Ecological effects occurring outside the land application sites

At Nabarlek the impacts of remobilised salts from the irrigation areas are observable in Gadjerigamundah Creek where the waters contain additional solutes, including ammonium (1991 average 3.6 mg N/L), sulphate (1991 average 73 mg/L and nitrate (1991 average 66 mg N/L) and have low pH (1991 observed minimum 4.4). The existence of biological impacts in Gadjerigamundah Creek is suggested by changes in fish community structure observed in a multi-year study commissioned by Queensland Mines Pty. Ltd. Because of high dilution, mining attributable effects on Cooper Creek water chemistry are scarcely detectable and effects on its biota are not expected to be observable. At Ranger increased concentrations of magnesium (up to 4.3 mg/L), sulphate (up to 17 mg/L) and uranium (up to 1.7 μg/L) have been observed in Magela Creek at site GS8210009 during the 1990-91 Wet season and salts derived from irrigation possibly contributed to these values. However the monitoring data presently available do not allow the effects of irrigation-derived solutes on Magela Creek water chemistry to be separated from those of solutes contained in released Retention Pond 1 (RP1) and Retention Pond 4 (RP4) waters. A model developed by OSS for predicting transport of solutes from the irrigation area to Magela Creek suggests that the irrigation area has the capacity to be significant source of additional solutes. Although no monitoring has taken place in Magela Creek to detect biological impacts in Magela Creek caused specifically by irrigation, sensitive procedures used to monitor waste water releases have not detected any impacts on biota. 3 refs., 4 tabs., 9 figs