Water zonation

it includes; fresh and marine water zonation.

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Water Zonation
Zonation refers to the patterns that are observed in a community over a distance, based on
the distinct fauna and flora found along the area. Although the different zones are characterized
by the dominant species inhabiting them, the separation of zones isn’t always a clear straight
line, but instead there is some overlapping of species, particularly where the zones meet.
Sometimes, however, the overlapping can disappear or be very small if one species completely
out-competes the others by predation or competition over resources, and we can see clear-cut
zonation.
The presence or abundance of a species in an area depends on different biotic factors, such as
altitude, temperature, and salinity, as well abiotic factors, like predation and competition for food
and space. This results in zonation, since every species is adapted to surviving specific
environmental conditions that are not found everywhere. For instance, as we go up a mountain
and the altitude changes, the species of plants and animals we find also change, depending on the
altitude that they can tolerate to exist at.
FRESH WATER ZONATION
Freshwater community consists of an array of organisms depending on the physico-chemical and
biological characteristics of the freshwater environment.
Freshwater habitats are divided into two major categories, lotic (lotus = washed, or running
water), and lentic (lenis = calm, or standing water) habitats.
Lotic habitats are those existing in relatively fast running streams, springs, rivers and brooks.
Lentic habitats are represented by the lakes, ponds, and swamps.
The above classification of the freshwater environments is based on two conditions: currents and
the ratio of the depth to surface area. Since lakes and ponds often contain currents or at least
wave action and since streams often harbor quiet pools or calm backwaters, the difference
between lotic and lentic waters is not very precise. However, temperature, light, currents, amount

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of respiratory gases, and concentration of biogenic salts are important limiting factors
influencing the organisms of all freshwater habitats.













A. Lentic Community
Lentic waters are generally divided into three zones or sub-habitats:
a. Littoral
b. Limnetic
c. pro-fundal
A small pond may consist entirely of littoral zone. However, a deep lake with an abruptly
sloping basin may possess an extremely reduced littoral zone.
a. The Littoral Zone:
It is the shore area of the lake or pond. The littoral zone consists of the area from the dry
land sloping to the open water and can be very narrow or very wide. Typically oligotrophic or

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young ponds have narrow littoral zones due to their steep sides and eutrophic or old ponds have
wide littoral zones due to their gently sloping shoreline and sides. The littoral zone is shallow
and gets a lot of nutrients from runoff and non-point source pollution. Therefore, it typically has
an abundance of aquatic plant and algae growth. Some other common inhabitants of the littoral
zone are cattails, reeds, crawfish, snails, insects, zooplankton, and small fish.

b. The Limnetic Zone:
It was generally classified as the open water area of the lake or pond. This is a much
larger section of water in oligotrophic or younger ponds and lakes than it is in eutrophic or older
bodies of water. Within the limnetic zone are two separate sections. The upper portion of the
limnetic zone near the surface of the water is the Euphotic Zone or Epilimnion (warm water
region). This is the portion of water that receives sunlight. The zone ends where the sunlight fails
to penetrate the water. The euphotic zone is where algae and other aquatic plants thrive (along
with the littoral zone). Also this is the typical area of dense fish populations because oxygen
levels are typically higher due to contact with the air.

c. The Profundal Zone or Hypolimnion (cold water region):
Below the euphotic zone is. The profundal zone is located below the thermocline where
the sunlight does not penetrate. Again, the size of this zone depends on the age and water clarity
of the pond or lake. The profundal zone typically has lower fish populations because of the lack
of oxygen during many parts of the year.

B. Benthic Zone
This is the final zone. This is the bottom of the pond or lake and consists of organic
sediments and soil. The benthic zone is the pond or lakes digestive system. This is where bacteria
decompose organic matter from dead algae, aquatic plants, and fish and animal waste. The more
organic matter in the pond, the more decomposition taking place. Decomposition can take place
either aerobically (in the presence of oxygen) or anaerobically (without oxygen). It is much
better to have aerobic decomposition because it is a faster process and the byproducts are easier
to handle. The benthic zone increases as the pond or lake ages.

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MARINE WATER ZONATION
 Oceans – bounty of wealth, opportunity and abundance.
 Food, energy, water, minerals, pharmaceuticals. International trade highway, climate
stabilizer.
 71% of the earth’s surface with an average depth of 3.8 km. and a volume of 1370 x 106
km3.
 178,000 marine species, 34 phyla.

Oceans - great mass of salt water covering the earth disc. Ancient formations separated from
each other by the continents. Antarctic, Arctic, Atlantic, Pacific and Indian.
Seas - varying area. Separated from the oceans by island chains, or by submarine ridges of sea
floor. Special characteristics due to separation from oceans and difference in mixing with ocean
water mass. Local climate also influences their uniqueness. North sea, Mediterranean sea,
Caspian sea, Arabian sea, Black sea, Red sea, Caribbean sea, Baltic sea etc
Vertical and horizontal divisions (realms).

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A. Pelagic realm

 Entire area of open water. Pelagic organisms occupy the area away from the bottom.
Have many zones.
 Two horizontal zones;
a. Neritic - overlies the continental shelves
b. Oceanic - other open waters
 Two vertical zones based on light penetration;
a. photic or euphotic - with abundant sunlight (depth varies with turbidity, ~ 100 -
200m lower boundary). Area of primary productivity. Synonymous with epipelagic
zone.
b. Aphotic zone – the permanently dark water mass below the photic zone. (a disphotic
transition zone b/w aphotic and photic is suggested by some marine biologists).
Disphotic zone receives sunlight not enough for photosynthesis. Synonymous with
mesopelagic (1000m lower boundary).

 Pelagic part of aphotic zone-Vertical divisions – viz .
a. Mesopelagic - (10oC , isotherm is its lower boundary in tropics or 700-1000m)
b. Bathypelagic – waters b/w 10 and 4 degree isotherm (b/w 700-1000 to 2000 -
4000m)
c. Abyssal pelagic - waters b/w 4000 – 6000m depth.
d. Hadal pelagic – open waters of deep oceanic trenches b/w 6000 & 10000m

B. Benthic realm
Organisms and zones of the ocean/sea bottom. Benthic realm - divided vertically into;
a. bathyal benthic zone - from continental slope (up to 4000m)
b. Abyssal benthic zone - encompassing broad plains (4000 – 6000m)
c. hadal benthic (6000 & 10000m).
d. Sublittoral or shelf zone - Benthic zone below the neritic pelagic zone on the
continental shelf. Illuminated and richly populated supporting several communities
like sea grass beds, kelp forests and coral reefs.

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REFERANCES:
https://biologydictionary.net/zonation/
https://www.biologydiscussion.com/biotic-community/3-major-zones-of-a-
freshwater-lake-with-diagram/4710
https://kascomarine.com/blog/pond-lake-zone-identification/
http://mesasmabi.com/wp-content/uploads/2018/12/ZONATION-OF-MARINE-
ENVIRONMENT.pdf