Effects of whole-lake base addition on thermal stratification in three acidic Adirondack lakes

Abstract

The effects of whole-lake base addition on the thermal characteristics of three acidic Adirondack lakes were investigated. Data describing patterns of thermal stratification were collected during the ice-free period from three limed lakes and from a nearby reference lake. Pre- and post-treatment data were analyzed to test the hypothesis that increases in light attenuation associated with reductions in lakewater acidity would significantly affect thermal stratification. Light penetration was significantly reduced throughout the post-treatment period. At the two shallow lakes (Cranberry Pond and Woods Lake), increases in light attenuation were accompanied by a decrease in hypolimnetic heating rates. Reductions in heat flux to deeper layers resulted in stronger temperature gradients within the water column and greater thermal stability. Woods Lake was maintained at a circumneutral pH for 4 yr. Throughout this period, hypolimnetic heating rates were lower, thermocline depth was shallower and thermal stability was higher relative to pre-treatment conditions. Stronger thermal stratification, coupled with increased phytoplankton production, resulted in a significant increase in hypolimnetic oxygen depletion. The reacidification of Cranberry Pond was followed by a gradual decrease in light attenuation. Decreases in light attenuation were accompanied by higher rates of heat flux to deeper layers and reductions in the thermal stability of the water column. Within 3 yr following liming, light attenuation, hypolimnetic heating rates and thermal stability in Cranberry Pond were comparable to values measured before treatment.