Limnol. Oceanogr., 44(3, part 2), 1999, 889–902

A paired whole-lake experiment was conducted on two remote, atmospherically driven lakes in the Experimental Lakes Area (ELA) to examine the stresses of trophic condition on air–water exchange and settling fluxes of polychlorinated biphenyls (PCBs). Lake 227 (L227) and Lake 110 (L110) are similar in volume, surface area, and watershed area but differ significantly in trophic status. The two lakes have similar access to atmospheric PCBs but eutrophic L227 may exhibit enhanced air to water exchange due to greater biotic uptake of dissolved PCBs. Settling fluxes of PCB were significantly greater in eutrophic L227 (40 ng m22 d21 in 1993; 29 ng m22 d21 in 1994) than in oligotrophic L110 (22 ng m22 d21 in 1993 and 17 ng m22 d21 in 1994). Dissolved SPCB concentrations were not significantly different in the two lakes (;0.3 ng liter21). Greater SPCB settling fluxes in L227 vs. L110 coupled with similar dissolved concentrations after June supports the hypothesis that air–water exchange supports the water column PCB concentrations. Surprisingly, SPCB fugacity gradients in both lakes indicated that net volatilization dominated during the entire ice-free period, requiring another source. A SPCB mass budget in the epilimnion of each lake over the stratified period showed that the major PCB losses were due to settling and volatilization. SPCB settling losses were 2.4 times greater in L227 than in L110 due to higher settling particle fluxes. The mass budgets suggest that the major PCB input to these remote lakes is from the watershed. Our results indicate the intimate environmental linkage between atmospheric, land, and aquatic PCB reservoirs. Two of the greatest problems affecting many freshwater lakes are eutrophication and contamination of fish with organochlorines, such as polychlorinated biphenyls (PCBs). For example, there are active programs to reduce both nutrient levels and PCB concentrations in several of the Great Lakes. Previous studies suggest there may be important interactions between PCB concentrations and trophic condition (Larsson et al. 1992; Taylor et al. 1991). An understanding of the interactions between trophic condition and PCB concentrations is essential for effective management. This study 1 Current address: Minnesota Pollution Control Agency, 520 Lafayette Rd., St. Paul, Minnesota 55155. 2 To whom correspondence should be addressed ([email protected]).