Supervising Scientist Annual Report 2003 - 2004
Supervising Scientist, Darwin, 2004
ISBN 0 642 24391 3
ISSN 0 158-4030
2 - Environmental assessments of uranium mines (continued)
2.2 Ranger (continued)
2.2.3 Off-site environmental protection
Surface water quality
Under the Ranger General Authorisation, ERA is required to monitor and report on water quality in Magela Creek downstream of the mine. Specific water quality objectives must be achieved. The Authorisation specifies the sites, the frequency of sampling, the analytes to be reported, and requires that increases in concentration must not lead to a breach of the annual load limit.
In addition, the Supervising Scientist conducts an independent routine monitoring programme that includes chemical, physical and biological monitoring in Magela and Gulungul Creeks.
The Commonwealth Environmental Requirements (ERs) for Ranger further reinforce the existing compliance framework as it relates to the protection of people and the environment. In particular, the ERs require that key variables that indicate the health of the Magela Creek system be defined so that any unusual change triggers an action by the company and potentially a response by the Commonwealth.
Water quality criteria for Magela Creek at the monitoring site downstream of Ranger mine have been set in accordance with Australian and New Zealand Environment and Conservation Council (ANZECC) and Agricultural and Resource Management Council of Australia and New Zealand (ARMCANZ) Water Quality Guidelines, and are described in detail in the Supervising Scientist's Annual Report for 2001-2002. The sequence and hierarchy of management actions where elevated values are measured follows the order:
- Focus level (a management threshold) — exceedance of a focus level triggers a watching brief and may require further sampling to verify whether an upward trend is occurring.
- Action level (a management threshold) — exceedance of an action level triggers investigative and/or corrective action.
- Limit or guideline:
- Limit (a compliance threshold) — the value of a parameter that must not be exceeded as a consequence of mining operations. Exceedance of a limit due to mining activities may constitute a breach of statutory requirements.
- Guideline (management threshold) — an upper (and lower for pH) guideline replaces a limit for some parameters whose values are influenced frequently by non-mining related events or whose effects are influenced by other parameters. Guidelines are set to assist in the interpretation of water quality measurements rather than for compliance purposes. The exceedance of a guideline is not a breach of statutory requirements.
Collectively these levels are referred to as the 'trigger values'.
Chemical and physical monitoring of Magela Creek
The first water chemistry sample for the Supervising Scientist's 2003-04 wet season surface water monitoring programme was collected from the Magela Creek downstream statutory compliance point on 23 December 2004, one day after the commencement of flow past the site for this wet season. Weekly routine sampling continued throughout the wet season with routine monitoring samples continuing to be collected as at 30 June 2004. Further sets of samples/measurements were collected in Magela Creek for investigative purposes (rather than for compliance monitoring) on:
- 26 March 2004 to 2 April 2004, the week following the Ranger potable (drinking) water contamination incident (section 2.2.4), and
- after 30 June 2004, by which time the central channel at the downstream monitoring site was a series of disconnected pools with flow at the compliance point almost negligible and lateral from the very shallow (<10 cm) east channel, and
- each routine sampling event, from the west channel at the downstream site, for continuing investigations into the cross channel variation at that site.
The full set of water quality data from the Supervising Scientist's routine monitoring of Magela Creek and the investigative sampling described in dot points one and two above are reported on the Internet at www.deh.gov.au/ssd/monitoring/magela-chem.html.
The highlights of the monitoring season are summarised below.
All indicators measured at the Magela Creek compliance point during flow were well within limits during the season, even during the first weeks when first flush effects often result in limits or guidelines being approached and occasionally exceeded. Compliance with the water quality limits and guidelines throughout the season provides reassurance that the aquatic environment has not suffered any deleterious effects from mining during the previous year. The results of the biological monitoring programme confirm this.
Overall, the water quality in Magela Creek this wet season was similar to that seen last season, and was demonstrably improved compared with that seen during the 2000-01 and the 2001-02 seasons (Table 2.6); smaller differences in upstream-downstream electrical conductivity and concentrations of manganese, magnesium, sulfate and uranium (Figure 2.5A) were seen in the last two seasons compared with the previous two seasons. These improvements have been attributed to a range of remedial works and water management practices implemented at the mine in recent years.
