The environment is not a static unit but is forever rejuvenating and maintaining itself by means of energy flow, and the cycling (renewing) of all matter. The ecosphere can be seen as one large machine consisting of several cycles and systems. Energy is necessary to drive these cycles is mainly provided by the sun.

Water is being recycled from the atmosphere through the soil, and biotic components in what is known as the hydrological cycle. Gasses like oxygen and carbon dioxide are constantly being circulated through ecosystems. Even soil with its minerals form part of a continuous cycle, called the sedimentary cycle.  Jointly we refer to these cycles as Earth’s biogeochemical circulation.

Figure 5.1: Energy required to run cycles in the ecosystem (soil, water and organisms) is provided by the sun.

Figure 5.2: Energy is supplied by the sun – used within the ecosystem – and passes out of it. mostly in the form of heat.

The sun provides the light and energy by which vegetation produces chemical energy (food) for all the consumers and eventually decomposers until the circle is completed and the organic matter is returned into the system for uptake by the roots of plants.

It was shown that organisms are always consumed by those positioned on higher levels on a food web (Fig4.4). As a result, each level of a food web contains less energy than the levels below it. The flow of energy and matter through ecosystems is diagrammatically portrayed in food chains, food webs, and ecological pyramids. (Fig4.7). With every transfer of nutrients from one componentor level to another, a large amount (up to 90%) of energy is lost.

As was illustrated, plants form the first, or bottom trophic level, called T1 (also known as autotrophs). Herbivores, for example antelope, form the second trophic level (T2), and carnivores like lions, form the third trophic level (T3). 

Top carnivores such as birds of prey occupy the fourth trophic level (T4). T5(tertiary carnivores) is represented by the decomposing organisms in the soil by which nutrients are returned to the above-ground circulation. From T2 to T5are called heterotrophs.

The division into trophic levels is not based on specific species, but on the function that species fulfil in the ecosystem-community. Trophic levels indicate the position of organisms within the food-chain. Food-webs on the other hand define the composition of ecosystems. There can be many individuals and a variety of populations within every trophic level; all linked to each other by the flow of energy (food). Trophic levels can be presented by varioustypes of ecological pyramidsto illustrate the function of the organic matter in ecosystems.  

Figure 5.3: The division of trophic levels is based on the function that a species fill in the ecosystem-community.

Figure 5.4: The division of trophic levels is based on the function that a species fill in the ecosystem-community.

A numbers pyramid shows the number of organisms in each trophic level without taking into consideration the size of the organisms. Under normal conditions there will be more individuals at T1 than T2, and again much fewer at T3 etc. The pyramid thus has a broad base which tapers to the top as shown in Fig. 5.5 (Grassland ecosystem and Pond ecosystem). This type of ecological pyramid could however over-emphasize the importance of a multitude of small organisms such as lice on a plant as seen in Fig. 5.5 (Forest ecosystem or Parasitic food chain on a single tree).

In the biomass pyramid (Fig. 5.6) the total relative mass of the organisms in each trophic level becomes less as you move upwards in the system. The specific kg can obviously vary from ecosystem to ecosystem. In an energy pyramid (Fig. 5.6) the total amount of energy present in each trophic level is shown.

It will therefore also reflect the loss of energy from one trophic level to the next. Here one can clearly see how the energy transfer from one trophic level to the next is decreasing. The energy pyramid is therefore more widely used to compare different ecosystems. This diagram illustrates the “Rule of 10” to which we have referred to previously. It means that only 10 percent of energy is being transferred between subsequent trophic levels. As example, an individual bird that eats a worm will get a mere 10% of the energy that the worm got from the leaves he ate.

Figure 5.4: The division of trophic levels is based on the function that a species fill in the ecosystem-community.

Figure 5.5: A biomass pyramid indicates the combined mass of all individuals on a particular trophic level. An energy pyramid indicates the combined energy present at each trophic level.

These trophic levels are in reality not always clear-cut simple units, because organisms often feed at more than one trophic level; some carnivores eat plant material as well, and some plants are carnivores; a large carnivore may eat both smaller carnivores and herbivores; animals can also eat each other – the bullfrog eats the crayfish, but crayfish also eat young bullfrogs.  Also, the feeding habits of a young animal, and consequently its trophic level, can change as it matures.

What is vital to remember is that there is always continuous movement of matter and energy through a system.

