How to study lake sediment

If your lake's looking murky, what's on the bottom can clue you in to what's happening on top

By Cottage LifeCottage Life

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What cottage groups can do

Like the fancy forensic work done by TV sleuths, this detective work doesn’t come cheap. The type of intensive analysis undertaken by the DFO costs roughly $10,000 per core, and few cottage groups have that kind of cash. Fortunately, the Lake of the Woods association can draw on 4,000 members, each paying $27 in annual dues. Members also make voluntary contributions to a fund that pays for environmental work on the lake, and help bankroll their own water-quality research program. This spending power allowed the association to build a research partnership with the DFO in 2002, formalized by a legal contract. By rolling the association’s project into other research underway, the DFO’s Winnipeg-based Freshwater Institute analyzed six cores from various spots in Lake of the Woods for the bargain rate of $33,000. The association paid $20,000 for two of the cores, and used a $13,000 grant (from the DFO) to support the rest of the work.

Since the feds began their work, the MOE has also responded to the algal concerns by launching its own study, using 17 cores to look at the difference between the south end of Lake of the Woods – where phosphorus has historically been higher – and the more pristine north. The MOE project takes samples only from the bottom and the top of the cores, a less expensive form of analysis. “You get a snapshot approach from comparing the top and bottom of the cores,” Paterson says, adding the survey will illustrate how much – and where – phosphorus levels have changed in the last 150 years. Paterson’s wider-ranging efforts should provide more context for the DFO’s work.

In her Winnipeg lab, Hedy Kling, a private algal specialist working with the cores, plots the changing makeup of Lake of the Woods through the lens of her microscope. Each glimpse into the sediment is a venture into an alien world of exquisitely beautiful creatures: sputnik-shaped grains of pollen, lace-like scales of chrysophytes, and the mandibles of zooplankton. In one core, as she sorts through the bodies of long-dead algae, plants, and animals, Kling says, “I can see a gradual increase in algae between the ’50s and ’70s, then a very rapid one starting in the early ’90s” – and the spike includes a burgeoning population of those toxic blue-greens. Moreover, the algal increase in some cores seems to follow a rise in Lake of the Woods’ cottage development.

That cottaging plays a role in making lakes murkier is nothing new, of course: Faulty septic systems and shoreline clearances typically cause the kind of nutrient-laden runoff that algae love. But with its 4,350 square kilometres and 14,600 islands, Lake of the Woods is no tiny inland lake, where cottagers are the most obvious impact. While its north end is hard-rock Canadian Shield country, the southern shore is fertile Minnesota prairie with a patchwork of farms and towns. Unfairly or not, the south end has long been blamed as the source of algae-feeding nutrients such as fertilizer and manure. The prairie soil is also naturally higher in phosphorus, so any erosion contributes to algal blooms.

How to make positive changes

The paleo survey is the first step in proving the lake is changing, and untangling the roles that cottages, farms, industries, and municipal sewage treatment systems play in that change. It’s also the first step in tackling the pollutants that turn beauty into beast. Gerry Wilson hopes the results will be a lever for political and environmental change. “There are always going to be naysayers. That’s why you need this kind of science. If you’re going to approach key decision makers, you have to have evidence. You’ve got to have facts and figures in order to change legislation.”

Backed with the knowledge gleaned from the Lake of the Woods sediment, David Hewlett envisions a cleanup effort that will turn back the clock – perhaps not restoring the lake to the days of Dawson, but “to the conditions of 1945, or 1960, or even 1980. The lake is a major source of relaxation and release from the stress of life, and we don’t want to see this incredible resource diminished,” he says.

For his part, Dawson might be gratified to know the “minute vegetable growth” he puzzled over so long ago is reappearing beneath a microscope and illuminating the workings of the aquatic world. It’s an example of how something as seemingly worthless as sediment can yield a treasure house of information – how the muck oozing through your toes can hold the key to a cleaner lake. L

Ray Ford, a writer and farmer in Powassan, Ont., still likes playing in the mud.

How other sleuths got their sludge

Lake of the Woods cottagers may be in on the ground floor of sediment research, but other lake associations have done similar work – and found innovative ways to pay for it. A few years ago, in Saskatchewan, the Big Shell Lake Watershed Stewardship Association used core samples to investigate phosphorus build-up linked to farm practices and shoreline development, and was able to fund it with a mix of federal and provincial in-kind grants.

During the summer of 2000, cottager Heather Stuart took cores from Ontario’s Salerno Lake to study the lake’s phosphorus cycle as part of her honours B.Sc. Now environmental director of the Salerno Devil’s Lake Cottagers Association, Stuart found the bark, needles, and debris left in the sediment from 19th-century log runs were contributing to the lake’s phosphorus levels. Because that phosphorus will be trapped in the lake for a long time, Stuart says cottagers have to be doubly careful not to add to it. “It means we have to be vigilant when it comes to inspecting septic systems and holding tanks.”

This article was originally published on October 3, 2005


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