Pallette Lake

A major aspect of this study was assessment of the role of groundwater transport in the overall Hg cycle. However, during the study period (1988-1990) Little Rock Lake was mounded (no groundwater inflow), but Pallette Lake had both groundwater inflow and outflow. Therefore, for the purposes of evaluating the importance of groundwater inflow and outflow on Hg transport, we extended our study to Pallette Lake. 

Figure 4. Mercury concentrations in littoral zone pore waters in Pallette Lake...

Figure 5. Comparison of groundwater mercury concentrations in samples taken from Pallette Lake using the dug-well and acrylic-tube sampling methods.

Advection and Diffusion of Hg from Sediments. In lakes such as Pallette Lake, which receive continuous groundwater inflow and outflow, advection and diffusion of chemical constituents can be important for littoral sediments. To assess the importance of advective and diffusive Hg fluxes, information on background groundwater concentrations, levels of Hg at the sediment-water interface, and flow rates of water must be determined. 

The isotopic compositions of four lakes (see Figure 3 for lake locations, in northern Wisconsin that are within 10 km of each other and that have hydraulic-residence times of about 10 years are plotted in Figure 4. The four lakes (Crystal, Pallette, Big Musky, and Sparkling) are groundwater flow-through lakes and have no surface inflows or outflows. Thus they have the same hydrological-budget components (they receive water from precip-... 

The accuracy of the estimates for Big Musky, Pallette, and Crystal Lakes depends on the accuracy of the groundwater-inflow estimate for Sparkling Lake (the index lake) and the validity of the assumptions for the index-lake method. The estimated error for groundwater inflow to Sparkling Lake, 7 cm/year (31), represents a minimum value for the errors associated with the estimates for the other lakes. Therefore, for lakes that receive relatively small amounts of estimated groundwater inflow, the relative error associated with the estimate increases and the utility of the method is reduced. 

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