3.1.2.2 Coastal Landforms+ (Sand dunes, Mangroves, Sea level, Mangroves) Flashcards
What inputs are required for a sand dune?
- Sandy beach
- Strong consistent onshore wind
- Supply of seeds for colonisation
- Obstacle
How do sand dunes form (up to grey)
New dunes develop on the foreshore called embryo dunes, providing a harsh environment for plants
- Very dry, high pH, few nutrients so few plants like sea-buckthorn and couch can survive and help more sand build up, forming fore dunes.
- As the plants grow and die, they add organic matter to the soil allowing more water to be retained and making the environment less harsh, allowing marram grass to dominate the ecosystem
- Marram grass deep rooted and tall so helps trap sand and grows quickly to keep up with the growth of the dunes. A high ridge of mobile yellow dunes develop.
- As more plants grow and die, the soil is richer and moister so more vegetation grows like dandelions and brambles. The extra organic content allows semi-fixed grey dunes to develop
What forms after grey dunes?
- At the back, supply of fresh sand is reduced so marram dies out. Wind speeds fall, EVT losses are low and the soil is moister so marshy vegetation can form
- Sometimes sand may be exposed to wind and blow away, lowering the surface. This can sometimes lower below the water table forming dune slack - puddles of water where water loving plants grow and rare amphibians breed. Eventually trees and grey fixed dunes predominate where the climax vegetation is found. Shells provide calcium to grasslands which can form oak trees whereas acid dunes have leached out calcium and form pine trees.
What is vegetation succession?
Evolution of plant communities over time from pioneer to climax vegetation.
- At each stage the plant community alter soil and microclimate to allow more species to grow, replacing one species after another.
- Eventually climatic climax is reached as vegetation is in a state of dynamic equilibrium so no further influx of species
-Sand dunes are psammosere as it is from bare sand to climax vegetation
What is the first stage of the development of sand dunes?
- Beach needs strong onshore wind, obstacle to trap wind, supply of seeds, flat land.
- Sand is deposited by wind, usually at the strand line - a line of zero velocity where sand is trapped by the accumulation of objects and materials, forming at high tide.
- Over time, sand accumulates around the objects - heavier particles settle first, making small ridges and lighter grains are transported over and settle on the other side. These accumulations are shaped at the backshore of the beach.
- Sand moves up the beach by saltation, which is the leapfrogging of sediment carried by the air. Once the particle hits the surface it causes ballistic impact, splashing sand on the ground upwards which joins the sand in the air, causing it to move further.
What is the second stage of the development of sand dunes?
As the dunes develop, vegetation starts to colonise however the environment is too harsh - saline, submerged, windy, unstable sand, arid, lacks organic content alkaline from shells.
- Fast growing pioneer species which are halophytic and xerophytic are able to grow, such as couch and sea buckthorn. This is called the pioneer stage, where embryo and fore dunes develop.
- The plants here have waxy winds to retain moisture and withstand winds. The thorn like leaves reduce transpiration. They are low to avoid winds and have deep roots to obtain moisture. Over time, this vegetation helps improve the conditions for future growth
- The roots stabilise the sand, add organic material and nutrients, allow more water into the ground, improve soils, taller and reduce sand behind it.
What is the third stage of the development of sand dunes?
As these begin to grow and retreat, yellow dunes form as more sand is trapped and the dune gets higher due to the supply of sand rising. Marram grass starts to dominate the ecosystem, further trapping sand and causing a high ridge of yellow dunes to develop.
- Marram grass is salt tolerant, thrive on being buried by sand, inrolled leaves reduce moisture loss, have long roots and underground rhizomes which stabilise the sand, allowing bursts of energy to growth out of the sand
- Marram has strong thick blades, deep roots, waxy inrolled leaves, hairy leaves, long tap roots for water, rhizomes to store energy, halophytic and xerophytic.
What is the impact of pioneer vegetation?
Plants trap sand and grow with the dunes, binding the sand with the roots. Decaying pioneer plants create more fertile growing conditions and less hardy plants grow and start to shade out the pioneers, outcompeting them. As the plants colonise the dunes, sand disappears and the dunes change colour from a yellow to grey colour as there is much more diversity - lichens give the grey colour as marram dies out.
