Lake Look: Change the Stance on Aquatic Plants

They touch the tips of swimmers’ toes, wrap around fish hooks, anchors, and paddles, and form underwater meadows near shorelines—native aquatic plants are ubiquitous in Lake Champlain Basin waterbodies. The roles these aquatic superstars play in lake ecosystems are often undervalued. It is not uncommon to hear native aquatic plants described as “yucky weeds”—let’s dispel this viewpoint! Grace Glynn, a wetland scientist with the Vermont-based engineering consulting firm DuBois & King reflects, “Our underwater flora is often overlooked, but these plants are like trees in a forest: a vital part of the system, providing the stage on which life plays out below the surface of our lakes.”

Native aquatic plants prevent pollution throughout the Basin’s waters: they absorb nutrients such as phosphorus (which fuel cyanobacteria blooms), trap and settle out suspended materials from upland runoff, and aid in erosion control by providing stability through their root systems. The feather-like leaves of northern watermilfoil and whorl-leaved watermilfoil trap detritus. Dense beds of dazzling blue and purple-flowered pickerelweed provide shoreline stabilization by buffering waves. Native aquatic plants serve as natural filters and foundations in the saturated world.

Water quality and the diversity of wildlife are maintained and improved by native aquatic plants. A cast of characters, from dragonflies and yellow perch to waterfowl and muskrats, rely on these plants for food, protection, and reproduction. Invertebrates—creatures lacking a backbone—attach to, feed from, and complete stages of their life cycle on aquatic plants. Snails graze on algae-coated plant surfaces, adult dragonflies and damselflies deposit eggs on plants, where they molt multiple times as larvae, and these insect larvae then hunt for prey among the plants or feed directly on plant tissue as they approach adulthood.

Fish depend on plants in myriad ways: as a food source, either by direct grazing or feeding on invertebrates that live amongst plants, as spawning habitat, and for protection from predators. The density and distribution of plants create optimal habitat for different species. For example, yellow perch need 25-50% plant cover and northern pike, more than 80%. Additionally, bass and northern pike use shallow vegetation zones for spawning.

Waterfowl rely on plants for food, shelter, and nesting material throughout the year. Canvasbacks, a diving duck, feed on the winter buds and stems of American eelgrass. The connection is so strong between the two organisms that their scientific names share the same Latin word: Vallisneria americana (American eelgrass) and Aythya valisneria (Canvasback). Great blue herons consume the nutlets (a small dry fruit) of softstem bulrush and a regional favorite, the common loon, uses aquatic plants to build their mounded nests along shorelines.

 

Semi-aquatic mammals, such as muskrats and beavers feed on native aquatic plants from leaf tip to tuber. Muskrats both consume the stems of northern wild rice and use them to build their lodges. Beavers and muskrats feed on the starchy tubers and leaves of common arrowhead.

With a better sense of how native aquatic plants provide value to wet places, we can dive into the physical distribution of these plants in their habitats. The littoral zone of lakes and ponds—the transition between land and water—is where native aquatic plants reside. The zone is divided into three categories based on a plant’s location within the water: emergent, floating-leaf, and submersed. The shallowest zone is the emergent plant community—from wet shores to knee-deep water. These plants can withstand fluctuations in water levels and stabilize shoreline sediments. They also have flexible reproductive strategies: if water levels are low, they reproduce using seeds that germinate on exposed moist substrates and if water levels are high, they reproduce by sending new shoots up from underground horizontal stems known as rhizomes. The middle zone, from knee-deep to about waist-deep and beyond, is the floating-leaf plant community. Extensive networks of rhizomes linked to long, flexible leaf stalks, ultimately support circular, leathery, floating leaves of plants like the yellow pond lily. Some plants in this category, such as common duckweed, are free-floating, meaning they have no attachment to lake bottom substrates. The last category, the submersed zone plant community, grows underwater, from shallow depths to many meters; their maximum depth of growth is limited by the availability of light.

“The aquatic life is not always easy for plants, who face challenges such as obtaining oxygen underwater. Seeing the ingenious ways they have adapted to life in the lake makes me appreciate them even more,” notes Glynn. Some native aquatic plants, like floating pondweed, have a thick cuticle (protective layer) on the surface of their leaves and stems, which offers protection and reduces the loss of moisture. Other leaves, like those of the submersed plant common waterweed, lack a cuticle, which aids in the exchange of gases between water and plant. If you cut a cross-section of some leaves or stems and observe the spongy tissue with a magnifying glass or hand lens, you can see a network of spaces that help leaves store gasses and stay afloat. There is no shortage of awe and wonder when it comes to the characteristics of underwater plant life.

Discussions of native aquatic plants merit a review of aquatic invasive species (AIS) too. AIS are a serious threat to the Basin’s communities; these plants impact the environment, the economy, and human health. Preventing the spread of AIS is essential to maintaining ecological integrity. AIS such as water chestnut negatively impact freshwater lakes, ponds, and rivers by shading out native species and competing for space. Before launching and before leaving a waterbody, clean, drain, and dry your boat and equipment. The Vermont Fish & Wildlife Department recommends the following spread prevention measures: “Drain all water from your boat, canoe, kayak, and other vessels and equipment used in the water. Clean off any mud and plant fragments and dispose of properly. Dry all damp areas of boats and vessels, such as live wells and bilges, with a towel and let air dry in the sun for at least five days before using in another waterbody. If this is not possible, rinse equipment with hot, high-pressure water.” Whether an individual, nonprofit, governmental agency, or commercial entity, we all play a role in preventing the spread of aquatic invasive species.

While people tend to lump all aquatic vegetation into the weed or invasive category, native plants are a key part of healthy water ecosystems and invasive plants a key threat. To help raise awareness of the vital roles native aquatic plants play in lake health, LCC is launching a native aquatic plants campaign! We will produce a suite of educational materials—identification cards, information sheets, and posters, as well as host formal and informal workshops to raise awareness about native aquatic plants and help people identify them. Our outreach will shed light on the form and function of a subset of native aquatic plants within the Lake Champlain Basin. Suzy Johnson, a New York-based LCC member, is excited to see the new materials: “Lake Champlain is such a valuable resource for our communities. It is critical for all who live and visit this pristine body of water to learn about its native plant species so that we can continue to conserve its natural resources which benefit us all—whether ecologically, economically or environmentally. This is particularly paramount now that climate change is an existential threat. Education is vital and this new native aquatic plants campaign will certainly contribute to raising awareness.”

If you’re interested in receiving updates about the project, email lcc@ lakechamplaincommittee.org. We extend a huge thank you to the Lake Champlain Basin Program (LCBP) and the New England Interstate Water Pollution Control Commission (NEIWPCC) for their funding support of this project.

Read other LCC pieces about native plants in and around the Lake Champlain Basin: Nature Note – Early Spring Wetland Greens, Nature Note – Woody What?, and Lake Look – Winter Shapes Lakeshore Grasslands.