Rates of sulphate removal in sulphate amended polyethylene enclosures placed in Georgetown Billabong
Internal Report 241
Buck P, Klessa DA, leGras CAA, Hunt C & Parry D
Supervising Scientist Division
About the report
Two 9000 L cylindrical polyethylene cylinders (water-tanks) open at each end were placed in the deeper parts (1.5-1.8 m) of Georgetown billabong during the 1996 early dry season. One enclosure was amended with magnesium sulphate to approximately 5 mM to determine whether sulphate might be selectively removed and the other enclosure was used as a control (no sulphate added). The concentration of sulphate in the treated enclosure was chosen to match that in Retention Pond 2 so that the potential for using a natural billabong to polish sulphate from restricted release zone waters could be examined.
Sulphate was removed at the rate of 0.70-0.95 moles week-1, which was equivalent to 0.13-0.18 moles week-1 m-2 and a half-time of between 147-204 days, but its removal did not appear to be selective compared with magnesium. The similar removal rate of sulphate and magnesium was attributed to a common rate limiting factor, with diffusion through sediment pore waters considered to be the most likely cause. In the latter part of the experiment, the enclosures were shaded in an attempt to increase carbon cycling and promote sulphate reduction but this had no appreciable effect on the rate of removal of sulphate.