| Median | Range | |||||
|---|---|---|---|---|---|---|
| Parameter | Limit | Year | Upstream | D'stream | Upstream | D'stream |
| pH | 5.2 - 7.2* | 2003-2004 2002-2003 2001-02 2000-01 |
6.2 6.1 5.8 (5.9) |
6.4 6.1 6.1 (6.0) |
5.3 - 6.7 4.8 - 6.7) 5.2 - 6.7 (5.3 - 6.4) |
5.5 - 6.7 4.8 - 6.7 5.7 - 6.7 (5.2 - 6.5) |
| EC (µS/cm) |
43 | 2003-04 2002-03 2001-02 2000-01 |
12 14 15 (10) |
15 15 19 (12) |
7.6 - 20 7.5 - 23 11 - 19 (7 - 19) |
8.5 - 21 9.0 - 23 11 - 31 (6 - 25) |
| Turbidity (NTU) |
56 | 2003-04 2002-03 2001-02 2000-01 |
2.4 2.0 2.0 (4) |
2.3 2.1 2.5 (4) |
1.0 - 25 0.8 - 9.5 0.7 - 5.8 (2 - 13) |
1.0 - 13 0.9 - 8.9 1.2 - 9.5 (2 - 17) |
| Sulphate‡ (mg/L) | EC must comply |
2003-04 2002-03 2001-02 2000-01 |
0.2 0.3 0.3 0.2 |
0.6 0.6 1.4 1.8 |
<0.1 - 0.8 <0.1 - 0.9 0.1 - 0.4 0.1 - 2.9 |
0.2 - 1.9 0.2 - 1.6 0.4 - 3.5 0.3 - 47 ff |
| Magnesium‡ (mg/L) |
EC must comply |
2003-04 2002-03 2001-02 2000-01 |
0.5 0.6 0.7 0.5 |
0.7 0.7 1.0 1.0 |
0.2 - 1.0 0.3 - 1.0 0.3 - 0.9 0.2 - 1.3 |
0.3 - 1.0 0.3 - 1.1 0.3 - 1.6 0.5 - 11 ff |
| Manganese‡ (µg/L) |
32 | 2003-04 2002-03 2001-02 2000-01 |
4.0 5.4 5.2 4.3 |
4.6 5.8 7.9 6.8 |
2.9 - 14 2.9 - 20 2.0 - 7.8 1.4 - 12 |
2.2 - 14 2.8 - 30 1.8 - 45 2.5 - 52ff |
| Uranium‡ (µg/L) |
5.8 | 2003-04 2002-03 2001-02 2000-01 |
0.018 0.019 0.011 0.017 |
0.041 0.053 0.038 0.095 |
0.007 - 0.045 0.007 - 0.079 0.001 - 0.024 0.003 - 0.041 |
0.017 - 0.104 0.016 - 0.101 0.014 - 0.198 0.006 - 0.971 |
Notes:
Italicised data in parentheses are ERA data
‡ dissolved (< 0.45 mm);
* pH limits are guidelines only;
ff - maximum value measured during first flush event at downstream site, no corresponding first flush measured at the upstream site downstream
During the greater part of the wet season, waste-water inputs to the creek are received from the minesite via Retention Pond 1, Georgetown Creek and, for a short period of controlled release, Djalkmara Billabong. Intermittent pumping of Djalkmara Billabong water into Magela Creek began on the 31 January 2004 and ceased in late March 2004. (This pumping is permitted under strict conditions based on results of 'whole of effluent' ecotoxicological testing, flow rates in Magela Creek and predictive modelling of expected concentration increases at the downstream Magela Creek statutory compliance point.) During Djalkmara pumping, a slight rise in uranium concentration downstream of the mine was noticeable in the early February data and again in early March (Figure 2.5B) — the uranium concentrations did not exceed 2% of the ecotoxicological limit on those occasions. The other downstream parameters showed little, if any, additional change during the pumping of Djalkmara Billabong.
The major event of the season with potential to impact on Magela Creek and human health was the contamination of potable water with process water at Ranger in late March. Daily measurements of uranium, manganese, electrical conductivity and pH were made (in late March 2004 - early April 2004) during the Supervising Scientist's investigation into the contamination incident (Section 2.2.4). The results demonstrate that no uncharacteristic change in any of the key water quality variables occurred at the downstream Magela Creek statutory compliance point throughout the incident, all results being within the normal range of measurements. The daily uranium values for this period are included in Figure 2.5B. The radionuclides measured in the creek water and the implications of the incident for the health of the people living downstream of the mine are discussed in Section 2.2.4.
Chemical and physical monitoring of Gulungul Creek
The first water chemistry sample for the Supervising Scientist's 2003-04 wet season surface water monitoring programme was collected from Gulungul Creek on 23 December 2004, one day after the commencement of flow past the site for this wet season. Weekly sampling continued throughout the wet season with the last of the routine monitoring samples being collected after 30 June 2004, when the creek had all but stopped flowing.
Key water quality data from the Supervising Scientist's routine monitoring of Gulungul Creek are available on the Internet at www.deh.gov.au/ssd/monitoring/gulungul-chem.html. The highlights of the monitoring season are summarised below.
