Coring is not just for apples anymore

On a brisk, breezy but sunlit day in early April, Lisa Doner, assistant professor of environmental studies and policy at Plymouth State University; one of her students, Victoria Santry; Don Kretchmer, local limnologist (study of lakes); and Karen Burnett-Kurie, executive director of the Lake Wentworth Foundation, ventured about a half mile out on Lake Wentworth pulling and carrying equipment. Their purpose – to collect a core sample of the sediment at the bottom of this ice-covered lake.

Setting up at one of the deepest locations on Lake Wentworth.
Setting up at one of the deepest locations on Lake Wentworth.

While Kretchmer was drilling a hole through the 21 inches of ice, Doner and Santry assembled the sediment coring equipment, including weights to help drive the collecting tube deeper into the bottom sediment. The total distance from the bottom of the lake to the top of the ice was 24.23 meters (79.5 feet). A round ball was pulled into the base of the tube once the sample was collected in order to retain the sediment within the clear cylinder. The tube was carried upright back to the shore, taking care to minimize disturbance during transport. Doing this while walking on ice can be problematic, but Doner has carried many such samples over the past seven years of core research.

This sample is the first of two that will be collected on Lake Wentworth and analyzed to determine factors that have influenced water quality over many years. Kretchmer says the 49 centimeter core (nearly 20 inches) collected “may cover 150 years or more years” of changes in the watershed.

Assembling the collecting equipment.
Assembling the collecting equipment.

“The processing of data will take a few months” adds Doner, who will oversee the work to be done at PSU. Further analysis will be completed by a lab in Minnesota. The results of the sediment investigation should identify the different materials and chemicals in the layers of sediment. These will be correlated with when they were settled and what was going on in the watershed in that time period.

Kretchmer explains: “We’ll likely be able to date the 1950s due to the radioactive layer that will still be noticeable from the nuclear bomb tests conducted by the U.S. and other nations, and we might even find impacts in the sediment from the tornado which traveled across the lake a few years ago.” He adds, “there could be unknown factors that come up such as lead sediment as well as the effects of changes in the surrounding land use and forest cover.”

Although a core was taken about 10 years ago by the New Hampshire Department of Environmental Services, the whereabouts of that sample is not known. An additional core will be taken from another deep location on Lake Wentworth this summer.

The core sample emerges from the hole in the ice.
The core sample emerges from the hole in the ice.

The analysis will be compared to the qualities of what a healthy lake should register. The amount of phosphorus is of particular importance for Kretchmer as that is the chemical that can cause significant growth of algae and invasive plants. The Lake Wentworth Foundation, one of the sponsors of this study, along with the Lake Wentworth Association, is a leading partner in the master plan for the Lake Wentworth and Crescent Lake Watershed with a goal of reducing phosphorus content by 15% in 10 years.

Results of the core analysis will be made public and will be published in a future newspaper article. Professor Donor, with the Center for the Environment at PSU, studies lake sediments to decipher past watershed changes. Her primary focus is on how climate interacts with other mechanisms for change including natural catastrophe (fire, flood, landslide, tsunami), human disturbance (agriculture, logging, development) and long-term trends (glaciations, tectonics, sea-level change).

The Lake Wentworth Foundation is a key leader in developing the Lake Wentworth and Crescent Lake Watershed management plan and a steward of over 160 acres of conserved land within the watershed. It is pursuing conservation of additional high-impact parcels in the watershed. For years, the LWF has provided support for water quality testing, milfoil treatment, and the lake host program led by the Lake Wentworth Association.

Information about the Foundation and its work is available on its website, www.lakewentworthfoundation.org or by contacting Karen Burnett-Kurie, Executive Director, at 603-534-0222.