Fig. 1.10 shows a salt marsh ecosystem at different distances from the sea. Both hard engineering and soft engineering approaches can be used to reduce the ...
Question 1 Report
Fig. 1.10 shows a salt marsh ecosystem at different distances from the sea.
Both hard engineering and soft engineering approaches can be used to reduce the impact of flooding on communities. Flooding is one of the most common and destructive natural hazards, affecting millions of people each year.
Flooding occurs when the volume of water in a river exceeds the capacity of its channel, causing water to spill over the banks onto the surrounding land. Urbanisation increases flood risk by replacing permeable surfaces with concrete and tarmac, which increases surface runoff and reduces infiltration into the ground.
(a) State the name of one plant species found in the lower marsh zone. [1]
(b) Describe the pattern of zonation shown in Fig. 1.10. [3]
(c) Explain how plants in the lower marsh zone are adapted to survive regular flooding by salt water. [4]
Answer Details
(a) One plant species found in the lower marsh zone [1]
Any one of: glasswort [1] or cord grass [1].
These are pioneer species that colonise the most seaward part of the salt marsh, where conditions are harshest due to regular tidal flooding and high salinity.
(b) Pattern of zonation in the salt marsh [3]
- Different plant species are found at different distances from the sea, forming distinct zones (this is called zonation). [1]
- The lower marsh, nearest the sea, is colonised by salt-tolerant pioneer species such as glasswort and cord grass. These species can withstand regular immersion in salt water. [1]
- Moving inland towards the upper marsh, species diversity increases and less salt-tolerant plants such as rushes and shrubs appear. These species benefit from the higher ground, which is flooded less frequently. [1]
Zonation occurs because the frequency and duration of tidal flooding decrease with distance from the sea, creating a gradient of environmental conditions. Each zone supports species adapted to its particular level of salt and water exposure.
(c) Adaptations of lower marsh plants to salt water flooding [4]
- Salt-excreting glands: specialised glands in the leaves actively pump excess salt out of the plant's tissues, preventing toxic salt concentrations from building up internally. [1]
- Succulent leaves and stems: thick, fleshy tissues store freshwater, which dilutes the internal salt concentration and helps maintain the water balance within the plant's cells. [1]
- Extensive root systems: deep or spreading roots anchor the plant firmly in the soft, unstable mud and allow uptake of water from the waterlogged substrate. [1]
- Aerenchyma: large air spaces within roots and stems allow oxygen to diffuse down from above-water parts of the plant to the roots, enabling aerobic respiration even when the roots are submerged in waterlogged, anaerobic mud. [1]
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