In the first three months of the wet season, the uranium concentrations at the Gulungul Creek downstream site were moderately higher than at the upstream site (Figure 2.6). From mid-March, the uranium concentrations at the downstream site were almost the same as those at the upstream site, though as in previous years downstream concentrations were slightly higher than upstream concentrations (Table 2.5). The higher uranium concentrations measured at the downstream site, while probably mine related, are not considered to have posed an environmental risk, the values remaining less than 5% of the limit at the most. Nevertheless, an investigation into the cause of the elevated uranium concentrations at the downstream site will be undertaken.
EC, pH and turbidity measurements recorded this wet season were similar to values measured in previous years (Table 2.7) and were similar at both the upstream and downstream sites for most of the season. As occurred last wet season, EC generally increased from the middle of the season at both sites and exhibited a sharp increase in the last month. The cause of the elevated EC will be investigated. It cannot be attributed to the common mine-related salts magnesium and sulfate, as concentrations of those variables at the downstream site were actually lower during this period than in previous weeks.
Overall, the water quality in Gulungul Creek was good during the 2003-04 wet season (although the uranium concentrations downstream of the mine were elevated relative to the upstream concentrations, the increase was very low compared with the limit) providing reassurance that there is a high degree of certainty that the aquatic environment of Gulungul Creek remained protected from impacts of mining.
| Median | Range | ||||
|---|---|---|---|---|---|
| Parameter | Year | Upstream | D'stream | Upstream | D'stream |
| pH | 2003-04 2002-03 2001-02 |
6.3 6.4 6.4 |
6.3 6.4 6.3 |
5.1-6.9 5.4-6.8 5.9-7.0 |
5.3-6.5 5.5-6.8 5.8-6.9 |
| EC (µS/cm) |
2003-04 2002-03 2001-02 |
15 17 18 |
18 19 21 |
9.8-19 10-24 13-24 |
11-28 8.1-24 16-26 |
| Turbidity (NTU) |
2003-04 2002-03 2001-02 |
1.1 1.1 1.1 |
1.8 1.5 1.4 |
0.7-5.3 0.4-4.5 0.5-3.5 |
0.8-4.3 0.9-13 0.9-4.7 |
| Sulphate‡ (mg/L) | 2003-04 2002-03 2001-02 |
0.3 0.2 0.2 |
0.5 0.5 0.3 |
0.1-0.8 <0.1-0.6 0.1-0.5 |
0.1-1.7 <0.1-1.4 0.1-0.9 |
| Magnesium‡ (mg/L) |
2003-04 2002-03 2001-02 |
0.8 0.9 1.0 |
0.9 0.9 1.0 |
0.4-1.2 0.6-1.6 0.7-1.4 |
0.5-1.1 0.5-1.5 0.8-1.3 |
| Manganese‡ (µg/L) |
2003-04 2002-03 2001-02 |
2.1 2.7 1.8 |
4.1 5.3 3.5 |
1.1-7.9 1.2-6.4 0.5-4.7 |
1.5-15 2.3-18 1.3-5.8 |
| Uranium‡* (µg/L) |
2003-04 2002-03 2001-02 |
0.057 0.069 0.045 |
0.105 0.124 0.071 |
0.035-0.139 0.029-0.197 0.023-0.292 |
0.067-0.279 0.056-0.251 0.045-0.133 |
Notes:
‡ dissolved (<0.45 mm),
* limit = 5.8 µg/L
Biological monitoring in Magela Creek
Based on eriss research since 1987, biological monitoring techniques have been developed that can be used to assess the environmental impact of uranium mining on aquatic ecosystems downstream of the Ranger mine. Two broad approaches are used: early detection studies and studies of natural animal populations and communities, the latter providing a better measure and assessment of overall ecosystem-level responses and their importance arising from any potential impact.
For early detection, creekside monitoring procedures have been developed and employed in Magela Creek; ERA staff have collaborated with eriss on this programme in past years. For ecosystem-level responses, benthic macroinvertebrate and fish communities from Magela Creek sites are measured and the results compared with historical data and comparable data gathered simultaneously in analogue control streams. Results of creekside monitoring and fish community studies conducted during the 2003-04 wet and early dry seasons and macroinvertebrate studies carried out up to 2003 are reported here.
Creekside monitoring
In this form of monitoring, effects of Ranger mine wastewater dispersion are evaluated using responses of aquatic animals held in tanks on the creek side to effluent waters. The responses of two test species are measured over a four-day period:
- reproduction (egg production) in the freshwater snail, Amerianna cumingi, and
- survival of black-banded rainbowfish, Melanotaenia nigrans, larvae.
