1.1.7

• Aeolian Transport is the first process of coastal dune formation and involves the movement and weathering of sand particles.

  -1% of the movement in when the sand is picked up and carried in the air (suspension). 

  -Aeolian transport of sand is mainly by saltation (95%). 

  -4% is by creep when sand particles are pushed along and collide into one another. 
• Sand dunes consist of sand that has been blown off the beach by onshore winds. Coastal sand dunes are common features of many coasts in mid-latitudes. 

  Dunes develop above the high-tide mark and can extend several kms inland.

  Sand dune systems consist of a sequence of ridges and troughs parallel to the shoreline. The height of the ridges varies from 1-2 metres up to 30 metres.
• Ideal conditions for sand dune to develop;

  1. Large quantities of sand, washed onshore by constructive waves
  2. Low beach gradient
  3. Large (macro) tidal range, creating a large exposure of sand that can dry out at low tide
  4. Dominant onshore winds, that will blow dried sand to the back of the beach
  5. An area of inland space for the dunes to develop

  Vegetation such as sea couch and marram grass to colonise the dunes once they have formed
• sand dune formation

  obstacles such as drift wood get dropped off at the beach

  wind blows sand up the beach ans get trapped behind the obstacle

  colonising pioneer plants such as marram grass grow on dunes and stabilise it with their roots and trap more sand

  creating an embryo dune

  as the plants die they add organic matter to the soil improving it for other plants to survive
• how do sand dunes develop (zonation)?

  1. Deposition of sand- embryo dune
  2. Constant supply of sand onshore from the beach supplies further dunes to develop, i.e foredunes will be formed and maintained if the loss of land is matched by new sand coming in. 
  3. This then leads to a series of dune ridges.

  However, you also need….

  Pioneer plants (survive a lack of water, high levels of salt, strong winds, low nutrients)- halophytes. They reduce wind speed- leads to deposition, and they bind the sand together.
• Progressing inland many characteristic features change and help determine the natural succession of the dunes. 

  -The drainage slows down as the land becomes more compact and has more humus (organic matter)

  -The pH drops as the proportion of seashell fragments reduces and the amount of humus increases.
• tidal mudflats

  Unvegetated depositional areas areas around the edges of estuaries.

  They are intertidal. At low tide you can see patterns of channels and rills, formed by freshwater from tributaries flowing across the mudflat to the sea. At high tide they are submerged. Sediment is deposited as river water and sea water collide. Flocculation deposits fine sediment. They can also develop behind spits.
• plant succession on salt marsh (1)

  initial plants of a halosere must be tolerant of both salt and regular inundation at high tide. These are called halophytes and include species like eelgrass. They slow the current and lead to further deposition.

  More mud is trapped, decaying plants help build up a soil so that plants such as cord grass can grow in. 

  A dense mat of vegetation builds up to 15cm high. Dead organic matter also helps to build up the surface, which grows in height between 1-25mm/year.
• plant succession on salt marsh (2)

  Growth of vegetation slows the spring and storm tides, and the vegetations traps more sediments. 

  This is a positive feedback loop.

  The saltmarsh has now increased in height, this means it remains exposed for longer between tides.

  As mud levels rise, complex creek systems develop that channel the tides and these deepen as the marsh becomes higher. They are formed because of erosion by tidal currents.
• plant succession on salt marsh (3)

  Hollows may form where seawater becomes trapped and evaporates, leaving salt-pans in which the salinity is too great for plants to survive

  As the land rises above sea level, rushes, brambles and reeds become established, eventually leading to the growth of trees such as birch, ash and then oak to complete the succession.
• Composition of coral

  Corals are marine polyps. Each polyp (soft-bodied organism related to jellyfish and sea anemones) is a sac-like animal, typically only a few mm in diameter and a few cms in length. They release calcium carbonate (CaCO3) which makes a protective skeleton around themselves.
• Some corals catch their food by using small stinging tentacles. The majority rely on a symbiotic (close association for their mutual benefit) relationship with microscopic algae known as zooxanthellae. 

  -These algae release nutrients via photosynthesis, which the polyps feed on. 

  -In return the algae are sheltered with the hard coral skeleton and obtain some minerals from the coral.
• coral formation

  Some corals catch their food by using small stinging tentacles. The majority rely on a symbiotic (close association for their mutual benefit) relationship with microscopic algae known as zooxanthellae. 

  -These algae release nutrients via photosynthesis, which the polyps feed on. 

  -In return the algae are sheltered with the hard coral skeleton and obtain some minerals from the coral.
• reef structure

  The back reef includes the shallow lagoon between the shore and coral reef. This habitat includes small patches of corals, sea grass beds, and sand plains. The back reef is often warmer because of the shallow depth, reduced water flow, and protection from waves. Salinity can also fluctuate due to fresh water inputs. In addition, sediment and runoff from shore can increase turbidity in this zone.
• reef structure

  •  reef crest is the highest point on the reef and can be exposed to the air during extreme low tides.

  The reef crest is a harsh environment, with the potential for the coral drying out and UV stress is high. Breaking waves also limit coral diversity to only a few species can persist in this high-energy zone, such as Staghorn coral. 

  Small crabs, shrimps, and other animals often live in the cavities under the reef crest, protected from waves and predators.
• fore reef

   ocean side of the reef begins the fore-reef, which continues down in depth to a sand plain. 

  Abiotic factors are less stressful compared to other zones and ideal for coral growth. 

  The highest diversity of corals is found in the fore-reef due to light accessibility. 

  Coral diversity is greatest around 15–20 m depth and dramatically decreases with increasing depth and the resulting lower light availability. 

  In addition, internal waves carry nutrients from deeper water to the fore-reef, providing additional food resources for coral reef communities.
• types of coral reef

  • Atoll Over time, a volcano or seamount surrounded by a reef erodes OR rising sea levels cause it to flood. 

  This forms an atoll with a lagoon in the centre.

  Fringing - The most common type of reef. They grow seaward directly from the shore. They form borders along the shoreline and surrounding islands. Often protected by a barrier island.

  • BarrierDevelop parallel to the shore, some at a considerable distance from it. 

  Tend to be large-scale structures, being quite broad and continuous in their linear length
• Mangroves are found in an area between latitudes of 25°N and 25°S

  A major restriction for where mangroves can live is temperature. 

  The cooler temperatures of northern temperate regions prove too much for the mangroves. 

  However, rising temperatures and sea level due to climate change are allowing mangroves to expand their ranges farther away from the equator and encroach on temperate wetlands, like salt marshes.
• formation mangrove:

  • Formed in the intertidal zone (along the banks of estuarine rivers)
  • Near the mouths of rivers 
  • Fresh and seawater mix
  • Abundant land sediments and organic matter are deposited
  • Sediment stabilises, mudflats develop 
  • In areas protected from tides and high-energy waves

  Sediments are rapidly colonised first by plants and then mangrove trees.
• Red mangrove plants create a barrier and can almost completely exclude the salt from entering their vascular system—over 90 percent of the salt from seawater is excluded. 

  The black mangrove pushes salt from the ocean water out through special pores or salt glands within their leaves. As the salty water evaporates, noticeable salt crystals often form on the surface of the leaves.