Not Just Slimy and Green: The Slough’s Aquatic Plant Scene
Blog post by Thomas Meinzen, Program Associate
Have you noticed how green the Columbia Slough is this time of year? The long, sunny days and warm, nutrient-rich water makes late summer an ideal time for algae and plants to thrive in the slow-moving Slough. These thick mats of aquatic vegetation can pose a serious impediment to paddlers, and even bigger consequences for water management and watershed health. But there’s more to these masses of green than meets the eye. The Slough is home to a fascinating variety of aquatic plants, including important indigenous First Foods, trap-door carnivores, and tiny water-filtering weeds. Learn more about a few species to look for on your next visit to the Slough:
Duckweed (Lemma minor) is one of the world’s smallest flowering plants!
Floating Filters: Duckweed (Lemma minor)
Duckweed is a common plant found on still and slow-moving water worldwide. It has tiny buoyant leaves like miniature lily pads, each connected to a sticky floating root. These sticky roots attach to birds’ feathers and feet as they leave the water, helping duckweed move from one body of water to another. Once on a pond or slough, duckweed typically spreads by dividing its leaves to create new plants, although in rare occasions it can produce tiny flowers and millimeter-long seeds. Duckweed has been shown to effectively take up heavy metals like lead and arsenic out of the water, as well as organic pollutants like pharmaceuticals, making it a valuable plant for bioremediation in urban watersheds like ours. Next time you see a patch of duckweed on the Slough, think of it as a hundred little water filters, each freckle of green making our watershed a little cleaner!
The Aquarium Classic: Elodea (Elodea canadensis)
Elodea is an abundant aquatic plant in the Slough, and one that can frustrate summer paddlers as they navigate through its long, heavy strands. Elodea’s oblong, translucent green leaves are arranged around the stem in groups (whorls) of three; you may recognize it as a common plant in many aquariums. Although a troublesome, introduced species in many parts of the world, Elodea is native to North America. Rooting in the soil at the Slough bottom, Elodea lives entirely underwater except for its small white flowers, which float on the water’s surface, allowing both wind and water to help spread its pollen.
A paddler plucks a strand of curlyleaf pondweed from the Slough near Whitaker Ponds.
Lasagna of the Slough: Curlyleaf Pondweed (Potamogeton crispus)
Curlyleaf pondweed is an invasive submerged aquatic plant introduced from Eurasia. It can be distinguished from the several species of native pondweeds in the Slough by its wavy leaves, which look a lot like green lasagna. Like Elodea, curlyleaf pondweed roots into the soil at the water’s bottom and can form dense, thick mats when nutrients and sunlight are abundant. These mats can pose serious challenges for paddlers and water managers.
Bladderworts have snapdragon-like flowers and sophisticated traps attached to their stems.
The Slough Speed Trap: Common Bladderwort (Utricularia macrorhiza)
Bladderwort is the Slough’s top plant predator! That’s right, this unique free-floating aquatic plant is a carnivore, supplementing its diet of sunlight with small animals, including mosquito and damselfly larvae, water fleas, and other aquatic invertebrates. Bladderwort has small pouches or bladders with sensitive hairs. When animals touch these hairs, they trigger the bladder’s “trap door” to open suddenly, sucking water and the animal inside. The bladder then snaps shut around the animal and consumes it with a concoction of digestive enzymes. Bladderworts can open and close their trap doors in less than a millisecond—the fastest trapping mechanism of any plant!
Enthusiastic Ancestors: Green Algae
Although algae shares many characteristics with plants, including photosynthesis and the green pigment chlorophyll, these simple organisms lack distinct parts, or tissues, and are much simpler than plants. Most scientists think that plants evolved many millions of years ago from green algae, so you can think of algae as the living ancestors of plants. Like aquatic plants, algae thrive on sunlight and nutrients such as nitrogen and potassium, and overgrowth can pose many problems for our waterways. When fertilizers and chemicals run off into the Slough, algae grows very quickly, or “blooms.” After this bloom of algae dies, the bacteria that decompose it use up most of the oxygen in the water, causing fish and other aquatic life to die for lack of oxygen. This process is called eutrophication, and it’s one reason why we should avoid using large amounts of fertilizers and chemicals in landscaping around businesses and on our lawns and gardens.
A Feathery Foe: Eurasian Watermilfoil (Myriophyllum spicatum)
This feathery, fast-growing invasive plant is one of the big bad beasts of the Slough. We’ll be focusing our next aquatic plant blog post on this species and how water management and habitat restoration can help stop its growth and keep our Slough healthy and full of biodiversity!
