FRESH WATER ECOSYSTEM

 FRESHWATER ECOSYSTEM

·       Freshwater ecosystem refers to the water found in Lakes, Ponds, Streams and any other body of water other than the sea.

·       Freshwater has less than one gram per liter of Dissolved solids, mainly Salts of which Sodium chloride. Plants and Animals living in freshwater would not usually be able to live in Salt water, because their bodies are adapted to a low-salt content.

·       Freshwater ecosystems are vulnerable to water pollution that arises from a range of human activities. They are also used as water supplies for human use.

·       The study of Freshwater Biology is called as Limnology.

·       Fresh water is not the same as potable water (or drinking water). Much of the earth's fresh water (on the surface and groundwater) is unsuitable for drinking without some treatment. Fresh water can easily become polluted by human activities or due to naturally occurring processes, such as erosion.

·       The place where Fresh and Salt-water meet is called an Estuary. Estuaries are usually shallow, sunlight can reach all levels of the water.

LIFE IN FRESHWATER ECOSYSTEM

·       A wide range of Plants, Animals and Microbes are found in Freshwater ecosystems.

·       Freshwater ecosystem supports a range of plant and animal ecosystems whose composition is shaped by the availability of Food, Oxygen, Temperature and Sunlight.

·       The smallest are the microscopic plants and animals known as Phytoplankton and Zooplankton, which form the bottom layer of freshwater food chains.

·       There are also many freshwater Invertebrates including Worms and Insects.

·       Among the freshwater Vertebrates, Amphibians, such as Frogs, live on land and water, while Fish are purely water-dwelling.

·       Many species of birds, such as kingfishers and ducks, live on or near freshwater.

CATEGORIES OF FRESHWATER ECOSYSTEM AND WATER ZONATIONS

·       Freshwater habitats are divided into two major categories,

1)    Lotic (lotus = washed, or running water) habitats

2)    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.

 ·       Lentic waters are generally divided into four zones or sub-habitats:

a)     Littoral zone

b)    Limnetic zone

c)     Pro-fundal zone

d)    Benthic zone

a) Littoral Zone

·       The Littoral zone is the near Shore area where Sunlight penetrates all the way to the sediment and allows aquatic plants to grow.

·       Nutrient-rich zone.

·       Light levels of about 1 % or less of surface values usually define this depth. The 1 % light level also defines the Euphotic zone of the lake, which is the layer from the surface down to the depth where light levels become too low for Photosynthesizers.

·       Aquatic life is diverse and abundant.

·       Within the Littoral zone, Producers are of two main types: Rooted or Benthic plants (Rooted in the Mud underwater) and Phytoplankton (Plant plankton) or Floating green plants (Pond Lillies and Algae).

·       The Consumers in Littoral zone includes Zooplankton, Flat worms, Snails, Insect larvae, Frogs, Fish and Turtles.

b) Limnetic zone

·       Middle surface region where Phytoplankton and Zooplankton live and produce.

·       Layer of open water where photosynthesis can occur and light does not penetrate to the bottom.

·       Most photosynthesis occurs in this part of the lake.

·       Many fish swim freely in this zone.

·       The Limnetic zone is shallower in turbid water than in clear and is a more prominent feature of lakes than of ponds.

·       Life in the Limnetic zone is dominated by Floating microorganisms (Plankton) and Actively swimming animals (Nekton).  

·       The Producers in this ecosystem are Planktonic Algae.

·       The Primary consumers include such Animals as microscopic crustaceans and Rotifers - Zooplankton.

·       The Secondary consumers are Swimming Insects and Fish. These nekton usually move freely between the littoral and Limnetic zones.

c) Profundal zone or Aphotic zone

·       Deeper open waters away from shore, colder and darker zone.

·       Located below the range of light penetration – so little to no light.

·       Temperatures typically colder (because sunlight does not penetrate).

·       Fish adapted to live in darker, cooler water live here.

·       The sediments underlying the profundal zone also support a large population of Bacteria and Fungi. These decomposers break down the organic matter reaching them, releasing inorganic nutrients for recycling.

d) Benthic zone

·       Bottom of a pond or lake, predominately inhabited by decomposers, insect larvae, and clams.

·       Sometimes little to no light, depending on the depth.

·       Bacteria live here to decompose dead plants and animals that drift down from the land and water above.

·       Fish adapted to live in darker, cooler water also live here.

FRESHWATER ECOSYSTEM THREATS

·       Many human activities threaten the health of freshwater ecosystems.

·       Acid Rain created from Sulfur (S) and Nitrogen oxide (NO) emissions turns many Lakes and Streams acidic, leaving them unable to support various Fish species.

·       The building of Dams to create Hydro-electric power plants blocks the routes of migratory Fish.

·       Deforestation adds silt to a stream or river and slows it down, which may increase flooding. Common chemical stresses on freshwater ecosystem health include Acidification, Eutrophication and Copper and pesticide contamination