Protecting aquatic ecosystems

Freshwater  snail test chambers are held in the floating toxicity monitoring containers.  Inset shows snails and their egg masses.

Freshwater snail test chambers are held in the floating toxicity
monitoring containers. Inset shows snails and their egg masses.

Based upon its research and development, the SSD adopts physical, chemical (including radiological) and biological control regimes to provide independent assurance that aquatic ecosystems of the Alligator Rivers Region (ARR) remain protected from current and past mining-associated activities in the region. This is in recognition that in this highly-valued area, such comprehensive and integrated assessments will provide assurance that the highest standards of ecosystem protection are being met.

Physical and chemical standards, and toxicology

Physical and chemical guidelines or standards have been set for the first stage in the control regime, in place for the regular wet-season dispersion of mine waste waters to streams (Ranger). Water quality standards are derived from laboratory-based toxicity testing and for this animals and plants tested may include fish fry, waterfleas, snails, hydra, algae and duckweed. (New experimental approaches to the development and derivation of sediment quality criteria for waterbodies in the ARR are currently under way.) Radiological standards are based upon human health considerations (Sauerland 2005). Water quality downstream of the mine is assessed against the guidelines and standards. The second stage consists of physical, chemical and biological monitoring programs conducted in downstream ecosystems to demonstrate that the expected high level of environmental protection has been achieved.

Stream monitoring program for Ranger

Staff and volunteers collecting and counting fish in a lowland billabong

Staff and volunteers collecting and counting fish in
a lowland billabong

The monitoring program incorporates physical, chemical and biological components. The techniques and ‘indicators’ used in the monitoring program satisfy two important needs of environmental protection: (i) the early detection of potential effects to avoid ecologically important impacts; and (ii) information on the ecological importance of any likely impact (biodiversity assessment). Monitoring techniques adopted by the SSD that meet these requirements are:

Early detection of short or longer-term changes

  • Water physico-chemistry:
    • Continuous monitoring: use of multi-probe loggers for continuous measurement of pH, electrical conductivity (EC), turbidity and temperature plus event-triggered auto-sampling in Magela Creek and Gulungul Creek; EC and turbidity in Ngarradj (Swift Creek), and
    • 'Grab' samples for radium assessment and water chemistry quality assurance/quality control (QA/QC) purposes: this includes pH, EC, uranium, magnesium, calcium, manganese, sulphate and radium. Samples are collected fortnightly from Magela Creek for radium analysis and every 4 weeks for QA/QC over the period of wet season flow in Magela Creek, Gulungul Creek and Ngarradj (Swift Creek).
  • Toxicity monitoring of reproduction in freshwater snails (four-day tests conducted at fortnightly intervals);
  • Bioaccumulation - concentrations of chemicals (including radionuclides) in the tissues of freshwater mussels from Mudginberri Billabong to detect far-field effects including those arising from any potential accumulation of mine-derived contaminants in sediments (sampled every late-dry season).

Assessment of changes in biodiversity

  • Benthic macroinvertebrate communities at stream sites (sampled at the end of each wet season); and
  • Fish communities in billabongs (sampled at the end of each wet season).

Early detection

In the field, toxicity monitoring is used for early detection of effects in the creek arising from dispersion of mine waters during the wet season. Reproduction of freshwater snails exposed to creek waters are measured during each wet season. This response in particular, has been shown to be sensitive to mine waste waters (possible X-reference to ecotox). Responses of the test animals are measured at two sites, one located upstream of Ranger (a control) and the other several kilometres downstream. Information gathered from both species since testing commenced (in 1992) has shown that responses are very similar at the upstream and downstream sites, indicating no effects of mine water releases.

Assessing the ecological importance of change using ecosystem-level responses

Studies of natural populations and communities of aquatic organisms – so-termed ecosystem-level responses – provide the best information about the ecological importance of impacts. Advantages of this approach are the potentially wide range of sensitivities shown by different species to toxicants, and the provision of information about the biological diversity in the ecosystem. In the case of the ARR, this involves counting macroinvertebrate (eg insect larvae, molluscs, shrimps) and fish species in the creek systems, downstream of mine sites and in control locations unaffected by mining. The control locations are situated both upstream of mine sites and in separate streams.