Coastal Environments Test 2

coastal sediment sources

sediment is weathered in different ways:

- weathering of rock

- activity of living organisms

- volcanic eruption

- chemical reactions

sediment is carried to coast in different ways:

- rivers

- wind

beach sediment color (red, green, black beaches)

1. Red Becahses are caused by Iron (oxides into a red color) 

Black Beaches are caused by Basalt (Volcanic Sads)

Green beaches caused by Olivine (Volcanic Sands)

sediment grain size analysis method

used to determine average sediment size

sieve analysis

a stack of sieves with large holes at the top, small at the bottom

sediment filters through and at the end you can tell what percentage stopped at each level (what percent of sample is each size)

you can use numerical treatment of grain size, using stats and graphs based on the sieve analysis to determine average grain size

oscillatory flow

as opposed to unidirectional flow

fluid motion reverses direction, flow is turbulent instead of smooth

this is what causes seafloor ripples

happens in ocean and lake waves

when water depth is 1/2 the wavelength or less, the oscillatory flow can contact theh seafloor and move sediment

in deeper areas, oscillatory flow doesn't move sediment

unidirectional flow

as opposed to oscillatory flow

like a river, water that starts in one place and ends in another place

is laminar as opposed to turbulent

sediment transport

difficult to predict how particles will move with flowing fluid

moving water transports sediment, but so does moving air (fluid is any material that is deformable under its own mass, including the atmosphere/air)

things that affect how sediment is moved

these things can be measured to know if coastal sediment will be moved by flowing water

slope

wind direction

wind speed

flow

water speed

water depth

sediment size

water movement affected sediment transfer

tidal currents

- tidal inlets can create sediment transport, like in ebb and flood tides

undertow and rip currents can be important for sediment transport. undertow is the flow of water offshore that pulls sediment out. rip current can carry sand from beach to significant distances offshore

bed shear stress

frictional force exerted by flow per unit area of bed

this controls entrainment and transport of sediment

shear stress parallel to any surface in a material

shear stress is created if principal stresses are unequally distributed

equation for bed shear stress

hjulstrom diagram

diagram that shows the function of the force of water and sediment transport

looks at particles transported, eroded, and deposited based on water speed and grain size

grain reynolds number

Increase means increase in grain size, shear velocity & turbulence, or a decrease in kinematic viscosity.

Measures Turbulence of a grain-fluid boundary

helps determine if waves have sufficient energy to carry out erosion in the specified location

delta

where fluvial river systems meat the ocean

marginal marine or lacustrine systems

the deposition rate far exceeds erosion rate (defined by progradation)

delta size

reflects the type of coastline

depositional coasts on passive margins make larger deltas

- larger drainage basins

- wider continental shelves

- finer sediment

erosional coasts on active margins create smaller deltas

- closer mountain ranges

- narrower continental shelves

- coarser sediment

delta classification

river dominated

wave dominated

tide dominated

river dominated delta

ex: mississippi river delta

aka "bird's foot delta"

weak tide and current flow

fine grained sediment

distributary channel, deposition dominant

abundant vegetation (marsh/mangrove)

tide dominated delta

ex: ganges brahmanputra river delta

lots of channels perpendicular to shoreline

reason is that there is a high tide range

tide is the most critical mechanism for sediment movement

tidal current velocity is greater than river current

redistribute sediment

linear ridges parallel to flow

grain size gradation

wave dominated delta

ex: nile river delta

waves coming in create longshore transport and smooth the coastline

waves are more powerful than the river channels are in terms of moving sediment

deflect river mouth

beaches, barrier ridges, spits

smooth front

cupsate form

eolian dunes

not very much vegetation

importance of deltas

hydrocarbon deposits/reservoirs

ecologically diverse and productive

major population centers

protection in cases of storms

what influences delta form

climate

slope

river velocity/discharge

sediment load

waves

tides

currents

winds

delta migration

estuary characteristics

partially enclosed body of water

where river systems meet marine systems

defined by transgression (water coming into land barrier)

often flooded river or glacial valley

transition from fully river to fully ocean (continental shelf) processes and conditions

salinity transition from fresh to salt water

bidirectional exchange of sediment, water, nutrients

highest biological productivity on earth

estuarian physiochemical conditions

key concentrations:

- dissolved ions (salinity), dissolved oxygen

- in poorly mixed estuaries there may be less oxygen available

dissolved organic carbon

- food for organisms to eat

- one of the reasons estuaries are so productive, there is ample food available

particulate organic matter

- also food

suspended sediment concentration

- organisms also have different tolerances to sediment concentration

- sediment blocks out light

- sediments bring nutrients

what happens when river systems meet marine systems

salinity distribution can change at any given point in the estuary based on external conditions; during a drought, during areas of more seawater intrusion

mobile animals can move around and find the area in the estuary that suits their needs (sessile organisms are out of luck if the salinity in their area changes)

estuary classification by formation/physiography

flooded river valley

fjord

bar built

tectonic

drowned river estuary

coastal plain

passive margins

tectonic estuary

movement created a low spot that is now filled with water

fjord estuary picture

these have a glacial origin

bar-built estuary

blind estuaries (barrier islands separate the enclosed estuary from the open ocean)

lagoon

estuary classification by mixing/chemical oceanography

this is based on circulation patterns of salt and fresh water (not on shape)

salt wedge

partially mixed

vertically (well) mixed

stratified

salt wedge estuary

sediment transported seaward

freshwater river output exceeds saltwater input

tides have minimal influence (water is not mixing)

buoyancy puts freshwater on top fo saltwater

partially mixed estuary

minor net transport

well mixed estuary

strong tidal influence (macro to mega tidal)

tidal currents exceed river output

salinity uniformly grades from the river to ocean

fjord estuary

aka stratified estuary

sediment is trapped

estuary is partially blocked by a sediment still preventing water circulation

freshwater is directly on top of salt water

list the four types of estuaries based on mixing and describe them.

List the four types of estuaries based on geography and describe them.

wave dominated estuary

microtidal and poorly mixed

transverse barrier bards common (barrier islands)

blind estuary common

primarily river deposition

not a lot of coastal wetlands

tide dominated estuary

macrotidal and well mixed

sand bars and channels parallel to axis from marine sources

lots of tidal flats exposed during low tide

importance of estuaries

provide natural habitat

economic resource

environmental services

coastal protection

estuaries as natural habitat

biological productivity

thousands of species depend on them to live, feed, reproduce

many marine organisms depend on estuaries at some point in their development

high levels of organic matter, enclosed nature provides protection, microhabitats with lots fo options (created by rising and falling tides, changes in water depths and chemistry)

estuaries as economic resources

commercial value, resources provide economic benefits for tourism, fisheries, and recreational activities

protected coastal waters of estuaries support public infrastructure, serving as harbors and ports

estuaries as environmental services

water draining from uplands carries sediments, nutrients, and other pollutants into estuaries. as the water flows through wetlands such as swamps and salt marshes, much of the sediments and pollutants are filtered out. this filtrations creates cleaner water

salt marsh grasses and other estuarine plants also help prevent erosion and stabilize shorelines

how estuaries provide coastal protection

wetland plants and oils act as natural buffers between the land and ocean, absorbing flood waters and dissipating storm surges

this protects upland habitat as well as valuable real estate from storms and flood damage

beach sediment properties

parent material

weathered continental rock most often delivered by rivers (size depends on competence, volume depends on capacity)

sometimes rock from localized cliff erosion or onshore transport

grain size varies but grains are generally well sorted

mature, rounded, polished, or frosted grains

terrigenous coastal sediment composition

determined by source material

- granite

- volcanic rock

determined by distance from coast

- long distance - more rounded - well sorted

determined by wave energy

- high energy - coarser grains - more rounded - well sorted

dunes

Wind can blow up larger dunes than water can create sedimentary features under the surface

Can reach over 1000 meters tall in some locations

beach morphology

erosional coasts: cliffs, rocks, pocket beaches

depositional coasts: sediment

in areas with large boulders: likely some eroding rocky headlands that are breaking down into boulders, rolled around and smoothed off by waves

in gravel beaches: smaller but still course, well sorted sediment; could be from a river or could be from gravel deposits behind beach

beaches like GoM

- carbonate and siliceous beaches

- carbonate beaches are made of the shells of living organisms

beaches with reddish-orange sediment: clay, iron presence

constructive waves

Long wave length and low frequency

Ex: swell during fair-weather, calm conditions

Wave slowly breaking onto beach without very much curve

Water has a "strong swash" - moves up high on the beach with a weak backwash

Usually more in the summer

During periods of constructive waves, sediment from greater depth than ½ wavelength is not being moved

destructive waves

Shorter wave length

Taller waves

As they approach the shoreline, they get taller, break, the wave plunges onto a steeper beach