Animals are exposed to a continuous flow of water pumped from upstream of the minesite (control site) and from the creek at gauging station GS8210009, some 5 km downstream of the mine. At each of the two sites, duplicate pumps in the creek feed water separately to: (i) in the case of snails, duplicate containers respectively, each container holding replicate (8) snail pairs; and (ii) in the case of fish, triplicate containers respectively, each container holding ten larval fish. At the end of each four-day trial, the mean number of eggs per snail pair and mean number of fish surviving per replicate are noted and compared for each of the upstream and downstream sites. Specifically, when data from the downstream site are subtracted from those at the upstream site, a set of 'difference' values can be derived. These difference values may be compared statistically for different parts of the time-series. For example, 'difference' data for the wet season of interest may be compared with those from previous years; if they differ significantly, using a Student's t test, it may indicate a mine-related change. Since about 1996, creekside trials have been performed approximately every other week during the wet season. Tests usually commence in December and cease in early April, the period of significant creek flow in Magela Creek.
The results of the creekside trials are plotted as part of a continuous time series of actual and 'difference' data in Figure 2.7A for snail egg production, and in Figure 2.7B for larval fish survival. Descriptions of the sources of creekside data and data quality issues are provided in the Supervising Scientist's Annual Report for 2001-02.
Eight creekside tests were conducted in the 2003-04 wet season (29 December 2003-2 January 2004, 12-16 January 2004, 26-30 January 2004, 9-13 February 2004, 23-27 February 2004, 8-12 March 2004, 22-26 March 2004 and 5-9 April 2004.) Only seven tests were conducted using larval fish, there being too few fish larvae available to conduct the final, eighth, test.
The seventh test, using both test species and conducted in the period 22-26 March 2004, coincided with the Ranger potable water incident. After results were acquired for this (seventh) creekside test, it was extended for an additional 4-day period, 26-30 March, using the same test organisms (fish and snails). This test is termed the 'seventh-extended test', results for which are depicted in Figure 2.7 as the eighth set of actual data counts for the wet season (while the results of the eighth snail test are depicted in Figure 2.7A as the ninth set of such data points). For the seventh-extended snail test, fresh egg-laying chambers were used (containing none of the previously-laid egg masses). Because the same test animals were employed in both tests, neither fish nor snail results for this extended period are strictly valid for a statistical comparison against other test results as there is lack of independence. Nevertheless, the results are certainly indicative of any potential water quality impacts.
The first snail test conducted for the wet season resulted in significantly different mean egg counts between the snail pairs of each duplicate water at the downstream site (Table 2.8, P<0.05). The inability to pool duplicate results negates the ability to calculate a 'difference' value for the creekside test and to use the results in the formal statistical test for change. Significant differences in mean egg counts between duplicate waters at the creekside sites is rarely observed and, as these results were observed downstream of the Ranger mine, warrants some discussion. The mean egg counts for the two duplicates, together with key associated water quality data taken on day 4 of the test, are summarised in Table 2.8. Mine contaminants, uranium and electrical conductivity (a surrogate for magnesium sulfate), are low in value in both duplicate waters. Phosphorus levels, however, are high in duplicate 1 waters (Table 2.8) and also relative to concentrations normally measured in Magela Creek (data not shown here). Egg production in snails is known to be responsive to ambient nutrient levels (Supervising Scientist Annual Research Summary 1988-89, p.80) and this may explain the higher egg production observed in these duplicate waters. Cross-channel variation in water quality is not uncommon at the downstream Magela location (Supervising Scientist Annual Report 2002-2003, p.29) and while the source of 'high' nutrient concentration at the duplicate 1 pump location is not known, it is not unusual for early Wet season runoff waters to be nutrient enriched.
| Duplicate no. and location of pump in west channel of downstream site | Mean egg count |
Uranium (µg/L) |
Conductivity µs/cm) |
Phosphorus (mg/L) |
|---|---|---|---|---|
| Duplicate 1, east side | 173.1 | 0.047 | 12 | 0.04 |
| Duplicate 2, west side | 88.6 | 0.058 | 13 | 0.012 |
Amongst all snail tests, egg production at upstream and downstream sites was very similar across all tests conducted for the wet season (Figure 2.7A). Using the data shown, 'difference' values for 2003-04 were compared with those from previous years. (The difference data shown and subsequently used in statistical analyses are those for valid tests only.) No significant difference was found (P>>0.05). The results for the seventh-extended test, while not included in the formal statistical analysis, lie well within the range of variability observed in the current and previous years (Figure 2.7A).
There were insufficient fish larvae in the seventh creekside test to run a valid test so that only three replicate fish tanks, each holding ten fish larvae, could be used at each of the two creekside stations instead of the normal six replicate tanks. While results for fish larvae arising from the seventh and 'seventh-extended' test are plotted, the 'difference' values for both tests are not plotted (per convention to signify their statistically invalid nature, Figure 2.7B).
