Monthly Archives: January 2012

Lake Wingra’s Complicated Relationship with Wisconsin’s Flu Season

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Jon Temte MD, PhD Credit: UW Department of Family Medicine

Several years ago, Jon Temte, a professor in the UW-Madison Department of Family Medicine, got interested in the variation of flu season from year to year in Wisconsin. He brought an undergraduate student into the study and began to have her look at all sorts of long-term datasets, from the dates of major winter holidays to the annual waterfowl kill from the duck and geese hunting seasons.

While Temte didn’t expect his work to veer toward limnological topics, in the twenty five years of data he used to examine the timing of flu season peaks in Wisconsin, one variable kept popping up – the date that Lake Wingra froze over.

Limnology wasn’t completely foreign ground to Temte. He had an MS from Oregon State University in biological oceanography and obtained a PhD in zoology at the UW. In fact his wife, Jo, did her graduate work at the Center for Limnology, receiving her MS in limnology and marine sciences as a student of John Magnuson. But the finding was, nonetheless, surprising.

We sat down to talk with Jon about his work in epidemiology and how he stumbled onto this connection between limnology and epidemiology.

CFL: What first got you into studying Wisconsin’s flu season?

Temte: “What I worked on in terms of my masters and PhD was the timing of reproduction in seals and sea lions and so I was very invested in seasonality and one thing led to another and I got more and more involved with work here [in Madison] at the state lab of hygiene. Similar to the study of lakes here, where we have the longest periods of study of freshwater systems in the world, [Wisconsin's] state lab of hygeine [has] very long term data for influenza in the state. And over the years in terms of family medicine I have probably done more public health than anybody in my department and that’s led to doing a lot with infectious disease and that led to doing a lot with vaccines and policy.”

“So, several years ago, I just got interested in looking at the variation of flu season here. From year to year it will change and, going back a good number of years, I started getting interested in what might be causing some of the change out there. Flu viruses and influenza as a disease tends to be very seasonal so we tend to think of it as a wintertime virus. So in the northern Hemisphere, we typically have it November through March and the Southern Hemisphere is six months different. And there’s been a lot of conjecture as to what causes that, but not a whole lot of good study.”

CFL: So, what made you look at ice on dates?

Temte: “The reason I knew about that and, now I’m dating myself, but, 25 years ago when Dale Robertson was at the CFL [Temte's wife, Jo, was then an MS student at the CFL and knew Dale's], they used to have a pool as to when the lake would freeze. And rumor has it, I don’t know if this is true or just legend, but he was excluded for participating because he was always too close [with predictions].  But the long and short of it is that the lake  freezing was a nice intergrating function of the accumulation of cold [in the ambient outdoor temperature]. So we started building some models of the timing of the peak of influenza [outbreaks in Wisconsin] and lake freezing and you know, plugged in Mendota and Monona and Wingra and Wingra was always the best predictor. And it turns out there were actually two variables that really stood out. One was the freeze of Lake Wingra and the second was the timing of Thanksgiving, which isn’t terribly variable, only varying between November 22nd and 28th.”

Correlation of Wingra freeze Date and Flu Peak Credit: Jon Temte

CFL: Can you explain why these two predictors are correlated with flu season?

Temte: “If you look at all of our recorded cases [of influenza] over a 25 year period and if you start looking at average temperature, flu really kinda tends to like it when our temperature dips below freezing and it starts going away, on average, when we warm up above freezing. It also turns out that, it seems like there’s a pretty good trigger out there, not just for flu but also another common respiratory virus called respiratory syncytial virus,  but they both really seem to get going around Thanksgiving. And that makes really good sense for something that likes to jump from human to human, because we have such wonderful social mixing [during Holidays]. And there is, at least historically, during this period of time, the dates of Lake Wingra freezing. So when you put everything together, the best model I could come up with is, you look at the freezing of Lake Wingra relative to the timing of Thanksgiving and [it's a good predictor of the timing of flu season]. The model is basically that, for each day Lake Wingra is delayed in freezing, the peak of influenza is delayed by about a little more than a day.”

