1. Low Energy Coastlines
GG3025
Lecture 2/3

2. Low Energy Coastlines Salt marshes Mangroves
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3. Low Energy Coastlines Characteristics
Estuarine
Saline
Temperature (temperate and tropical)
Shelter
Shallowness
Ebb and Flow Currents
Tidal range
Maritime Salt marsh and Intertidal Flats

4. Salt marshes Typified by: Vegetated sward Drainage creeks and pans
Wadden (intertidal flats)
Seasonal algae (Enteromorpha sp.)
Sea grasses
Vegetation succession (salinity/submersion)
Sometimes a vertical front/cliff to the saltmarsh separating from the intertidal flats

5. Salt marshes Rich ecology, highly productive (land to sea transition)
Conservation interest – flora and fauna
Subject to external influences such as:
Drainage
Pollution
Land reclamation
Changing land-sea relationships

6. Salt marshes
Accumulation of fine sediments often in estuarine or margins of a bay or lagoon environments:
Settling lag
Flocculation
Biological aggregation
Colonised by vegetation
Sediment settles through vegetation trapping, low current velocities
Sediment recycling (ebb and flow channels)

7. Salt marshes Sediment sources:
Rivers
Sea
Variable composition: silt, sand, clay, and organic content
Windblown content in some cases

8. Salt marshes Studies have focused on:
Models for salt marsh development
Marsh Creek and Pan formation
Growing/Decaying landform
Salt marshes are studied in terms of hundreds rather than thousands of years (rocky coasts)

9. Salt marshes Upper level of the intertidal zone
Clay and silts/silty clays often deposited on coarser sediments e.g. sands/gravels
Distinguished from mud flats by vegetation
Intertidal flats (wadden) comprise sand, silt, clay and mud (cohesion and plasticity)
Mud originates from the land/estuary
Sand/Silt from the sea
But very generalised description

10. Salt marshes Sediment distribution
Sediment grain size making up the wadden tends to decrease further inland
Decreasing energy of wind and tide
Complicated by localised tidal circulation
Suspended material settles out of the water column (lag in settlement)

11. Salt marshes Scour lag during the ebb because of sediment cohesion
Vegetation traps sediment
Water covers wadden and the marsh via channels
Settling of sediment
Flocculation and biogenic trapping

12. Salt marshes
Sediment trapped by vegetation due to wave dampening and impeding tidal flow
Chemical micro-environment leading to clay flocculation
Algal mats
Colonies of intertidal animals
Invertebrates trapping sediment
Clay aggregation leads to increase in settling velocity – flocculation (especially where different salinities)

13. Salt marshes
Sediment supply to salt marshes may be seasonal due to variations in:
Physical Processes (reduced river flow in summer)
Biological Processes (reduced algal activity in winter/plant growth in summer)

14. Salt marshes
Sediment Recycling: continued minor erosion and deposition in channels through channel mobility, undercutting of creek banks, water circulation through the marsh, slumping
Pan and Creek Formation: proto-pans are areas of standing water, proto-creeks the intertidal ebb and flood channels

15. Salt marshes Characteristics (research and field observation):
Pans often non-vegetated (salinity) whilst partially colonised pans
Pan enlargement is often active
Channel pans have been found… possibly due to siltation/blockage of primary creeks, lateral spread of vegetation to create roofed and unroofed creek
Plant debris stranded on marsh can cause marsh plant death and a secondary pan due to tidal scour
Erosion of marsh fronts causing toppling of vegetated blocks to create fringing secondary marsh and secondary pans

16. Salt marshes Problems:
No evidence of pan shallowing as a result of pan extension
Water spilling from one pan to another (leading to pan extension) not supported as pans fill from bottom during rising tide
Channel pans possibly created through silting creeks could be reversed through sub-surface water movement and this may provide new explanations for pan and creek development – including new pans on a mature marsh