HOW LOW CAN YOU GO? CAN YOU GO DOWN LOW? - INVESTIGATING THE ROLE OF LOWSTANDS AND EVAPORATIVE CONCENTRATION IN THE ONSET OF MEROMIXIS IN GREEN LAKE, FAYETTEVILLE NY

Green Lakes State Park located 13 km east of the city of Syracuse, New York, contains two meromictic lakes, Green Lake and Round Lake. Meromixis is a result of salinity-driven stratification of the water column with ions derived from dissolution of dolomite, gypsum, and halite in the bedrock. While it is well established that the monimolimnion is enriched in conservative ions such as Na⁺, K⁺, and Cl^- compared to the overlying mixolimnion, the origin of this contrast is still not fully understood. Previous studies suggest two chemically distinct groundwater sources, one entering the lake in the monimolimnion and one in the mixolimnion with advective and diffusive mixing at the chemocline. This study investigates a new formation mechanism; the relic-sump model, that asserts stratification was created by evaporative concentration during past low lake levels. At least four lowstands over the last 10 kyrs, ranging from 2-9 meters below present-day, have been documented. The hypothesis was tested using a dataset of lake and groundwater chemistry. To start, the ratio of conservative ions (Na⁺, K⁺, Cl^-) was compared between local groundwater, mixolimnion, monimolimnion, and interstitial water samples and was shown to be consistent suggesting a shared water source. The primary difference being that the mixolimnion is ~1.5-2.3 times concentrated relative to groundwater, and the monimolimnion is ~2 times concentrated relative to the mixolimnion. Mechanisms of lake water concentration were tested using groundwater flux estimates based on the hydrologic model of Takahashi et al. (1968). Preliminary results suggest closed-basin behavior could create monimolimnion concentrations from local groundwater within 6-60 years via evaporitic concentration with constant lake level. Alternatively, volume reduction by evaporation to a 9-meter low-stand can create monimolimnion concentrations, when starting with a basin filled with chemically uniform groundwater. Further models using the USGS PHREEQC software can provide temporal constraints on the evolution of lake chemistry. The findings of this study have the potential to add to our current understanding of the formation of high-latitude meromictic lakes, a rare limnological phenomenon that has abundance within Silurian-age bedrock of New York State.