We will now look at the major cycles in the ecosphere. Each of these cycles has an underlying reservoir supporting it, where elements or compounds are stored for various periods of time before they once again take active part in the cycle. In the case of the hydrological cycle, the ocean is the main reservoir. The atmosphere is the reservoir for the gaseous cycles, and the crust of the earth, the reservoir for the sedimentary or soil cycles. There are also exchange pools where elements or compounds are held for short periods of time. Clouds are exchange pools in the hydrological cycle and the bodies of organisms serve as exchange pools for various chemicals in the biotic community. Cycles that transport chemicals such as life-supporting nutrients, pass through both the biological and geological world and therefore we can refer to these as biogeochemical cycles.

The water or hydrological cycle, in its simplest form, consists of water that evaporates from the surface of the oceans, and this moisture is carried by wind over the continents where it condenses, forms clouds, and fall to the earth as rain, hail, or snow. Part of the water sinks into the ground whilst about 70% reaches the atmosphere again in the form of vapour as a result of evaporation and transpiration from leaves of plants. The rest eventually reaches the sea as run-off via rivers and underground aquifers – and the whole process is continually being repeated.

Figure 5.6: Clean water is vital to maintain all forms of life.

Figure 5.7:  Carbon forms the basic building block of all organic compounds

In the cooler regions of the earth, like the north and south poles, water might be trapped for very long periods in the form of snow or ice. Water might also be temporarily ‘stored’ in lakes, ponds and wetlands. As water flows to the oceans, it carries with it minerals as a result of the weathering of rock and eroded soil assisting in the sedimentary circulation.

Organisms also play an important part in the water cycle as up to 90% of their body weight consists of water. Without water many essential body functions in humans and animals will not be possible, and without water, plants will not be able to take up and transport chemicals or produce energy in the form of carbohydrates for herbivores, or produce their ‘waste’ products namely carbon dioxide and evaporated water.

The quality of water resources, collected in ‘temporary pools’ such as dams and wetlands, and even the sea, are being threatened by various forms of pollution at an extraordinary rate. Water collected from evaporated molecules that returns to the earth in the various forms of precipitation used to be clean from all impurities, but even this is no longer the case as even this ‘cleansing method’ of nature has been affected by air pollution, resulting in acidic rain (Fig. 2.5).

The carbon dioxide cycle can be discussed as an example of the gaseous cycles. Carbon is extremely important for life on earth as it forms the basic building block of all organic compounds, together with hydrogen. The main reservoirs for carbon dioxide are the oceans.

The natural carbon cycle can be seen as a nearly perfect cycle because under natural conditions almost as much carbon is set free through the process of respiration as is bound by photosynthesis. The interference of humans with this cycle is of crucial importance. Due to industrialization, the burning of fossil fuels release enormous amounts of carbon dioxide in the atmosphere. This causes the so-called “Greenhouse” effect leading to “Global warming” that is in turn made worse because of deforestation and animal husbandry.

Green plants on land and in water take up carbon dioxide and through the process of photosynthesis convertthe carbon into carbohydrates. From the plant, the carbon can move three possible ways: it can be released into the air through the process of respiration; it can stay in the plant until it dies; or it can be eaten by animals. From the body of the animal the carbon can also move three possible ways: from land animals it can be released into the air through respiration; and from there it can be taken up by another plant through photosynthesis; or from oceanic animals it can be dissolved in the ocean. 

Figure 5.7:  Carbon forms the basic building block of all organic compounds

Two things can happen to the carbon in a plant or animal when it dies: it can be respired into the air as decomposers assimilate and decompose dead material; or it can be buried intact and eventually form coal, oil, or natural gas.These are natural fossil fuel resources and can be pushed to the surface by (orogenic) forces inside the earth and released through volcanoes.

But when we artificially expose fossil resources to the environment by extraction and by burning fossil fuels, huge excesses of carbon dioxide are being released into the atmosphere and this is having a compounding negative impact on the natural environment. In essence global warming happens because of an over-abundance of carbon dioxide in the atmosphere allowing more heat from the sun to be reflected back to the earth than escaping into space. As more carbon dioxide is being released into the atmosphere more carbon also enters the oceans causing amongst others the bleaching of coral reefs. The disappearing forests are crucial for the recycling of carbon on land. Similarly the disappearingof tropical coral reefs has major negative impacts on the survival of food chains in the ocean.

Figure 9: Birds play an important role in returning phosphor from the ocean to the land. The accelerated release of phosphor-enriched fertilizer and sewage has burdened natural water systems causing eutrophication.

