Towards a complete mass balance and model for PCBs and PAHs in a small rural lake, Cumbria U.K.
Limnol. Oceanogr., 45(4), 2000, 881-894 | DOI: 10.4319/lo.2000.45.4.0881
ABSTRACT: This paper summarizes the processes of exchange/fluxes for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in a small well-studied rural lake, Esthwaite Water in northwest England. Measure-ments of PCB and PAH concentrations have been made in rain, air, water, dated sediment cores, and sediment trap samples over a 2-yr study period and used to determine fluxes to and from the lake. A steady state mass balance model was used to construct an input-output budget for the chemicals and to investigate the relative importance of transport into and out of the lake. The hydraulic transport from the lake was the most important loss mechanism for both PCBs and PAHs. Volatilization, not sedimentation, is currently the dominant loss process for PCBs in the water column, whereas, sedimentation exceeds volatilization for PAHs. The data further suggest that the current sediment-water flux is upward for PCBs and downwards for PAHs, indicating that the sediments might be acting as a secondary source for PCBs but continue to act as a sink for PAHs. Riverine, catchment runoff, or both are believed to be the most important input for PCBs and PAHs to the lake although direct aerial deposition to the lake is also important for PCBs. Differences in the mixtures of compounds in the various compartments suggests sig-nificant fractionation of PCBs and PAHs in the air-water-sediment system in the lake.