Aquatic Forest

By Linda Curtis, Botanist

Years ago, I talked with divers who had taken their underwater video cameras into the depths of Cedar Lake in Lake Villa, one of the few lakes in Lake County that still has excellent water clarity.  A diver loaned me the video later, and I as watched the underwater scenes on screen, I was amazed because I was seeing an aquatic forest much like a layered tropical rain forest.

From my canoe, I could only see the canopy of the plants.  But from the diver’s view, I could now see the layering. The lowest layer included shade tolerant plants, like coontail, a primitive aquatic plant, and the macroalgae Chara. By comparison, the lowest layer in summer in the Ryerson Forest ecosystem includes wildflowers and sugar maple seedlings, which are also shade tolerant.

Ecosystems, whether forest or aquatic, have similar system structures. The system begins with plants that are the basis of the entire food system.  No plants = no food. This may be an impossible concept for people who want to cut down forests or herbicide the aquatic plants.  Why are the songbird populations dwindling and why must we restock the lakes with fish?

So, what if a forest is cut down or a lake is nuked with herbicides? Nature’s orderly plan will recover the soil with plants in a process called ecological succession. Before the settlers introduced “ weeds,” the first plants to re-colonize a forest or lake were the native plants.  Today, over half of our plants are from Europe or Eurasia and are the first ones to grow quickly and take over.

So, are there plants from Europe and Asia in both forest and aquatic ecosystems?  Yes.  There is garlic mustard and buckthorn in forests and water milfoil and curly Potamogeton  in lakes. They monopolize the landscape, reducing the natural diversity.

In a forest, plant diversity provides a color feast for the eyes, especially in autumn when viewed from an airplane. Each species has its own autumn colors.

Aquatic plant diversity appears not as colors, but instead, as a myriad of form and texture when seen from a canoe in the clear water of Cedar Lake.  If you want to see over 30 clean aquatic plants in one lake from a boat on Cedar Lake Park, and treat your eyes to a diverse and healthy ecosystem, do it while the Lake is still clean and clear.

One broad ecological principle is that the greater the biodiversity, the healthier the ecosystem.  When you visit a high-quality forest like Ryerson Forest, you will see many species of trees, herbs, shrubs, mushrooms, etc.  And, that’s what biodiversity means, not just numbers of plants or animals, but numbers of different species of plants and animals, and all the fungi and bacteria with them.

Biodiversity can also mean many kinds of communities within an ecosystem. Ryerson Forest has a river floodplain forest as well as mesic forest. Cedar Lake has a floating bog mat on the western side of Cedar Lake, and is a protected DNR Preserve. The water there is brown in color and tests as acid, while the eastern portion of the lake is clear and slightly alkaline.  Because of the different water chemistry, plants grow in their area of tolerance or preference to pH acid  to neutral and to pOH alkaline.  For example, Bladderwort, a carnivorous plant that lives in nutrient-poor acidic waters, captures small creatures like diatoms and copepods in its trapdoor bladders, then digests them.

The main water body of Cedar Lake is remarkably clear.  Several northern aquatic plant species still survive from the time of  glacial melt-down and retreat, and require the pristine water to continue growing. If the water becomes polluted or shady from algae, they can’t survive.  Most of Cedar Lake’s aquatic plants are on the State of Illinois Endangered or Threatened list of plants.  Several fish are also on the protected list.

Cedar Lake’s only island is east-west oriented, possibly from the cleaving of glacial ice block that split and formed the lake over 10,000 years ago. The sunnier southern shore of the island is different from the shaded northern shore, and as a result, the micro-climate enables shade-tolerant plants to grow there. This is similar to the ravine effect seen in forests along Lake Michigan.  The ravines have creeks draining east into Lake Michigan.  The ravines that receive the most sunlight on the south-facing slope will have different plants from those on the north-facing slopes .

Many aquatic plants are perennials.  If you think about it, our deciduous trees are perennial in that their leaves die, and the trees become dormant over winter. So, too, aquatic plants upper portion of leaves die and decay in winter leaving the perennial rootstocks still alive in the hydrosoil.  They sprout in April and May and grow toward sunlight, just as trees bud, and grow upward twigs with leaves .

