Carbon is an element. It is part of oceans, air, rocks, soil and all living things. Carbon doesn t stay in one place. It is always on the move!

Transcription

1 The Carbon Cycle Carbon is an element. It is part of oceans, air, rocks, soil and all living things. Carbon doesn t stay in one place. It is always on the move! Carbon moves from the atmosphere to plants. In the atmosphere, carbon is attached to oxygen in a gas called carbon dioxide (CO 2 ). With the help of the Sun, through the process of photosynthesis, carbon dioxide is pulled from the air to make plant food from carbon. Carbon moves from plants to animals. Through food chains, the carbon that is in plants moves to the animals that eat them. Animals that eat other animals get the carbon from their food too. Carbon moves from plants and animals to the ground. When plants and animals die, their bodies, wood and leaves decay bringing the carbon into the ground. Some becomes buried miles underground and will become fossil fuels in millions and millions of years. Carbon moves from living things to the atmosphere. Each time you exhale, you are releasing carbon dioxide gas (CO 2 ) into the atmosphere. Animals and plants get rid of carbon dioxide gas through a process called respiration. Carbon moves from fossil fuels to the atmosphere when fuels are burned. When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas. Each year, five and a half billion tons of carbon is released by burning fossil fuels. That s the weight of 100 million adult African elephants! Of the huge amount of carbon that is released from fuels, 3.3 billion tons enters the atmosphere and most of the rest becomes dissolved in seawater. Carbon moves from the atmosphere to the oceans. The oceans, and other bodies of water, soak up some carbon from the atmosphere.

2 Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and other greenhouse gases, Earth would be a frozen world. But humans have burned so much fuel that there is about 30% more carbon dioxide in the air today than there was about 150 years ago. The atmosphere has not held this much carbon for at least 420,000 years according to data from ice cores. More greenhouse gases such as carbon dioxide in our atmosphere are causing our planet to become warmer. Carbon moves through our planet over longer time scales as well. For example, over millions of years weathering of rocks on land can add carbon to surface water which eventually runs off to the ocean. Over long time scales, carbon is removed from seawater when the shells and bones of marine animals and plankton collect on the sea floor. These shells and bones are made of limestone, which contains carbon. When they are deposited on the sea floor, carbon is stored from the rest of the carbon cycle for some amount of time. The amount of limestone deposited in the ocean depends somewhat on the amount of warm, tropical, shallow oceans on the planet because this is where prolific limestone-producing organisms such as corals live. The carbon can be released back to the atmosphere if the limestone melts or is metamorphosed in a subduction zone.

3 The Nitrogen Cycle Nitrogen cycle is not only a biological cycle; it is also a geographical cycle. It illustrates the way atmospheric nitrogen and other nitrogenous compounds go through a transformation. About 70% of the earth's atmosphere is made up of nitrogen. Thus we can say that earth's atmosphere is the largest source of nitrogen. This nitrogen becomes a part of many biological processes and is also part of most essential components that serve as the foundation stones of life like DNA, RNA, proteins and the like. All living beings need nitrogen to sustain life on earth surface. However, the nitrogen that is present in the atmosphere is not usable in its form by any living organism. Nitrogen Cycle: How is atmospheric nitrogen converted? Leguminous plants are plants that have nodules in their roots so that they can absorb atmospheric nitrogen. This process is called Nitrogen fixation, which is necessary otherwise it would be impossible for living beings to use atmospheric nitrogen. Fixation also occurs when the atmospheric temperature is high and also due to lightening since this is when the nitrogen is converted to nitrogen oxides. The chances of such nitrogen fixation are very less. The bacteria present in the nodules in the leguminous plants contain nitrogenase enzymes that help in the reaction of hydrogen and nitrogen, which helps to get ammonia. Ammonia is further is converted into organic compounds. This is the juncture where the leguminous plants establish a symbiotic relationship with the bacteria present in the nodules. Bacteria help to produce ammonia and in return they take carbohydrate from the plant. Such leguminous plants can be planted in soils that have poor fertility so that atmospheric nitrogen can be trapped in the soil and it benefits the plant. This is how plants receive their share of nitrogen but in case of animals, irrespective of the class and species, they receive it only by eating these

