Environmental cycles Important for UPSC prefim and mains
Biogeo Chemical Cycling or Nutrient Cycling Energy flow and nutrient circulation are the major functions of the ecosystem. We have studied about energy flow through trophic levels in the previous posts Energy is lost as heat forever in terms of the usefulness of the system. On the other hand, nutrients of food matter never get used up. They can be recycled again and again indefinitely. Carbon, hydrogen, oxygen, nitrogen and phosphorus as elements and compounds make up 97% of the mass of our bodies and are more than 95% of the mass of all living organisms.
n addition to these, about 15 to 25 other elements are needed in form for the survival and good health of plants and animals. These elements or mineral nutrients are always in circulation moving from non-living to living and then back to the non-living components of the ecosystem in a more or less circular fashion. This circular fashion is known as biogeochemical cycling (bio for living; geo for atmosphere) Among the most important nutrient cycles are the carbon nutrient cycle and the nitrogen nutrient cycle. There are many other nutrient cycles that are important in ecology, including a large number of trace mineral nutrient cycles.
Biogeochemical Cycles The e Water Cycle Water storage in ice and snow Water storage in the atmosphere Condensation Surface runoff Water storage USGS Ground-water storage
Nutrien t Cycles Based on the replacement period, a nutrient cycle is referred to as Perfect or Imperfect cycle A perfect nutrient cycle is one in which nutrients are replaced as fast as they are utilized. Most gaseous cycles are generally considered as perfect cycles. In contrast sedimentary cycles are considered relatively imperfect, as some nutrients are lost from the cycle and get locked into sediments and so become unavailable for immediate cycling Based on the nature of the reservoir, there are two types of cycles namely-
Gaseous Cycle - where the reservoir is the atmosphere or the hydrosphere water cycle, carbon cycle, nitrogen cycle, eto. and . Sedimentary Cycle - where the reservoir is the earth's crust [elements mostly found in earth's crust] - phosphorous cycle, sulphur cycle, calcium cycle, magnesium cycle etc.
carbon Cycle tGaseous Cycle] Carbon is a minor constituent of the atmosphere as compared to oxygen and nitrogen. However, without carbon dioxide life could not exist because it is vital for the production of carbohydrates through photosynthesis by plants. It is the element that anchors all organic substance:s from coal and oil to DNA (deoxyribonudeic acid: the compound that carries genetic information). Carbon is present in the atmosphere, mainly in the form of carbon dioxide (CO2)
Carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms. Carbon from the atmosphere moves to green plants by the process of photosynthesis, and then to animals. By process of respiration and decomposition of dead organic matter it returns back to atmosphere. It is usually a short term cycle. Some carbon also enters a long term cycle. It accumulates as un- decomposed organic matter in the peaty layers of marshy soil or as insoluble carbonates in bottom sediments of aquatic systems which take a long time to be released. In deep oceans such carbon can remained buried for millions of years till geological movement may lift these rocks above sea level. These rocks may be exposed to erosion, releasing their carbon dioxide, carbonates and bicarbonates into streams and rivers.
. Fossil fuels such as coals, oil and natura gas etc. are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels. When they are burned the carbon stored in them is released back into the atmosphere as carbon-dioxide
Co, in Atmosphere Organic Compound (Plants) Organic Compounds (Animals) Carbonates in Water Inorganic Carbonates (Shells) Coal Petroleum Limestone
* Q1. Consider the following: Photosynthesis Respiration Decay of organic matter Volcanic action . Which of the above add carbon dioxide to the carbon cycle on Earth? 1 and 4 only . 2 and 3 only . 2,3 and 4 only . 1, 2, 3 and 4
Answer: c) Photosynthesis takes out CO, from carbon cycle. Rest all ads CO 2.
Answer: b) Sunlight (free energy) is converted into carbohydrates (potential energy) using water and carbon dioxide. Oxygen is released in the process.
