Supervising Scientist Report 116
Storrs MJ and Finlayson M
Supervising Scientist, 1997
ISBN 0 642 24315 8
- Preliminary pages (PDF - 531 KB)
- Chapters 1-3 (PDF - 1.1 MB)
- Chapters 4-6 (PDF - 1.1 MB)
- Chapters 7-8 (PDF - 608 KB
- References and Appendices (PDF - 2.3 MB)
- At the request of the Northern Territory Parks and Wildlife Commission an overview of the conservation status of wetlands in the Northern Territory (NT) is presented as a background resource and discussion paper for the development of a wetlands policy. The conservation value of wetlands and the threats that they face have been described within a framework of sustainable utilisation of resources and maintenance of biological diversity. Thus, an information base for conservation managers has been summarised. Strategic directions have been indicated, but it is stressed that a strategy for the proposed wetland policy has not been presented. A process of intra-governmental and community consultation is required to produce such a strategy.
- The information contained within this report is presented on a biogeographical basis at two different levels. For general purposes three broad regions of the NT were considered - northern, central and southern. For specific planning and management purposes the Interim Biogeographical Regions of Australia (IBRA) have been used. Datasets pertaining to wetlands in the NT have been identified and described in a comprehensive Appendix. Information on nature reservation, wetland resources, land uses and dominant threats to wetlands is also presented in Appendixes with summary points made in the text. A comprehensive bibliography is attached.
- Wetland definition and classification within the NT require further attention. Commonly used definitions and classifications are not generally useful within the NT context. A simplified classification was used in this overview, but its limitations were recognised. The categories of wetlands identified were - coastal salt marshes, mangrove swamps, freshwater lakes and swamps, floodplains, freshwater ponds, and seasonal and intermittent saline lakes. It is stressed that classification should be used to promote unity of purpose and not serve as a dampener to further innovation and management.
- Current inventory information for NT wetlands is deficient. Unless this situation is greatly improved wetlands management and conservation will, in part, need to rely on an uneven information base. Inventory information is particularly poor in the central and southern regions of the NT. The further development of a meta-database to hold records of all databases pertaining to wetlands is strongly supported. A thorough synthesis of the many databases identified in this overview would greatly assist resource planners and researchers.
- Much of the information used for general descriptions of the wetland habitats of the NT is readily available in published reports. It need not be repeated here. It is pertinent, however to point out that these habitats are an invaluable component of our national biological diversity and require further strategic management. The monsoonally influenced wetlands across the northern coastal zone are well studied and undoubtedly of high conservation value given the diversity of plants, animals and habitats. However, those of the semi-arid and arid zones are less well known, but given the nature of the environment are also undoubtedly highly valuable.
- The conservation status of individual wetlands of the NT has not been assessed and indicators of ecological integrity have not been developed. Further assessment, monitoring and audit of the conservation status of wetland habitats and ecosystems is needed. For this to be successful baseline information on the ecological character of the wetlands is required and should be coupled to effective monitoring programs. Monitoring programs should be well designed and be able to answer discrete objectives within realistic timeframes.
- The nature reserve system is one of the most valuable assets for the maintenance and management of genetic, species, community and landscape diversity, as well as key ecological functions and processes. The existing network of reserves does not offer comprehensive protection of the faunal or floristic diversity of wetlands. Further assessment of the need for reserves is required along with the development of off-reserve conservation arrangements. Wetlands are well represented in reserves in the northern region, but this is not the case in the central and southern regions.
- Existing or emerging threats to wetlands include: plant and animal pest species; fire and burning regimes; overgrazing; pollution and contamination; tourism and recreational activities; and water regime and physical modification. These do not affect all wetlands, but there are few wetlands that have not undergone some level of adverse change in ecological character.
- A list of weed species in NT wetlands is presented. Many plant species have caused problems and major control programs have been successfully implemented for some of them. However, very little is actually known about the ecological change wrought by these species. The major weed species are Acacia nilotica (prickly acacia), Brachiaria mutica (paragrass), Cenchrus ciliaris (buffel grass), Eichhornia crassipes (water hyacinth), Mimosa pigra (mimosa), Parkinsonia aculeata (parkinsonia), Prosopsis limensis (mesquite), Salvinia molesta (salvinia) and Tamarix aphylla (Athel pine).
- Paragrass is a pasture species that has spread from grazing land to conservation reserves. Two less widely spread species, Echinochloa polystachya (aleman grass) and Hymenachne amplexicaulis (olive hymenachne), similarly threaten to invade nature reserves. These species form monocultures and adversely affect the structure and functions of the wetlands concerned. In many cases these species are still being deliberately introduced without a thorough analysis of the risks that they pose.
