The Dune Ecosystem and Dune - Beach Exchange

ExpectationsExpectations? ??

Objectives• Definition• Littoral Active zone• The importance of Sand Dunes.• The Physical environment.• Relationship between sand transport and wind

velocity.• Different Ways of Wind blown Sand Travels.• Formation of Dunes.

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Objectives-continued•Steps of dune formation.•Dune Vegetations.•The Primary Colonization of Aeolian sand•Features of different zones.•Adaptations.•Dune Fauna•Adaptation features of dune fauna•Food Chain of Dune ecosystem

• Definition• Coastal dunes are positioned between the drift

land at the top of the beach and the land word limit of Aeolian sand transport.

• Coastal dunes are often back sandy beaches

• Studying Marine beach and surf zone without some treatments of coastal dunes would be incomplete.

• Littoral Active zone• Shores, beaches and dunes together form

linked system called “Littoral Active zone”.

• The main features of Littoral active zone:

• 1- Extensive Aeolian sand transport.

• 2- Strong wave driven sand transport.

• 3- Sand exchange between dune and beach.

• The beach/ surf zone is marine wave driven ecosystem.

• The dune field is terrestrial wind controlled system

• The importance of Sand Dunes• Stable sand dunes play an important part in:• 1- Protecting the coastline. They act as a buffer against

wave damage during storms.

• 2- Protecting the land behind from salt water intrusion.• • 3-This sand barrier allows the development of more

complex plant communities in areas protected from salt water inundation, sea spray and strong winds.

• • 4-The dunes also act as a reservoir of sand, to replenish

and maintain the beach at times of erosion.

• Activity 1:Activity 1:• You have studied that Physical Habitat

Structure of Sandy Coastal line is determined by: Sand, Water, and Air

• What are the most important physical factors that affect coastal dunes? And Why?

The Physical environmentThe Physical environment

The amount of sand moved by the wind

depend on

The moisture content

Of the sand

The wind speed Over

the sand surfaceGrain size

WindWind Sand transportSand transport

• Relationship between sand transport and wind velocity

Little sand is transported during rainy weather? Give reason

When the sand water content exceeds 2%, very strong winds are necessary to move the particles.

For dune sands, movement is initiated at about 4 m.s-1 and increases dramatically at wind speed above 10 m.s-1

• Different Ways of Wind blown Sand Travels

Wind blown sand travels in three ways

Suspension Dust only sub-sand Particles moving in suspension

By Bouncing or Saltation75% of transport is by saltation

By Creeping or rollingOnly 25%

The rougher the sand surface, the lower the rate of transportation

• Formation of Dunes

• Both ways gradually expanding to form more extensive and complex system.

•Dunes can form in two major ways:

The vegetation trap wind blown sand

The sand forms ripplesWithout vegetation

Steps of Dune Formation

Slip faces have an angle of repose=34◦.

.

1) After disturbance has initiated a dune, slip

and wind ward faces develop once dune Height exceed 1m.

2) Sand is then transported up the Windward and slip face.

3)Foramtion of slip face creates wind shadow.

4) When sand transport ceases, the slip face slowly moving forward as sand traverses it.

•The rate of advanceThe rate of advance of such dunes is highly variable, ranging from 1m to 10 m /year.

It is depending on:

Wind RegimeDune Height

•Dune Vegetations

Clear four vegetation zones can be distinguished at right angles to the shore.

• Activity 2:Activity 2:• On studying two different beaches. the

following items were recorded • 1- Rainy coastal dunes.• 2- Dry coastal dunes• 3- Instable shore line.• 4- Stable shore line• You are required to know the characters of

coastal dunes that match with the adjacent fig.• Comment and use Alexandria city as an

example.

• Where and when can those zones occur?

• Those zones can occur across typical coastal dune systems in any part of the world where:

• 1- Rain fall is sufficiently high

• 2-The shore line is sufficiently stable.

• The Primary Colonization of Aeolian sand• The primary colonization of Aeolian sand along the coast

consists of Micro-organisms.

• Micro-organisms are: 1- Bacteria

2- Algae

3- Fungi

What is the importance of those aggregates?

