Environmental Water Requirements of Vallisneria nana in the Daly River, Northern Territory
N Rea, P Dostine, S Cook, I Webster and D Williams
Conservation and Natural Resources, Department of Infrastructure Planning and Environment, and CSIRO Land and Water, Canberra
Department of the Environment and Heritage, 2003
ISBN 0 7245 4830 0
- Environmental Water Requirements of Vallisneria nana in the Daly River, Northern Territory - Summary (PDF - 254 KB)
- Environmental Water Requirements of Vallisneria nana in the Daly River, Northern Territory - Full Report (PDF - 3,675 KB)
About the report
The objective of the Commonwealth's Environmental Flows Initiative (EFI) was to assist state and territory water resource agencies meet the COAG Water Reform requirements for making environmental water allocations. The NT received support due in part to the focus on water resource development shifting to Northern Australia and the concurrent lack of understanding about tropical water resources and their sustainable use. Intensive development of water resources is proceeding in the Daly Basin without an understanding of ecological requirements or environmental constraints.
Between 1985-1997, groundwater use in Australia increased by 88% and the trend is continuing.
Irrigation accounts for 76% of that groundwater use. Already, 30% of groundwater management areas are overused compared with their estimated sustainable yield, while a further 30% are fully or over allocated (NLWRA 2001). The COAG Water Reform Framework stipulates that environmental water requirements are to maintain the 'health and viability of river systems and groundwater basins'.
Shadwick (2002) stated that the intention of the COAG strategic framework to safeguard water resources not only depends on the successful adoption of the water reforms but on simultaneous natural resource management. Governments need to ensure that: 'integrated approaches to natural resource management are in place and there is full recognition of the interdependency of the different natural resource components, including water.' Recent approaches to determining environmental water requirements take an ecosystem, catchment wide and multi-disciplinary perspective (Arthington et al. 1998). Holistic approaches argue that the essential features of a riverine ecosystem need to be protected to achieve geomorphological, water quality and ecological objectives and to maintain the rivers' functional integrity.
To protect the ecological character of groundwater dependent ecosystems, groundwater supply rate and quality needs to be maintained. While the landscape is vegetated, the majority of water infiltrates throughout the catchment to recharge groundwater aquifers. Run-off is filtered of large sediment loads and associated organic matter, nutrients and pollutants. Land clearing poses a significant threat to rivers and wetlands through reduced recharge and adverse changes to the quality and sediment load of wet season run-off. In the Daly Basin, unregulated land clearing and agricultural expansion within the catchment, along with plans to extract and divert large quantities of surface and groundwater pose a significant risk to the regions' ecology. Alterations to the water regime are forecast from flood harvesting into off-farm storages and the construction of regulatory devices. Alterations to the water regime in the dry season are more likely in the short term because extraction from surface and groundwater systems is greatest at a time when water is most scarce.
The Daly is a perennial tropical river, kept flowing in the dry season through groundwater discharge from the Jinduckin, Tindall and Oolloo aquifers. The river is presently unregulated and compared with riverine ecosystems in southern Australia, is relatively unimpacted. The middle reaches of the Daly River are listed on the National Estate as an important wetland area in the Daly Basin biogeographic region, and a major breeding and dry season habitat for a variety of flora and fauna.
This project focuses on the major riverine plant, Vallisneria nana R.Br., the key habitat for many turtle species, including the endangered pig-nosed turtle. The importance of macrophytes in the ecology of running waters is well established (food, breeding, refuge, slow currents, trap organic matter, sediments and nutrients, reduce turbidity, stabilise banks, shade, cool temperatures, cycle and compartmentalise nutrients, metals and carbon). It is speculated that Vallisneria species were once considerably abundant in the regulated inland rivers of south-eastern Australia. Their loss is attributed to adverse changes in water quality and flow (Roberts and Sainty 1996, Bailey et al 2002). V. nana in the Daly River is a keystone habitat. Without it, there would be a cascade of adverse changes across the food web. Faced with the forecast and present development pressures in the Daly River Basin, it was clear that provision of conditions to maintain V. nana is critical to ecology of the river and the region in general.
The understanding of the functional role of riverine plants is not matched by knowledge of their growth or ecological requirements. This project addresses this gap. V. nana in the Daly River provides an opportunity to examine the ecology and requirements of riverine plants, and to understand why they disappear so easily. The overall objective of the project was to make recommendations about the environmental conditions needed to sustain V. nana and its functional role in the Daly River.
Note: This report is related to the 'Recommended Environmental Water Requirements for the Daly River, Northern Territory, Based on Ecological, Hydrological and Biological Principles' report available from the Supervising Scientist Division web site.