The lid goes on

If you wonder what happens in your lake after the ice forms, the answer is: Not a great deal. Sure, fish still bite, some more readily than others (bass being among the reluctant).

But in general, things get quiet, still and dark down there under that translucent, snow-covered sheet. The three inputs that make your lake so very much alive in high summer – light, heat and oxygen – are much less abundant.

Only cold-blooded creatures spend winter in the water (though foraging otters may come and go through near-shore holes in the ice). In temperatures not much above freezing, fish move around sluggishly; reptiles and amphibians stay mostly still or outright hibernate. Aquatic insects winter in the bottom sediments.

Except to the extent that it receives inflows from a stream or groundwater springs, your lake becomes essentially a sealed container. Very little oxygen gets in. The deeper the snow cover, the less light can penetrate, and the less oxygen plants produce from photosynthesis.

And vegetative life itself is limited. The rooted aquatic plants (weeds if you will) have long since died back. The populations of plankton – the tiny critters and one-celled algae that form the base of the lake food chain – have plummeted. Whatever oxygen was dissolved in your lake’s water at the time ice formed steadily declines through the winter.

If you’re able to look through clear ice to the bottom, you may see places where occasional bubbles of gas issue from the muck and rise until they meet the ice cover. But biochemical activity and life in general slow to a crawl. For fish and other lake creatures, it becomes a question of survival until spring.

Imagine what it’s like down there, under the ice. There’s barely a sound. Maybe the noise of a roaring wind penetrates sometimes. But there’s no sound of wave action. No splashing as eagles strike carrion fish on the surface. No swirling noises as loons dive down to fish. No whine of outboard engines. Just unbroken silence.

On windless days and nights, before the snowmobile trails open, it’s a lot like that up here on the surface, too. It’s a time to treasure the quiet, to feel life’s pace slow down, to enjoy a sort of suspended animation that lasts until spring.

If it feels miraculous to see the earth burst forth with life as the weather finally turns warm, how much more so to ponder the way lake life blooms again when at long last the ice recedes.

The loons: Still here

A week ago I saw them, through the living room window, in a frame of white pine boughs and trunk, far out on the lake, in a perfect row, four white spots on deep blue.

 

I had my suspicion but reached for the binoculars to confirm, steadying by pressing one barrel against the glass. Yes, loons, even at long distance, their shapes unmistakable, slowly swimming toward me, white breast feathers lit by a low sun.

 

So, they were still here. Or maybe these were not Birch Lake’s resident loons but migrants coming south from Canada. I was surprised to see them after all the cold, in winter plumage for sure (though so far off that even at 8X magnification I couldn’t discern the colors clearly).

 

I worried for them a little, the lake’s southwest lobe largely iced over and a crust on the main lake starting to push out from shore. I have heard stories of loons getting iced in, though it does seem somehow they know enough to leave before it’s too late.

 

The fact remains, loons need a lot of space in which to take off. Just as a jet plane is marooned at an airport with a too-short runway, loons are stuck if there isn’t enough water on which to run and flap up to takeoff speed. The qualities that makes loons adept divers and hunters – short wings for streamlining underwater, and bodies less buoyant than those of other birds (solid bones instead of hollow) – are handicaps when it’s time to get airborne.

 

If loons live on your lake, you surely know the sound they make as they take flight. It’s that sound Fred Flintstone’s feet made as he ran his stone-wheeled car up to travel speed: Pat-a-pat-a-pat-a-pat-a-pat-a...And not just a few pat-a’s. Loons have to beat their webbed feet over a long distance to lift clear of the water.

 

Ducks? Startle them and they seem to leap right up, airborne in an instant. Loons, on a calm day, might need to skim 600 to 700 feet along the surface. They need less room if able to take off into a wind, which provides lift, and yes, they do aim themselves upwind if they can, without the benefit of the wind sock human pilots use. Once in the air, they fly fast, some 50 miles per hour, though their flight is energy-intensive. Soaring is out of the question; the wings must beat every second.

 

So there they were out on the lake in the middle of an Arctic cold front, in all likelihood gone by the next morning or maybe even that same evening. Anyway, I will assume so. It looks like a long, long time before they come back.

Closing Time

I hope you were among the fortunate souls who spent last weekend at their lake homes or cabins. I met several such folks as I took a solo paddle, my last of the season, around the shoreline of Birch Lake, at Harshaw.

This was a prototype October Saturday afternoon, clear sky, temperature mid-50s, the softest of breezes, the lake’s surface smooth, oaks and birches still holding their colored leaves, the air scented like (to borrow a phrase from Garrison Keillor) fine brandy.

When traveling alone in our red Kevlar Old Town, I always assume the bow seat and paddle stern first; sitting farther amidships keeps the canoe flat instead of nose-up in the water. At this season there’s something appropriate about paddling “backwards”: The trip is more about looking back than forward.

