Vegetation its important in stabilising coastlines in either sand dunes or salt marshes

What is the order of sand dunes?

What is the order of sand dunes?

Embryo, Fore, Yellow, Grey, and Mature

The sequence of sand dunes (gibralta point)

Embryo

• Saltation and creep starts to build up sand when caught on an obstacle

• Salt wort and sea rocket grow and trap sediment and stabilises it

• The vegetation have waxy leaves and deep roots

• Mobile dune

• Least soil nutrients and vegetation

Fore Dune

• Has salt tolerant vegetation e.g. couch grass

• Mobile dune

Yellow dune

• 30-40 years old

• Has even more vegetation which has accumulated even more sediment

• Marram grass further stabilises and traps sand

Grey Dune

• Plants die and provide soil with nutrients

• Soil is fertile

• Lichens give grey appearance

• Less exposed to salt water meaning there is more diverse vegetation

• E.g. Dewberry and Sea Buckthorn

Mature Dunes

• 250+ years old

• Brown, nutrient rich soil

• Shrubs, oak and maple trees

• Moist soil as it is closest to the water table

• Most soil nutrients and vegetation

What is saltation?

The movement/skipping of small sediment

What is creep?

The surface movement of larger sand particles

What requirements are there for the formation of sand dunes?

• lots of sand + constructive waves

• A large tidal range that allows for sand to dry

• A wide backshore so sand can accumulate

• Onshore prevailing winds

The sequence of the formation of salt marshes

• forms in sheltered conditions where salt and fresh water mix and flocculation occurs

• Shore becomes muddy and microscopic algae growth consolidates the mud and increases the hight of the mudflat

• Pioneer plants(cordgrass) eventually develop into vegetation and allows for more diverse vegetation e.g. sea aster and marsh grass

• Vegetation traps more sediment and dead organic material and helps the marsh to grow 1-25mm annually

• Mud levels rise creating creeks and channels

• However a hollow may form into salt-pans that are too salty for vegetation

• As land rises above sea level it becomes established and oak and ash trees can grow and can even turn into woodland with no intervention

How does vegetation stabilise sediment?

• roots of plant bind sediment particles together

• When submerged plants act as a protective layer so water does not erode it

• Plants reduce wind speed due to wind friction

What are dune slacks?

Low-lying areas within dune systems that are seasonally flooded and where nutrient levels are low

What is flocculation?

• negatively charged clay clumps with positive salt water and becomes too heavy to float