Duckweed Hypothesis

Duckweed is a small free floating aquatic perennial (Briggs, 1925). They are made up of a small leaf usually smaller than 5 mm, dependant on the species, which float on stagnant or slow moving water in groups of two or three, or individually (Gifford 2004). Lemna Minor was used in this experiment. They are usually seen in late spring to autumn, although some species remain green throughout the winter, while still more form a turion underwater in winter months and surface again in spring (Guha, 1997).

They reproduce either by flowering (which is rare), or by vegetative reproduction (Gifford 2004), which allows for rapid or exponential growth. A frond can produce 10-20 new fronds before it dies. Each new frond is an exact genetic clone of the

The Aim of this Project

The aim of this project is to study the factors that affect the growth of a duckweed population. This investigation can be useful for the purposes of mass duckweed production for biofuel or for water purification, or for the purpose of understanding how best to prevent the growth of duckweed in a pond, pool, lake or dam where it is unwanted.

The results of this project will also will also be helpful in the study of population ecology and the factors that influence the growth of any population e.g. the presence of resources in a habitat. This factor will be replicated by changing the amount of fertiliser each group of duckweed fronds receives. Other factors affecting population size include space available for expansion of the population and competition for resources (such as sunlight) and type of reproduction of the organism. These factors were represented by a limited space provided for the duckweed to grow in and by choosing a species of duckweed that reproduces vegetatively. By studying the duckweed population it will be possible to draw conclusions about its type of growth curve (logistical or exponential) and reasons for this, and also about the advantages and disadvantages of vegetative and sexual reproduction in

Vegetative reproduction is much faster than seeding and flowering, (which is rare in duckweed, but still possible (Hillman, 1961)) and in summer the “doubling times” for the plants can be as short as 2-3 days (Newman, 2013). Also, because each “daughter frond” is a genetic clone or copy of its mother, there is no difference between their genetic growth potential (Landolt et al, 1987)

Duckweed growth can be inhibited by animals that consume duckweed as part of their diet. These animals include fish like Grass Carp and koi fish, semi aquatic bird species like the mallard and wood ducks, as well as pond snails, crane flies, beavers and eastern painted turtles (Devaney, 2016).

Duckweed will grow better and faster in water whose surface is not disturbed. Disturbances like boat traffic, flowing water or wind can decrease the growth of duckweed (Newman, 2013). However, growing in undisturbed water sometimes causes the duckweed to pile up in layers, and often the bottom layer will be cut off from sunlight and will die because they were unable to photosynthesise (Newman, 2013). A thick cover of duckweed also prevents sunlight from reaching other organisms in the water and stops the growth of algae, which decreases carbon dioxide production from algal respiration, which can decrease the pH levels of the water (Newman, 2013). Complete coverage of the water will result in oxygen depletions that will kill