Long-term copper partitioning of metal-spiked sediments used in outdoor mesocosms
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Understanding the effects of sediment contaminants is pivotal to reducing their impact in aquatic environments. Outdoor mesocosms enable us to decipher the effects of these contaminants in environmentally realistic scenarios, providing a valuable link between laboratory and field experiments. However, because of their scale, mesocosm experiments are often complex to set up and manage. The creation of environmentally realistic conditions, particularly when using artificially contaminated sediment, is one issue. Here, we describe changes in geochemistry over 1.5 years of a sediment spiked with four different concentrations of copper, within a large freshwater mesocosm facility. The spiking procedure included proportional amendments with garden lime to counteract the decreases in pH caused by the copper additions. The majority of copper within the spiked mesocosm sediments partitioned to the particulate phase with low microgram per liter concentrations measured in the pore waters and overlying waters. The minimum partition coefficient following equilibration between pore waters and sediments was 1.5 × 104 L/kg, which is well within the range observed for field-contaminated sediments (1 × 104 to 1 × 106 L/kg). Recommendations are made for the in situ spiking of sediments with metals in large outdoor mesocosms. These include selecting an appropriate sediment type, adjusting the pH, allowing sufficient equilibration time, and regular mixing and monitoring of metal partitioning throughout the experimental period.
KeywordsToxicity test Copper Risk assessment Sediment quality Manipulation
Interim sediment quality guideline
The PhD research was carried out with an iMQRES scholarship from Macquarie University and support from CSIRO’s Water for a Healthy Country Flagship. The authors thank Alexander Michie and Lois Oulton for their help in setting up the mesocosm infrastructure and Joshua King and Steven Leahy for their help in ICP-AES analysis. Many thanks also to Graeme Batley for his advice and edits of the manuscript. Mesocosm construction was funded by a Macquarie University Research Infrastructure grant to Grant Hose.
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