- Mimosa is considered to be a major menace to the floodplains of the northern region of the NT. Management emphasis has centred on control techniques including the release of biological control agents. Integrated control programs incorporating biological control along with the use of herbicides, mechanical removal, burning and revegetation are increasingly being used. A 'search and destroy' policy has been successful in Kakadu National Park, but elsewhere expensive chemical control programs are still being undertaken. Post-control rehabilitation deserves a lot more attention.
- Salvinia is a widespread weed species but, as with many other species, its effect on the wetlands has been little studied. Biological control can be effective, but in some instances must be integrated with chemical control.
- The main feral animal pest in the northern coastal wetlands was formerly Bubalus bubalis (Asian water buffalo), which was responsible for the widescale destruction of native vegetation. Large herds now only exist in parts of Arnhem Land following a successful eradication program directed towards protecting the domestic livestock herd. The rapid removal of buffalo has resulted in further large scale change with both native and alien plant species overgrowing stream and billabong banks and spreading across the floodplains.
- Other animal pest species include Camelus dromedarius (camel), Equus caballus (horse), Equus asinus (donkey), Oryctolagus cuniculus (rabbit), Sus scrofa (pig), Bufo marinus (cane toad) and exotic fish. Pigs have caused widescale damage, but control is often difficult. Cane toads pose an ever increasing threat, although evidence to support the extent of the threat is not conclusive.
- The incidence of fire on the coastal floodplains has increased since the removal of large numbers of buffaloes. Vast areas of the central and southern regions of the NT are burned every year including many intermittent or episodic wetlands. Little direct analysis of the effect of fire on the wetlands has occurred.
- Soil erosion following overgrazing of wetlands is a major issue in the central and southern regions of the NT. Again, however, very little is known about the actual effect of such changes on the wetlands. Pastoralism is a major land use and is generally considered to have been detrimental to the ecological character of many wetlands.
- Tourism is an increasingly important industry with localised impacts due to high visitation numbers expected to increase. Recreational fishing for barramundi has already seen the introduction of regulatory measures. Other fish may be subject to similar pressure. Waterfowl hunting can also result in lead poisoning of waterfowl from ingested lead pellets.
- Land uses as diverse as mining, tourism, urbanisation and agriculture all bring a threat of water pollution. Mining has attracted a lot of attention and is now more often subject to strict regulation. Less is known about the effect of agricultural chemicals on wetlands. Salinisation of the coastal wetlands is an increasing problem and could be exacerbated by climate change processes.
- As many NT wetlands exhibit both physical and biological linkages it is extremely difficult to separate them into discrete management units. The physical linkages are best illustrated by the seasonal freshwater flooding of the coastal floodplains and mangroves. Biological linkages are shown by highly mobile or migratory species such as waterbirds and fishes. Successful conservation management and abatement of threats needs to take these linkages into account. Even large reserves, such as Kakadu National Park, are affected by activities that occur far from the park itself. For effective conservation a suite of interconnected wetland sites may be needed. In some instances, conservation covenants or management agreements may have to be placed across complexes of wetlands regardless of land tenure.
- The NT has adopted a multiple use policy for its wetlands. This policy attempts to encourage different land uses and to provide a balance with conservation objectives. Current land uses are not generally intensive, but even the extensive grazing industry has resulted in widespread degradation of valuable wetland habitat. Conservation can be compatible with multiple land use under a sustainable development ethic, but conflicts can also occur. Holistic approaches and consultation, such as that underway in the lower Mary River, should be further developed and supported by local initiatives.
- Given that many conservation issues in wetlands need to be immediately addressed, management actions have to rely on currently available information. However, every step must be taken to improve the information base. Key actions for wetland conservation include: development of a sound inventory of wetlands; development of regional land use and consultative processes that address both local and global scale issues; extension of the reserve system based on a systematic assessment of conservation needs across biogeographical regions; improved off-reserve conservation measures; risk analysis and effective control of pest species; cooperative management structures for grazing; protection of critical habitats through truly multi-sectoral approaches; and continued attention to public awareness and education.
- Some of the above actions may need to be accompanied by changes to legislative and administrative structures to reflect the multi-sectoral nature of wetland functions and uses. It may be profitable to employ a consultative approach to a review of the interaction between legislation and the multi-sectoral values placed on wetlands.