“Why I think this makes sense is, if you have people getting together and it’s really cold, you really accelerate influenza. On the other hand if you have people together and it’s warm out and moist, I mean look at Thanksgiving this year, it was pretty warm and certainly not icy temperatures and you kind of lose that little kick you get from [a cold, dry] Thanksgiving.”

CFL: Obviously there are times when Lake Wingra’s freeze doesn’t correspond with flu season, but this correlation is a fairly strong signal?

Temte: “Basically what we do is take the amount of variability in the peak and we can explain away maybe a third of that variability just from this one factor being the freezing of Lake Wingra compared to the timing of Thanksgiving. Which isn’t too bad. In biological systems, you know, an r squared in the .35′s is interesting.”

 “So we examined this period from 1980 to 2005 and I haven’t done it for a bit now, but for subsequent years it seems to hold pretty true.  I can usually [predict the flu peak] within a couple of weeks once I know when Wingra is freezing over.”

CFL: What do the predicted effects of global warming mean for this correlation and flu in general? If the virus likes cold, dry weather, it seems warmer, wetter winters might disrupt flu season.

Temte: “Well this is where you get into kind of the wild speculation. You take a year like this one where there’s just not much going on. We had very warm. moist air in December, there’s nothing going on flu-wise and then you pull the kids out of school for a week and a half. And even though they’re mixing with people and there’s a lot of travel going on, there just isn’t any background [for the flu] to get going. So we’re still seeing right now virtually no flu [in Wisconsin], which is incredibly, incredibly rare. The grand mean date for influenza in Wisconsin is January 21st and we’ve only had a handful of cases in the state so this is incredibly unusual. And once we see [an uptick in the reported cases of flu] we figure on about 6 or 7 weeks until we hit the peak. But now we’re already looking at 6 or 7 weeks from now which gets us into March and we start to get warmer air and conditions less favorable for the virus, so if we keep on this we’re likely not to see much at all.”

“So we’re kind of getting into the wild speculations that some of the respiratory viruses are prone to becoming less significant in areas that undergo significant warming. There’s actually a interesting paper from England looking at the end of respiratory syncytial virus, and they’re finding long term trends that, with increasing ambient average temperatures, you shorten the season considerably. And they even speculate that, if this warming trend continues, the season gets so short it goes away.”

CFL: This study must’ve been an interesting departure from your typical epidemiological studies. 

Temte: “I just look at the lake freeze and it’s kind of this magical function of all these variables you can’t measure. When you do things like this, it’s very nice to have discrete things and a lake freezing date is a very discrete point in time. And to get there, you have all these functions of temperature and wind speed and how much the water is mixing, and all these things contribute, but it really stuck out as a kind of interesting predictor here. Who would’ve thought that the freezing date of a lake and the timing of epidemics have anything to do with each other?”

 

Climate change & variability: where does 2011′s late freeze rank?

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Credit: UW Communications

We here at the CFL have been eagerly awaiting word so we could anoint the winner of our annual Lake Mendota “Ice On” pool. Well, the state climatology office has made it official – our fair lake finally donned its winter mantle of ice on January 14th. (Congrats are in order to payroll and benefits specialist, Val Seidel, who correctly guessed when Lake Mendota would be “frozen from Picnic Point to Maple Bluff and 50% covered).

While this winter offered an unusually long wait for lake ice, it wasn’t record breaking. That distinction goes to 1931 when Madison residents had to wait until January 30th before they could entertain thoughts of ice fishing, snowshoeing or skiing on the Yahara chain’s largest lake. This year is tied with 1999 as the third-latest “ice on” date. A chart, kept by the North Temperate Lakes Long-Term Ecological Research site can be found here.

But this year’s late date is another data point supporting a long-term trend – Madison lakes are getting ice later, and they’re thawing out sooner. Consider this ice on data from the last 150 years.

Historic "Ice On" dates on Lake Mendota since 1853. Credit: Aaron Stephenson

As you can see on the graph, “ice on” dates are all over the place. For example, right after 1931′s record late freeze, in 1932 Lake Mendota froze over earlier than average on December 10th. Such variability, or “noise” on the graph, makes it hard to find patterns. Thankfully, Lake Mendota has a hundred and fifty years’ worth of records.

