Origin of Chloride in Wetlands, Lakes, and Rivers of the Michigan Lowlands

Chloride in the surface water of Michigan's Saginaw Lowlands (SLA) is related to subsurface saline water, consistent with the hydrology of the Michigan Basin and similar geochemical fingerprints between subsurface saline water and the surface waters. Chloride is also found in surface waters of the Michigan Lowlands (ML), which is influenced by similar hydrology as the SLA. Thus, we hypothesize that subsurface saline waters are the major source for chloride to surface waters within the ML. If true then the geochemical fingerprints of the surface waters should be consistent with this source. To test this, the geochemistry of lakes, rivers, and wetlands were sampled and compared to previously collected groundwater geochemistry (USGS MI RASA). Data were reduced via geochemical modeling, Piper plots, and solute-solute plots. Geochemical modeling results show that streams are different than wetlands and lakes with respect to the distribution of calcite, dolomite, gypsum and quartz saturation. However, the relationship between calcium and magnesium appears to be more complex than simple equilibrium theory. Piper plots show patterns in dominant anions of the wetlands, streams and lakes that reflect those of shallow groundwater; however, dominant cations of the lakes do not. They also reveal anthropogenic sources to wetlands and streams. Sodium-chloride ratios vary across the watershed indicating the possibility of interaction with subsurface saline waters, but anthropogenic sources of chloride (e.g., road salting) appear more dominant. Lack of clear evidence for subsurface saline-surface water interaction may be the results of 1) the dominance of anthropogenic activities obscuring the saline water fingerprint, or 2) the differing lithologies of the two areas (clayey soils in the SLA vs. sandy soils in the ML). The results do show, how with a common source (e.g., ground water), the geochemical fingerprints of lakes, streams, and wetlands differ because of different within system processes.