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.
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.
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.
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.
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.
Producers: Primary producers are divided into three groups, periphyton, phytoplankton, and macrophytes.
Grows on substrates such as rock, mud, sand, leaf litter, etc.
Algae suspended on the water column.
Macrophytes:An aquatic plant that is easily visible.
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.
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.