Environment, Ecology and Ecosystems | Geography

ENVIRONMENT, ECOLOGY AND ECOSYSTEMS

• Our planet is the only place in the universe that supports life.
• Life on Earth requires a variety of organic and inorganic nutrients.
• These nutrients continuously recycle through the interactions of organisms and their environments.
• Recycling chemicals essential to life involves both geological and biological processes.
• These pathways are called biogeochemical cycles and have three things in common.
• Reservoirs – These are where the chemical is held in large quantities for long periods of time.
• Exchange pools – This is where the chemical is held for only a short time.
• Residence time – It is the length of time a chemical is held in an exchange pool or a reservoir.
• The oceans are a reservoir for the water cycle, while a cloud is an exchange pool.
• Water may reside in an ocean for thousands of years, but in a cloud for a few days at best.
• The biotic community also serves as an exchange pool and also move chemicals from one stage of the cycle to another.
• For instance, the trees of the tropical rain forest bring water up from the forest floor to be evaporated into the atmosphere.
• Coral polyps take carbon from the water and turn it into limestone rock.
• The energy for most of the transportation of chemicals from one place to another is provided either by the sun or by the heat released from the mantle and core of the Earth.
• Earth has a number of cycles.
• Of which only four are very important for living organisms. They are
• water
• carbon
• nitrogen
• phosphorous

The Carbon Cycle

• Respiration takes carbohydrates and oxygen, combines them to produce carbon dioxide, water and energy. Photosynthesis takes carbon dioxide and water produces carbohydrates and oxygen.
• The outputs of respiration are the inputs of photosynthesis, and the outputs of photosynthesis are the inputs of respiration. The reactions are also complementary in the way they deal with energy.
• Photosynthesis takes energy from the sun and stores it as carbohydrates; respiration releases that energy. Both plants and animals carry on respiration, but only plants can carry on photosynthesis.
• The chief reservoirs for carbon dioxide are the oceans and the rocks.
• Carbon dioxide dissolves readily in water.
• Once there, it may precipitate as a solid rock known as calcium carbonate.
• Corals and algae encourage this reaction and build up limestone reefs in the process.
• On land and in the water, plants take up carbon dioxide and convert it into carbohydrates through photosynthesis.
• This carbon in the plants now has three possible fates.
• It can be liberated to the atmosphere by the plant through respiration.
• it can be eaten by an animal or it can be present in the plant when the plant dies.
• When an animal or a plant dies, two things can happen to the carbon in it.
• It can either be released by decomposers to the atmosphere or
• It can be buried intact and ultimately form coal, oil or natural gas.
• The fossil fuels can be mined and when burned releases carbon dioxide to the atmosphere.
• The carbon in limestone or other sediments can only be released to the atmosphere when a volcano erupts or when they are pushed to the surface and slowly weathered away.
• Humans have a great impact on the carbon cycle because when we burn fossil fuels we release excess carbon dioxide into the atmosphere.
• This means that more carbon dioxide goes into the oceans and more is present in the atmosphere.
• This rise in the atmosphere causes global warming.

The Nitrogen Cycle

• The nitrogen cycle is one of the most difficult of the cycles to learn, simply because there are so many important forms of nitrogen and because organisms are responsible for each of the interconversions.
• Nitrogen is critically important in forming the amino portions of the amino acids which in turn form the proteins of our body.
• Proteins make up skin and muscle, among other important structural portions of our body and all enzymes are proteins.
• Since enzymes carry out almost all of the chemical reactions in our body, it’s easy to see how important nitrogen is.
• The chief reservoir of nitrogen in the atmosphere, which is about 78% nitrogen.
• Nitrogen gas in the atmosphere is composed of two nitrogen atoms bound to each other. It is a pretty non-reactive gas; it takes a lot of energy to get nitrogen gas to break up and combine with other things, such as carbon or oxygen.
• Nitrogen gas can be taken from the atmosphere in two basic ways.
• First, lightning provides enough energy to “burn” the nitrogen and fix it in the form of nitrate, which is nitrogen with three oxygens attached.
• This process is duplicated in fertilizer factories to produce nitrogen fertilizers.
• The second form of nitrogen fixation is by nitrogen-fixing bacteria, who use special enzymes instead of the extreme amount of energy found in lighting to fix nitrogen.
• These nitrogen-fixing bacteria fix nitrogen either in the form of nitrate or in the form of ammonia.
• Most plants can take up nitrate and convert it to amino acids.
• Animals acquire all of their amino acids when they eat plants or other animals.
• When plants or animals die or release waste the nitrogen is returned to the soil.
• The usual form of nitrogen returned to the soil in animal wastes or in the output of the decomposers is ammonia.
• Ammonia is rather toxic, but, fortunately, there are nitrite bacteria in the soil and in the water which take up ammonia and convert it to nitrite.
• Nitrite is also somewhat toxic, but another type of bacteria, nitrate bacteria, takes nitrite and converts it to nitrate, which can be taken up by plants to continue the cycle.
• There are denitrifying bacteria which take the nitrate and combine the nitrogen back into nitrogen gas.