What is the final stage of psammosere?
At the climax stage taller plants such as trees and complex plant species can grow whilst other plants die out due to competition for light and water.
Dune slacks may also occur when the lack of sand behind the dune causes it to fall below the water table level, creating little pools of water where water-tolerant plants grow. The climatic climax population is in the woodland areas where there is often a community of heathland, wood and trees. Pine, oak and birch often found here.
What are the characteristics and plants in the 5 dune stages?
Embro/fore: onshore winds, humus build up, sand builds up, alkaline.
Small, low growing individual halophytic plants may grow
e.g. Saltwort, couch, sea holly
Yellow: surface blown away and replenished by fresh sand, reduced wind speed, top high above sea level.
Salt tolerant, buried by sand, inrolled leaves, long tap roots, underground rhizomes stabilize sand, marram
Grey: increased humus, surface lichens, sand no longer accumualtes, marram dies out.
Many plants co-exist, stabilizing plants, increased organic matter e.g. lichen, creeping willow, scrub, mosses, grassland, thyme
Dune slack: damp, low lying hollows, high water table in winter, soil is acidic and pH variable. Moisture loving plants settle here such as pennywort and pettlewort, orchid species, hawthorn
Heath: acidic soil, increased organic matter, nutrient rich, sheltered. Acid loving plants co-exist - woody e.g. woodland and trees, pine and oak
How do psammosere conditions change as you move inland
Plant characteristics - more abundant and increased diversity
Soil - decreasing pH, decreasing aridity (more moist), increasing stability, increasing organic content, decreasing salinity
What are some threats to sand dunes?
Human: interception of LSD from groynes and jetties, removal of sand, footpath erosion, pollution from agriculture, afforestation, levelling for development, water abstraction, conversion into agricultural land, littering and campfires, trampling, rising sea levels, pollution
Natural: erosion, fall in water table, overgrazing - frees space for coarse vegetation and makes more unstable, recreational use damages plant life, development causes waste and loss of vegetation, invasive species shade out other plants and fix nitrogen into soil
Why do sand dunes need conserving? What are some ways to conserve them.
- Natural sea defence
- Tourist attraction
- Recreation
- Habitats to rare diverse species - research purposes
Management:
- SSSI, Beach Rebuilding and marram plantation
- Stabilising loose sand can be done using wooden sand fences. development of footpaths.
What is the basic succession of sand dunes?
- Onshore winds blow on a fine wide sandy beach, the sand is entrained and transported by saltation and deposited at the strand line at the foreshore above the high tide mark, where there is 0 velocity
- Sand accumulates on an obstacle forming low lying embryo dunes. Halo/xerophytic species like couch grass colonise the dune, stabilising it and accumulating more sand by reducing velocity and building up the fore dune
- Stable dunes grow and get a wider variety of pioneer plants like marram grass which colonise the dune making it larger and more stable
- Dying plants provide humus and organic content, crucial for further colonisation and stabilisation. Rhyzome roots of the marram are deep lying and bind the sand together, enabling dunes to become less mobile and more fixed. This shelters the sand and allows for more accumulation, setting the yellow dunes further back the beach.
- With more plants and perennials they die and improve organic content, allowing more water retention and higher pH allowing more plant species to live and survive. The ageing dunes eventually grow and retreat further, creating sheltered grey dunes due to increased organic content from lichens.
- In time the grey dunes are fixed by the roots of diverse species. Eventually the roots rise above the water table and become fixed, rich areas in climatic climax - in the UK is oak woodland.
What are coastal saltmarshes?
Coastal ecosystems of plants usually associated with landforms of deposition. They have varying vegetation on them as you move inland.
They are halosere ecosystems as they are salty, forming in sheltered locations such as estuaries, rias, behind spits and bars - areas which lack erosion, wave action, have a good supply of sediment and frequent fresh and salty water
How do saltmarshes form
In sheltered locations - estuaries, rias, behind spits and bars - need good supply of mud, silt, clay where there is brackish water.
