National Wetlands Update September 2012
Issue No. 21, September 2012
Rewetting - response of arid floodplain wetlands following extensive drought
Cherie Campbell, Murray-Darling Freshwater Research Centre, Mildura
Abundant aquatic macrophytes following
environmental watering at Scotties Billabong.
Management intervention, in the form of environmental watering during the drought, may have enabled wetlands to respond more favourably to the 2010–11 flood. However, other processes associated with the flooding, such as sediment deposition, may have inhibited the development of submerged macrophyte communities. This article reports on monitoring of vegetation communities in the lower Murray-Darling Basin, specifically at two of The Living Murray (TLM) icon sites, Hattah Lakes and Lindsay-Mulcra-Wallpolla Islands (LMW), as well as wetlands in New South Wales (NSW) downstream of the confluence of the Murray and Darling Rivers.
Prior to the flooding in 2010–11 the last overbank flow in this region of the Murray River was in 2000-01, which inundated most wetlands and low-lying parts of the floodplain. During the drought, environmental water was delivered to a number of wetlands to maintain ecological values, with individual wetlands receiving between one and 10 watering events from 2004 until spring 2010.
Following inundation in 2010–11 there was mass germination of wetland species as the floodwaters receded. Positive signs of resilience and recovery potential include the establishment of swamp lily (Ottelia ovalifolia ssp. ovalifolia) at a wetland site dry for 10 years; high plant species diversity, including a relatively large number of flow-dependent plant species listed as vulnerable in Victoria, such as lagoon nightshade (Solanum lacunarium) and jerry-jerry (Ammannia multiflora); and a large number of river red gum and black box seedlings.
Germination of River Red Gum seedlings and a
diversity of wetland plants following flood
recession at Mulcra Island flood plain. (C.Campbell)
Preliminary results indicate wetlands that received environmental water during the drought typically responded to the 2010–11 flood with greater abundance and diversity of wetland plants than wetlands without management intervention. However, a paucity of submerged macrophytes were observed following flooding, including at wetlands known to have developed very abundant and diverse macrophyte communities following environmental watering. One potential explanation is sediment deposition during the recent flood. Dense mats of nardoo (Marsilea spp.) rhizomes could be felt underneath about 50 centimetres of sediment at Scottie's Billabong on Lindsay Island.
It is hoped that on-going monitoring will help identify how management intervention during the drought may be influencing the response of successional wetland vegetation communities as the sites continue to draw-down and dry.
LMW and Hattah Lakes monitoring is funded by The Living Murray program which is a joint initiative funded by the NSW, Victorian, South Australian, Australian Capital Territory and Australian governments, coordinated by the Murray-Darling Basin Authority. The provision of environmental water and associated monitoring of wetlands in the NSW Lower Murray-Darling Catchment has been funded by Murray-Darling Wetlands Ltd. (formerly the Murray Wetlands Working Group) and the NSW Office of Environment and Heritage.
For further information contact: Cherie Campbell, Murray-Darling Freshwater Research Centre, Mildura, email@example.com.
Jerry-Jerry (Ammannia multiflora), vulnerable in
Victoria, was frequently observed post-flooding at
Mulcra Island flood plain. (C.Campbell)