4 plants, thus making it a part of the food chain. This is the best way for animals to take in nitrogen since the other ways can have some harmful effects as well like if nitrogen dissolves in water, which it does at times, it can affect the oxygen level in the blood of an infant and also lead to the disorders like blue-baby syndrome. It can also be a threat to the aquatic life since nitrogen enhances the growth of algae which increases the oxygen demand, and that might lead to the death of aquatic animals. Process of Nitrogen Cycle First the atmospheric is converted into a form that can be utilized by living beings, which can be done by Nitrogen fixation (biological or Industrial) or the combustion of fossil fuels. Once it is converted, it is absorbed by the plant body, which is disintegrated in the system. Nitrogen is converted into ions of nitrite and ammonium, which are in turn converted into amino acids, nucleic acids and most importantly chlorophyll. Now the plant, throughout its life span converts nitrogen and uses it but when it dies, or even if an animal which has nitrogen in its body dies, it gets mixed with the soil in the form of organic matter. This nitrogen is again converted into ammonia by bacteria present in the soil; hence the process is called ammonification. The ammonia is then converted into nitrates with the help of bacteria in the soil. It is oxidized and then the ammonia is converted into nitrites. Once converted into nitrites, these nitrites are again converted into atmospheric nitrogen, the form they were prior to fixation and this achieved with the help of bacteria like Pseudomonas and Clostridium. Thus inert atmospheric nitrogen that was converted into usable nitrogen is again released into atmosphere. This is the process of Nitrogen Cycle that establishes a balance between the nitrogen that can be used and inert nitrogen in the atmosphere of earth. Interesting Facts about Nitrogen Cycle:

5 The nitrogen cycle is an important part of the terrestrial ecosystem. This element is found freely in the atmosphere, living and organic matter, and the oceans. Although the element is found in abundance, it can only be absorbed by plants as the ammonium ion or the nitrate ion. Its toxicity is the reason behind a limited consumption by plants. Other life forms, like animals and man, receive the required amount of nitrogen vital for metabolism and reproduction via the consumption of organic matter. The conversion of atmospheric nitrogen into a form that life forms can use is an important spoke in the nitrogen cycle. Nitrogen, as an essential nutrient, can be derived in four ways. In biological fixation, the symbiotic bacteria fix nitrogen to become organic nitrogen. In industrial N-fixation, atmospheric nitrogen and hydrogen are combined to form ammonia, with the help of a catalyst. During the combustion of fossil fuels, nitrogen oxides are released as exhaust. Another process that aids in the conversion of atmospheric nitrogen is lightning. The extensive cultivation of legumes, the Haber-Bosch chemical fertilizer processing, and vehicle exhaust have forced humans to look into synthetic means to transfer nitrogen trace gases from the atmosphere, to enrich the land. The increase in nitrous oxide in the atmosphere due to forced agricultural fertilization and biomass burning has resulted in the destruction of atmospheric ozone, acid rain, smog and drastic alteration of the atmospheric chemistry. Nitrogen present in the atmosphere and plants is highly soluble. This enables it to enter groundwater. However, this is not a growth-enhancing development, rather a global concern. The dissolved nitrate interferes with blood-oxygen levels and causes methemoglobinemia. Nitrate-concentrated groundwater also results in eutrophication or a high algal population, which results in the premature death of aquatic life-forms.

6 Phosphorus Cycle Phosphorus is an important element for all forms of life. As phosphate (PO 4 ), it makes up an important part of the structural framework that holds DNA and RNA together. Phosphates are also a critical component of ATP? the cellular energy carrier? as they serve as an energy?release' for organisms to use in building proteins or contacting muscles. Like calcium, phosphorus is

7 important to vertebrates; in the human body, 80% of phosphorous is found in teeth and bones. The phosphorus cycle differs from the other major biogeochemical cycles in that it does not include a gas phase; although small amounts of phosphoric acid (H 3 PO 4 ) may make their way into the atmosphere, contributing? in some cases? to acid rain. The water, carbon, nitrogen and sulfur cycles all include at least one phase in which the element is in its gaseous state. Very little phosphorus circulates in the atmosphere because at Earth's normal temperatures and pressures, phosphorus and its various compounds are not gases. The largest reservoir of phosphorus is in sedimentary rock. It is in these rocks where the phosphorus cycle begins. When it rains, phosphates are removed from the rocks (via weathering) and are distributed throughout both soils and water. Plants take up the phosphate ions from the soil. The phosphates then moves from plants to animals when herbivores eat plants and carnivores eat plants or herbivores. The phosphates absorbed by animal tissue through consumption eventually returns to the soil through the excretion of urine and feces, as well as from the final decomposition of plants and animals after death. The same process occurs within the aquatic ecosystem. Phosphorus is not highly soluble, binding tightly to molecules in soil, therefore it mostly reaches waters by traveling with runoff soil particles. Phosphates also enter waterways through fertilizer runoff, sewage seepage, natural mineral

