In Situ Measurement of Eddy Diffusion Fluxes of Trace Hydrophobic Organic Contaminants across the Water-Sediment Interface in Lakes

While difficult to measure, approximating reliable eddy diffusion fluxes of trace hydrophobic organic contaminants across the water-sediment interface (WSI) is important for contaminant fate and remediation strategies. Here, we present an updated bottleneck boundary theory and a corresponding theoretical model to quantify these fluxes. Our innovative, field-based approach integrates passive sampling and eddy diffusion modeling at high vertical resolution. We performed an in situ measurement at an offshore site in Dianshan Lake, Shanghai. High-resolution passive sampling revealed vertical concentration gradients of polycyclic aromatic hydrocarbons from the sediment to the air. Vertical eddy diffusivities in the water column were calculated by using the heat flux-gradient method. Mass transport through the overlying water column above the interface was eddy diffusion-controlled and thus was well described mathematically. Using this framework, the WSI fluxes aligned well with independently measured concurrent water–air exchange fluxes. In principle, this methodology is broadly applicable to any dissolved species that diffuses across aquatic interfaces.