You tend to think, as autumn closes down, on what was instead of what will be. My annual spring canoe reconnaissances are about watching for life in the shallows, spotting painted turtles released from hibernation, following smallmouth bass across the reef on the lake’s east end, spying on walleyes hunkered deep in sunken tangles of brush.

On this mid-October ride, there was of course little life to observe other than a somewhat heavier-than-usual clouding of green algae. The fish had gone deep. Several small ducks in a cluster skittered away and up well before I could get close enough for an identification.

I did encounter several lake neighbors enjoying the day in various ways: one man disassembling a pier, ratchet wrench periodically rasping; another enjoying a drink while seated atop a short stairway of timbers; a woman at the end of a pier with a small black dog that barked at me sharply; a man and wife prepping a pontoon boat for storage, two fishermen in boats working rocky points, presumably for muskies.

From here on there would be few days like this. It’s hard at such times not to regret the decline of the seasons and to long, far prematurely, for spring. It’s too soon to embrace the idea of November’s bleakness and then the long winter. So, while taking in the glory of the day, we tend to scan back over the good times of spring and summer past.

As I pulled the Old Town from the lake and tipped it over on shore, for the last time until next year, the couple from three lots down paddled by in their canoe, just two more lake country folks lucky enough to enjoy this day, around or on the water.

This turnover isn’t for dessert

Right now many Northwoods lakes are going through (or soon will) something called the fall turnover. It’s a phenomenon as beneficial as it is interesting. 

Fall turnover is a restorative process, a bit like opening doors and window in a long-sealed, musty basement and letting lots of clean, fresh air course through.

A previous column in this space told how lakes stratify (form layers) in summer – warmer, lighter water above and colder, denser water below. At the height of the warm season, these layers don’t mix very much because the difference in density between surface water (at, say, 80 degrees F) and deep water (at, say, 40 or 45 degrees) is considerable.

So as the summer wears on, all kinds of materials sink from the surface water into that cold bottom layer. Plant parts, algae, fish carcasses, dead insects and more drift down and decompose, consuming oxygen. As a result, the oxygen down there can become quite depleted.

What would happen if your lake remained stratified all the time? Those deep waters would become largely lifeless, hospitable mainly to organisms that thrive in anaerobic (without oxygen) conditions.

But fortunately, along comes the fall turnover, generally sometime in late September or early October (likely on the early side this year because of all the chilly weather). In simple terms, what happens is that the surface water gradually cools, and the difference in density between the surface and deeper water decreases, so that eventually wind and wave action can mix the layers together. And that means the lake, from surface to bottom, becomes infused with oxygen.

This is great for all manner of lake creatures – especially fish that dwell in the depths – that need oxygen to make it through the winter.

How can you tell if your lake has turned over? Well, for one thing, the water suddenly becomes cloudier than usual because the mixing action brings up nutrients and debris from the bottom. You might even notice a hint of sulfur scent (like rotten eggs) as decomposing material comes to the surface. When the turnover is complete, the water becomes clear again, likely more so than in high summer.

Some anglers say fishing is tougher during the turnover because with oxygen available everywhere, the fish are more scattered.

Different lakes experience fall turnover in different ways. Deeper lakes take longer to turn over. Shallow lakes may not turn over at all because they never actually stratify in the first place – wave action keeps them well mixed all through summer. The turnover itself can play out in a few days in some lakes, or during a week or more in others.

So watch for signs of turnover in your lake. It’s another seasonal milestone, like ice-in and ice-out, that can be fun to track over the years.

The bounty of the benthos

Leaving an airport, you see signs that say Ground Transportation. After flying at 36,000 feet and a few hundred miles an hour, that travel mode seems quite unglamorous.

So it is with life on at the bottom of a lake, which the limnologists (freshwater biologists) call the benthos. Up above in the water column the fish are like the aircraft and birds of our dry-land world. Creatures less appreciated live on (an in) the “ground” below.

It’s appropriate at this season to think about the benthos, because that’s where a lot of lake life is heading as the water gets cold and winter comes on. The term “benthos” comes from a Greek word, “bathys,” which means “deep.” It’s a zone much richer in life than most of us appreciate.

Of course, crayfish live on the bottom, as do clams, mussels and snails. Aquatic insects like mayflies and damselflies also live on the bottom, or buried in sediment, at stages of their metamorphosis from egg, to nymph, to winged adult.

These creatures are important links in the lake food chain. They eat algae or sunken plant matter and in turn provide food for fish (as anyone who has ever caught bluegills with nymphs or perch with wigglers can attest). An assortment of worms can also be found in upper layers of bottom sand and muck.

Leopard frogs and bullfrogs become benthos dwellers in winter. They do not (as many believe) dig into the bottom – the sediment contains too little oxygen to get them through until spring. Instead, they lie on the bottom, or only partly bury themselves. Some may even swim around slowly from time to time.

