INTERNAL WAVES AS DRIVERS OF CHEMICAL CHANGE IN THE BELHURST CASTLE HOLE IN SENECA LAKE, NY

Seneca Lake, a freshwater lake, occupies a N-S trending basin with a maximum depth of 188 m. Wing et al. (1995) characterized waters from the Belhurst Castle Hole, a local topographic depression. They found waters with conductivities up to two times that of lake water and interstitial waters yielded brackish chemistries. The maximum depth of the hole is 60.5 m and the morphology of the depression prevents water from mixing below the sill depth of 46 m. The ponding of waters below the sill was thought to be transient, as it was hypothesized that internal waves and seiches reaching 46 m and deeper flushed out the hole on a periodic basis. To test these findings, we systematically sampled waters above and into the hole to document changes in conductivity and major ion chemistry from April – August 2017. CTD casts and meter-scale water sampling found conductivities up to three times that of surface lake water in the deepest waters. Conductivity decreased from >2100 µS/cm at 59 m to ~730 µS/cm at 46 m and to 645 µS/cm at the surface. The pH of bottom waters ranged from 7.8 – 8.1 compared to 8.3 – 8.9 for surface waters. Temperatures increased from 8.8° at 59 m to 9.2° at 46 m and to 10.1° – 25°C at the surface. While measured parameters (e.g., conductivity, pH and temperature) did vary, we did not document a flushing event whereby conductivity was lowered to that of open lake waters (630 – 730 µS/cm). Bathythermograph and wind velocities were compiled from the Seneca Lake monitoring buoy and compared to samplings and CTD casts to document whether internal waves were driving the variation in chemistries. Southerly wind velocity vectors compiled over the sampling period identified disruptions to the temperature structure at depth (30 – 50 m) in Seneca Lake that could not be accounted for by fetch and depth limited waves. Water sampling that occurred after surge activity with temperature disruptions > 46 m depth were found to have lower conductivities than samplings with shallower disruptions. This finding supports the idea that the chemistry of ponded waters in topographic lows in lakes can be disrupted by internal waves. In addition, samplings after heavy rain events (>25 mm) were also found to have lower conductivities suggesting the possibility of sublacustrine springs associated with the Belhurst Castle Hole.