UNDER ICE TRANSLATION OF WINTER SURFACE CONDITIONS TO DEEP LAKE STRATA

For three consecutive winters, 2014-2017, a mooring at Deep Haven Deep, Squam Lake, NH has captured under-ice water temperature variations at 15 minute intervals from 3-26 meters water depth. Squam Lake (N 43.77-43°, W 71.58-48°) has a maximum water depth of 30 m and a surface area of 2737 ha. It experiences annual summer stratification in the upper 15 meters and reverse stratification throughout the water column after ice cover develops, usually in December. This reverse stratification ends abruptly with ice-out and the beginning of wind-driven mixing.

The deepest basin, Deep Haven Deep, receives inflows from three small tributaries that enter the northern end of the lake. Numerous islands, peninsulas and coves limit the fetch and potential for internal seiches. The lake is generally well-oxygenated (5-14 mg/L), oligotrophic (TP < 5 ppb), with high water clarity (secchi depth: 4.3-7.2 m), with bottom anoxia in the lowest 5 m. Despite the apparent high water quality of Squam Lake, a recent report suggests inputs from new or archival stores of DDT in at least two northern tributaries (Vogel, 20117), and a drastic decline in loon breeding success since 2005.

Detailed analyses of the temperature data suggest that even during ice cover, some weather-related events create perturbations throughout the entire water column. Many of these disturbances can be correlated to high stages in local rivers, suggesting that flood waters create sub-ice flows with wide-ranging effects. Other events may be the response to snow-no snow conditions, and intervals of extremely low atmospheric temperatures. With whole-water-column response to under-ice inflows during local flood events, the presence of DDT in the sediments of two of the tributaries near the mooring is concerning. It suggests the potential for contaminant transport throughout the water column in winter.