of seiches

They regulate freshwater estuary composition and exchange water between rivers and lakes.

Great Lakes tides

The Great Lakes have small tides, but seiches act more like tides for exchanging water.

Temperature and freshwater estuaries

Temperature differences can cause stratification and mixing; warmer conditions can form layers while cooler weather can cause lake turnover and nutrient mixing.

Why stream temperature changes matter

Shallow streams respond faster to temperature changes than deeper lakes, influencing salinity, dissolved oxygen, and pH.

Estuary classification by geomorphology

Classification based on the origin and shape of the estuary basin.

Coastal plain estuary

Also called a drowned river valley; forms when rising sea levels flood river valleys.

Coastal plain estuary valley shape

V-shaped valleys cut by rivers.

Coastal plain estuary characteristics

Often shallow, sediment-rich, and associated with spits, barrier islands, and sand bars.

Sandbar

Submerged or semi-exposed long underwater ridge or transient strip of sand.

Spit

Linear finger of sand with one end attached to land and a hooked or curved tip.

Barrier island

Completely detached large, broad island running parallel to the coast.

Water body behind a sandbar

Shallow trough or surf zone.

Water body behind a spit

Estuary or protected bay.

Water body behind a barrier island

Lagoon, sound, or salt marsh.

Key difference between sandbar, spit, and barrier island

A sandbar has no mainland attachment, a spit has one end attached, and a barrier island is completely detached.

Bar-built estuary

Created when barrier beaches/islands, sandbars, or spits partially isolate a lagoon from the ocean while receiving freshwater from the mainland.

Fjord formation

Glacially carved U-shaped troughs filled with seawater after glacial retreat.

Ria estuary

Wider, shallow inlet with gentle slopes, often formed by erosion along the coast.

Deltaic estuary

Forms at river mouths where sediment deposition creates distributary channels and tidal flats.

Lagoon

Shallow body of water separated from the open ocean by a barrier reef, sandbar, or barrier island.

Does a lagoon necessarily have river inflow?

No; a lagoon can use precipitation as its water source.

Is every lagoon an estuary?

No. Estuaries require river inflow.

Tectonic estuary

Forms when tectonic subsidence creates a depression that encourages freshwater and saltwater mixing.

Tectonic estuary example

San Francisco Bay along the San Andreas Fault.

Estuary habitat variation

Estuaries contain several types of habitats that determine which organisms can survive.

Environmental factors that vary along an estuary

Salinity, temperature, water levels, and light levels.

Organic accumulation in estuaries

Common.

Why estuary plants need strong root systems

Irregular surfaces, high-energy winds, waves, and tidal action require strong roots.

Estuary organism coping mechanisms

Moving out of unfavorable areas, closing shells, digging burrows, and excreting excess salts.

Osmoregulation

Process by which fish maintain water balance by drinking saltwater, absorbing water through the gut, and excreting solutes through gills and kidneys.

Gill chloride cells

Cells involved in excreting excess salts through fish gills.

How fish respond to hypoxia

Fish increase respiratory water flow and oxygen consumption.

Tree adaptation to high-energy winds

A low-hanging tree with numerous crowded branches is an efficient form.

Wind adaptation of tree trunks, roots, and branches

They may flatten and grow in a plane parallel to the wind direction.

Estuary food web

Complex, interrelated trophic system supporting diverse organisms and many top predators, including humans.

Primary producers in estuaries

Phytoplankton plus several other types of primary producers.

Zooplankton diet

Phytoplankton.

What eats zooplankton

Carnivorous plankton-eating fish, small fish, fish larvae and young of larger fish, and omnivores.

Why estuaries are called nurseries of the sea

Juvenile forms of many marine animals live and feed in estuaries before returning to the sea.

Detritus

Dead organic material.

Role of bacteria and fungi in estuaries

They break down dead organic material and support detrital food webs.

Detrital food web

Food web supported by detritus and organisms that consume decomposing organic material.

Benthic

Bottom-dwelling or bottom-oriented.

Examples of benthic estuary organisms

Clams, oysters, and mussels.

How clams, oysters, and mussels feed

They filter plankton and other organic matter from the water.

Deposit feeders

Organisms such as worms that move through bottom sediments to find food deposited in or on the sediments.

Examples of bottom feeders

Shrimp, crabs, many estuarine invertebrates, and many estuarine fish.

Bottom feeder

Aquatic animal that feeds on or near the floor of a body of water.

Top of estuarine food web

Carnivores and omnivores, including fish, birds, and humans.