Aquatic and riparian vegetation
Aquatic and riparian vegetation is important for the health of waterways, contributing to the balance of oxygen, nutrients and sediment, and providing habitat and food for fauna.
Aquatic plants and algae grow within the waterway channel. Some are completely free floating (e.g. filamentous green algae) but most have roots or root-like structures in the sediment and can have floating leaves (e.g. water lilies), structures emerging from the water (known as emergent plants e.g. water ribbons) or be completely under water. These are known as submerged plants and include curly pondweed and seagrasses.
Riparian vegetation grows along banks of a waterway extending to the edge of the floodplain (also known as fringing vegetation). This includes the emergent aquatic plants growing at the edge of the waterway channel and the ground cover plants, shrubs and trees within the riparian zone.
Riparian vegetation often shows zonation in the plant species present as the environment changes from permanently or seasonally aquatic habitats in the waterway channel and floodplain wetlands, to frequently flooded habitats along the banks and close to the channel, to drier habitats at the edge of the floodplain.
A typical cross section of native plant species of the lower south-west of Western Australia is shown in the diagram below.
Typical cross section of native plant species of the lower south-west of Western Australia (Source: Revegetation –Revegetating riparian zones in south-west Western, River Restoration Manual Report No. RR4).
The following guides provide information about aquatic and riparian plants in Western Australia:
- Native vegetation and creeks of south Western Australia
- Native vegetation of estuaries and saline waterways in south Western Australia
- Riparian plants of the Avon catchment
- Aquatic plants of the Canning River (River Science 19)
- Macrophytes and macroalgae in the Swan Canning estuary (River Science 20)
Aquatic plants, algae and riparian vegetation play an important role in keeping waterways healthy by:
- absorbing nutrients from water flowing into a waterway - over the land surface and through groundwater - and from the waterway itself
- slowing the water flowing over the land surface into a waterway – this allows sediment and pollution in the overland flow to deposit in the fringing zone, reducing sedimentation and pollution of the waterway
- stabilising the banks and bed of a waterway. Plant roots bind the sediments to reduce erosion
- oxygenating a waterway – oxygen is a by-product of photosynthesis, the process by which plants and algae make sugars from carbon dioxide and water using sunlight
- providing elements for the food web such as carbon, nitrogen and phosphorus
- providing habitat for aquatic fauna and terrestrial fauna, such as turtles and frogs, including migration corridors
- shading a waterway – this helps to control water temperature and reduce the growth of phytoplankton which helps prevent algal blooms
- providing a physical barrier to prevent access by stock - which can lead to erosion and nutrient inputs - and to prevent the spread of weeds via the waterway.
Further information is available in this document: The values of the riparian zone.
The value of riparian vegetation and its role in maintaining the physical condition and ecological health of waterways is clearly recognised. Riparian vegetation is one of the waterway values protected by the provision of a foreshore area or foreshore reserve during the land planning and other approval processes – see foreshore condition assessment for further information.
The historicremoval or degradation of riparian vegetation through activities such as land clearing for agriculture, grazing, mining and weed invasion has resulted in the degradation of many waterways.
The following documents provide information about managing riparian vegetation:
- Identifying the riparian zone (Water Note 11)
- Protecting riparian vegetation (Water Note 10)
- Long-term management of riparian vegetation (Water Note 29)
- Weeds in waterways (Water Note 15)
- Revegetation - revegetating riparian zones in south-west Western Australia (River Restoration Manual report no. RR4) and other chapters of the River Restoration Manual.
The presence and condition of aquatic and riparian vegetation are important indicators of the health of a waterway. They form part of the assessment of waterways in the Foreshore condition assessment and the South West Index of River Condition.