Supervising Scientist Division

Supervising Scientist Annual Report 2002 - 2003: Ecological Risk Assessment

Supervising Scientist, Darwin, 2003
ISBN 0 642 24383 2
ISSN 0 158-4030

3 - Environmental research and monitoring (continued)

3.5 Ecological Risk Assessment

The Ecological Risk Assessment programme provides advice on the significance of threats to the biological diversity and functioning of tropical wetlands in the Alligator Rivers Region and elsewhere.

Activities in 2002-03 included:

3.5.1 Publication of ecotoxicological testing protocols for Australian tropical freshwater ecosystems

Over the past 20 years, the Supervising Scientist and various collaborators have developed the most comprehensive suite of ecotoxicological testing protocols in Australia and possibly the world, for tropical freshwater species. The protocols have been used routinely to investigate the toxicity of contaminants associated with mining operations in the Alligator Rivers Region as well as the toxicity and risks of non-mining related contaminants (eg herbicides) to local tropical freshwater species.

Recently, these protocols were fully described, peer-reviewed and published as the Supervising Scientist Report Ecotoxicological testing protocols for Australian tropical freshwater ecosystems (SSR173). The report describes in full seven toxicity testing protocols including information on the test organisms and associated culturing/husbandry details, test equipment, test procedures, data recording, test acceptability criteria and statistical analysis, as well as providing historical and recent references to all of the research testing protocols from the past 20 years. This compilation represents a significant milestone in the history and development of the Supervising Scientist's ecotoxicology programme and highlights the achievements over 20 years of a large group of researchers and technical staff.

The ecotoxicological testing protocols are a key asset for the Supervising Scientist, while the report itself represents a valuable resource for Australian and international ecotoxicologists.

3.5.2 Assisting indigenous Traditional Owners in Kakadu to manage floodplain vegetation using traditional fire regimes

Boggy Plain is a major freshwater wetland located on the South Alligator River floodplain. It supports many freshwater floodplain vegetation communities typical of Kakadu National Park, and a diversity of wetland fauna. Additionally, Boggy Plain and associated wetlands to the south comprise one of the most important dry season refuges for magpie geese in the Northern Territory. In some years, up to 85% of the total Northern Territory magpie goose population have gathered to feed at Boggy Plain. Boggy Plain is also an important area for Aboriginal people who hunt geese and long-necked turtle, and collect water plants and other floodplain resources. The use and management of this important wetland by Traditional Owners represents many of the natural and cultural values of Kakadu.

Boggy Plain, which is not exposed to potential mining impacts, offers a valuable contrast to similar floodplain environments in the Magela Creek catchment of Kakadu that are exposed to potential mining impacts. Further, the threats and current impacts on Boggy Plain are typical of those facing much of the low-lying Kakadu wetlands. These include the impact of feral animals (especially pigs), weed infestations (small infestations of para grass have recently been reported), and the potential for salt water intrusion to cause significant modification of freshwater habitats. Research and monitoring of multiple landscape-scale impacts at Boggy Plain aims, through its use as a control site, to assist in distinguishing between impacts caused by mining-related disturbances and other anthropogenic or natural influences. It should also provide valuable information to assist in the management of the natural and cultural values of this area and potentially other areas within Kakadu.

eriss is collaborating with local Aboriginal people and Parks Australia North to help assess the dynamics of vegetation change over different spatial and temporal scales using remote sensing in conjunction with ground based survey information. Changes in floodplain vegetation are being assessed using:

The focus of this particular project is the influence of changes in fire regime on the vegetation.

According to traditional management practice, floodplain ecosystems such as Boggy Plain need to be burnt periodically to maintain their natural and cultural values. Traditional Owners consider that Boggy Plain has not been burnt correctly over the last decade or so, allowing the native grass Hymenachne acutigluma to spread over much of the plain. This grass forms a dense monoculture that limits access for hunting and gathering of traditional foods. It also threatens to reduce habitat diversity for many other wildlife species, spatial heterogeneity and the abundance of other wetland vegetation - all key World Heritage values. In particular, the native water chestnuts (Eleocharis spp.) and wild rice (Oryza spp.), important food plants for magpie geese, appear to be displaced by dense Hymenachne cover.

Traditional floodplain burning regimes have been recently reinstated and are specifically aimed at reducing Hymenachne cover and promoting the spread of Eleocharis, other wetland plant species and open water. Areas of Hymenachne were effectively and extensively burnt in the late dry season of 2002. Remote sensing scenes were captured immediately before burning, and early in the following dry season. Preliminary results strongly suggest that traditional floodplain burning practices are an effective way to reduce dense Hymenachne monocultures, which were replaced by other species in areas that had been burnt. Figure 3.12 illustrates this change in a small portion of the flood plain. Figure 3.13 shows the decrease in Hymenachne cover and relative change in wetland vegetation for the area.

Figure 3.12: The graph shows the large relative change in composition of vegetation in this area.

Figure 3.12: The graph shows the large relative change in composition of vegetation in this area.

Note: Change in an adjacent unburnt area of the floodplain (control) was negligible over the same time.

Figure 3.13: The effect of fire on floodplain monocultures of native Hymenachne grass.

Figure 3.13: The effect of fire on floodplain monocultures of native Hymenachne grass.

Note: Fire produces a far more diverse and heterogenous community structure compared with unburnt areas of Hymenachne. This change is illustrated for a small area of the floodplain with maps produced from remotely sensed data for the same area before burning in 2002 and after vegetation has re-established in 2003. The area that was burnt lies below the white line.