INSIGHTS INTO THE EARLY CHEMICAL EVOLUTION OF LAKES IN TERRAINS DOMINATED BY UNCONSOLIDATED SEDIMENTS: GEOCHEMICAL CHARACTERIZATION OF TILL-HOSTED SURFACE WATERS IN WESTERN NY

Aqueous geochemical studies of lake water typically focus on natural lakes that record a balance between the regional hydrologic budget and the bedrock geology rather than the overlying unconsolidated sediment. The Hanley Biological Preserve, located in an agriculturally-dominated setting in upstate NY, is comprised of diverse ecosystems: forested ridges, open fields and small ponds hosted in till. Weathering of the till by rainwater provides a different suite of cations than local storm events and groundwater. To determine whether mineralogical variation of the underlying glacial till could factor into the hyper-localized changes in water chemistry, sediment samples were collected from forested ridges, stream cut-banks, and pond rims, and analyzed using X-ray diffraction (XRD). Dolomite and calcite collectively account for almost all of the minerals that can have a significant effect on water chemistry. Calcite and dolomite decrease in abundance with depth below the O-horizon, and were lowest in muds from the ponds. Higher sulfate in the till-reacted waters suggest pyrite oxidized to sulfate, but pyrite was not detected in any samples. Overall, weathering of the till provides a different suite of cations than the local bedrock geology. If this mineralogical heterogeneity controls the solutes documented in the preserve, then early chemical evolution of lakes and ponds in western New York initially reflected a till- rather than bedrock-derived cation chemistry. Given the widespread nature of tills in the region and their mineralogical heterogeneity, till reacted waters can range from dilute to fresh. In contrast to the tills, storm events carry their own unique signatures. Calcium is the dominant cation in the rainwater, elevated sodium is associated with Great Lakes storm tracks, and elevated sulfate is associated with Gulf Coast and mid-continent tracks, and chloride with Atlantic coastal storm tracks. Storm signatures are lost through reaction of rainwaters with the till and evapo-concentration of the ponds. If this mineralogical heterogeneity controls the total solutes then early chemical evolution of lakes need not start as dilute. The initial chemical composition of till hosted lakes, immediately after glaciation, likely reflected a till- rather than bedrock-derived cation chemistry.