Changes in the thermal structure of freshwater lakes within Cape Cod National Seashore (Massachusetts, USA) from 1996 to 2014 (original) (raw)

Inland Waters, 2018

Abstract

Abstract Freshwater lakes throughout many parts of the world have undergone substantial warming in response to climate change. In southern New England, within Cape Cod National Seashore (CCNS; Massachusetts, USA), numerous freshwater lakes known as “kettle ponds” scattered throughout the landscape have exhibited increasing surface water temperatures for the past 2 decades. In this study, we examined changes in summer air temperatures, wind speeds, underwater light transmission (3 of the primary factors influencing lake thermal structure), and the temperature profiles of 9 ponds from 1996 to 2014. Mean, minimum, and maximum daily air temperatures all increased significantly while mean daily maximum and average wind speeds declined. The attenuation of light to 50% and 25% of surface intensities occurred at significantly greater depths in 7 ponds, whereas the depths at which light transmission was 1% of surface values increased in 3 ponds. Thermocline depths became shallower in 2 ponds while temperature between surface and bottom waters increased in 6 ponds. Bottom waters exhibited significant cooling in 4 ponds while Schmidt stability values (which indicate the strength of thermal stratification) increased in 5 ponds. Thermocline depth among ponds was positively correlated with light transmission variables for the majority of years between 1996 and 2014, and all temperature variables were significantly correlated with mean daily air temperature. The patterns indicate a general strengthening of thermal stability during the summer and seem to be related to increasing local air temperatures and reduced wind speeds. Implications of changes in the thermal properties of CCNS ponds are discussed in the context of potential physical, chemical, and ecological processes.

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