Across all fish tests, survival at upstream and downstream sites was similar (Figure 2.7B). There was some reduced larval fish survival at the upstream site relative to the downstream site, but this was not as marked as in previous years (particularly the period 1999/00 to 2002/03, Figure 2.7B). In the previous Supervising Scientist Annual Report (2002-03) it was noted that 'difference' (upstream-downstream) data for the two periods 1991-92 to 1995-96 and 1999-2000 to 2002-03 were significantly different from one another as a consequence of the reduced larval fish survival at the upstream control site in the period 1999-2000 to 2002-03. (Possible causes are discussed in the 2002-03 Supervising Scientist Annual Report.)
With the inclusion of 2003-04 data, the same significant difference was observed (1991-1992 to 1995-1996 versus 1999-2000 to 2003-04, P=0.003). However, when 'difference' results for 2003/04 were compared separately with results for the two time periods (1991-1992 to 1995-1996 and 1999-2000 to 2002-03) no significant differences were found.
The results for the seventh-extended fish test that was conducted over the period of the Ranger drinking water incident, while not included in the formal statistical analysis, lie well within the range of variability observed in the current and previous years (Figure 2.7B). In particular, fish survival was found to be consistently high at the downstream site over the eight-day period of both consecutive tests.
From the collective creekside results, it is concluded that there were no adverse effects of dispersed Ranger mine waste waters - including contaminated drinking water - on either of the creekside test species over the 2003-04 Wet season.
Monitoring using macroinvertebrate community structure
Macroinvertebrate communities have been sampled from a number of sites in Magela Creek at the end of significant wet season flows, each year from 1988 to the present. The design and methodology have been gradually refined over this period to meet the needs of cost efficiency and improved ability to confidently attribute any observed changes to mining impact. The most significant refinement that took place in the study occurred in 1994 when there was a reduction from ten sites sampled in Magela Creek to just three, as well as commencement of sampling at sites in three additional control streams. Since 1994, there have also been three changes to sampling and sample processing methods.
The refined (1994) design for this macroinvertebrate study was based on the principle of gathering macroinvertebrate samples from sites in Magela Creek upstream and downstream of Ranger, and also from similar paired upstream and downstream sites in three adjacent 'control' streams that are generally unaffected by any mining activity. In recent years, it has become evident that Gulungul Creek has been receiving some small quantities of mine contaminants from Ranger. Given its doubtful role as a true control stream, it is more appropriate now to consider this stream in the same category as Magela Creek, that is, 'potentially disturbed'. The design of this study, therefore, is now a balanced one comprising two 'potentially disturbed' streams and two control streams.
Samples were collected from each site at the end of each wet season (between April and May). For each sampling occasion and for each pair of sites for a particular stream, a dissimilarity index is calculated. This index is a measure of the extent to which macroinvertebrate communities of the two sites differ from one another. A value of 'zero' indicates identical macroinvertebrate communities while a value of 'one' indicates totally dissimilar communities, sharing no common taxa.
Research elsewhere in the Alligator Rivers Region has shown significantly 'higher' dissimilarity values for locations upstream and downstream of point sources of disturbance compared with values recorded in both the pre-disturbance, baseline period and in undisturbed control streams; the higher dissimilarity is a consequence of the 'altered' (disturbed) macroinvertebrate community structure at (the) site(s) downstream of such point sources.
Analysis of the full macroinvertebrate data set from 1988 to 2003 has been completed and results are shown in Figure 2.8. This figure plots the paired-site dissimilarity values using family-level (log-transformed) data, for the two Magela catchment streams and two Nourlangie catchment (control) streams.
Inferences that may be drawn from the data shown in Figure 2.8 are weakened because there are no pre-mining (pre-1980) data on which to assess whether or not significant changes have occurred as a consequence of mining. Notwithstanding, the plots show that the mean dissimilarity value for each stream across all years is approximately the same (~0.3) and that the values are reasonably constant over time. Confirming this, single-factor ANOVA shows no significant difference in the mean dissimilarities between the two treatment groups, 'control' vs 'potentially disturbed' streams.
The same dissimilarity indices used in Figure 2.8 may also be 'mapped' using multivariate ordination techniques to depict the relationship of the community sampled at any one site and sampling occasion with all other possible samples. Samples close to one another in the ordination indicate a similar community structure. In the ordination derived using the data from Figure 2.8, the sites sampled in Magela and Gulungul creeks downstream of Ranger are depicted for each year of study, together with all other control sites sampled over the same time period (Figure 2.9). Because the data-points associated with these two sites are interspersed amongst the points representing the control sites (including data from 2003), this indicates that these potentially-impacted sites have macroinvertebrate communities that are not dissimilar to those occurring at control sites.
