Lentic Systems

By: Simrun Saini

Ponds and Lakes


  • Lakes and ponds are known as lentic systems.
  • They are sets of inland freshwater habitats that are all around the earth.
  • They provide essential resources and habitats for aquatic and terrestrial organisms.
  • Lentic systems only take up about 3 percent of the earth's surface.
  • Human need for freshwater and human activities are threatening lentic systems.
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Size, Formation, and Succession


  • Lentic systems can be as small as a pond that fills up during rain events and then dries out or as large permanent bodies of water such as lakes.

  • There are many ways that lakes can be formed -

    • The geologic uplift of mountains can lead to depressions that fill with water to create lakes.

    • The subsidence of land along faults between tectonic plates has lead to the formation of deep rift lakes.

    • Lakes can form in the crater of an inactive volcano

    • The movement of glaciers can also lead to the formation of lakes and ponds.

    • Rivers can also lead to the formation of lakes.

    • Humans also have the ability to create lentic habitats.

  • Once the lake is formed, lentic systems grow through successional development in which the body of water is gradually transformed and brought into the terrestrial landscape.

  • Successional development is guided by sedimentation of inorganic and organic matter into the lentic system.

  • Sedimentation rates are influenced by the size and depth of the lentic system, the surrounding terrestrial landscape, climate, productivity, and decomposition.

  • Shallow ponds provide an excellent example of successional development.

Thermal Stratification

  • The structure of ponds and lakes are determined by factors such as turbulence, temperature, water clarity, habitat size, and water depth.

  • Thermal stratification occurs when the temperature increases and there isn't as much wind.

  • This produces layers in the water column, the upper warm-water epilimnion is separated from the lower cold-water hypolimnion by the thermocline.

  • Inverse stratification is when cold water rests over warm water because and occurs during winter.

Light Transmission

  • A critical factor when concerning lakes and ponds is light transmission, which is required for photosynthesis in primary producers.

  • Most of the time the water column is divided into the photic and aphotic zones.

  • In the photic zone the light penetration is greater than 1% and plants go through photosynthesis.

  • Opposite of that light penetration is less than 1% in the aphotic zone and respiration exceeds photosynthesis.

Nutrients Input and Cycling

  • In all ecosystems, nutrient inputs and cycling have important impacts on the structure and function of lentic systems.

  • Nutrients are transported into lentic systems via terrestrial run-off, groundwater flow, atmospheric deposition, rock weathering, and direct input from terrestrial systems.

  • The three most important nutrients are nitrogen, carbon, and phosphorus.

  • These are essential to all organisms.

  • Oligotrophic systems are characterized by low nutrient supply and low primary productivity while eutrophic systems are characterized by high nutrient supply and high primary productivity.

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Biotic Structure

There are three zones:


Littoral Zone: Much of the species diversity is concentrated in this zone near the shore.


Limnetic Zone: This is the zone of open water where light is still able to enter the water and support photosynthetic algae.


Benthic Zone:
The sediment at the bottom.

Food Webs

Producers: Primary producers are divided into three groups, periphyton, phytoplankton, and macrophytes.


Periphyton:

Grows on substrates such as rock, mud, sand, leaf litter, etc.


Phytoplankton:

Algae suspended on the water column.


Macrophytes:

An aquatic plant that is easily visible.


Consumers:


  • The consumer species that can be found in lentic habitats include worms, snails, amphibians, crustaceans, insects, reptiles, fish, and birds.

  • Herbivorous groups such as snails, amphibian larvae, and crustaceans play a major role in controlling primary productivity and algal blooms.

  • These groups are also a important resource for predators.

  • When primary producers, herbivores, and predators are all together in an environment, then a food web is formed where species interact both directly and indirectly with each other.
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Patterns in Species

  • There are many biotic and abiotic factors that change the increases in habitat areas, such as permanence, water acidity, and predation pressure.

  • All of these can play important roles in guiging species richness and community structure.

  • Physical environmental factors such as hydroperiod and water chemistry can limit the wideness of species distributions due to physiological constraints.

  • Factors such as competition and predation can limit the abundance of a species.

Threats to Lentic Ecosystems


  • The biodiversity of freshwater habitats is increasingly threatened by human activities, habitat loss, eutrophication, acidification, chemical contamination, global warming, and exotic species.

  • Problems include too much phosphorus in the Lentic systems and all the exotic species that are introduced into lakes and ponds threaten lentic systems.

  • Precautions are being taken to help solve these problems.