Archive of results for toxicity monitoring
Figure 1 monitoring results for freshwater snail egg production for wet seasons between 1992 and 2008. Note the last three tests in 2006-07 and the first test for 2007-08 used the in situ monitoring method (see text below).
Results for each wet season are reported annually in the respective Supervising Scientist Annual Reports (See chapter 2). Data collected post 2008 are available on the current Explanatory notes on toxicity monitoring page.
Figure 2 Flood damage to the upstream creekside toxicity testing infrustructure, March 2007. (A) flood waters 1.5m deep at the creekside laboratory. (B) Pontoon used for pumping water to the creekside laboratory being salvaged, the pontoon was upturned during the flood (see inset).
Toxicity monitoring results using freshwater snail egg production (Amerianna cumingi) for each test from 1992 to 2008 are shown in figure 1. The mainstay of toxicity monitoring during this period was the ‘creekside’ monitoring technique (see background info). However, data derived from ‘in situ’ monitoring were substituted when ‘creekside’ monitoring data were not available (figure 1).
In situ monitoring data were used after a very large flood (late February and early March 2007) damaged the creekside monitoring infrastructure during the 2006–07 wet season (see photos in figure 2). In situ monitoring data were also used during very low flow conditions that occurred during the first toxicity monitoring test of 2007–08 (water levels at this time were too low for the creekside pumps to operate).
Since the 1991-92 wet season the upstream-downstream difference values plot around the running mean (figure 1) indicating that concordance between snail egg production at both the upstream and downstream sites has remained relatively constant over this time. These results indicate that no adverse effects on freshwater snails of water discharged from the Ranger minesite to Magela Creek are evident during this time.
Figure 3 Toxicity monitoring results for larval black-banded rainbowfish survival for wet seasons between 1992 and 2006.
Results for each wet season are reported annually in the respective Supervising Scientist Annual Reports (See chapter 2). Toxicity monitoring for larval black-banded rainbowfish survival was discontinued after the 2005-06 wet season. This decision was based on this species being much less sensitive than the snail reproduction response (toxicologically) to Ranger mine wastewaters and it suffered inherent natural high mortality rates at the upstream control. Across all tests (1991/92 to 2005/06) larval fish survival at the upstream and downstream sites has remained relatively constant over time. Typically, reduced survival was observed at the upstream site relative to the downstream site (figure 3). This issue was discussed in the Supervising Scientist Annual Report 2002-03 (pp 31-33, section 2.2.3).
Further information and interpretation of the results for each wet season can be found in the Supervising Scientist Annual Report for the year of interest.