Why Oxygen is important for life?
Oxygen
is the one of the limiting factor for the life. Since most of the life forms
are aerobic except few, they inhibit in the water with high Oxygen content. Vertical
distribution of phytoplankton and fishes are influenced by the DO. So they are
restricted to surface layers of the mot water body. When Oxygen is reduced to
zero or limited aerobic life forms are replaced by anaerobic life.
Oxygen is essential for cellular respiration
of aerobic life. Some of anaerobic life
forms are inactive until Oxygen is available again such as Chirognomid larvae.
Animals which have Hemoglobin in the blood can tolerate for low Oxygen level
because hemoglobin has ability to grab, store and transport four Oxygen
molecules once into inner cells in the body. Ex: Tubifex sp
Variation in the
lentic ecosystem
Lentic
ecosystems are the standing water bodies such as lakes, ponds, marshes and
swamps. Dissolved Oxygen content (DO) is influenced by the temperature,
community respiration and decomposition. Amount of Oxygen is determined by the
diffusion, water circulation (water mixing) and photosynthesis. The rate of
diffusion of Oxygen in the lentic ecosystem is less compare to the
atmosphere. Water circulation determines
the vertical Oxygen distribution throughout the water column.
Photosynthesis is varying
according to the depth as well as time of the day. Therefore amount of Oxygen produced by
photosynthesis is also followed by such fluctuations and variations. In the
morning photosynthesis and DO is less due to the less solar intensity. From
morning to noon, photosynthesis and DO are high due to the increasing solar
intensity. The highest DO and photosynthesis is recorded in the noon due to the
maximum solar intensity. DO and photosynthesis are aging decreasing from noon
to evening due to the decreasing solar intensity.
When consider the variation of DO according to the depth,
maximum DO is reported slight below the water surface because photosynthesis is
limited in the surface due to the photo-inhibition of photosynthetic organisms.
Photosynthesis is reduced gradually due
to the decreasing light penetration. But community respiration is high. So
Oxygen is largely consumed by organisms.
At
the bottom of the deep lakes, Oxygen availability is limited or zero because
photosynthesis is not taken place due to the absence of light. Community
respiration is also high. But large amount of Oxygen is consumed by decomposing
organism. Therefore bottom of the deep lake does not support aerobic life.
But
in the case of shallow lakes, DO is high in even bottom due the high light
penetration. Plant growth can be found at the bottom. Therefore large amount of
oxygen is produced. Although decomposition is carried out, DO does not become
limited due to the high productivity. Therefore bottom of the shallow lake
supports the aerobic life.
When
the solar intensity is increasing in the absence of strong winds, a temperature
gradient is created from top to the bottom. Thermociline acts as a density
barrier between warm surface water and clod bottom water. It causes water
stratification and prevents water mixing. Therefore DO on the surface layer is
not transported to bottom layer. So bottom layer interfere with limited Oxygen
supply and cannot support aerobic life anymore. But suddenly wind action can
break the stratification and start the water mixing.
Doing
the some period of the year, surface temperature falls, bottom temperature and
surface temperature become similar .Therefore since there is no density
barrier, water starts to missing. Oxygen availability is high throughout the
water column. It supports aerobic life.
Solubility of Oxygen in the water is directly affected by the
water temperature. If the water temperature is high, it reduces the Oxygen
solubility in the water. Low
temperatures increase the Oxygen solubility.
Variation in loctic ecosystem
Loctic
ecosystems are moving water bodies such as waterfalls and rivers. Since lotic
water bodies are shallow compare to the lentic water bodies, DO is high
throughout the water column because plant growth can be found due to the high
light penetration. Turbulence increases the DO.
Stratification is rarely occurred in lotic systems, water circulation is
continuously carried out. Therefore availability o Oxygen throughout the water
column is high.
Variation
of DO is taken place from upper reaches to lower reaches. DO is near saturation
in upper reaches due to the fat river flow and turbulence. DO is limited is less
in lower reaches due to the low rate of photosynthesis because sedminets tend
to deposit due to slow flow rate. It restricts the light penetration.
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