Some aquatic plants can grow up to the water surface and flower. This exposes their flowers to the air where they can be pollinated by insects. In the forest, some flowering trees, like black cherry, are also pollinated by insects, but  most trees have no petals and so are wind pollinated.

The forest canopy can be open, as in open oak woods and closed and shady as in sugar maple forests. Similarly, some aquatic plant beds are open, meaning they have spaces between their leafy stems and fish swim easily. Conversely, there are jungle forests with masses of Eurasian milfoil that tangles swimmers and fishes alike. That introduce water plant survives under the lake’s winter ice cover, so in spring it has a head start, ahead of the native perennial underwater plants.  When Eurasian milfoil reaches the surface, it turns sideways and continues to grow horizontally, with floating stems. The shade causes the native plants to grow poorly, and after a few years will deplete their rootstocks, and they die out, leaving even more room for the milfoil.

Slope gradient and moisture gradient are related I forests, and we find oak-hickory forests on drier uplands and sugar maple – mixed forest in lower moister areas, followed by silver maple and willows growing at the edge of a lake or river.

Aquatic ecosystems are also affected by slope in the lakebed. Some plants, like annual Naiads, grow along the lakeshore in shallow water, and others grow in the slope midway to deeper water, even to 20 feet depths in Cedar Lake, where growth is limited from water pressure.

Although most aquatic plants can grow well in 3 – 6 feet of water, the water clarity in Cedar Lake allows sunlight to reach the lake bottom, so plants can grow in deeper areas. Like young spindly saplings that grow in the shade of older trees, the aquatic plant grow leaner, and the leaves and nodes become more elongated.

Another comparison of the forest and aquatic ecosystems is fire. Now, don’t ask if fire is a factor in aquatic ecosystems.

But “chemical fires” such as herbicides, have the same function.  They kill the plants, and their nutrients remain. In aquatic ecosystems, the nuked plants decompose and are reduced to their fertilizer nutrients. In forests, the fire turns the plants into ashes, a salt and mineral form of fertilizer.  So, the next growth of new trees has a well-nourished beginning, but the first succession is different, often not the same species of trees as were burned in the fire.

Unfortunately for aquatic systems, the first plants to recover and re-colonize are introduced curly Potamogeton and the Eurasian milfoil.  So, the pesticide treadmill persists because each treatment is a temporary fix, and the nutrients that produce bumper crops of plants have not been removed.

The wind affects both forest and aquatic ecosystems.  Did you notice that once in the forest, it is not as windy as the open fields?  Plants that are in deeper water also have the same benefit of being out of the wind driven waves. However, some plants like sago and water stargrass can grow in shallow water because they have thin needle leaves that ride the waves  that would tear other plants apart.

Both degraded forests and aquatic plant beds can be replanted, reseeded, and restored.  We have an Arbor Day, but we still do not have an aquatic day. Who will be our champion?

That is, of course, a major difference of values.  We have forest preserves, but not aquatic preserves unless they are within another ecosystem.  We have few high quality lakes  in Lake County to preserve. Most of our lakes lose sight of a secchi disk, a clear water measurement, at 4 feet. Cedar Lake’s water clarity has been due to mostly natural shorelines and a limited watershed, but several of the surrounding watersheds are contributing to lawn fertilizer run off, and new driveways and parking lots add pollutant –laden fast water run-off as well.

I am in favor of creating a new status for Cedar Lake as an endangered ecosystem, rather than just giving an endangered or threatened status to the plants and fish there.  In order to increase awareness of its value, I have talked to the DNR and the State Endangered Species Board about a bryozoan that Dr. Marsh and I found that lives only in Cedar Lake in Illinois. I recommended this small creature that is less than an inch long for a protective status. A rare sponge also grows only in Cedar Lake in Illinois.

In conclusion, terrestrial and aquatic ecosystems have similar structure, but different species.  Basic principles of ecology apply, including, “To save a species, save the ecosystem.”  For humans, to save a lake ecosystem requires an educated  awareness of that systems uniqueness. With that perception, perhaps we can preserve a lake as well as a forest.

Back

 copyright © 2014 Linda Curtis, botanist


Comments are closed.