Collectively, these result provide good evidence that changes to water quality downstream of Ranger as a consequence of mining in the period 1994 to 2002 are not sufficient to have adversely affected macroinvertebrate communities.
Note: The dashed vertical lines delineate periods for which a different sampling and/or sample processing method was used. Dashed horizontal lines indicate mean dissimilarity across years.
Note: Data from 2003 are indicated by the enlarged symbols.
Monitoring using fish community structure
Sampling of fish communities in billabongs is conducted in late April to the end of June of each year. Two types of data are gathered, using non-destructive sampling methods:
- Visual observation data from two deep channel billabongs: Mudginberri Billabong on Magela Creek about 12 km downstream of Ranger, and directly exposed to any released mine waters ('exposure' billabong, 1989-present); and Sandy Billabong on Nourlangie Creek (control billabong, independent catchment, 1994-present).
- Data from 'pop-nets' set in shallow weedy lowland billabongs, in various combinations, from 1994 to the present:
- 'Directly exposed' billabongs in Magela Creek adjacent to and downstream of Ranger mine. These sites are directly exposed to contaminated surface flows from the minesite;
- 'Indirectly exposed' billabongs in Magela Creek downstream of the mine. Whilst not directly receiving mine waste waters, the sites can receive contaminated creek water, indirectly, by back flow ('pseudo' controls);
- 'Control' billabongs in Nourlangie Creek (Sandy and Buba) and East Alligator River (Cathedral) (true controls). These sites cannot receive contaminated water as they are in different catchments with no mining activity.
The design for both approaches is amenable to the comparisons: (i) directly exposed billabong(s) versus control billabong(s) from independent catchments (Nourlangie Creek and East Alligator River); and/or (ii) directly exposed billabongs versus indirectly exposed billabongs in Magela Creek, recognising that this second approach is confounded by possible movement of fish between the two billabong types (channel and shallow lowland) in the same stream system.
Channel billabongs
In this sampling technique, visual observations are made upon fish communities inhabiting the littoral zones of deep, sandy-bottomed channel billabongs. Five sites are sampled in each of Mudginberri and Sandy billabongs, each site surveyed repeatedly (five times) along a 50 m transect set parallel to the shore. Typically, the transect is set immediately adjacent to steep banks with dense, over-hanging or submerged pandanus palms. Observations are made through the front of a boat with custom-made, clear, perspex-viewing dome.
The basic design entails the simple pairwise comparison of fish community data between Mudginberri (directly exposed) and Sandy (control) using multivariate dissimilarity indices. These indices and rationale for their use are explained above in the section 'Monitoring using macroinvertebrate community structure'. While data for Mudginberri Billabong have been gathered since 1989, only the results since 1994 are shown here, the period from which the additional control billabong (Sandy) has been sampled. A plot of the paired-site dissimilarity values using log-transformed data, from 1994 to the present, is shown in Figure 2.10. As was performed with macroinvertebrate data, the same dissimilarity indices used in Figure 2.10 were also mapped in an ordination to depict the relationship of the community sampled at any one site and sampling occasion with all other possible samples (Figure 2.11).
Note: The dashed horizontal lines indicates mean dissimilarity across years.
Shifts in fish community structure have been observed in both billabongs over time (Figure 2.11) and while the sites do not faithfully 'track' one another from year to year, the patterns and extent of 'meandering' are not too dissimilar. In the last two years, there has been a return in both sites to a reasonably common community structure that is also similar to that found at the commencement of the paired-site study in 1994.
Note: Lines follow the trajectory of sites over time.
Of note, there has been a significant decline (P<0.05) in the paired-site dissimilarity measures over time (Figure 2.10). The site trajectories in the ordination confirm that in the early years of the study, there was some divergence in the community structure of the two billabongs, with the temporal shifts in Mudginberri Billabong being particularly pronounced (Figure 2.11). The Bray-Curtis dissimilarity measure based upon relative abundance data is highly influenced by data from the most abundant taxa. Confirming this, when the dataset across both billabongs and all years was reduced to just the four most (numerically) dominant fish species, the resulting dissimilarity measures correlated highly with the original values (P<0.0001) with the significant decline in the measures over time still preserved. The abundance values for these fish species and corresponding paired-site dissimilarity values are shown in Table 2.9.
