Did you ever feed the ducks that live by the pond when you were younger? Ponds historically had a range of uses by people, from water for agriculture and communities, providing habitat for local and migrating species to a decorative feature for the garden. Compared to some ecosystems such as the desert biome, the freshwater pond ecosystem is a small-scale ecosystem that is found in many places across the UK. However, its size doesn't mean it is less valuable or should be overlooked. Let's look closer into what is happening inside and around the pond, the relationship that the inhabitants have with each other and the environment, and the threats to the ecosystem.
Pond ecosystem definition
So, how do we define a pond ecosystem? The pond ecosystem is an aquatic ecosystem that exists in an enclosed small body of water, shallow enough to have light penetrating through the water, which supports various types of aquatic plants and animals. The abiotic and biotic components create a unique environment for the pond ecosystem to thrive.
Read the article Ecosystems as it touches upon how ecosystems work and will be helpful to understand the basic components of an ecosystem.
Freshwater pond ecosystem
The freshwater pond ecosystem consists of the areas of the pond bottom, mid-water, pond surface, pond margin, and above the pond system. Let's look into each component and how they are interrelated in the ecosystem.
At the pond bottom, there are low levels of oxygen and light, and as organic matter falls to the bottom of the pond, it is home to decomposers and scavengers.
Decomposers are organisms that break down organic material, such as dead animals, plants, and faeces to be recycled and put back into the soil as nutrients. Examples would be aquatic worms, bacteria, and fungi.
Scavengers feed on decaying animals and plants, such as rat-tailed maggots and water-scavenger beetles.
The mid-water is where the fish and the aquatic insects live, and food is found on both the surface of the pond and the bottom of the pond. Animals living here breathe through their skins and gills. Some examples include the stickleback fish and dragonfly nymphs. On the pond surface, there is a lot of light and oxygen, and the animals found here breathe through lungs, gills, and skin such as ducks, tadpoles, and midge larvae. In the pond margin or the edge of the pond, there is lots of light and oxygen creating a habitat for plants like marsh marigolds to thrive. The plants that grow there provide shelter for insects and small animals, for example, frogs and damselflies. Above the pond system is where birds and insects such as kingfishers, herons, and dragonflies live. They feed in and around the pond.
Nutrient cycling in the freshwater pond ecosystem
Nutrients are vital in ecosystems as they are food that fuels the growth of animals and plants. In the freshwater pond ecosystem, nutrients can be found from three sources.
- One source is the chemicals in the atmosphere that are washed out by rain
- When rocks and minerals are weathered and broken down into the soil, they add nutrients
- Bacteria absorb chemicals from the atmosphere and are stored in the soil.
Nutrients that are found in soil are taken in by producers such as plants for growth. Consumers eat the producers gaining the energy to grow, and when producers and consumers die, they are broken down by decomposers into organic matter and into nutrients.
Nutrients are transferred through the ecosystem in many ways, this can be seen through Gersmehl's model.
Fig. 2 - Germehl's model of nutrients through the ecosystem
The model shows the movement of nutrients that flow through the ecosystem. The stores of nutrients are represented by the circles whereas the arrows show the flow of nutrients.
The size of circles and arrows represent the number of nutrients flowing or being stored. The three stores are living biomass, organic litter, and soil. Biomass refers to the living organisms in the pond. Organic litter is organic matter that decays like leaves or dead animals.
Pond ecosystem food chain
The balance of the pond ecosystem is regulated by the food chain. The food chain is how each organism gets food and passes on energy and nutrients from one organism to another. It is made up of producers and consumers.
Producers are organisms that make energy from the environment such as water, light, and carbon dioxide, and usually begin the food chain.
Consumers are organisms that receive energy from eating other organisms.
An example of a pond ecosystem food chain would be the first producers, phytoplankton, and aquatic plants like algae that photosynthesis to create glucose from sunlight. Then there are consumers such as small aquatic animals like caddis who would eat producers for their sugars. There are also consumers who would eat other consumers to receive energy for example small fish like a stickleback who eats the caddis and birds like the kingfisher who would eat the fish.
The food chain shows who eats who whilst the food web is the food chain that exists in an ecosystem.
Pond ecosystem food web
The food web of the pond ecosystem shows the relationships between all the producers and consumers.
From the diagram, you can see at least four different food chains. The detritus, algae, and microscopic plants are producers who are at the beginning of the food chains and are eaten by the primary consumers of midge larvae, blackflies, mayflies, and aquatic worms.
The primary consumers are then eaten by the great diving beetle, stonefly, caddis, and dragonfly who are the secondary consumers.
The secondary consumers are eaten by fish who are the tertiary consumers (also fish can be secondary consumers as they feed on mayflies as well.)
Then the tertiary consumers are eaten by quaternary consumers, herons, and kingfishers.
Threats to pond ecosystem
As pond ecosystems are reliant on the balance between biotic and abiotic components, changes to either can threaten the ecosystem. There are both natural and human-made threats to the pond ecosystem.
Natural threats
Lack of rainfall can cause the water levels in a pond to drop. Without water, the pond margins can dry out and the plants die. Less water leads to lower oxygen levels. This can then lead to fewer fish in the pond.
Natural succession can also be a threat to the pond ecosystem. Natural succession is a series of processes of habitats and species changing in an environment. In the case of the pond, over time it is filled up with soil and plant debris which leads to the pond becoming dry land.
Human-made threats
Introducing another species into the pond such as a predatory fish could decrease the number of insects that are usually preyed on by frogs and affect the numbers of the population. Removing another species can be just as destructive as a species reliant on the species for energy could die out without it. Both change the balance of the food web and affect the pond ecosystem.
There have been examples of ponds being drained to make space for farming. This completely destroys the ecosystem. The fertiliser used in farms leeching into the pond can also affect the ecosystem as it can cause algae to thrive and use up the oxygen in the water and the other organisms in the water die of lack of oxygen. Pesticides can also be leaked into the pond to pollute and kill the living organisms in the pond.
Pond Ecosystem - Key takeaways
- The pond ecosystem is an aquatic ecosystem in a small enclosed body of water. It is shallow enough to have light penetrating through the water, which supports various types of aquatic plants and animals to thrive.
- Abiotic and biotic components exist in the areas of the pond bottom, mid-water, pond surface, pond margin, and above the pond system.
- Nutrients are vital in ecosystems and there are cycles of nutrients that are found in soil that are taken in by producers such as plants for growth, consumers eat the producers gaining the energy to grow, and when producers and consumers die they are broken down by decomposers into organic matter and into nutrients.
- A food chain, looks at one relationship between producers and consumers. A food web shows the relationship between all the producers and consumers.
- There are natural and human-made threats to the pond ecosystem. Natural threats include lack of rainfall and natural succession. Human-made threats are caused by introducing or removing species from the ecosystem, polluting the pond with fertiliser or pesticides, and draining ponds for more space for farming.
References
- Fig. 2 - Germehl's model of nutrients through the ecosystem (https://commons.wikimedia.org/wiki/File:Nutrient_cycle.svg) By Kayau (https://commons.wikimedia.org/wiki/User:Kayau) Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
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