8 deposits, and wastes from other industrial processes. These phosphates tend to settle on ocean floors and lake bottoms. As sediments are stirred up, phosphates may reenter the phosphorus cycle, but they are more commonly made available to aquatic organisms by being exposed through erosion. Water plants take up the waterborne phosphate which then travels up through successive stages of the aquatic food chain. While obviously beneficial for many biological processes, in surface waters an excessive concentration of phosphorus is considered a pollutant. Phosphate stimulates the growth of plankton and plants, favoring weedy species over others. Excess growth of these plants tend to consume large amounts of dissolved oxygen, potentially suffocating fish and other marine animals, while also blocking available sunlight to bottom dwelling species. This is known as eutrophication. Humans can alter the phosphorus cycle in many ways, including in the cutting of tropical rain forests and through the use of agricultural fertilizers. Rainforest ecosystems are supported primarily through the recycling of nutrients, with little or no nutrient reserves in their soils. As the forest is cut and/or burned, nutrients originally stored in plants and rocks are quickly washed away by heavy rains, causing the land to become unproductive. Agricultural runoff provides much of the phosphate found in waterways. Crops often cannot absorb all of the fertilizer in the soils, causing excess fertilizer runoff and increasing phosphate levels in rivers and other bodies of water. At one time the use of laundry detergents contributed to significant concentrations of phosphates in rivers, lakes, and streams, but most detergents no longer include phosphorus as an ingredient. Although very little phosphorus is needed by plants, it is a very important and needed for all plant growth. The Phosphorus that plants use is contained mostly in the earth s crust rather than in the atmosphere, this phosphorus is released with the weathering of rock caused by wind, water and geologic uplift. The recycling of phosphorus tends to be very localized, with plants up taking the phosphorus from the soil. Animal's uptake the phosphorus in the plants they eat, and return it to the environment in their waste. The phosphorus excreted by animals is in an organic form, which is converted to an inorganic form by microorganisms. Some of the phosphorus is the system

9 is lost, by leaching and erosion this phosphorus eventually reaches the oceans where it remains until it undergoes geologic uplift. The erosion of exposed rock or the use of manmade phosphate fertilizers replaces this lost phosphorus. Water Cycle Nature has an amazing way of recycling all its elements. If you notice nature never wastes even one iota of anything, it saves it entire, be it water, air or organic fertility. If man would not have meddled with nature's ways we wouldn't have had problems of water pollution, ozone layer depletion or global warming because nature knows the way to maintain ecological balance. Water Cycle is one of those processes wherein water is recycled again and again. What is Water Cycle? It is the continuous movement of water from the surface of the earth, that is the water bodies on surface of the earth to air and vice versa. This is an unending circle of precipitation that is being formed, absorbed and being created in multiple states of matter: solid, liquid and gas. Step Of water Cycle The water from the water bodies of the earth evaporates by using the heat of the sun and turns in to water vapor that is the gaseous form of water. The water vapor rises in to the air. The next step is that the water vapor when it rises above the hot atmosphere of earth, it stars cooling. Due to the cooling of water vapor, the water vapor again changes into tiny droplets of water, which form clouds as the next step. In the third step these tiny water droplets become bigger and bigger as a result of which the clouds bearing them become heavier and when they become too heavy for the clouds to hold any more, the

10 rain falls from the clouds. If the atmosphere is cold enough then the form of precipitation changes from rain to snow and sleet. In the last step the rain or the melted snow flows back into the water bodies like rivers, lakes and streams. The river eventually takes the water towards the oceans, which are the biggest water bodies and the biggest source of water vapor. It takes approximately nine days to complete water cycle and it keeps o repeating itself again and again. Processes involved in the Water Cycle The processes that are involved in the Water Cycle are as follows: Evaporation- The process of water converted to water vapor due to the heat of the sun. Condensation- The vapor cools and the vapor is transformed into tiny droplets of water again as the temperature decreases. Precipitation- Water comes back to the surface of the Earth in the form of rain, snow and hail. Run Off- When some water stays on the surface of the earth and the rest flows into the water bodies like rivers, lakes, reservoirs, it is called run-off. Percolation- When the water on the surface of the earth seeps down underground it is called Percolation. It later forms aquifers in the low-lying regions. The water cycle helps in providing the right amount of water at the right times and at the required places. It helps in agriculture and some water is also stored underground so that it can be used when there is no precipitation. "Age" of Water One thing that many people don't realize is how old water is. Scientists agree that matter (usually) cannot be created or destroyed. So essentially, the water you drink today has been in the water cycle for a very long time. In fact, it's thought that a water molecule can spend 3,200 years in an ocean before repeating through the water cycle and up to 10,000 years for water stored in caves deep underground.

11