The phosphorous cycle is an important example of a sedimentary cycle. When we consider sedimentarycycles, we need to keep in mind that it consists of two phases: the salt solution; and the rock phase. 

Because of its weight, heavy phosphor molecules never rise into the air. It is always part of an organism, dissolved in water, or exists in the form of rock. When a rock containing phosphorous elements is exposed to water – especially if the water has some acid in it- the rock is weathered and goes into solution with the water it has been exposed to. Plants rooted in this rock or soil, absorb the phosphate and use it for example to constitute their cell membranes. Animals feeding on this plant will use phosphor for example as a vital component in bones, teeth, and shells. 

Figure 5.8:  An effective phosphorous cycle is important as phosphate is a vital component in bones, teeth and shells

And when the animal or plant defecates or dies, the phosphor is again returned to the soil or water as decomposers break the corpses down to a consumable form for other plants.  

This cycle occurs repeatedly until the phosphorous settles on the ocean floor. Here it becomes part of the sedimentary rocks that have been formed over millions of years. When the rock is ultimately brought to the surface, for example as result of crustal movement, the seafloor may tilt and become exposed to the elements and to weathering.

In nature, marine birds play an important role in returning phosphor from the ocean to the land. Phosphor enters their systems through the bones of fish they eat and the accumulation of their defecation is known as guano. People used to mine the phosphate from guano, or they mined it from areasthat were once covered by the sea, to be used as fertilizer. Eventually this has lead to a situation where an overabundance of phosphate concentrations is released into the natural water system due to run-off from cultivated land. It causes a situation known as ‘eutrophication’ where a shortage of oxygen in the water is experienced because of the increased activity of algae thriving on phosphate. The rest of the natural aquatic life in the water body is no longer able to survive in the oxygen-deprived water and they die.

 

Figure 10: As in the case of the Jordan River, if a system is not actively linked with the total environment around it, it stops to function.

The effectiveness of cycles in nature has been greatly affected by overproduction and the various forms of pollution. When too much pressure is exerted on the natural system it will eventually stop to function. When stagnation occurs, death follows inevitably. The Dead Sea is an example. Here water flows from the Golanhighlands along the River Jordan into the Dead Sea, which has no outlet. The salts washed out of the soils over thousands of years accumulate in this inland lake. No life exists in the Dead Sea. It is an ecosystem that has stopped functioning because there has been such a build-up of dissolved substances that it could no longer circulate in the ecosystem and support natural life. In nature nothing can survive in isolation. If a system is not actively linked with the total environment around it, it perishes.Everything is of necessity actively (functionally and dynamically) linked to everything else for the sake of survival.

It is clear that natural systems work in harmony to sustain life on earth. Itis also clear that we as humans harm the quality of our natural resources by inhibiting the natural rhythm of nature when we for instance,

* mass-produce materials like plastic and nuclear waste, that cannot be recycled naturally;

* continually increase our dependence on fossil fuels causing air pollution and inhibit the gaseous cycle  to cleanse water vapour from impurities; and

* over-saturate rivers and estuaries with organic waste material to such an extent that marshes and reeds are no longer effective water purifiers.

Figure 11: Until we have found a safe method to recycle or  neutralize nuclear waste, we are jeopardizing the lives of future generations.

 It is important to take note that because of the population explosions and increasing consumer demand, human activities are tampering with, and thus putting ever-increasing pressure, on ecosystem cycles. By reason of various mining activities, we have exposed the earth’s buried rocks to the elements, resulting in much quicker weathering and erosion and thus an accelerated movement of elements in the global sedimentary cycle. This can also clog the system’s circulation. The extraction of coal and oil to be used as energy recourses is releasing carbon dioxide into the earth’s atmosphere about seventy times more rapidly than one would expect naturally. This affects the gaseous cycle. Humans have an enormous capacity to increase the rate of movement of materials in both the sedimentary and biological cycles. An interruption in any one of the cycles will have a catastrophic impact on our livelihood. 

Figure 12: Due to activities such as mining we have accelerated the movement of sediments through the natural system.

The removal of the forests of the world wil seriously inhibit, or stop, the CO2 cycling to the point that not only the global temperatures will soar,  but we ourselves could  eventually suffocate.It is time for us to re-think our relationship with nature. Unless we find and implement sustainable methods of production, agriculture, waste disposal, transport… the list goes on, our resource base will continue to deteriorate, putting unbearable pressure on an increasing world population.

All land use must urgently apply the basic laws of nature to ensure sustainability.