Supervising Scientist Division

Supervising Scientist Annual Report 2002 - 2003: Ecosystem Protection

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

3 - Environmental research and monitoring (continued)

3.3 Ecosystem Protection

The Ecosystem Protection programme provides advice on the protection of aquatic and terrestrial ecosystems during and after mining activities in the Alligator Rivers Region and on the conservation and management of tropical wetlands.

Activities in 2002-03 included:

3.3.1 Identification of highly significant aquatic habitats and native species of Kakadu National Park

The development, within eriss, of a programme of landscape-wide research in Kakadu National Park has complemented the dedicated monitoring programmes aimed at assessing any identified impacts of mining in the Alligator Rivers Region (see Sections 2.2.3 & 2.3.3).

The landscape studies aim to provide information to help manage and conserve the natural World Heritage values of Kakadu and develop a monitoring programme capable of distinguishing possible mining-related impacts at the landscape scale from effects due to other causes.

One area of this research focuses on the natural World Heritage value of Kakadu listed as 'unique, rare or important (including iconic) plant or animal species/associations of conservation significance'.

An aspect of this that has received greater attention recently is the aquatic fauna of the seeps and springs of the stone country of Kakadu. Of particular interest are the crustacean groups: isopods (family Amphisopodidae); freshwater crabs (family Sundathelphusidae); and prawns and shrimps (families Atyidae and Palaemonidae) that occur in these habitats. Most of these species are endemic, occurring only in this region. Distributions are often limited to single streams or springs, and most species are undescribed.

Apart from mining impacts, these endemic species may be vulnerable to the invasion of cane toads (including eggs and tadpoles), through either toxicity (direct contact or consumption) or competition with tadpoles for food and space. Cane toads are now well established in Kakadu and eriss and collaborators are moving quickly to complete surveys of key sites in the Park.

While many sites in the stone country seeps and springs have been previously surveyed by eriss, Park rangers and others, additional sites have been identified and a new sampling programme initiated. The current surveys have involved local Aboriginal Traditional Owners in the field sampling (Figure 3.2).

eriss is also collaborating with scientists from other organisations to distinguish and describe new species collected from the sites. A taxonomic group of particular interest is the phreatoicidean isopod crustaceans of Kakadu.

Work over the past decade by eriss and scientists from the Australian Museum has uncovered at least 15 'morphotypes' or suspected species of the genus, Eophreatoicus. To date, a suite of morphological characters entered onto a computer database has facilitated identification of these species. Recent collections made in 2003 have added to this database. The differences between specimens collected at Leichhardt Springs and a tributary of North Magela Creek are a good case for comparison. Although these two sites are separated by only 24 km, the differences between these species are substantial (Figure 3.3).

As a further confirmation of the morphological species concepts for these isopods, a scoping study of the genetic differences amongst isopods from various sites has commenced. This preliminary study, being carried out in laboratories of the Evolutionary Biology Unit at the Australian Museum, is testing various sections of mitochondrial and nuclear DNA for ease in recovery and for differences within and between populations.

Preliminary results of DNA analysis (Figure 3.4) demonstrate a high degree of genetic differentiation between the populations of the two sites, thus confirming the morphological system developed to date. Next steps include testing for other DNA sequences and expanding the study to seven different populations that were sampled by eriss in the early dry season of 2003.

3.3.2 The ecological effects of magnesium sulphate in Magela Creek

Magnesium sulphate (MgSO4) is a major contaminant of Ranger mine waste waters. A study has been initiated by eriss to examine the effects of this salt on the ecology of Magela Creek downstream of Ranger through laboratory ecotoxicity tests using natural creek water on specific species, and field experiments on various animal and plant communities. The results of laboratory ecotoxicity tests were described in the Supervising Scientist's 2001-02 Annual report. The main findings were:

Subsequent to this reporting, field 'mesocosm' experiments examining community-level effects have been completed. Using natural settings and relatively large-scale and replicated sampling containers, mesocosms attempt to better mimic treatment effects on plant and animal populations and communities, compared with single-species, laboratory toxicity tests.

The mesocosm tests used 3000 L fibreglass tubs placed on the creek bed (Figure 3.5). Each tub was seeded with resident creek communities during the recessional flow period in the early dry season. The tubs were sampled for macro- and microinvertebrates, diatoms on artificial substrates, and chlorophyll pigments (as a surrogate for phytoplanktonic abundance and broad type). Five different MgSO4 dose treatments were used with replicates for each. Sampling was conducted prior to dosing of the tubs, then twice after dosing. Dosing was conducted over geometrically-increasing concentrations of MgSO4, similar to those used in the laboratory experiments.