Micro-organisms aggregation

Reduces wind erosion

Increases soil moisture

Increases nutrient status of the sand

Features of Different zones

• Zone I: Pioneer zone closest to the sea• It establishes itself to the highest reach but

destroyed by extreme storms.

• It is occupied by Creeping grasses, herbs with rhizomatous and stoloniferous growth.

• Dune pioneer represents the most physically controlled zone/Give reasons

• It has the highest sand transport rate.

• Heavy salt load.

• Temperature extreme.

• Plants occupy this zone characterized by:

• Rapid growth to outpace sand accumulation.

• Succulence to store water.

• Cuticular protection against salts and glands to exclude it.

• Their seeds are dispersed by water and wind.

• Zone II: Shrub communities • Mixture of zone I and psammophytes plants from other

habitats. • Seeds are dispersed by wind and birds.

• Zone III: The scrub-thicket zone • It typically has a flat canopy due to wind pruning. (dwarf

trees and compact canopy)• No sand movement.• Only develops where rainfall

exceeds about 250 mm/ year.• Seeds dispersal by birds.

• Zone IV:Thicket or forest only• Develops in areas of high rainfall behind the

shelter of larger dunes

• Occurs where rainfall is exceed 700mm /year

• Seeds dispersal by birds.

Adaptations

1. Presence of succulents, water savers to overcome sand dryness.

2. Some succulents may folds or shed their leaves or reduce leaf area.

3. Restrict transpiration by having thick or ability to close stomata.

4. Spreading roots can rapidly take up the rainfall .5. Deep roots that may go down to the water table.6. Many plants absorb dew.

A major feature of dunes is edaphically dry and that dryness may be increased by salt load

Special adaptations to Zone I and merely Zone IISpecial adaptations to Zone I and merely Zone II1. Leaves: light colors, high reflectance, as well as

transpiration cooling to reduce heat load.2. Salt stress is prevented by:

Protective cuticle and glands that excrete salt.Flowers that may turn upside down after pollination so avoid excessive salt load.

3. Wind stress and sand accumulation may be: Compensated by: rapid growth in response to sand burial and low growth forms with tough leaves.

4. Pollination is accomplished by:Having the flowers situated below the leaves for protection.By making use of wind pollination.By anthers opening only in favorable condition.

Dune FaunaDune Fauna• Fauna of coastal dune is limited consists of arthropods

and vertebrates (insects, birds and mammals).• Crustaceans are important near shore.• Mollusks represented on lime rich soil.• Arachnids and frogs have been recorded.• High moisture dune soil supported rich interstitial

biota (bacteria, fungi and meiofauna).• Dune fauna has limited diversity and respond to

vegetation (positive relationship).• Diversity increases away from the sea due to:• Decline of salt spray and sand movements rates.• Coastal dune are endemics not abundant.

Adaptation features of dune faunaAdaptation features of dune fauna1. Behavior:is the most important adaptations of

animals. Rhythmic activity is a key adaptation e.g. tidal rhythms.

2. Ability to burry or to burrow rapidly.

3. Flotation to survive flooding.

4. Dune animals need to be tolerant to flying sand, heavy salt load and absence of protective litter.

• Activity 3:Activity 3:• A-Distribute the following fauna in its appropriate

zone: crustaceans, insects, vertebrates, interstitial fauna.

• B- in which side those items increase or decrease: grazing of fauna, psammophyllic life, salt spray & biological interactions.

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1. Initial dominance by crustaceans

2. Increasing abundance and diversity of insects

3. Increasing importance of vertebrates.

4. Increasing development of interstitial fauna.

5. Increasing impacts of fauna on vegetation due to grazing

6. Decreasing specialization of the fauna for psammophyllic life

7. Decreasing adaptation to salt spray

8. Increasing biological interaction.

Food Chain of Dune ecosystemFood Chain of Dune ecosystem

Grazing pathway

A detritus pathway

Interstitial biota

Interstitial fauna

Grazers

Detritivorous

Predators

Bacteria, Fungi and meiofauna

Worms

Insects

Mammals and birds

•Summary