John Magnuson, director emeritus of the Center for Limnology and our resident ice expert, says the long history of record keeping may have something to do with a bygone industry.

“Each one of our lakes in the late 1800’s had an ice storage facility,” he remarked in a recent talk about this late-arriving winter. “Individuals would make a living going out and sawing chunks of ice out of our lakes, dragging them up and burying them in sawdust in these storage facilities.” Those chunks of ice were used in the summer to cool that revolutionary precursor to the refrigerator, the ice box.

“it was not made in an adjacent freezer,” Magnuson says, “That ice was made on a lake and people cut it. We harvested it. Madison even used to ship ice to New Orleans.”

These ice houses were a form of income and essential to storing perishable food like milk and other creamery products, so residents were interested economically on when the ice formed and how soon they could go out and cut.

Another reason for keeping ice records could’ve been for transportation, Magnuson says. In the horse and buggy days, it was far quicker to pull a sleigh across Lake Mendota than head around the shore when trying to get somewhere on the other side.

Of course there’s also always the “Leopold affect.” People often keep records of things like the first pasque flower bloom or the first robin’s arrival and, perhaps, these phenological observations were reason enough to start charting lake ice.

For whatever reason, we’re lucky to have the resulting data. With so many variables like El Nino events or sunspots or North Atlantic oscilations to consider, divining a trend amid the noise requires a long dataset. “There’s so much noise in this system,” says Magnuson, “that even if you use our fancy statistics, you can’t even see a trend until you get out about 50 years or so.”

With 150 yearts at our disposal, though, the signal is unmistakable. Lake Mendota is, on average, freezing over later and thawing out earlier.

Taken alone, Magnuson says, this is not much evidence of anything. But add Lake Mendota’s century and a half of data to other temperate lakes with similar seasonal changes, and the evidence is undeniable – climate change is changing our lakes. It might not explain all of the changes and it certainly can’t be blamed on the year to year variability, but the trend that emerges is one where early freezes happen later and the late freezes happen, well, even later.

“We often use the lake as a very simple example of what climate change is doing,” Magnuson says. “You don’t need a thermometer. All you need is a good pair of eyes and a high enough location. You need to be a curious person about the seasons around you and just write down the ice date every year”

 

 

 

The Curious Case of the American Eel

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A researcher at Ontario's Glenora Fisheries Station tags and measures an eel brought in by a fisherman. The eels are then transported past the St. Lawrence Seaway's main dams so they can swim out to sea to spawn. Credit: Adam Hinterthuer

When most people think of eels, they immediately turn their thoughts to the ocean. Perhaps, even, to the “electrical” variety. But there was a time in this country when eels inhabited nearly every river and stream east of the Mississippi. The American eel spawns in a region of the Atlantic Ocean called the Sargasso Sea. In its larval phase, it’s carried by ocean currents to the Eastern U.S. coast. It matures along the way and, upon reaching South Carolina, or Maryland, or the St. Lawrence Seaway, it is able to swim up into freshwater environments to live out most of its adult life.

This makes the eel, catadromous – in a reverse of the salmon life history, it makes its pilgrimage to be born and to die out at sea, rather than at the headwaters of a freshwater river.

The American eel was once a staple food of native Great Lakes tribes and it’s estimated that the eel once made up nearly half the fish biomass in Lake Ontario.

But the most prolific fish no one’s ever heard of is now a rare sight in any U.S. waters. A recent story in the Chesapeake Bay Journal explains why.

Another good story from our neighbors up north ran a few years ago in the Canadian magazine, The Walrus.

A cliche among stories of endangered organisms is that “you don’t know what you’ve got til it’s gone.” The story of the American eel may unfortunately be one where no one ever knew what they had.

