Using diffusive gradients in thin-films for in situ monitoring of dissolved phosphate emissions from freshwater aquaculture

The high concentrations of phosphorus and suspended matter in freshwater aquaculture are often an environmental concern and given the difficulties for sample preservation, an in situ monitoring tool would be most useful. The diffusive gradients in thin-films (DGT) technique can be used for on site monitoring and also has the advantage to integrate measurements over time and thus partly record ephemeral concentrations peaks. In this study, several DGT deployments were done in fisheries in different geographical areas: Québec, Canada and Lancashire, UK. The results obtained using the DGT technique were compared with standard measurements. The deployment periods varied from 24 h to 21d. The results show that the DGT technique can be used to measure reactive phosphorus in freshwater aquaculture up to 4-day deployment periods before biofilm buildup on the DGT device begins to interfere with diffusion and measurements. We obtained good reproducibility in the phosphorus determinations and moreover, this technique integrates daily and hourly variations of phosphorus and the DGT sampler is easy to use and deploy.