by Pam Willison
One in a Thousand!
During Warbler Weekend at Tally Lake, Whitefish Lake Institute Executive Director Mike Koopal presented unique information on Tally Lake. Mike’s working hypothesis is that the lake is meromictic, meaning the deep lake water doesn’t mix with the surface water, leading to a depletion of dissolved oxygen at depth. Compared to holomictic lakes like Flathead and Whitefish Lakes that completely mix twice a year, scientists predict that there is only one meromictic lake to every 1,000 holomictic lakes.
Mike has pieced together information to tell the story of why Tally Lake may be meromictic. The lake is ringed by mountains which shelter it from winds. It is also the second deepest lake in Montana at 445 feet, meaning wind energy would have to be strong to mix the water. It also has a trapezoidal cross section, meaning there is more water at depth than in most lakes. The lake has a brown color from the humic (organic) matter input from its watershed. That darker color rapidly absorbs sunlight and heats the lake up quickly forming a very strong shallow thermocline that is resistant to mixing.
But the story doesn’t end there. Mike has documented an historic landslide at the far end of the lake that raised the lake elevation 40-50 feet. Now, the lake inlet and outlet are at the same end of the lake, decreasing any flow-through energy. Mike is awaiting data analysis from a sediment core he helped collect from the lake last summer. He is curious whether the core will substantiate a sub-hypotheses that the lake is partially meromictic, meaning that it does mix every 50-75-100 years based on unique meteorological events. There’s more to come from Mike’s work on Tally Lake. He is assembling a team of scientists to further analyze lake conditions and publish a paper on this most fascinating and unique resource.
Camping and Birding Galore
In addition to the informative presentation recapped above, the Tally Lake Warbler Weekend, held June 2-4, provided glorious weather, great birding, good fun, and a notable increase in participation (possibly weather related?). There were over 50 attendees during the weekend, with nearly 25 people camping. The Saturday potluck was well attended, and the desserts were well worth the trip – chocolate cake, rhubarb tarts, cookies, brownies!! Although there were no rare bird sightings, 53 species of birds were spotted, including a pair of Osprey demonstrating aerial mating behavior.