Wave does not travel as far up the beach

During winter weather conditions, there are usually more storms, higher winds, and more destructive waves

longshore sediment transport

Longshore current

Waves meet shore at angle

Creates longshore transport

Moves sand on the beach in the direction of the longshore current

sediment ripples

They are a common feature of beaches

From oscillatory wave motions over the seafloor

spit formation/migration

Large deposit of unconsolidated material transported by longshore drift

Generally in the form of a peninsula

Build off headlands in the direction of longshore drive

Something carves a channel until the spit is completely cut off

Island continues to migrate

Example: cape henlopen spit in the delaware bay

aeolian sediment transport

sand dunes

Eolian (wind)

dunes formed through fluid migration of wind

three methods of barrier island formation

Longshore transport (sand is carried out along the coast to form a peninsula called a spit, which then breaks off and forms the island)

Sandbars are created, sea level falls, and sandbars are now long, thin islands off of the short

Sand dunes might become islands if the water level rises enough to fill in behind the sand dunes but leave the sand dunes above water

barrier island formation

Make up 13-15% of the world's coastlines

Narrow and long (longest ones in the world are in Texas)

Loose sand, not connected to any underlying substrate

Sometimes will have pockets of marsh/wetlands between the island and mainland (in the "lagoon")

barrier island over-wash processes / migration

Islands move towards the land during large storm events

Will not become part of the shore, the lagoon will still be there

Coastline will retreat as well

often, when a hurricane hits a barrier island, it will carry sediment as an overland flow from the island to the area behind the island

tidal inlets sediment dynamics

Opening in the shoreline that connects ocean to bays, lagoons, at tidal creek systems

Maintained by tidal exchange in and out of semi-enclosed body of water

Most geomorphically dynamic portions of barrier island systems

- Relevant for placement of structures

Migrate along-shore

Interrupt longshore transport of sediment

value of tidal inlets

ecosystem support: pathway for marine species between open ocean and protected estuary/lagoon

commercial and recreational fisheries

marine navigation: access to protected harbors/port infrastructure

inlet formation

Storm wash-over

Waves breach dunes

Inlet cut from back

- Escaping water

ebb/flood tidal shoals

An inlet where sand is carried from outside the lagoon inside, and as soon as it passes into the lagoon the energy of the water lessens and the sediment is deposited

Forms wetlands behind an island (on the side of the mainland)

Over time, inlets move along the island in the direction of longshore transport

lagoons

Highly enclosed coastal embayments

Typically, elongate and parallel to the coast

Often found shoreward of barrier islands or reefs

Typically, little or no freshwater input and minimal tidal exchange

- Means that from a wildlife standpoint, they are "stressed" ecosystems

Restricted flow leads to unique processes and habitats

- Elevated salinity

- Often considered a stressed ecosystem

inlet sediment bypassing

tidal prism

volume of water entering and leaving the inlet every tidal cycle

Approximately surface area of enclosed body multiplied by the tidal range

Fastest flood and ebb tide currents occur in between high and low tides (flood is between the low and high; ebb is between high and low)

inlet migration

Migrate along-shore

Interrupt longshore transport of sediment

tidal flats

Primarily mesotidal and microtidal coasts with minimal wave action (or wave protection)

Low relief coastal environments

Intermittently exposed with tidal cycles

Estuaries, barrier backshores, shorefaces, deltas

Flat sediment (mud) plains cut by a network of drainage channels

Commonly marsh covered in temperate climates

May have mudcracks and evaporites in arid environments

coastal wetlands

low wave energy

- protected by coastal water bodies

variable salinity

- marine and freshwater influence

arial extent

- defined by sediment infilling, wave energy, and tidal range

marsh setting

Play a very important role in climate

Carbon from plants gets locked up with sediment, buried, and then compressed in the earth to become rock

