Happy Holidays from Bradley Lake!

The majority of our summer visitors have packed up and seasonal camps have closed, while full-time lake residents and the lake itself prepare for the long winter months ahead.

First, fall turnover occurs. Reduced solar energy no longer warms surface waters and the upper layer of the water column cools. Each lake cools at a different rate; smaller, shallower lakes cool quicker than large, deeper lakes. Cold water is denser than warm water and as the upper water cools and the lake’s thermal layers weaken, wind activity causes lower and upper waters to mix. This process typically occurs during the months of October and November. After fall turnover, water temperatures and nutrient concentrations are essentially the same from top to bottom and the lake is said to be isothermal. By the end of November, many New Hampshire lakes have reached their maximum density at 39º F (4 º C). The coldest water temperatures (1 º to 3 º C) cover the top of the lake. The lake usually freezes over with its first permanent ice layer on a cold calm night.

Fall turnover also cues seasonal changes for aquatic life. Aquatic animals decrease metabolic rates and plant photosynthesis is slowed by the changes in day length and cooler temperatures. The activity of cold blooded aquatic animals drops during the winter months, but does not entirely stop. The drop in water temperature reduces their body temperature and signals them to seek appropriate shelter. Some frogs may survive over winter by burrowing down in leaf litter, while others head for the bottom of the lake. Reptiles, like the snapping turtle, continue their normal routine of eating and mating. Fish increase their level of body glucose to build up tolerance to the cold. This acclimation period can be a stressful time for fish and although fish remain active throughout the winter months, their movement is restricted.

Algae, or phytoplankton, go through many changes as winter approaches. Winter algae populations are affected by nutrient availability, cold water temperature and decreased sunlight penetration. The winter algae community is typically dominated by small and often motile algae. These species are cold-water and low-light tolerant and are found in a narrow layer of light penetration beneath the ice cover. In New Hampshire, Diatoms are typically the dominant winter algae. Cyanobacteria typically don’t do well under winter conditions and some produce akinetes or special resting cells. These specialized cells allow cyanobacteria to over-winter in lake sediments and live off of the stored nutrients. Planktonic animals, or zooplankton, are dominated by three major groups: Rotifers, Cladocera, and Copepoda. Over the winter months, perennial zooplankton lower population densities and female adults become predominant; while other zooplankton produce resting eggs during unfavorable winter conditions.

Many plant species remain active during the winter months and continue to photosynthesize under the ice. Hardy winter plants like Pondweed and Arrowhead help to oxygenate the water and provide habitat for fish and wildlife. Other plant species have a different means of winter survival. Some plants produce an abundance of protected seeds before the frost. These seeds remain dormant in the sediment until the spring. Bladderwort and Milfoil have special vegetative structures called turions. These winter buds develop during the late summer and early fall. In some species, the buds detach from the plant, while in others, they may remain attached and the buds sprout green shoots in the spring. Water lilies contain a rhizome shoot structure, in which a modified stem called a rhizome, stores carbohydrates and nutrients in order to survive the winter.

Luckily, New England lakes have a high specific heat. This property allows lakes to go through slow temperature changes and allows aquatic species time to adapt to seasonal changes, making them a perfect place to call home.