Stable isotopes of hydrogen and oxygen in lower Michigan inland lakes

Stable isotopes of hydrogen and oxygen have been used as climate proxies in many different settings. Evaporation from midwestern inland lakes should imprint a discernible isotopic signature due to evaporation, but this signal is complicated by many factors such as precipitation and short residence time in the lakes. A series of two small lakes in the Huron basin were studied for three years for evidence of an evaporative isotopic signal. Water samples collected during long (10-14 day) dry periods showed clear isotopic evidence for evaporation, with an enrichment of as much as {dollar}1.5perthous{dollar} in {dollar}rmdeltasp{lcub}18{rcub}O{dollar} and a decrease of as much as {dollar}6perthous{dollar} in the deuterium excess between the inlet and the outlet of the two lakes. Analysis of other sets of samples shows that often the system is complicated by other factors, and this evaporative effect is harder to discern although is probably still present.; A simple numerical model of the lake system was developed to try to handle these additional complications. Both the isotopic composition and the water temperatures are modeled, with calibration being provided by temperature measurements. The model successfully duplicated many of the measured properties of the physical system including the water temperatures and to a lesser extent the isotopic measurements. A numerical model of this type could easily be extended to cover a variety of situations in Lower Michigan, including other lakes and possibly entire drainage basins. Such a model could be used to predict the response of a hydrologic system to climate change, or to measure or correct for evaporation. Based on the model and the isotopic measurements, evaporation from open water surfaces in the Huron Basin is a significant isotopic effect that may need to be accounted for in paleoclimate studies.