Nitrogen Fixing Nitrogen to Ammonia (N2 to There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms. Nitrogen needs to be 'fixed', that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. Nitrogen fixation on earth is accomplished in three different ways: By microorganisms (bacteria and blue-green algae),
. Nitrification Ammonia to Nitrates Ammonium ions can be directly taken up as a source of nitrogen by some plants Others absorb nitrates which are obtained by oxidizing ammonia and ammonium ions. Ammonia and ammonium ions are oxidized to nitrites or nitrates by two groups of specialized bacteria. Ammonium ions are first oxidized to nitrite by the bacteria Nitrosomonas and/or Nitrococcus. The nitrite is further oxidized to nitrate with the help of the bacterium Nitrobacter. These steps are called nitrification. These nitrifying bacteria are chemoautotrophs.
o he nitrate thus formed is absorbed by plants and is transporte the leaves. In leaves, it is reduced to form ammonia that finally forms the amine group of amino acids, which are the building blocks of proteins. These then go through higher trophic levels of the ecosystem. Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia. Nitrification also plays an important role in the removal of nitrogen from municipal wastewater. The conventional removal is nitrification, followed by denitrificatioin
Nitrogen in Denitrifcation Nitrogen ixatiom Nitrates Protoplasm (green plants) Protoplasm (animals) Nitrification Nitites Ammoniica Ammonia Nitrification Atmospheric and industrial Fig.14.6: Nttrogen-cycle tn nature
Denitrification - Nitrate to Nitrogen Nitrate present in the soil is reduced to nitrogen by the process of denitrification. In the soil as well as oceans there are special denitrifying bacteria (Pseudomonas and Thiobacillus), which convert the nitrates/nitrites to elemental nitrogen. This nitrogen escapes into the atmosphere, thus completing the cycle.
Step 1: N2 Fixing Nitrogen - Ammonia or Ammoniur Step 2: Nitrification Ammonia or Ammonium Ions Nitrite Nitrate Step 3: Ammonification Dead Matter Animal Waste (Urea, Uric Acid) Ammonia or Ammonium Ions. Dead Matter + Animal Waste (Urea, Uric Acid) - Ammonia or Ammonium lons [most of it escapes into atmosphere. Rest is Nitrified (Step 2) to nitrates] Nitrate [some of it is available for plants. Rest is Denitrified (Step 4)]
Q3. Which of the following adds/add nitrogen to soil? Excretion of urea by animals Burning of coal by man Death of vegetation . Select the correct answer using the codes given below. . 1 only .2 and 3 only 1 and 3 only . 1, 2 and 3
Q4. Consider the following: Carbon dioxide Oxides of Nitrogen Oxides of Sulphur . Which of the above is/are the emission/emissions from coal combustion at thermal power plants? . 1 only .2 and 3 only 1 and 3 only . 1, 2 and 3
Burning coal releases CO, CO2, sulphur dioxide and oxides of nitrogen- air pollutants. * Answer: d) 1, 2 and 3.
Q5. What can be the impact of excessive/inappropri use of nitrogenous fertilizers in agriculture? Proliferation of nitrogen-fixing microorganisms in soil can occur. Increase in the acidity of soil can take place Leaching of nitrate to the ground-water can occur. . Select the correct answer using the code given below. 1 and 3 only 2 only * 2 and 3 only 1,2 and 3
Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia. . Agricultural fertilization and the use of nitrogen fixing plants also contribute to atmospheric NOx, by promoting nitrogen fixation by microorganisms. Excess NOx leads to acid rain. Acid rain lowers pH of soil (increase in acidity of soil) The legume-rhizobium symbiosis is a classic example of mutualism-rhizobia supply ammonia or amino acids to the plant and in return receive organic acids as a carbon and energy source. So, excessive/inappropriate use of nitrogenous fertilizers can make the plants independent of both symbiotic and free living nitrogen fixers. Fixers don't get the food from the plants due to broken relationship and other factors. So their population decreases. . Answer: c) 2 and 3 only
Phosphorus plays a central role in aquatic ecosystems water quality. Unlike carbon and nitrogen, which come primarily from the atmosphere, phosphorus occurs in large amounts as a mineral in phosphate rocks and enters the cycle from erosion and mining activities. This is the nutrient considered to be the main cause of excessive growth of rooted and free-floating microscopic plants (phytoplankton) in lakes [Eutrophication] . The main storage for phosphorus is in the earth's crust. On land phosphorus is usually found in the form of phosphates.
By the process of weathering and erosion phosph enter rivers and streams that transport them to the ocean * In the ocean phosphorus accumulates on continental shelves in the form of insoluble deposits After millions of years, the crustal plates rise from the sea floor and expose the phosphates on land After more time, weathering will release them from rock and the cycle's geochemical phase begins again.