Diatoms: Where lake life begins

Weeds are springing up in your lake by now, or will soon – but the most significant plant growth that’s happening is not obvious to the eye.

As the water warms and sunlight continues to penetrate deep, diatoms are proliferating. These are one-celled algae that multiply profusely in colder water, which is high in silica and nutrients that built up over the winter.

“Diatoms use silica to build their cell walls,” according to an article in Minnesota Conservation Volunteer magazine. “They grow quite rapidly and often give the water a brownish hue. Because they cannot regulate their buoyancy in water, diatoms rely on currents or wind and wave action in lakes to keep them in the lighted zone, where sunlight penetrates shallow water. In the absence of wind, waves or currents, diatoms settle to the bottom of the lake and die.”

Later in the season, other kinds of algae take over. But a few more words about diatoms are timely and appropriate. For one thing, diatoms, seen under a microscope, are incredibly beautiful – the many species exist in a variety of symmetrical shapes.

More important, diatoms are an important part of a lake’s phytoplankton – the tiny plants that float in the water and form the base of the lake’s food chain or, to put it differently, the foundation for the lake’s food web. Diatoms and other phytoplankton perform the same basic function as grasses in prairies that support grazing animals.

Just like large rooted plants, diatoms live by photosynthesis. They make their food from sunlight, carbon dioxide and nutrients; they are called primary producers. Diatoms become food for plant-eating zooplankton – small animals like Daphnia (water fleas). These in turn are eaten by smaller fish, including game fish and panfish fry, which in turn become food for larger fish – bass, walleye, northern pike.

This of course is an over-simplified description of the food web, but it illustrates how important the diatoms and other phytoplankton are. Without them the food web would collapse – there would be no fish.

Another function of diatoms is that through photosynthesis they release oxygen. In fact, the diatoms, other phytoplankton, and larger aquatic plants make a net positive contribution to the dissolved oxygen on which fish and other lake creatures depend. 

So as you watch the water lilies, cabbage weeds, bulrushes, coontail and other plants pop up in your lake this summer, give a thought to the diatoms, out there by the billions, not doing much besides floating, yet helping to make the whole lake system function.