Understanding Energy Sources & Biogeochemical Cycles
Natural Gas
Natural gas is a mixture of combustible gases found underground, often associated with liquid petroleum. The primary component is methane, with smaller proportions of other hydrocarbons like ethane, butane, and propane. Natural gas formation parallels oil formation, resulting from the fermentation of accumulated sediment matter. Initially, natural gas found in oil fields was burned off as waste. However, the need for new energy sources and the discovery of vast natural gas reserves led to solutions for storage and transportation. Its extraction is relatively simple and inexpensive due to the natural pressure that allows the gas to flow. Transportation occurs via pipelines, and for international transport, it is liquefied at very low temperatures.
Nuclear Energy
Nuclear energy originates from reactions between the nuclei of radioisotopes, based on Einstein’s famous formula (E=mc²). This formula explains that the mass difference between atomic nuclei and the sum of their protons and neutrons is due to the energy used in their formation. Energy is released when particles are released from a nucleus. Two primary processes utilize nuclear reactions: fission and fusion.
Nuclear Fission
Bombarding a heavy nucleus with neutrons causes it to decay into two smaller nuclei, releasing significant energy. This process also releases two or three neutrons, which can trigger further fissions, creating a chain reaction. This chain reaction is the principle behind the atomic bomb and the operation of nuclear reactors.
Nuclear Fusion
Two very light nuclei combine to form a heavier, stable nucleus, releasing substantial energy. This fusion requires overcoming electrostatic repulsion forces through thermal energy. Fusion reactions occur in fusion reactors and are considered a potential source of cheap energy due to the abundance of fuel (hydrogen). While technical challenges remain, it is considered a future energy source. It has also been used for military purposes in hydrogen bomb production.
Hydropower
Hydropower is derived from the energy of flowing rivers. Dams, constructed with dikes or barriers, block the valley’s mouth, allowing water to accumulate. The accumulated water is then channeled through a pipe to a turbine, generating electricity by harnessing the dam’s gradient. This process converts the potential energy of the water, due to its height and mass, into mechanical energy in the turbine and finally into electrical energy in the generator.
Stored water in reservoirs can also regulate river flows, mitigate risks to water supply for towns and industries, and support recreational activities. As long as the water balance remains positive, water is continuously renewed, making hydropower a sustainable, low-cost energy source with minimal maintenance requirements. Hydropower remains the most widely employed renewable energy source for electricity generation.
Alternative Sources of Energy
Alternative energy sources are considered viable replacements for conventional sources, offering the advantages of being clean and, importantly, renewable. These energies are believed to be the future.
Solar Energy
While all energy sources indirectly derive from the sun, solar energy refers to the direct utilization of this inexhaustible and free resource. Generated by nuclear fusion in the sun, solar energy reaches Earth as electromagnetic radiation. Since it cannot be directly stored, it is converted into thermal or electrical energy. The primary methods of harnessing solar energy include thermal conversion, photovoltaic conversion, and solar architecture.
Photovoltaic Conversion
This process directly converts light into electrical energy through the photovoltaic effect. When solar radiation hits a semiconductor material, it generates electron movement, creating a potential difference that can be harnessed by electric generators. This is achieved using silicon photovoltaic cells mounted on solar panels, which capture sunlight and convert it into direct current. This energy is stored in batteries to provide power during non-daylight hours. Photovoltaic conversion is pollution-free and produces electricity silently. However, it requires significant space for installation and can have a visual impact.
Wind Energy
Wind energy, harnessed by humans since ancient times, is now utilized by converting the kinetic energy of wind into electricity using wind turbines. These turbines, the fundamental components of wind farms, consist of a steel tower topped with a windmill with two or three blades that rotate around a horizontal shaft connected to a generator. They must be oriented to face the wind directly. The advantages and disadvantages of wind energy are similar to those of solar energy: it is inexhaustible, clean, and free, but also dispersed, intermittent, and random. Negative aspects include visual impact and potential harm to birds. Galicia and Andalucia in Spain are communities with high wind potential.
T.9: Biogeochemical Cycles
Carbon Cycle
The primary pathway of the carbon cycle involves the conversion of carbon dioxide (CO2) into living matter through photosynthesis. Another route involves the biochemical fixation of CO2 in the shells and skeletons of organisms. Carbon returns to the atmosphere through cellular respiration, primarily by decomposers breaking down organic waste in sediment or soil. Some carbon is sequestered in sedimentary rocks through a slow process. This carbon re-enters the cycle through the burning of fossil fuels and organic matter or dissolution by carbonated water acting on carbonate rocks. Increased fossil fuel use in the 20th century has led to higher CO2 emissions, raising atmospheric CO2 levels. The long-term effects on the biosphere and climate are a significant concern.
Nitrogen Cycle
Despite nitrogen comprising 78% of the atmosphere, most organisms cannot directly utilize it. It must be converted into assimilable forms like nitrate before incorporation into living matter. Organisms capable of fixing atmospheric nitrogen include nitrogen-fixing symbiotic bacteria and fungi, as well as free-living nitrogen fixers like aerobic bacteria, anaerobic bacteria, and cyanobacteria.
Human intervention in fertilizer production has significantly increased nitrogen fixation, potentially exceeding natural fixation by terrestrial ecosystems. Mismanagement of fertilizers and nitrogenous waste can lead to the rapid eutrophication of aquatic environments.
Ammonification: After nitrate assimilation, organic waste products containing nitrogen are processed by decomposers into ammonia.
Nitrification: The conversion of ammonia to nitrates occurs in two stages: Nitrosomonas convert ammonia to nitrite, and Nitrobacter convert nitrite to nitrate.
Denitrification: The conversion of nitrate to molecular nitrogen is carried out by certain fungi and bacteria under anaerobic conditions, primarily in poorly ventilated or organic-rich soils.
Oxygen Cycle
The oxygen cycle is complex due to the various chemical forms and combinations of oxygen. It exists as molecular oxygen (O2), as part of water (H2O), and in organic compounds. Significant oxygen accumulation occurred only after the evolution of photosynthesis. Oxygen is abundant, but its solubility in water is limited. Photosynthetic oxygen production primarily occurs in illuminated areas. Once oxygen is depleted, the decomposition of organic matter becomes strictly anaerobic, releasing methane, hydrogen, ammonia, hydrogen sulfide, carbon dioxide, and organic acids.
Sulfur Cycle
Sulfur is a component of amino acids, which are the building blocks of proteins. Most sulfur incorporated by organisms is first mineralized as sulfate by decomposers. Sulfur can enter the atmosphere as sulfur dioxide from the combustion of coal and petroleum. Inorganic sulfur, as sulfate, can be transformed into elemental sulfur or hydrogen sulfide under anaerobic conditions by sulfate-reducing bacteria. Hydrogen sulfide in anaerobic aquatic environments is harmful to most organisms. Natural sulfur sources include volcanic emissions and dimethyl sulfide released by seaweed. Human activities, particularly fossil fuel combustion, contribute significantly to atmospheric sulfur dioxide emissions.
Phosphorus Cycle
Phosphorus is a crucial nutrient for organisms, playing a vital role in nucleic acids, phospholipids, ATP, and the skeletal structures of organisms. It is ecologically significant as a limiting nutrient in ecosystem productivity. Producers require phosphorus in the form of inorganic phosphate. Decomposers release inorganic phosphate back into the environment, making it available to producers. A significant portion of phosphate is lost from the food web through sedimentation. The deposition of phosphorus in skeletons and shells represents a long-term loss of phosphorus from ecosystems.