In this unit, we will study environmental balance with a view. to-describing the nature of the balance in the hydrological cycle, carbon cycle, nitrogen cycle, food chain, and mineral nutrient cycle using appropriate environmental variables.
Environmental balance, sometimes called ecological balance is a situation in which all the components of an environment are in equilibrium within the environment. For instance, the vegetation type of an environment (given the environmental factors on which this vegetation type thrive on), will be in equilibrium (balance) with the environment as long as the factors of the environment do not change, i.e. the vegetation type will continue to remain the same with the unchanging environmental factors. An ecosystem is a functional unit of space which involves many complex interrelationships.
It is a dynamic unit of the natural environment which has a complex balance. The nature of this complex balance may properly be understood through the description of some ecological models which show the flow of energy and the cycling of matter within the ecosystem.
The Hydrological Cycle
The hydrological cycle refers to the continuous circulation of water from the sea through the air to the land and back to the sea. It is a process by which environmental equilibrium is maintained.
This ecological model is used to show the endless interchange of water between the sea, the atmosphere and the land. The model shows what happens when water evaporates from sea and land and is later transformed into water vapour. The water vapour ascends the atmosphere and forms clouds and later condenses as precipitation and falls as rain, snow, sleet or hail to the ground surface. Precipitation forms the surface runoff which flows into streams, rivers, sea, etc. Some infiltrate into the sub-inner surface layers as ground water to join springs and rivers, while some may remain in the ground as soil moisture.
Part of the precipitation evaporates back to the atmosphere, while some may be retained in lakes, ponds, etc., to be later evaporated. Some may be absorbed by plants to be transpired or even be stored in the roots or plant tissues where the dead of the plant may help to return this water to the cycle.
The Carbon Cycle
The carbon cycle is the movement of carbon into the atmosphere as carbon dioxide (CO2), and its eventual return to the earth’s surface where its absorbed and stored by plants during the process of photosynthesis.
The carbon cycle is another ecological model that shows the interdependence that exists between the components of an ecosystem. In the carbon cycle, first, there is the interrelationship between plants and the atmosphere as it is from the atmosphere that plants obtain carbon dioxide that they need. Man and other animals, give out carbon dioxide through the process of respiration.
Two levels of interdependence within the ecosystem are shown by the carbon cycle. In the first instance, the abiotic component (i.e. the atmospheric gases) maintain an interdependence with the biotic component (plants and animals). In the second place, there is an interdependence within the biotic components themselves. The herbivores, carnivores and decomposers, pass on energy and matter. Man is not left out, as he contributes to the carbon in the atmosphere through burning of fossil fuel such as peat, coal, petroleum, liquid gas and the burning of wood.
The Nitrogen Cycle
The nitrogen cycle is a complex process that involves the presence of nitrogen in the atmosphere, soil, plants and animals, and the exchange of the nitrogen within the ecosystem. The nitrogen cycle depends on the activities of various bacteria in the soil and other environmental processes. The nitrates in the soil are absorbed by plants which build them up into protein for the use of animals which eat plants. When the plants and animals die, they are decomposed by the action of certain bacteria. The nitrogen in the decomposed plants and animals return to the environment in the form of ammonia. This ammonia is oxidised to nitrates by the action of the nitrifying bacteria.
The action of these bacteria is very important in replenishing the environment with nitrates which plants and animals depend upon for their source of protein. Some of the nitrates which are not reabsorbed by plants may be lost either by leaching from the soil into sediments at the bottom of the sea or they may be broken down by denitrifying bacteria. Such soil bacteria obtain energy by breaking down compounds or nitrogen to gaseous nitrogen, which is eventually released into the atmosphere. Since atmospheric nitrogen cannot be directly utilised by green plants, it has to be absorbed in rain and drops to the ground, then absorbed by soil bacteria which combine it with other elements to produce nitrogen compounds. This process is due to the action of the nitrogen-fixing bacteria which may be found in certain root nodules of leguminous plants, or may exist free in the soil.
The main features of the cycle is that the amount of nitrogen available in the atmosphere is maintained by a balance between the processes which withdraw nitrogen from the atmosphere and those that add nitrogen to it.
Food Chain and Food Web
The interdependence that exists within the biotic components can be used to depict the linkage formed by the feeding relationships between the plants and animals within the biotic components.
The linkage involves the flow of energy from plants (producers) to the primary consumers (herbivores), and then to the carnivores (secondary consumers). There may be several carnivores in the series of secondary consumers such that the first on the chain represents the prey to the second and so on. This type of linkage of consumer levels and their nutritional sequences is known as the food chain. The food chain in general is formed by a series of organisms existing in an ecosystem through which energy flows.
A food chain is an important ecological system for the maintenance of environmental balance. It is an arrangement where an organism passes on to the next organism and less energy is stored up. Therefore as one moves up the food chain, less energy is transferred and less energy is stored. The energy that is transferred can be represented in the shape of a pyramid called energy pyramid.
The pyramid of energy is one very important way of maintaining environmental balance. The pyramid is so arranged that the total energy used by the organisms in an ecosystem or lost to atmosphere is replaced through photosynthesis. Any attempt to increase the rate at which energy is transferred within the ecosystem will lead to the disturbance of the balance. For example, if there are too many herbivores in an area, they will soon eat up the vegetation such that food will become scarce for them and they must migrate or they will die in large numbers.
It is common to have a very complicated relationship in which an organism may feed on many different organisms and in turn be fed upon by many different organisms. Such complicated feeding relationship is called the food web. A food web is the nutritional relationship between the various organisms that are interconnected in the ecosystem. The arrangement in energy usage and transfer is the same as in food chain and maintains an environmental balance. The food chain and food web are therefore significant to the functioning of the ecosystem.
The Mineral Nutrient Cycle
The mineral nutrient cycle often referred to as the biochemical cycle is another ecological system which is important for the environmental balance and the functioning of the ecosystem.
Plants depend on some chemical substances called mineral nutrients in order to grow and function properly. These nutrients include nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, manganese, iron, zinc, copper, chlorine, carbon, hydrogen, oxygen and other trace elements which are derived from the soil. Among these elements, carbon, hydrogen and oxygen come from the atmosphere while the remaining ones come from the soil. These nutrients move around in the ecosystem in cycles.
These minerals are obtained from the soil or from the atmosphere by plants for their life processes. The minerals enter into the plant tissues (biomass). From the plants, the nutrients are passed on to plant eating animals (herbivores) and flesh eating animals (carnivores).
When plants die or shed their leaves or when animals die or excrete, the dead organic materials decompose and the mineral nutrients are released back to the soil or to the atmosphere as the case may be. The mineral nutrient cycle therefore shows the interaction between biotic and
abiotic components of the ecosystem through the exchange between plants, soils and the atmosphere.