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Life in Freshwater

Primary Production and Detritus

Primary production is the phrase used to describe the organisms which carry out autotrophic nutrition, mainly photosynthesis although chemosynthesis is possible. Light is used by phototrophs to split water molecules and combine the hydrogen with carbon dioxide within chloroplasts to generate carbohydrates. With the inclusion of other simple nutrients, like nitrates, sulphates and phosphates, amino acids can be formed. Primary production occurs in the green plants and various types of algae which occur in the pond. The large plants are called macrophytes whilst the more microscopic algae and attached diatoms are microphytes.

All of this material that is produced is potential food for the herbivores.

Although there may be a considerable amount of plant material growing the main source of food may not be to graze these plants but to eat the dead material. Decaying organic matter may have more nutrients that an animal can utilize than a living one. For example material like lignin and cellulose contain important elements for animals but they cannot make use of them as they cannot digest it. Conditioning of leaf material for animals to consume is therefore very important. The table below attempts to breakdown (excuse the pun!) this process into the sequence of events.

Various shortened terms are used both here and elsewhere in freshwater, i.e.

DOM is Dissolved Organic Matter

FPOM is Fine Particulate Matter

CPOM is Coarse Particulate Matter

 

Time (Days)

Stages

Weight Loss

Process

1

Leaf Arrives

0

Gets wet

3

Leaf saturates with water

5-25%

Soluble material leaches out of the leaf to become DOM

10

Microbes colonise the leaf which has become soft and damaged by possible movement

5%

Respiration of material by microbes begin to mineralize to CO2

20-50

Invertebrates colonise and provide physical breakdown while microbes continue to chemically breakdown cells

20-35%

The microbes create an increase in the protein content available; ideal for animals that are colonizing and eating the leaf

100-250

The leaf is converted to FPOM

15-25%

Animals continue to feed and release faeces, thus breaking the organic matter into FPOM and

The FPOM produced is detritus suitable for filter feeders to consume

 

See also Primary Production in Rivers

 


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