Plantlet The Blogging Platform of Department of Botany, University of Dhaka
Biomass
Biomass is the weight of living matter per unit area at a given time at a given place.
Future of Biomass
In aquatic ecosystem, produced biomass may either enter into food chain or undergoes destruction.
In lentic waters, nutrients present in biomass get recycled, except sedimentation of small fraction. In lotic water organic and inorganic substances and associated particles to them transported from one place to another and finally brought to sea.
For releasing nutrients from body of dead organisms and from other sources of organic matter, bacterial action is necessary. Roughly 40% of all organisms present in aquatic habitats decomposed by bacteria. Plankton undergoes decomposition quickly.
Release rate of organic matter as percentage of total organic content present in zooplankton.
- 21% is released immediately.
- 36% after four hours.
- 50% after one day.
- 75% after 10 days but with relatively slow rate.
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Release rate of P (as percentage of total P present) from zooplankton into water.
- 50% after four hours of their death
- 70% within one day
Release rate of P (as percentage of total P present) from phytoplankton into water.
- 25-75% within few hours of their death.
Release rate of P (as percentage of total P present) from detritus.
- 30-40% P is up-taken by bacteria after recycling via autolytic processes.
Two main ways of decomposition of organic matter.
- Autolysis
- Bacterial degradation
Autolysis
At senescence (loss of a cell’s power of division and growth), cells of organisms become weaker, loss control over cell membrane and secretes autolytic enzymes.
It dissolves different parts of organism via biochemical reactions and helps releasing cellular content into environment.
However release rate varies according to different organism.
| Organism/community | Percentage of total organic content |
| Tubifex sp. | 68 |
| Zooplanktonkton community (75% Cladocera order) | 57 |
| Zooplankton community (86% Copepods) | 35 |
| Microalgae (Haematococcus pluvialis) | 33 |
| Submerged aquatic plant, leaf of Callitriche hamulata | 16 |
| Diatom, Melosira sp. | 15 |
Bacterial Decomposition
Usually dead bodies of organisms are attacked by bacteria within 24 hours, more probably it starts some time earlier in aquatic habitats. Planktonic organisms after losing their cellular control, starts sinking to depth.
In Lake Constance, Germany diatom takes 60 days to reach 200 m depth.
In that lake 85% of total primary productivity recycled in euphotic zone and 15% reaches to bottom.
In shallow lake, Plusssee within 5 m depth 70.0-93.1% organic matter get recycled.
Probably after releasing from dead organisms dissolved organic matter uptaken by bacteria and reaches to top consumer by passing phytoplankton primary production.
Bacteria → Zooplankton → Fish
Important groups of aquatic bacteria
Depending upon (i) sources of energy, (ii) electron donor, (iii) sources of carbon, aquatic bacteria can be grouped under three categories.
- Chemoorganotrophic
- Chemolithotrophic
- Photolithotrophic
Chemoorganotrophic
Organic matters are electron donors; they could be aerobic and anaerobic carbon synthesizer and sulfur synthesizer.
Aerobic Carbon Consumer
List of bacteria responsible for aerobic decomposition of carbohydrate and hydrocarbon in aquatic habitats.
| Organic matter | Decomposing bacteria |
| Cellulose | Cytophaga, Sporocytophaga |
| Lignin | Pseudomonas sp. |
| Chitin | Achromobacter, Flavobacterium |
| Benzene | Pseudomonas aeruginosa, Micrococcus sphaerutilus |
| Phenol | Pseudomonas rathonis, Vibrio cuneata |
| Petrol | Pseudomonas aeruginosa, P. fluorescens |
| Crude oil | Pseudomonas aeruginosa, Achrobacter |
Anaerobic carbon consumer
At anaerobicity, bacteria use oxygen from NO2–, NO3– and SO43- to reduce organic matter.
Some facultative anaerobs, which can consume free molecular oxygen as well as oxygen from NO3– e.g., Pseudomonas aeruginosa, P. denitrificans, etc.
Aerobic: C6H12O6 +6O2→6CO2+6H2O, ΔG = -2870 kJ
Anaerobic: 5C6H12O6 + 24KNO3→12N2 + 24KHCO3 + 6CO2 + 18H2O, ΔG = -2700 kJ
Anaerobic reactions of carbohydrate decomposition yields molecular nitrogen, used in sewage treatment plant for removing nitrogen.
Similarly Desulfovibrio disulfuricans can also uptake oxygen from sulfate.
Bacterial spp. available in aquatic habitats to convert organic compounds containing nitrogen, sulfur, hydrogen sulfide, methane, iron, manganese, etc. anaerobically are:
List of other bacteria associated with this process
| Organic matter | Decomposing bacteria |
| Cellulose | Bacillus cellulasae dissolvens, Clostridium cellobioparus |
| Pectin | Cytophaga, Flvobacterium, Pseudomonas, Bacillus, Erwinia |
| Chitin | Bacterium chitinovorum |
Source:
- Class lectures of Professor M Khondker Moniruzzaman, University of Dhaka
(Many of the points here are paraphrased and also taken from some sources like internet and books. If any misquote, mistake or misinformation is found, only the author is to blame.)
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