Common reed
Common reeds (Phragmites australis), along with Bullrush (Typha domingensis), are often viewed with disdain in constructed wetlands. Whilst no-one would specify Typha domingensis for a constructed wetland due to its vigorous nature, rapid growth and ability to grow in deep water (up to 2m) right across wetland basins, Phragmites australis is a different story.
Phragmites australis is highly valuable in constructed wetlands due to a range of factors. It pumps oxygen into its root zone and supplies organic matter to the sediments in winter when it dies back. Both of these processes enhance water treatment. Its upright nature and rigid stems allow water to pass through dense reed beds and other plants can find light and substrate to grow within the stands. Over winter, Phragmites australis dies back and can look dead, however, new leaves will regrow rapidly from its large rhizomes in late winter-early spring when sediment temperatures rise. This makes it an ideal water treatment plant because it turns over its biomass annually using nutrients from the stormwater or wastewater stream. Many animals also utilise Phragmites australis reedbeds as habitats, including the endangered Australasian bittern (species name).
Phragmites australis forms dense reed beds that can withstand variable water regimes and is excellent for bank and sediment bed stabilisation. It will only persist in areas where water is permanently available to the roots, however, their water source may be groundwater in drier conditions, if surface water is not available. These photos are from the River Murray in June 2012 after a flood recession and show the high-water mark on the Phragmites australis steams and live leaves and tissues held high above the flood. Note the bank has not been eroded by the high flows. The resilient nature of Phragmites australis means that it can choke channels and waterways and may need to be controlled in some situations. It does not, however, grow into deep water and therefore it is usually controlled in its growth in constructed wetlands by the relatively shallow depth of the macrophyte zones (where it grows) compared to the deeper open water zones where it is not wanted.
Habitat needs: still or slow-flowing fresh or brackish water. Grows on edges of lakes, creeks, rivers and estuaries, as well as in areas with groundwater discharge. Can withstand high flows and standing water up to 1m depth (and thus occurs up the elevation gradient from Typha domingensis which can withstand deeper water). Phragmites australis plants can be flattened by high flows, but these will recover unless the flows are high enough to scour the rhizomes and whole plants out of the channel. Can withstand brackish water up to 10,000 ppm total dissolved salts.
Identification notes: rigid, many-noded stems up to 15cm in diameter and up to 6m tall; leaves are alternate to 18-70cm long with a ligule of hairs; flower heads (inflorescence) form a drooping panicle 15-40cm long that appears purple in late summer when in tight buds turning to grey when the seed heads are mature and fluffy. Spread is usually by clonal vegetative expansion, but seeds can also be fertile and spread by the wind. Can be confused with pampas grass, bamboo or Arundo donax.
Conservation status: Cosmopolitan species distributed worldwide, although there are some morphological differences between Eurasian and American plants. Common, found in all mainland States except Western Australia.