Initially mudflats are formed from rivers or gentle tides which deposit silt and mud, aided by flocculation as the negatively charged clay ions are charged by the salt, causing flocculation and coagulation to plants.
-The mud flats are intertidal, and pioneer vegetation colonises and develops into a halosere succession, helping secure the mud and encouraging further accretion.
What are the 4 sections and the halosere succession? Describe the first 2 section
Split into 4 sections - tidal muflats, lower marsh, upper marsh, marsh uplands.
The mudflats are covered with salt water for most of the day but sometimes uncovered. Algae and eel grass survive in these conditions and trap more mud, raising the mudflat level
As the surface is at a higher level, the period of inundation is reduced and glasswort can colonise the mudflats and trap more mud at the low marsh. This area is flooded in high tide so the inundation period is reduced, developing a sward zone where the surface is only covered for a few hours a day.
-The plants here are halophytic and cope with the inundation by the sea due to roots and rhizomes helping plants to grow. They have spongy tissues in the roots, allowing for gas exchange between air and roots
What are the last 2 sections?
As the high tide continues to rise and be slowed by friction, more material builds up via accretion. As mud levels rise, complex creek systems develop which channel the tides as the marsh grows higher and the tides erode the creeks deeper.
- If this land builds up above high tide, the succession in plants may lead to the growth of oak trees in Britain
- Hollows may also form where sea water is trapped and evaporated, leaving salt pans where salinity is to great for plants to survive.
What are the stages of plant succession in a salt marsh, including how long the area is inundated?
- Pioneer zone - algae and halophytic plants - not submerged 4 of 12 hours a day, anaerobic conditions due to waterlogged, high pH
- Lower-middle high marsh - not submerged 8 of 12 hours, high tide and tidal water only inundated at spring tides - broken up by creeks and salt pans
Upper high marsh zone - only covered by spring tides, freshwater plants - upper sward zone
Climatic climax - no flooding, trees succeeded
What are the threats to salt marshes?
- Industrial pollution
- Eutrophication
- Dredging removes sediment and affects tides and currents
- Commercial usage and activities erode
- Grazing tramples species
- Reclamation makes tidal areas narrower, energy concentrated
- Sea level rise
- Storms cause eroison
- Changing temperatures and rainfall patterns
Why are salt marshes important?
- Support great range of wildlife
- 80% in UK have SSSI or NNR status and are managed and protected.
- Shorelines and bulkheads with salt marshes are better defended and have less erosion as the changes divert erosion elsewhere. Improving the habitat for wildlife and vegetation increases nutrients and water quality, dampening the effects of pollution.
How are salt marshes protected?
- Conservationist practitioners manage threats
- Marine protected areas raise public awareness of role they play
- Managed retreat, reversed land reclamation
- Create border to buffer from eutrophication
- Create marine habitats
What are isostatic and eustatic sea level changes?
Eustatic - rise and fall in sea level due to increase/decrease in volume. This is due to climate change either through global warming storing more water or releasing water through melting. Water also expands through warming up and takes up more space. It has risen about 130m in the last 20,000 years
Isostatic - movement of land in response to release of weight of the ice. When an ice cap melts, sediment is deposited or tectonic changes occur so the processes lead to the depression or elevation of the Earth’s crust, changing the sea level in that place. When the weight of an ice cap is removed isostatic rebound occurs as the land expands. The mantle forces the land back up when the weight is removed. In an ice age, the thickness increases and causes the land to lower - when melted the released pressure causing it to rise isostatically?
What are emerged coastlines?
Features previously underwater emerge as the sea level falls, creating raised beaches - beaches and wave cut platforms higher than current sea level, relict cliffs no longer eroded by waves.
Relict cliffs often have features of marine erosion such as caves and wave cut notches
-The angle becomes less steep of the cliff and vegetation gradually colonises the slope.
-This may also cause coastal planes and raised mudflats.
-They are features of an initial rise in sea level followed by a rise in land due to isostatic rebound.
-A common evidence for this is when there is vegetation as the area is no longer subject to marine processes. Sand and shingle is found above the current beach level or on top of cliffs way above where they could be reached as a result.
