Sonar Imagery of Shoreline Tufa Deposits and Bathometric Mapping at Green Lakes State Park, NY

Abstract

Green Lakes State Park, located in Fayetteville, New York, holds two deep and narrow meromictic lakes which are hypothesized to be plunge pools associated with the retreat of the Laurentide Ice Sheet (~13,000 years ago). Today, the catchment area for Green and Round Lake is small and the lakes are mainly groundwater fed. This groundwater flows through the Syracuse formation and the gypsum-bearing Vernon Shale and discharges into the lakes rich in calcium, magnesium and sulfate. Tufa deposits are located at sites of groundwater discharge. Tufa deposits are thrombolitic microbialite structures, mainly composed of calcite accreted during cyanobacterial photosynthesis. The tufa deposits vary in size from meters to tens of meters and are found in various locations along the lakeshores. Here, we update the bathometric mapping using sonar techniques and provide the first sonar imagery of the nearshore environment to identify the locations of tufa deposits. Sonar data was collected with a Humminbird SOLIX 12 CHIRP MEGA SI + G2 with frequencies of 50/83/200/455/800 kHz & 1.2 MHHz during the summer and fall of 2019 and 2020. The sonar data was analyzed using Reefmaster, Sonar TRX, ArcGIS and Google Earth. Results indicate, both lakes exhibit steep slopes about 30° and the maximum depths detected at Green and Round Lake were ~175 feet and ~159 feet below the lakes’ surfaces. Sonar imagery reveals numerous locations of woody debris and clearly shows tufa deposits. In Green Lake, we identify 14 locations of tufa deposition, those being previously discovered and newly discovered, most concentrated on the East and West shores. Tufa deposition was limited in Round Lake with 4 localities of tufa found each consisting of multiple distinct tufa heads all concentrated on the eastern and southern shore. Our work provides data needed to refine prior bathometric mapping and provides a new viewpoint for understanding tufa geometry and the locations of tufa formation. These data will aid in understanding the link between groundwater discharge and tufa formation. It will also help with ongoing and future conservation efforts of this unique site.