| Fish species B, C | Bray-Curtis dissimilarity D | ||||||
|---|---|---|---|---|---|---|---|
| Year | Site A | Craterocephalus stercusmuscarum | Melanotaenia splendida inornata | Ambassis spp | Amniataba percoides | All species | Four-most abundant species |
| 1994 | MUD SDC |
579 473 |
441 21 |
58 20 |
16 67 |
67 | 0.157 |
| 1995 | MUD SDC |
303 258 |
176 7 |
63 3 |
10 43 |
0.263 | 0.245 |
| 1996 | MUD SDC |
286 290 |
1341 76 |
162 16 |
8 39 |
0.229 | 0.181 |
| 1997 | MUD SDC |
529 441 |
23 149 |
12 333 |
19 42 |
0.205 | 0.168 |
| 1998 | MUD SDC |
171 243 |
208 20 |
14 9 |
8 38 |
0.272 | 0.149 |
| 1999 | MUD SDC |
253 131 |
215 103 |
35 28 |
16 46 |
0.163 | 0.076 |
| 2000 | MUD SDC |
125 149 |
167 46 |
12 18 |
8 35 |
0.188 | 0.106 |
| 2001 | MUD SDC |
211 173 |
65 27 |
58 36 |
22 54 |
0.156 | 0.073 |
| 2002 | MUD SDC |
178 158 |
65 45 |
32 273 |
15 30 |
0.176 | 0.096 |
| 2003 | MUD SDC |
395 355 |
101 15 |
40 46 |
17 23 |
0.137 | 0.071 |
| 2004 | MUD SDC |
637 215 |
21 10 |
17 42 |
16 43 |
0.174 | 0.119 |
Notes:
A MUD, Mudginberri Billabong; SDC, Sandy (channel) Billabong;
B Relative abundance expressed as mean number of fish observed per 50 m transect;
C Bold/italicised values refer to species whose abundance at one site is <10% of the abundance at the other site on any one occasion,
D Calculated on log(x+1) data.
Large discrepancies in the abundances of fish populations of the same species between billabongs are particularly influential in inflating dissimilarity measures. Such instances are identified amongst the dominant fish taxa of the two billabongs in Table 2.9. It appears that the particularly high abundances of Chequered rainbowfish (Melanotaenia splendida inornata) and to a lesser extent Sailfin perchlets (Ambassis spp) in Mudginberri Billabong in the early years of the study are mainly responsible for the elevated paired-site dissimilarity measures derived for that period. Both species observe very significant migrations in Magela Creek after wet season spawning and recruitment on the (downstream) floodplain (ARRRI Annual Research Summary 1987-88). Whilst a component at least of the variation in these migrations and their magnitude is likely to be accounted for by short- and longer-term rainfall and discharge patterns (this aspect is being investigated, see also ARRRI Annual Research Summary 1990-91), the migration phenomenon is perhaps more remarkable for its relative absence in Nourlangie Creek (eriss unpublished data). This probably explains to some extent the smaller magnitude and/or variability in numbers of the same two fish species in Sandy Billabong.
To be of maximum value in monitoring and assessing mining-related change, any significant changes in metrics used to summarise population and community responses need to be explained and understood fully so that natural and mining-related change can be distinguished. Hence an important task in future will be to better understand the dynamics and factors affecting populations of key fish species in streams adjacent to ARR minesites.
Shallow lowland billabongs
The abundance of fish captured by pop-net sampling in shallow billabongs for the period 1994 to 2004 is shown in Figure 2.12. Abundances in 2004 showed a decline over 2003 results for most exposed and control billabongs. The exception was Baralil Billabong where fish numbers increased slightly.
The changes in fish abundances in 2004 are all within the range of natural variation observed for each location since sampling commenced in 1994. An exception to this was the control site, Buba Billabong, which recorded a lower abundance and species count than in any previous year. However, with no mining or other major human activity in the Buba catchment, this decline is considered to also represent natural variation in the fish community.
The number of fish species recorded in each billabong has varied only slightly over the 1994 to 2004 period by comparison with fish abundance (data not shown here).
The East Alligator control site (Cathedral Billabong) was not sampled in 2004 due to unseasonably late rains making access across the black soils plains impossible. A new access road will be sought in the 2004 dry season to reduce the possibility of omission of the billabong in future sampling.
Multivariate ordination was used to compare the fish community structures in the three exposure types (Figure 2.13). The data points for different sites tend to occupy different areas of the ordination indicating differences in community structure among sites. The area enclosed by data points for each billabong in years prior to 2004 is shown as a polygon to indicate their 'natural' location in the ordination space. There is considerable overlap amongst the directly exposed, indirectly exposed and one of the control sites, Buba Billabong. This indicates a close similarity of the fish communities amongst these sites and that the differences that do occur in fish community structure amongst these sites are natural differences and are not related to any form of exposure to potential mining effects. Fish community structures in the other two control sites (Sandy and Cathedral) do not overlap with those in the other sites and lie at opposite sides of the ordination indicating quite different fish communities. The position of these control sites relative to other sites, however, has remained quite constant over time.