 

Animal Planet: Lake Mendota Edition

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Gulls and common mergansers enjoy Lake Mendota in January - Credit: Adam Hinterthuer

An interesting scene has been playing out in Lake Mendota lately. Right outside the doors to Hasler Lab, common loons and common mergansers are busy fishing all day long. In January, this is undoubtedly easier than in the summer. Low productivity in the lake means crystal clear waters and the cold temperatures mean sluggish fish. It would be easy pickings, if it weren’t for one other variable – the gulls.

Herring and ring-billed gulls are what’s known in the animal world as “opportunists.” While the loons and mergansers are busy working for their meal, the gulls wait patiently for one of the diving ducks to surface with a fish in its beak – they then make a charge, scare the successful fisher away and gobble up any dropped fish.

A merganser had just surfaced with a fish in its beak when this gull chased it away, then returned to eat the dropped fish. Credit: Adam Hinterthuer

The scene is one we at the CFL usually enjoy during the fall migration, so it’s definitely interesting to see it all unfold in the middle of January. By this weekend, though, temperatures should finally drop enough to give Lake Mendota its winter cover of ice. Then the fish will be safe from the mergansers and the mergansers safe from the gulls.

Until then, we’ll enjoy a view associated with an entirely different season.

January 10th and Lake Mendota is more reminiscnet of Spring. Credit: Adam Hinterthuer

 

The Chill Factor: What Less Lake Ice Means for Ecology, Economy and Ourselves

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A few days before Christmas, I was headed down John Nolen Drive on a last-minute shopping excursion when I noticed a couple of fishermen out on Lake Monona – in a boat.

Now, it’s January 4th, and there’s still no snow on the ground in Madison and most of our lakes are dominated by open water.

January 4, 2012 and Lake Mendota is still waiting for ice cover. Credit: Adam Hinterthue

Curious about what such late freezes might mean for both lake inhabitants and shoreline residents, I sat down for a talk with the Center for Limnology’s director emeritus, John Magnuson. Turns out that the biggest consequence of shorter ice cover on our northern lakes might mean a lot more to humans on the shoreline than the organisms that call the water home.

That’s not to say nothing in the lake feels the effect of later ice on and earlier ice off. For example, certain species of algae have evolved to take advantage of the still waters that occur once a lake has iced over. While present in the lake most of the year, these tiny algae float to the surface when the frozen lake’s waters still.  In winter, they become the dominant class of plankton.

“It’s a survival mechanism that works pretty well for them,” says Magnuson, “but in current conditions, these algae aren’t doing so well. At this time of the year when the lake is still open, the slightest bit of wind is enough to mix the lake from top to bottom. They’re not hurt by mixing, but they out compete a lot of the other algae when the water’s really still under the ice.”

Magnuson admits the ecological impacts are subtle. The more obvious effects are on human use of the lakes.

“Right now, when it’s cold [outside] but the lake’s not frozen, is not a great recreational use time on Lake Mendota,” he notes.

Usually this time of year, I would pass cross-country skiers and ice fishermen on any pre-Christmas drive past Lake Monona. And these outdoor pursuits are part of Wisconsin’s winter economy. Sure, ice fishing and snow shoeing may not be big drivers in Madison’s economic engine, but, says Magnuson, “In the northern part of the state, winter recreation is an economic subsidy for the area.”

Despite all of this, perhaps the biggest problem we have with an open-water Lake Mendota in January is less tangible. An ice-less Lake Mendota in January just doesn’t “feel right.”

“Human beings have a strong sense of place,” says Magnuson. “They get homesick or long for the country they immigrated from, and in Wisconsin, our sense of place includes the four seasons and that includes winter. And in our area, that sense of place includes lakes. And these are important to us. This sense of place affects how we see ourselves and what we do in their lives and what we hope our children will get to do in their lives.”

But, says Magnuson, our sense of place may need to shift to accommodate the new normal. And that means greater variability and a shorter lake ice season. “Historically [in the mid-1800's] Lake Mendota had about 4 months of ice. And right now we’re averaging about three.”

Maybe the ecological or economic impacts of that change aren’t catastrophic, he says, but “on the other hand, I’m unhappy. I’m actually sad that we’re losing winter as we knew it.”