Painted and snapping turtles, on the other hand, do burrow into soft lake bottom mud and hibernate. In that state, they need very little oxygen and can absorb it through exposed mucous membranes in the mouth and throat.

An important function of the small benthic creatures (the worms and inserts) is that they allow scientists to assess water quality in a lake (or stream). A researcher can take “grab samples” of the bottom sediment, sort out and identify the organisms it contains, and get a good idea how healthy the lake is.

One measure they use is species diversity. In general, the more different creatures they find, the better the water quality. Another criterion is pollution tolerance. If a bottom sample is rich in immature forms of mayflies and stoneflies, which are sensitive to pollutants, that indicates good water quality. But if only midges and worms are present, that signals polluted water.

So while we get ready to “hibernate” for the winter, it’s good to think about the importance of all those creatures spending the cold season on and under the benthic blanket.

How acid or alkaline is your lake?

A characteristic you can’t see or feel can have subtle or significant effects on life in your lake. It’s called pH, and it’s a measure of how acid or alkaline your lake’s water is.

We know that water molecules contain two atoms of hydrogen and one atom of oxygen (H₂O). However, some of those molecules actually exist as positively charged hydrogen ions (H⁺) and negatively charged hydroxide ions (OH^-).

In pure water, those ions exist in essentially equal numbers. But when chemicals are added to water, the balance can shift in one direction or the other. A solution with more hydrogen ions is acidic; a solution with more hydroxide ions is basic, or alkaline.

pH is measured on a scale from zero (extremely acidic) to 14 (extremely alkaline). Pure water, which is considered neutral, has a pH of 7. Relating this to common substances, lemon juice is a fairly strong acid (pH just over 2), while household ammonia is strongly alkaline (pH about 12).

Lake waters are not that strongly acidic or alkaline. Their pH falls generally in a range from about 6 to 8, close to neutral. Interestingly enough, natural rainwater is fairly acidic (pH about 5.6), and air pollutants like sulfur dioxide and nitrogen oxides can lower the pH significantly – causing the harmful phenomenon of acid rain.

Fortunately, most lakes contain substances that neutralize (or “buffer”) acids, thus keeping the pH stable. One of the most important of these is calcium carbonate (limestone).

How does pH affect life in your lake? That’s complicated, but it determines how well certain fish species, plants, insects and other life forms survive and reproduce. For example, at pH below 6.5, walleye spawning is inhibited, and smallmouth bass disappear below pH 5.5.

pH can also determine the extent to which certain pollutants are released into the water from sediments in the lake bottom. For example, a change in pH can cause more phosphorus to dissolve in water, making it available to feed algae. In addition, many scientists believe that higher acidity is related to the release of toxic mercury into lake water. The mercury then can accumulate in fish.

pH and its effect on lake life is a complex subject. In healthy lakes, the effects are mostly subtle – pH is just one of many qualities that make each lake unique.

Who decides where the school goes?

Hundreds of perch schooled off our pier last week. The problem? They were an inch and a half long, which means nano hooks, water flea bait, very sharp filet knife.

Looking down at that swarm of black-striped fry, moving in unison, I couldn’t help wondering: What holds that school together? Why are they schooled in the first place? And which fish decides where the school goes?

The first thing to appreciate is that these fish don’t “decide” anything. They don’t form the school out of conscious strategic thinking. The behavior is built into their genes; it conveys certain evolutionary advantages that promote survival.

First off, it’s easier for a predator to track down and capture a solitary fish than to eat fish in a school. This seems counter-intuitive, since we’d think attacking a school would amount to the proverbial “shooting fish in a barrel.” However, scientists have found that a school confuses predators. A school moving together, the sides of multiple small fish flashing in sunlight, can appear to a predator as one large fish, discouraging attack. In addition, the sheer numbers of fish in a school disorient predators, making it hard for them to zero in on one individual.

Another advantage to schooling is that more eyes watching means greater ability to find food. Schooling also helps fish conserve energy – in effect they’re able to draft on each other. The principle is the same employed by bicycle racers, one closely following another to reduce wind resistance.

But how does a school of fish move as one? According to an article on the North Carolina Aquariums website, “Each fish maintains an exact spacing from its neighbor. As they swim, they follow the movements of their neighbors and change their course in unison. Vision is the primary sense used to hold their place in a school. Visual markers play a big role – each member of a school follows some key feature of the fish around it, usually a stripe or spot on their bodies, fins or tails. The vibration-detecting lateral line, a row of sensory cells that runs along the sides of the body, also provides information about neighbors’ movements.”

A closer look at the school of perch off our pier showed the individual fish contentedly picking off white specks in the water – likely Daphnia (water fleas) or some other zooplankton. Those of us here on Birch Lake can only hope the schooling behavior helps those perch grow to catchable, edible size. Time will tell.