Question

Lake ecosystems: In the water column of a lake are different zones with respect to oxygen and light . A. Describe the different zones and conditions briefly

B. Which of the following processes would you expect in which zone? (Note: some of the processes could take place in all zones, others might not happen at all.) (7 pts)

-Nitrification

-Anammox

-Denitrification

-Purple-sulfur bacteria

-Algae

-Nitrogen fixation

-Sulfate reduction

Answer 1

• Lake ecosystem are commonly lentic ecosystem. A typical lake has three major zones--a) littoral zone, b) limnetic zone and c)benthic zone
• Littoral zone is a zone near shore area and these regions receives direct sunlight, they contains greater variety of consumers than other zones , most of the aquatic plants (both rootes and also floating plants)are found here due to large amount of nutrient runoff. The major producers found here are rooted plants, phytoplanktons and algaes. The cynobacteria present over there can fix the nitrogen. Snails , insects and smaller fishes are also seen in this zone.
• limnetic zone--this zone includes all the areas beyond the littoral zone and they extends to the depth where rate of photosynthesis is equals to the rate of respiration (compensation level). The upper portion of limnetic zone is called Euphotic zone. This region receives direct sunlight , they have algae and other aquatic plants grown along with littoral zone. They also have dense fish level due to high oxygen content.
• below this Euphotic zone it is Profundal zone of limnetic zone where sunlight won't penetrate. All animals of profundal zones are adapted to withstand low oxygen concentration,
• next zone is Benthic zone--- they consists of organic sediments and soil,this zone is also known as digestive system of lake, the bacterias at the bottom zone bring most of the decomposition of organic matter and those sediments are mineralised and nitrogen and phoshorous are put back for circulation. Denitrification process, where fixed nitrogen is released back to atmosphere by denitrifying bacterias happens in this zone.Nirogen is released back also by anammox, whre the ammonium oxidising bateria oxidise ammonium into dinotrogen in anoxic condition by using nitrite also occurs here.