Application of a mass-balance model to predict PCDD/F turnover in a Baltic coastal estuary

Abstract

A dynamical, process-based mass-balance model was applied to quantify the transports of polychlorinated- p-dibenzodioxins and dibenzofurans (PCDD/Fs) to, within and from the Kallrigafjärden Bay, a coastal estuary in the Baltic Sea, and to predict the PCDD/F levels in the water and sediments of the bay. Before the modelling, a one-year sampling programme was implemented in 2007–2008 to measure the flows of PCDD/Fs in tributaries entering the system, the fluxes from the adjacent sea and the levels in water, sediment and fish within the estuary. The collected data set was used as input data to the model and for validation purposes. The model was originally developed and tested for suspended particulate matter and phosphorus in Baltic coastal areas. In this work, it was run monthly without any tuning of the original model variables. The simulation results compared favourably with the field measurements of levels of 15 PCDD/F congeners in the water and sediments of the bay. The dominating fluxes of PCDD/Fs were the exchange with the adjacent sea, followed by riverine input, atmospheric deposition and sediment burial. Although the sediment-water exchange was of minor importance for the overall mass-balance due to the rapid water turnover and limited areas favourable for the long-term deposition of fine sedimentary matter, sensitivity analyses indicated that the model’s predictive capability was improved with about 5% by taking the sediment burial and release into account.