The Occurrence of Fish Kills, and their Causes missing in the Darwin-Katherine-Jabiru Region of the NT
E-Publications; E-Books; PublicationNT; Report ; 36/1992
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Power and Water Authority
Report ; 36/1992
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Technical Report WRD92036 Viewed at 15:07:57 on 29/07/2010 Page 9 of 54. 9 in shady Camp Billabong are low dissolved oxygen concentrations. In January 1987, oxygen concentrations were <0.1 mg/l in the main part of the Billabong two days after the death of 1200 fish (unpublished data, PAWA). In November 1987, 5000 fish died in Donkey Camp Pool, a portion of the Katherine River. The Pool is 6 km long, 40-50 m wide and 3-4 m deep in the dry season and in Noverr~er basal discharge declines to about 0.2 m3/s. The fish deaths were attributed to low dissolved oxygen concentrations, with possible additional harmful effects from toxic humic compounds (Towns end et al. 1992). Metal and pesticide toxicity were discounted as possible causes. The first wet season run-off from a tributary of the river entered Donkey Camp Pool causing turbidity and colour to increase and, probably, oxygen concentrations to drop. A similar event nine days later caused significant water quality changes and resultant fish deaths. Pool water was displaced with cool run off which had a substantial organic load and high oxygen demand. Colour, turbidity, iron and manganese were at least an order of magnitude higher, and coliform organisms several orders of magnitude higher, than typical dry season values. Furthermore, the pool was thermally stratified with low surface dissolved oxygen concentrations (about 1 mg/l) and anoxic at depth. The dead fish were concentrated at the end of the Pool, having been carried by the flood wave or moving ahead of the anoxic water and becoming trapped at the Pool's outflow where it
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