Threats to saltmarshes
The total number and area of salt marshes has been declining for many years. The main cause is enclosure, which removes the habitat from tidal inundation. This normally occurs in areas where the level is high enough and the area big enough for embankment to take place. This is usually achieved by the erection of a tidal barrier, sea wall or other structure designed to keep the sea out. This destroys the salt marsh as other uses, notably conversion to intensive agriculture, takes place.
Infilling for ports and harbours and other infrastructure completely destroys the habitat and with it any opportunities for restoration. Some areas outside the reclaimed zones can produce new marshes where relative sea level is falling or there is an abundant supply of new sediment and conditions suitable for growth of new plants. With climate change and associated sea level rise this is becoming much less prevalent and the process of 'coastal squeeze' occurs in many areas, especially around the margins of the southern North Sea.
Other threats include:
- Climate change
- Excessive agricultural use
- new developments (e.g infrastructure, urban, rural)
- building of levees, drainage, seawalls and retaining walls
- Coastal erosion
- Pollution and industrial waste water
- Rubbish dumping
- Invasion by weeds such as Spartina Rice Grass (Spartina anglica) and Tall Wheat-grass (Lophopyrum ponticum). These are northern hemisphere saltmarsh grasses introduced to Australian salt marshes.
Feral animals such as rabbits, foxes, cats, goats and deer threaten native plants and animals through grazing, competition and predation. Exotic weeds, such as bridal creeper, African boxthorn, radiata pine and Salvation Jane also represent significant threats.
The coast is a highly attractive natural feature to humans through its beauty, resources, and accessibility. As of 2002, over half of the world’s population was estimated to live within 60 km of the coastal shoreline. This makes our coastlines highly vulnerable to human impacts from daily activities that put pressure on these surrounding natural environments.
In the past, salt marshes were perceived as coastal ‘wastelands,’ causing considerable loss and change of these ecosystems through land reclamation for agriculture, urban development, salt production and recreation.