Delineation of Flow Paths, Capture Zones and Source Areas, Allequash Basin, Vilas County, Wisconsin

Background/Need: Lakes, streams, and wetlands in Wisconsin are well connected to the groundwater system. Consequently, the chemistry of groundwater may appreciably influence the chemistry of surface waters, and vice versa. The testing of tools to identify source areas of recharge and geologic controls on groundwater chemistry is therefore crucial to understanding and protecting both groundwater and surface water. One area where water resources protection is becoming increasingly important is the Northern Highlands Lake District (NHLD) located in northern Wisconsin, which is currently experiencing pressures from increasing development. As population increases within the NHLD, assessing groundwater flow and chemistry prior to further development will help efforts to mitigate effects of development and protect and maintain the ecology of these lakes. It is believed that the Allequash basin, a sub-basin of the Trout Lake watershed in Vilas County, Wisconsin, is representative of many other basins located within the NHLD.

Objectives: Four main objectives were addressed in this study, as follows: (1) to determine the spatial and temporal characteristics of source waters (terrestrial vs. lake/wetland) for groundwater along three transects within the Allequash basin using δ¹⁸O data and to use this water isotopic signal to trace groundwater flow paths within the transects; (2) to characterize both the spatial and temporal variability of groundwater chemistry within the transects using δ⁸⁷Sr and major ion concentration data and to investigate controlling factors on groundwater chemistry; (3) to examine the effects of lake level fluctuations on groundwater flow direction within the Allequash basin and relate these changes in flow direction to temporal changes in groundwater chemistry; and (4) to delineate capture zones for selected lakes and streams.