Biogeochemistry and effects of copper, manganese and zinc added to enclosures in Island Billabong, Magela Creek, northern Australia

Abstract

Three large plastic enclosures (5 m diam, volume 40 m3) were used to study the effects of copper, manganese and zinc, on the phytoplankton community in Island billabong, a floodplain billabong (waterhole) situated in the Magela Creek in tropical northern Australia. Copper was added to one enclosure, and manganese and zinc to another, to give initial concentrations around ten times the normal wet season values. The enclosures and the billabong were monitored over a ten week period towards the end of the dry season, with the enclosures allowed to stabilise for four weeks before the metals were added.The control enclosure adequately simulated the temperature and pH changes in the billabong. The trends in conductivity, dissolved oxygen and major ion concentrations were similar in the enclosure and the billabong, with the minor differences observed attributed to either epiphytic growth on the enclosure walls (influenced dissolved oxygen, pH and bicarbonate concentration) or ingress of sulphate-rich groundwater into the billabong (influenced sulphate concentration and conductivity). Major differences in both the composition of species and the size of the phytoplankton populations were observed between the three enclosures and between the control enclosure and the billabong. This variability reflects the great natural variability in the phytoplankton communities in tropical lentic systems, and means that enclosures are unlikely to adequately simulate the biological communities in the billabongs.The control enclosure appeared to simulate quite well the longer term changes in total concentration and speciation of the three metals (copper, manganese & zinc) in the billabong. The mean concentrations of copper and zinc were similar in the two systems, although the mean concentration of manganese in the billabong was almost double that in the enclosure, possibly due to ingress of manganese-enriched groundwater. Particulate forms dominated the speciation of copper and manganese. There was considerable short term variation in both total metal concentration and speciation in both the enclosure and the billabong. This variability appears to be a feature of these small tropical waterbodies.The added heavy metals were found to have minimal detrimental effect on the phytoplankton community in each metal-loaded enclosure. The high natural variability in the phytoplankton community in these tropical systems will make it difficult to separate natural changes from those caused by low level contamination from mining operations should this occur.All three metals were rapidly removed from the water column, so that by the end of the six week period, only ca. 5 % of each added metal remained in the water column. Association with the particulate matter (phytoplankton, abiotic particulate matter and MnO, in enclosure 2) followed by sedimentation was the major removal pathway. Epiphytes growing on the enclosure walls appeared to have a minor influence (< 10% of the total amount of metal added) on the removal of the added metals. For copper, upt...

Weight‐of‐Evidence Approach for Assessing Removal of Metals from the Water Column for Chronic Environmental Hazard Classification

“…Numerous studies have demonstrated metal removal in surface waters. These include the following: 1) removal of Cd, Cu, and Zn in riverine systems (Thomann 1984;Mills et al 1985) and Cd, Zn, and Pb in estuaries (Di Toro et al 2001b); 2) removal of various metals (including As, Co, Cs, Cu, Fe, Hg, Mn, Ni, Sn, and Zn) in laboratory, microcosm, and mesocosm studies representing lacustrine systems (Baccini et al 1979;Gächter 1979;Santschi et al 1986;Diamond et al 1990b;Hart et al 1992;Hommen et al 2016;Bird and Evenden 1996;Schäfers 2003;Smolyakov et al 2010aSmolyakov et al , 2010bRand et al 2011); and 3) removal of metals (including As, Co, Cs, Cu, Fe, Hg, Mn, Se, Sn, and Zn) in whole-lake field studies (Effler et al 1980;Hesslein et al 1980;Santschi et al 1986;Bird et al 1995;Haughey et al 2000;van Hullebusch et al 2002van Hullebusch et al , 2003avan Hullebusch et al , 2003bvan Hullebusch et al , 2003cLiu et al 2006). Studies on Cu are particularly plentiful given the use of Cu sulfate as an algaecide in ponds, lakes, and reservoirs.…”