Notes: Not all sites have been sampled each year. Sampling in Djalkmara Billabong was discontinued after mining at Pit 3 closed its connection to Magela Creek.
Note: Ordination calculated for 2 dimensions, stress = 0.18. The areas enclosing points for years 1993 to 2003 for each billabong are shown as polygons. (Only the relevant polygons are highlighted.) The position of data for 2004 is indicated separately as filled symbols for comparison with previous years.
The reasonably-well defined locations of each of the billabongs in the ordination over the ten years of sampling provide a useful basis for detecting and assessing change. In particular, departure from the natural patterns in community structure in exposed sites could indicate adverse effects of mining activity. The results for 2004 lie within, or very close to, these natural positions in the ordination space and indicate there was no discernible effect of mining activity on fish communities.
The potential of this detection procedure was illustrated by an outlying data point for Corndorl Billabong in 2002. This departure from the natural pattern was due to a large increase in the amount of the floating weed, Salvinia molesta, in Corndorl in that year (Supervising Scientist Annual Report, 2002-2003).
It is also interesting to note that no detectable shift in fish community structure has been observed since the arrival of cane toads (Bufo marinus). Cane toads were detected in the vicinity of Sandy and Buba Billabongs prior to the 2003 sampling. They have since colonised the Jabiru area and are assumed to have occupied all monitoring sites in 2004. Toadlets were spotted amongst the aquatic vegetation at Georgetown Billabong and fringing margins of Corndorl Billabong.
The small variation in dissimilarity values for fish communities in channel billabongs and the similarity of 2004 fish communities in shallow and channel billabongs to the respective communities found in previous years indicate there is no evidence of any adverse effects of mine waste waters arising from the Ranger minesite on fish communities of Magela Creek.
Radiological exposure of the public
The International Commission on Radiological Protection (ICRP) recommends that the exposure of members of the public to radiation from a practice such as uranium mining from all exposure pathways should not exceed 1 mSv per year. The National Health and Medical Research Council (NHMRC) has implemented this value in their 'Recommendations for limiting exposure to ionising radiation'. To put this number into perspective, the average natural radiation dose in Australia is approximately 2 mSv, but it can be significantly higher in geological provinces with high natural uranium and thorium mineral occurrences such as the Alligator Rivers Region.
The main exposure pathways during the operational phase of a uranium mine are the airborne pathways through the dispersion of radon decay products and dust from the minesite and the aquatic pathway through the incorporation of radionuclides into bush-foods from the Magela Creek system downstream from Ranger mine.
The best present estimate of total committed effective dose arising from water releases from Ranger is about 0.5 µSv per year for people living at Mudginberri Billabong, downstream from Ranger mine. Radium-226 in mussels is the dominant contributor to this dose. Monitoring data for mussels from billabongs upstream and downstream from Ranger mine show that there was no significant increase in radium-226 loads in mussels of the same age compared with data from two decades ago.
Since January 2002, the Supervising Scientist Division has conducted an atmospheric monitoring programme at Jabiru, Jabiru East and close to Mudginberri, measuring radon decay products and long lived alpha activity concentration of dust. The results are periodically compared to results of ERA's atmospheric monitoring programme. Figure 2.14 shows the results of this comparison for the last two years.
In their annual reports, ERA calculates the annual dose to the public caused by activities on the minesite and dispersion of radon decay products, using a model that discriminates between radon concentration in the wind sector from Ranger and radon concentration from other, background sectors.
The model also accounts for the times when the wind was blowing from different directions. For 2003 it was estimated that the maximum dose received by Jabiru residents from the inhalation of radon decay products amounted to 0.011 mSv, which amounts to 1% of the recommended annual dose limit.
Note: Data are extracted from the ERA and SSD radiological monitoring programmes.
Incidents in which vehicles left the Ranger minesite without adequate radiation clearance were investigated by the Supervising Scientist during 2003-04. These incidents resulted in radiation exposure to three members of the public. The doses involved have been estimated to be about 1 mSv which is the dose limit for members of the public. This issue is reported more fully in section 2.2.5 of this Annual Report.
Contents
- Letter of Transmittal
- Foreword
- Supervising Scientist's Overview
- Abbreviations
- 1 - Introduction
- 2 - Environmental Assessments of Uranium Mines
- 3 - Environmental Research and Monitoring
- 4 - Statutory Committees
- 5 - National Centre for Tropical Wetland Research
- 6 - Communication Liaison
- 7 - Administrative Arrangements
- Appendix 1 - ARRTC Key Knowledge Needs
- Appendix 2 - List of Publications 2003-04
- List of Tables
- List of Figures