Lake Invaders

Raise the Cost of Conservation Efforts

by Adam Hinterthuer, Limnology News – Number 24, Fall 2015

Jake Walsh taking a sediment core on Lake Gogebic on the Wisconsin/Michigan border. Photo: Carol Warden

Jake Walsh spends his days at the CFL chronicling an all-out war in Lake Mendota. He’s now ready to put a price tag on the collateral damage.

The battle is between two tiny species of zooplankton – Daphnia pulicaria, a voracious native grazer of algae in our lakes and Bythotrephes longimanus, or the spiny water flea, a voracious invasive predator of our algae-grazing friends.

The problem, says Walsh, is that “as phosphorus pollution leads to algae blooms and lower water quality, we are also losing the critters that keep that algae at bay.” When their numbers are abundant, Daphnia pulicaria can eat algae almost as fast as it grows. In fact, this leads to the “clear water phase” we often experience each spring in our lakes.

But, since a group of undergraduate limnology students first discovered spiny water fleas on a Lake Mendota field trip in 2009, says Walsh, “we’ve lost over 80% of our Daphnia pulicaria, the big Daphnia that eat a ton of algae. I used to pull in hundreds of thousands of [them] in a single sample during fall sampling. This fall, I often only found a single tiny individual in my net.”

The result is murkier waters. Since 2009, CFL scientists have documented a 3-foot loss of water clarity in Lake Mendota, which is where the price tag comes in.

According to previous economic surveys, the value of 3 feet of water clarity in Lake Mendota is, at a county level, $140 million. That number seems big, but clear water affects almost every way that we experience a lake. It means better fishing, better boating, better swimming, more valuable lakeshore property, and fewer harmful algae blooms.

Making matters worse, the 2013 Yahara CLEAN engineering report estimated that restoring 3 feet of water clarity – primarily by reducing agricultural runoff – could cost upwards of $170 million. That’s nearly a third of a billion dollars to get a single lake’s water quality back – all thanks to one tiny crustacean.

The invasive spiny water flea has researchers wondering – what’s the price of green water?

How can microscopic crustaceans add up to such a steep bill? The answer lies in what may seem like an unrelated problem. Being “the dairy state” comes with its own price tag, which we often pay for in the form of water clarity. Cows create a lot of solid waste and that manure is loaded with nutrients. Dairy farmers spread manure on fields to fertilize corn and soybean crops, but some runs off into nearby waterways and downstream to our lakes. While there are other sources of phosphorus in our waters, studies have linked more than 80% of the input to these agricultural sources. In our lakes, those nutrients, primarily phosphorus, are just as good at growing algae as they are at growing crops. And now there are fewer Daphania to eat it.

Walsh is currently working on a number of projects, including coring the lake sediment to see how far back the invasion extends. He’s already found water flea eggs preserved in sediment from before 2009. He’s also designed a population model that could help researchers figure out where and when the spiny water flea might become abundant in other Wisconsin lakes. “If we can figure out where spiny water flea is most likely to become abundant and have problems,” Walsh says, “we can be more efficient with where we allocate our money.”

Considering the steep cost of dealing with the aftermath, it’s an important pursuit. For anyone who loves a lake, Walsh’s work reinforces the message of cleaning boats and fishing tackle and not transferring live bait from lake to lake – all measures that can help keep the spiny water flea from hitting our lakes, and our wallets, quite so hard.