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Figure 3.3.2 Total Kjeldahl Nitrogen (TKN) and Total Kjeldahl Phosphorous (TKP) in the
Condamine River and Loch Eaton ring tank waters. The red dashed line indicates a major
pumping event
3.3.3 General Observations
Any variability in the quality of water within the ring tank was largely associated with riverine
pumping events that introduced water with high levels of clay turbidity and low levels of dissolved
oxygen. Water introduced from bore supplies did not negatively influence water quality and indeed
may have served to mitigate the impacts of riverine waters harvested in early and late 2001.
During the summer (November to March) of 2001/2002, 2002/2003 and 2003/2004 enough water was
harvested from high flow events from the Condamine River to result in a net exchange of waters from
the aquaculture ring tank of up to 4 times its volume.
Ring tank water depth varied throughout the year depending on the amount of water being harvested
and that which was required for irrigation. In 2002 and 2003, the lack of opportunity to harvest
riverine water resulted in relatively low water levels being maintained within the aquaculture ring tank
for an extended period. While this water was maintained the other storages on farm were emptied. In
late 2003 and early 2004 the harvest of large volumes of riverine water, combined with relatively low
water levels within the ring tank resulted in a large flushing event. The low DO levels in riverine water
and the high levels of suspended solids reduced water quality and resulted in a significant stress event
for fish which resulted in significant stock losses (Refer to Chapter 4).
3.4 Discussion
Water quality within the ring tank was detrimentally affected by water harvesting activities during
periods of high river flows. Twice during this study a series of riverine pumping events were
responsible for introducing large volumes of ‘run off’ water into the aquaculture ring tank. Surface
waters that drain into rivers during storm events typically carry high levels of plant matter, bacteria
and dissolved organic matter that has been leached from soils and vegetation. These waters are also
generally high in turbidity resulting from suspension of fine clay particles. The resulting impact on
water quality in the ring tank was both immediate and lasting with fish mortality, reduced feeding and
poor growth the observed outcomes.
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