The community structure (taxa and their relative abundances) amongst tubs of different treatments (including control) is being quantified to determine the concentration at which MgSO4 significantly alters the communities. This is achieved through multivariate Non- Metric, Multi-Dimensional Scaling ordinations (NM-MDS), as well as ANOSIM (ANalysis- Of-SIMilarity), the latter approach being used to determine community No Observed Effect Concentrations and Lowest Observed Effect Concentrations.

Figure 3.2: Collecting aquatic invertebrates from Leichhardt Springs in Kakadu National Park

Figure 3.2: Collecting aquatic invertebrates from Leichhardt Springs in Kakadu National Park

Figure 3.3: Comparison of Eophreatoicus species from two sites.

Figure 3.3: Comparison of Eophreatoicus species from two sites.

Note: These two reproductive females from North Magela Creek and Leichhardt Springs belong to separate species. In addition to their relative size (see 1 mm scale bars) and colour, the eyes are different sized, their cuticle differs in roughness, the last body segment (pleotelson) has a different shape and the appendages on the pleotelson (uropods) have different decorations.

Figure 3.4: Eophreatoicus species: Sequence of DNA bases from a section of the 16s mitochondrial genome (screen image from a sequence analysis programme).

Figure 3.4: Eophreatoicus species: Sequence of DNA bases from a section of the 16s mitochondrial genome (screen image from a sequence analysis programme).

Note: The top two rows (E4 & E5, 6, 7) are from two specimens from Leichhardt Springs and the bottom three rows (E9, 10, 11) are from two specimens from North Magela Creek, with the last two rows from the same individual as a check on the consistency of the sequencing reaction. Each DNA base (A G C T) that is the same within a column is not repeated below. These bases show a high degree of divergence between the two sites but high constancy within species/sites. The level of divergence (approximately 15%) is typical of that seen between different genera in other crustaceans.

Figure 3.5: Setting-up the field mesocosm experiment, seeding tubs with creek sand and water with their associated biological communities.

Figure 3.5: Setting-up the field mesocosm experiment, seeding tubs with creek sand and water with their associated biological communities.

Photo: C McCullough

The ordination (former) approach depicts the community structure of samples graphically, in a reduced (typically two or three) dimensional space. The closer samples (in this case replicate tubs) are together in ordination space, the more similar is their community structure. A change in community structure would be inferred if replicates from a particular concentration were 'separated' from those of the controls. Interspersion of replicates of different treatments in ordination space, on the other hand, would imply no significant difference in community structure.

Figure 3.6 illustrates this concept and shows that differences in community structure appear to occur only at the highest concentration for natural macroinvertebrate communities (note the separation of the symbols depicting the highest concentration). Amongst macroinvertebrates sampled, the main response appeared to be a reduction in zooplankton algal grazers at the highest concentration. Diatoms did not respond to increased MgSO4 concentrations of the range used in the mesocosm treatments, whilst phytoplankton biomass (Figure 3.7) and abundances of zooplankton grazers were reduced at lower MgSO4 concentrations.

The information (chronic data) derived from both the single-species laboratory and community-level field experiments are being compared and the results will be used to derive both a safe dilution to release MgSO4 to Magela Creek as well as a national trigger value for magnesium toxicity in soft waters. This trigger value will meet the criteria of a high-quality locally-derived water quality standard as promoted in the new Australian and New Zealand Water Quality Guidelines. At this stage, field mesocosm results appear to be in agreement with laboratory results and indicate that the salinity of Ranger mine effluent waters is unlikely to be causing any harm to aquatic ecosystems of Magela Creek.

Figure 3.6: NM-MDS ordination of mesocosm macroinvertebrate responses to increasing concentrations of MgSO4

Figure 3.6: NM-MDS ordination of mesocosm macroinvertebrate responses to increasing concentrations of MgSO4

Figure 3.7: Response of chlorophyll (as a surrogate variable for phytoplanktonic biomass) to MgSO4 treatments in mesocosm experiments.

Figure 3.7: Response of chlorophyll (as a surrogate variable for phytoplanktonic biomass) to MgSO4 treatments in mesocosm experiments.

Note: Treatments 1 to 5 refer respectively to control (creek water), 2.5, 7.5, 22.5 and 62.5 mg/L Mg2+. Week 0 refers to sampling prior to dosing with MgSO4 and weeks 4 and 7 to sampling at these respective intervals after dosing. Error bars represent one standard error about the means.