“The amount of contamination that plants can remove from aquatic environments depends on the amount and type of pollution, the plant species used, and the size of the floating wetlands.”

                                ~ Susan Cosier

When I was a kid in Texas, we used to go out to farms and ranches owned by our dad’s clients. My brother and I were often left to our own devices while our folks visited with the adults. We could wander through the corrals and barn and usually ended up at a nearby “stock tank” — a manmade pond for watering the cattle.

Older “tanks” were surrounded by vegetation except for the areas where the cattle came to drink (and deposited most of their poop). The rest was just packed dirt and mud. If you are unfamiliar with them, you may not know that cattle are not particularly neat or tidy. In fact, they will poop pretty much anywhere, including in their water source. Consequently, most tanks were murky and, well, untidy. However, for a couple of kids wandering around a hot, dry, dusty ranch, it was very attractive.

Usually the tanks were shallow, particularly around the edge, so wading was mostly preferred. I’ll also note that the water was not the purest, so there was little incentive to dunk your head. However, the cooling effect of being in the water was often worth any unpleasantness.

There was a natural response to the nutrient nature of the water, though. With plenty of sunshine, algae grew prolifically. In particular, what we called duckweed was rampant. Now, this duckweed is long and stringy, and grows in bunches. Rooted in the bottom of the pond, it reached to the surface for the sunlight. (I may have noted that most of these ponds were kinda shallow.)

Wading into the ponds often required pushing through masses of duckweed to find a so-called clear spot. We had fished some of these tanks, and knew that various creatures could be found there — fish, crawdads, turtles and (occasionally) snakes. (I admit that snakes terrify me. You may not know that Texas is home to all of North America’s poisonous snakes, but I do, and we often encountered one on our country adventures.)

My older brother was sensitive to my concerns and took great delight in scaring me at any opportunity. I remember a conversation about water moccasins as we were wading through the duckweed. I contended that they wouldn’t bite you under water (where you couldn’t see them). He countered with a question — what do water moccasins eat? He let me ponder this as we were waist deep in murky water and duckweed. I finally realized that they ate fish, catching them under water. So much for my peace of mind …

While we never did see water moccasins while we were in the water, another hazard did present itself. As you waded through the duckweed, it could wrap itself around your arms or legs. My brother quickly identified the weaponization possibilities, and would wrap strands around an arm, push it together into a ball, then sling at his unwary younger brother. I can tell you that the experience of being hit in the head with a wet, muddy, stringy ball of duckweed is nowhere as pleasant as it sounds.

Of course, that led to retaliation and the duckweed wars could go on for a while. Uprooting it stirred up the mud from the bottom, so the battlefield quickly became roiled with mud and weed. Usually I was engaged enough to forget about my fear of underwater attacks by water moccasins while in the throes of battle. 

Somehow, I came to realize that the farm ponds with the clearest water were the ones with the most duckweed. In spite of cow intrusions, the duckweed patches seemed to lead to clear areas (except where it had been roiled by the duckweed wars).

It’s no secret that aquatic plants serve to remove nutrients and pollutants from the water, just as the duckweed did for the farm ponds. Journalist Susan Cosier writes about the use of floating vegetation to remove water pollutants, “Like natural wetlands, floating versions provide a range of ecosystem services. They filter sediment and contaminants from stormwater, and laboratory experiments show that some plants have the ability to lock up some chemicals and metals found in acid mine drainage. These systems take up excess agricultural nutrients that can lead to algal blooms and dead zones, and recent research suggests they could be used to reduce manmade contaminants that persist in the environment.”

The duckweed on the farm ponds would form a mat at the surface. The idea of floating mats of vegetation has the advantage of less underwater impediment, making the conditions better for various aquatic creatures, which is very important for habitat restoration. (It also reduces the availability of ammo for duckweed wars.)

“What we’re trying to create is this model urban waterfront. We want other cities to know that there are ways to incorporate natural habitat, to bring back the ecosystem services that were lost because of industrial development.”

                                                ~ Charmaine Dahlenburg

Additional information:

Susan Cosier, How Floating Wetlands Are Helping to Clean Up Urban Waters, November 22, 2022, YaleEnvironment360