http://www.mobot.org/jwcross/duckweed/
The Charms of Duckweed
An introduction to the smallest flowering plants
The family of duckweeds (botanically, the Lemnaceae) are the smallest flowering plants. These plants grow floating in still or slow-moving fresh water around the globe, except in the coldest regions. The growth of these high-protein plants can be extremely rapid. Lemna is one of the best known of this group and has been the subject of much research. Researchers are using these plants to study basic plant development, plant biochemistry, photosynthesis, the toxicity of hazardous substances, and much more. Genetic engineers are cloning duckweed genes and modifying duckweeds to inexpensively produce pharmaceuticals. Environmental scientists are using duckweeds to remove unwanted substances from water. Aquaculturalists find them an inexpensive feed source for fish farming. ... ... Duckweed physiology, biochemistry & molecular biology Links to on-line research. Nutritional composition ...
http://www.geocities.com/RainForest/Canopy/3631/
Mr. Wastewater's Duckweed Application Page - by Louis Landesman
Duckweed - The Super Plant
Duckweed consists of 4 genera of monocot plants belonging to the family Lemnaceae. The Lemnaceae consist of 4 genera: Lemna, Spirodela, Wolffia and Wolffiella. Of these 4 genera Spirodela is the largest and Wolffiella is the smallest. Duckweed normally reproduces by budding (asexual reproduction) although it is capable of sexual reproduction. Duckweed may be the most promising plant for the twenty-first century for the following reasons:
Duckweed produces more protein per square meter than soybeans.
Duckweed is easier to harvest than algae or other aquatic plants.
Duckweed can be used to feed fish, poultry and cattle.
Duckweed can purify and concentrate nutrients from wastewater (sewage effluent).
Duckweed provides food for wildlife, especially waterfowl. ...
http://aquat1.ifas.ufl.edu/levapic.html
Aquatic, Wetland and Invasive Plant
Particulars and Photographs
University of Florida, Center for Aquatic and Invasive Plants
Lemna valdiviana
Small duckweed
Small duckweeds are floating plants. They are commonly found in still or sluggish waters. They often form large floating mats.
Small duckweeds are tiny (1/16 to 1/8 inch) green plants with shoe-shaped leaves. Each plant has two to several leaves joined at the base. A single root hangs beneath.
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http://www.ntrnet.net/~skilli/duckweed.htm
Duckweed Aquaculture
A NEW AQUATIC FARMING SYSTEM
FOR DEVELOPING COUNTRIES
Paul Skillicorn, William Spira
and William Journey
THE WORLD BANK
EMENA TECHNICAL DEPARTMENT
AGRICULTURE DIVISION
TECHNICAL WORKING PAPER
DUCKWEED AQUACULTURE
Nutritional value Fresh duckweed fronds contain 92 to 94 percent water. Fiber and ash content is higher and protein content lower in duckweed colonies with slow growth. The solid fraction of a wild colony of duckweed growing on nutrient-poor water typically ranges from 15 to 25 percent protein and from 15 to 30 percent fiber. Duckweed grown under ideal conditions and harvested regularly will have a fiber content of 5 to 15 percent and a protein content of 35 to 45 percent, depending on the species involved, as illustrated in figure 2 . [see next footnote] Data were obtained from duckweed colonies growing on a wastewater treatment lagoon and from a duckweed culture enriched with fertilizer.
Duckweed protein has higher concentrations of the essential amino acids, lysine and methionine, than most plant proteins and more closely resembles animal protein in that respect. Figure 3 [see next footnote] compares the lysine and methionine concentrations of proteins from several sources with the FAO standard recommended for human nutrition.
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Cultured duckweed also has high concentrations of trace minerals and pigments, particularly beta carotene and xanthophyll, that make duckweed meal an especially valuable supplement for poultry and other animal feeds. The total content of carotenoids in duckweed meal is 10 times higher than that in terrestrial plants; xanthophyll concentrations of over 1,000 parts per million (ppm) were documented in poultry feeding trials in Peru and are shown in figure 4 . [see next footnote] This is economically important because of the relatively high cost of the pigment supplement in poultry feed.
[Footnote: Source: Haustein et al, 1988.]
