SUBSURFACE STRATIGRAPHY AND AQUEOUS GEOCHEMISTRY AS INDICATORS OF HYDROLOGY IN BEACH-RIDGE COMPLEXES: TWO CASE STUDIES FROM THE UPPER GREAT LAKES

Surface-water and groundwater systems can be viewed as representing end members of a hydrologic continuum that exists between local (shallow) flow systems and regional (deep) flow systems. In beach-ridge filled embayments throughout the Great Lakes, the extent to which these flow systems interact is a primary control on hydrology. The linkages between these flow systems, however, are poorly understood and conventional methods of investigation (including groundwater modeling and water level measurements) may fail to quantify these interactions.

We have used an integrated approach of water sampling for aqueous chemical indicators and groundwater flow modeling to study Negwegon State Park in Alpena, MI and Lake Superior State Forest in St.Vitals Bay, MI. Samples from surface water and groundwater wells installed into the upper aquifer were analyzed for field parameters and major ions (specific conductance, temperature, pH, Eh, and alkalinity). Samples were distributed along transects originating at the Lake Huron beach and extending 1500 and 800 meters inland, respectively.

Preliminary results from work at St. Vitals Bay and Negwegon State Park suggest that we can identify end members of the hydrologic continuum at each site using water chemistry indicators. Furthermore, the distribution of flow systems is influenced by the presence or absence of low conductivity zones (clay layers) that are indicated by data collected from ground penetrating radar, vibracores, continuously recorded pressure transducers, and aqueous geochemistry.