The Phosphorous Cycle

• The phosphorous is the simplest of all cycles. Phosphorous has only one form, phosphate, which is a phosphorous atom with 4 oxygen atoms.
• This molecule never makes its way into the atmosphere; it is always part of an organism, dissolved in water or in the form of rock.
• When rock with phosphate is exposed to water especially water with a little acid in it, the rock is weathered out and goes into solution.
• Plants take this phosphorous up through their roots and use it in a variety of ways.
• It is an important constituent of cell membranes.
• Animals obtain their phosphorus from the plants they eat.
• Animals, by the way, may also use phosphorous as a component of bones, teeth and shells.
• When animals or plants die the phosphate may be returned to the soil or water by the decomposers.
• There it can be taken up by another plant and used again.
• This cycle will occur over and over until at last the phosphorous is lost at the bottom of the deepest parts of the ocean, where it becomes part of the sedimentary rocks forming there.
• Ultimately, this phosphorous will be released if the rock is brought to the surface and weathered.
• Two types of animals play a unique role in the phosphorous cycle.
• Humans often mine rock rich in phosphorous. For instance, in Florida, which was once seafloor, there are extensive Phosphate mines.
• The phosphate is then used as fertilizer.
• This mining of phosphate and use of the phosphate as fertilizer greatly accelerates the phosphorous cycle and may cause a local overabundance of phosphorus, particularly in coastal regions, at the mouths of rivers and any place where there is a lot of sewage released into the water.
• Local abundance of phosphate can cause the overgrowth of algae in the water; the algae can use up all the oxygen in the water and kill other aquatic life.
• This is called Eutrophication. The other animals that play a unique role in the phosphorus cycle are marine birds.
• Their birds take phosphorous-containing fish out of the ocean and return to land, where they defecate.
• Their guano contains high levels of phosphorous and in this way marine birds return phosphorous from the ocean to the land.
• The guano is often mined and may form the basis of the economy in some areas.
• In the biosphere, a group of organisms with their total assemblage of components entering into the interactions through biogeochemical cycles is known as an ecological system or more simply an ecosystem.
• G. Tansley, a botanist, introduced the ecosystem concept in the year 1935.

Major Components of an Ecosystem

• Ecosystems are composed of a variety of abiotic and biotic components and they function in an interrelated fashion.
• Some of the important components are – Soil, atmosphere, radiation from the sun, water and living organisms.
• Soils contain a mixture of weathered rock fragments, highly altered soil mineral particles, organic matter and living organisms.
• Soils provide nutrients, water, a home and a structural growing medium for organisms.
• The vegetation found growing on top of the soil is closely linked to this component of an eco-system through nutrient cycling.
• The atmosphere provides organisms found within ecosystems with carbon dioxide for photosynthesis and oxygen for respiration.
• The processes of evaporation, transpiration and precipitation, cycle water between the atmosphere and the Earth’s surface.
• Solar radiation is used in ecosystems to heat the atmosphere and to evaporate and transpire water into the atmosphere.
• Sunlight is also necessary for photosynthesis.
• Photosynthesis provides the energy for plant growth and metabolism and organic food for other forms of life.
• Most living tissue is composed of a very high percentage of water, up to and even exceeding 90%.
• The protoplasm of a very few cells can survive if their water content drops below 10% and most are killed if it is less than 30 – 50%.
• Water is the medium by which mineral nutrients enter and are translocated in plants.
• It is also necessary for the maintenance of leaf turgidity and is required for photosynthetic chemical reactions.
• Plants and animals receive their water from the Earth’s surface and soil. The original source of this water is precipitation from the atmosphere.

Ecosystem Types

• The ecological communities in the biosphere interact with their environment and create a variety of ecosystems. These ecosystems fall into two groups – Water and Land.
• Water ecosystems include life forms of the marine environments and the freshwater environments of the land.
• Marine eco systems include open oceans, coastal estuaries and coral reefs.
• Freshwater ecosystems include lakes, ponds, streams and marshes.
• Land ecosystems consist of land plants and animals spread widely over the upland surfaces of the continent.
• Land ecosystems are largely determined by climate and soil and, in this way, closely woven into the fabric of physical geography.
• The land ecosystems consist of two basic types such as
• Natural
• Cultural
• The largest recognizable division of the natural ecosystem is the “Biome”.
• Although the biome includes the assemblage of plant and animal life interacting within the biosphere, the green plants dominate the biome physically as compared with that of other organisms.
• In geography, the concept of natural vegetation represented by biomes; and the vegetation sustained in a modified state by humanity are like the two sides of a coin. Natural vegetation can still be seen over vast areas of the wet equatorial climate where rain forests are scarcely touched by humans.
• Much of the Arctic Tundra and the needle leaf forest of the subarctic zones is in a natural state.
• In contrast, much of the continental surface in the middle latitudes is almost totally under human control through intensive agriculture, organizing or urbanization.
• Humans have influenced vegetation by moving plant species from their indigenous habitats to foreign lands and foreign environments.
• The eucalyptus tree is a good example.
• From Australia, the various species of eucalyptus have been transplanted to such far – off lands as North America, North Africa and India.