A monoculture of Nile tilapia and a polyculture of Chinese and Indian carp species were observed to feed readily on fresh duckweed in the Mirzapur experimental program. Utilizing duckweed in its fresh, green state as a fish feed minimizes handling and processing costs. The nutritional requirements of fish appear to be met completely in ponds receiving only fresh duckweed, despite the relatively dilute concentration of nutrients in the fresh plants. The protein content of duckweed is compared with several animal feed ingredients in figure 5 .
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Urea contains approximately 45 percent nitrogen and is the most commonly available and lowest cost nitrogenous fertilizer. Urea is the most efficient form of nitrogen supply to terrestrial crops, but its volatility in water and its elevating effect on pH makes it problematic for hydroponic applications. When applied to water with a pH above 7.0, nitrogen losses through ammonia volatility can often exceed 50 percent. For example, urea is applied to the duckweed crop in Bangladesh at the rate of 20 kilograms per hectare per day (kg/ha/day), which is equivalent to 9.0 kg/ha/day of nitrogen. Assuming a 50 percent loss before the crop is able to utilize the nitrogen, 4.5 kg/ha/day is then available to support growth. This is enough nitrogen to sustain a yield of at least 1,000 kg/ha/day of fresh duckweed and is adjusted seasonally as growth rates accelerate in moderate temperatures.
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A dense crop cover also reduces dissolved oxygen in the water column and suppresses nitrifying bacteria. An increase in anaerobic bacteria enhances the denitrification process and swings the nitrogen balance further in favor of ammonium over nitrate. This tends to lower pH as ammonium ions are assimilated by duckweed. The ability to form a mat over the surface of the water is one of the competitive advantages of duckweed. ...
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Duckweed-fed carp polyculture
Practical objectives The fish production methodology discussed in this study extends carp polyculture by: (1) making more efficient use of top-feeding carp varieties that live in the more highly oxygen-saturated surface zone of ponds; (2) making more efficient use of bottom-feeders to extract marginal nutrients from fish fecal matter before they can contribute to pond BOD; and (3) simplifying pond management to a single input -- duckweed, a floating biomass feed.
A duckweed-fed fish pond appears to provide a complete, balanced diet for those carp that consume it directly, while the feces of duckweed-feeding species, consumed directly by detritus feeders, or indirectly through fertilization of plankton and other natural food organisms, provide adequate food for remaining bottom and mid-feeding carp varieties.
Early results suggest that the duckweed carp polyculture methodology permits increases in carp polyculture production to between 10 and 15 metric tons/ha/year in non-aerated ponds, and it also increases the financial and economic viability of the production system.
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http://www.fishfarming.com/recirc.html
Facing the Economic Reality of Sustainable Commercial Aquaculture
What is the number one problem facing the rapid advancement of sustainable aquaculture? For many commercial operations, the answer is simple - bad economics. The hard reality is that, all too often, the bottom line gets in the way of the development of innovative solutions for sustainable aquaculture. But what if there were a system that could actually result in huge operational cost reductions from year one and greater profits on the bottom line? Sound too good to be true? Well then, perhaps you have never heard of duckweed.
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What is the Value of Duckweed to Sustainable Tilapia Culture?
Perhaps the most important feature of these little aquatic plants to freshwater fish culturists is that they are extremely efficient absorbers of ammonia, nitrate, phosphorous, potassium, magnesium, calcium, sodium, chlorine, boron and iron. In a properly designed water recirculation and purification system, duckweed can remove as much as 99% of the nutrients and dissolved solids in wastewater. Unquestionably, the potential contribution of duckweed to the advancement of sustainable freshwater aquaculture is enormous, yet surprisingly very little research has been done in this area.
The Integrated Tilapia & Duckweed Farming System
In the integrated tilapia and duckweed recirculating system, the fish and the waters of the tilapia growout ponds provide the nutrients upon which the duckweed will thrive. In turn, the duckweed removes unwanted nutrients and waste products from the system, converting the nutrients into plant biomass. This plant biomass, in turn, becomes a high protein food for the tilapias. While all this is going on, water within the integrated system is conserved and purified. The entire system is a natural and sustainable approach to aquaculture.
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page created November 19, 2001, Tucson, Arizona, USA