Today is World Wetlands Day, and guest Blogger Anne Jensen tells us why the 2011 flood is cause for celebration for Murray-Darling Basin wetlands.
Guest Post by Dr Anne Jensen, Dr Anne Jensen is an environmental consultant with extensive experience in natural resources management particularly relating to water issues and the environment. She is a Consulting Scientist to the Water Research Centre of the Environment Institute. Anne competed her PhD study in 2008 with the School of Earth & Environmental Sciences at the University of Adelaide on the topic, ‘The role of seed banks and soil moisture in recruitment of semi-arid floodplain plants: the River Murray, Australia,’ with the goal of investigating optimum conditions for application of environmental flows. Previously Anne was CEO of WetlandCare Australia, a not-for-profit conservation company which has coordinated multiple wetland projects in South Australia, New South Wales and Queensland. She has strong international networks in wetland and natural resource management through involvement with Ramsar, UNESCO, Ducks Unlimited, and government agencies in the UK, USA, Canada and Denmark.
2011 is the 40th anniversary of World Wetlands Day, which is held on 2 February every year to celebrate the signing in Ramsar, Iran in 1971 of the Convention on Wetlands of International importance.
The vision of the convention is to halt loss and degradation of wetlands, and to promote wise use and conservation of these wetlands, recognising that many wetlands include human communities living in wetlands and dependent on the wetlands for their livelihoods. This vision is supported by 160 countries which are signatories to the convention, with 1912 wetland sites listed around the world, covering more than 186 million hectares.
Australia was the first signatory at the Ramsar meeting, and has 65 Sites, with 12 sites in the Murray-Darling Basin, including the Macquarie Marshes, Gwydir wetlands, Hattah Lakes, Chowilla, and Coorong and Lower Lakes.
Wetlands are among the most important of all our natural resources, providing an important range of environmental, social and economic services. They are considered biodiversity hotspots, with a wide variety of species reflecting the varied water regimes which range from permanent to temporary to ephemeral conditions. Important ecosystem services include water filtration, flood buffering, retention of sediment and nutrients, fish nurseries, waterbirds which prey on agricultural insect pests, and drought refuges.
The wetlands of the River Murray below the Darling Junction at Wentworth have been severely affected by drought conditions since 2002. Prior to the drought effect, water for wetlands was much reduced due to the effects of dams retaining small to medium floods in order to provide water for irrigation and town supplies. Wetlands of the Lower Murray floodplain had not seen effective over-bank flows since 1996, and the drying impacts were apparent with more than 75% of river red gums along the length of the valley dead, dying or stressed.
The ecosystems of the Lower Murray floodplain survive dry periods and droughts by storing moisture in the soil and shallow water tables during wet periods and floods. These moisture stores were depleted by the lack of over-bank flows, followed by severe drought conditions. Research results indicated that a minimum of 10% soil moisture is required to maintain river red gum seedlings, and that 10-25% soil moisture is the optimum condition to maintain healthy growth. The natural cycles of rain and flood would have provided maximum soil moisture in late spring and early summer, to support regeneration.
Larger floods provide larger moisture reserves and tend to generate ‘boom’ recruitment, with millions of seedlings. These can establish dense stands of trees which mark the outer limits of floods, providing a natural map of the extent of inundation. Stands of trees from 1956, 1974 and 1981 can be found throughout the valley.
The movement of water across the floodplain in sheet flows and flood channels is critical to the life cycles of wetland species such as Murray cod, yabbies, tortoises, frogs and waterbirds like Ibis and Spoonbills. The process of wetting dry wetland beds triggers a chain of emerging organisms which create a rich food chain to support their life cycles. Tadpoles become frogs, waterbird chicks fledge and fish spawn in the wetlands across the floodplain. As the waters recede, many find their way back to the river mainstream, along with a rich supply of carbon and micro-organisms to support life downstream.
The current floods bring a precious opportunity to recover from 14 years without over-bank flows. There is enough water available to allow it to spill out onto the floodplain in sheet flows, to infiltrate into the soils and replenish the shallow freshwater lenses which overlie the highly saline regional groundwater. These lenses have been exhausted by the lack of floods and the extended drought, so that the river red gums had their roots in salt water. Now they will get a new lease of life from the floods, and the moisture reserves will be topped up for future years.
It is a critical investment for the future of all communities who are reliant on a healthy River Murray system, to ensure that there is enough moisture to keep the ecosystem services of the Murray floodplain functioning. The 2011 flood is cause for celebration for Murray-Darling Basin wetlands on World Wetlands Day!
Guest Post by Dr Anne Jensen, if you would like to contribute your research to a guest blog on The Environment Institute Blog email firstname.lastname@example.org.