Duckweed: Not Just for Ducks

By Lee Lattimer

The Wood­land Trail takes the vis­i­tor to a pond that was, until the con­struc­tion of a dike in 2008, a sea­son­al wet­land. This now year-round pond is home to many frogs, drag­on­flies, tur­tles, and ducks. The green growth that cov­ers the pond’s sur­face might be mis­tak­en for algae. It’s actu­al­ly duck­weed (Lem­na spp,), a high-pro­tein food source for water­fowl con­sid­ered to be the small­est flow­er­ing plant in the world. 

Duck­weed is a very small free-float­ing plant that con­sists of one to three fronds, with a root (or root hair) pro­trud­ing from each frond. It forms dense colonies in qui­et water, often includ­ing more than a sin­gle species. This co-min­gling of species is indi­cat­ed by dif­fer­ent shades of green and is evi­dent in the Wood­land Pond.

One curi­ous aspect of the duck­weed is its abil­i­ty to with­stand dry con­di­tions or declin­ing tem­per­a­tures. Late sum­mer flow­er­ing pro­duces starch-filled struc­tures more dense than the fronds. The plants then sink to the bot­tom, become buried in the mud, and rise to the sur­face in spring. Thus one might con­sid­er the duck­weed a migra­to­ry plant!

Duck­weed is being explored for many prac­ti­cal uses. One is a form of ethanol. Duck­weed can dou­ble its mass every few days. By manip­u­lat­ing con­di­tions dur­ing its grow­ing peri­od, its starch con­tent can be increased and lat­er bro­ken down and fer­ment­ed into ethanol. Since duck­weed can be har­vest­ed reg­u­lar­ly, some­times dai­ly, it can pro­duce up to four times the ethanol per acre as corn. The use of ethanol does not increase the amount of car­bon in the atmos­phere. Since plants take in car­bon (in the form of CO2 ) as they are grow­ing, the car­bon released dur­ing burn­ing results in a net bal­ance, while fos­sil fuels cause a car­bon increase as they release car­bon that was once stored in the earth.

Duck­weed can also be used as a water puri­fi­er. As it grows, it has a sub­stan­tial need for nutri­ents, espe­cial­ly phos­phates and nitro­gen and ammo­nia. As the plant uptakes these ele­ments, it adds them to its bio­mass. This process fil­ters and cleans sewage and waste water. If tox­ic pol­lu­tants are not present, the duck­weed can be skimmed off and used for fer­til­iz­er or to feed fish. It can also be used to feed ani­mals, but a reten­tion peri­od in clean water is nec­es­sary to ensure that the bio­mass is free of water-borne pathogens.

The duck­weed is tru­ly a small plant with big poten­tial appli­ca­tions, thus prov­ing the old adage that good things come in small packages.

Fall 2016

Volume 34 , Number 4

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