Carbon is sequestered for millions of years

Marshes have LOTS of CO2-consuming plants

The microbes living in the marsh eat organic matter, and the byproduct of that process is methane (marshes release large amounts of methane into the atmosphere)

salt marsh vegetation

in temperate areas: salt marsh (salt tolerant grasses)

high marsh

Spartina patens (saltmeadow cordgrass)

- Smaller plants - flatter ground/platform

Juncus gerardii (needle rush)

- Above spring high tide line because it is not salt-tolerant

low marsh

Spartina alterniflora (smooth cordgrass)

- Dense communities - closest to ope water

Phragmites australis (roseau cane)

- Dense communities - closest to open water

salt marsh sediment processes

Sedimentological Conditions:

- Fine grained sediment (mud - silt/clay)

- Organic rich sediment (Peat)

- Supports biological productivity

mangrove coasts

Rhizophora magal (red mangrove)

- Most seaward species - extends below tide line

Avicennia germinans (black mangrove)

- Low intertidal zone

Lagunacluaria racemose (white mangrove)

- High intertidal zone

Primary distribution control - temperature

- Very low freeze tolerance

Mangroves serve in many ways as a seawall due to dense structure of roots

ecosystem services of mangrove coasts

Highly productive habitat

Carbon sequestration

Storm buffering

Sediment trapping - elevation gain

reef environments

Coastal environment built entirely from organisms

Piles of intergrown organismal skeletons and sediment that form a rigid wave-resistant interlocking framework

- Oyster

- Stromatolite (algal)

- Anilid (worm)

- Coral

coral reefs

Most densely populated and diverse communities on earth (over 1 million species)

Driven by photosynthesis

- Tropical

- High energy

Organisms

- Coral (½ of reef biomass)

- Algae

- Fish

- Echinoderms

- Arthropods

coral

Phylum cnidaria (stinging cells)

Small animals (polyp)

Radial symmetry

Colonial

Bio-precipitation of calcium carbonate skeletal structure - coral structure

coral reef types

fringing

barrier

atolls

table reef

fringing coral reef

most common type of reef, grows directly from land and creates a border along the shoreline

Flat portion of reef extends out and then crests to drop off into the water

barrier coral reef

form parallel to land kind of like a barrier island; grow further out to sea and are separated from the shore by a lagoon

coral symbiosis relationship

Symbiotic relationship with zooxanthellae

- Dinoflagellate,

- Autotrophic - source of coral nutrients

coral reef distribution

threat to coral reefs

Coral bleaching• - Corals expelling their symbiotic zooxanthellae

Rising ocean acidity

Rising oceantemperature

atoll formation process

over time, a volcano or seamount surrounded by a reef erodes or rising sea levels cause it to flood; leaves the form of an atoll with a lagoon in the center

carbonate factories

warm water carbonate factory:

- Shallow-marine tropical waters supporting rapidly calcifying communities of organisms that rely on photosynthesis for energy

- Waters supersaturated with calcium carbonate which maybe precipitated as ooid sand or lime mud.

- Coral Reefs with symbiotic algae

physical factors controlling carbonate formation

the ones that control CO2 concentration

Temp (higher temp means less CO2 means more carbonates in warm water)

Pressure (lower pressure means less CO2 means more carbonates in shallow water)

Degree of agitation (higher agitation means less CO2 means more carbonates in well-aerated water

Salinity (lower salinity means reduced concentration of foreign ions means more carbonates in less saline waters)

biological factors controlling carbonate formation

Direct extraction (bio-mediated precip as hard parts/skeletal material)

Photosynthesis (consumes CO2, more carbonates in high primary production areas)

Organic decay (produces CO2, less carbonates in areas of decay)

Feeding (reshapes and aggregates carbonates - pellets)

Bacterial activity (promotes precipitation)

ecosystem services from reefs

habitat

coastal protection from waves/storms

fisheries

water quality (particularly oyster and coral reefs)

sand bars

Sometimes there are multiple sand bars attached to a shoreline

Types

- Out from beach and cured to one side in direction of longshore transport

- Directly out from beach perpendicular

- Parallel to beach in small spurts

- Arch shapes against beach

classification of beaches

Along a continuum - reflective to dissipative

Reflective: steep beach, almost like a wall (most wave energy is reflected back off shore)

Dissipative: very gentle slope that extends a long distant (wave orbital hits gentle slope and breaks, wave energy is dissipated by ramp shape)