Biogeochemical cycles Flashcards
What is a biogeochemical cycle?
A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the abiotic compartments are the atmosphere, hydrosphere and lithosphere.
What are the two groups of biogeochemical cycles?
From the standpoint of the Earth as a whole, there are two groups of biogeochemical cycles:
Perfect, or gaseous, cycles: cycles which have a large gaseous, easily exchangeable, reservoir which makes them less likely to get out of balance –> nitrogen, carbon, oxygen.
Imperfect, or sedimentary, cycles: cycles which involve the more earthbound elements and large portions of the supply may become unavailable for long periods of time, thus disturbing the cycle (calcium, phosphorus, iron).
Key notions of biogeochemical cycles
- Some chemicals cycle quickly and are readily regenerated for biological activity. They typically have a gas phase, are soluble and carried by the hydrologic cycle.
- Other chemical elements are relatively immobile and returned by geological processes. They typically lack a gas phase and are insoluble.
- Chemicals with gas phase are stored in the atmosphere cycle rapidly.
- Those without an atmospheric phase end up in deep-ocean sediment and recycle slowly.
- Evolution of life has altered the biogeochemical cycles
- The continuation of processes that control biogeochemical cycles are essential for maintenance of life.
What are nutrients?
Nutrients are chemical substances (single elements and simple inorganic compounds) found in every living thing on Earth. They are necessary to the lives of people, plants, animals, and all other organisms. Nutrients help break down food to give organisms energy. They are used in every process of an organism’s body like survival, growth and reproduction.
Difference between energy flow and matter cycles?
The key difference between energy flow and matter cycling is that energy flow shows the energy transmission from one trophic level to next trophic level in food chains while matter cycling shows the flow or cycling of elements through the living and nonliving parts of ecosystems.
Energy flows through an ecosystem, while matter cycles within it:
–> Energy enters an ecosystem when producers carry out photosynthesis, capturing energy from the sun and storing it as chemical potential energy. During this process, matter from the environment (CO2) is taken in and rearranged into organic molecules (sugars). These molecules can power the producers’ life processes via cellular respiration (which releases CO2 and heat), or they can be stored as biomass.
–> Next, energy and matter move up the trophic levels as producers are eaten by primary consumers, and so on. Some of the organic material eaten by consumers is used for cellular respiration (again, releasing CO2 and heat), some is stored as biomass, and the rest is excreted as waste.
–> Dead producers, consumers and their waste provide matter and energy to decomposers. Decomposers transform matter back into inorganic forms that can be recycled within the ecosystem.
So, the energy that enters an ecosystem as sunlight eventually flows out of the ecosystem in the form of heat. In contrast, the matter in an ecosystem is continuously recycled as atoms are combined and recombined in different ways.
What are the essential nutrients for life?
Of the 103 known elements only 24 are required for life. Macronutrients are required in large amounts and the most important ones are: carbon, hydrogen, nitrogen, oxygen phosphorus and sulfur. Micronutrients are required in small/moderate amounts (some are dangerous in big amounts). For life to persist, elements must be available at the right time, right amount and right concentrations relative to one another, otherwise they become a limiting factor.
Even if the nutrient elements are in the soil or in water of an area, they may be unavailable to organisms. Nitrogen is an example of an element present in the atmosphere but unavailable to organisms because it requires other passages to become available. Some organisms can only utilize an element when it is present in a specific compound. PH also affects the availability by either changing the chemical form of the element or by interfering with the uptake of that substance.
Explain the water cycle
Water is essential to life on Earth. In its three phases (solid, liquid, and gas), water ties together the major parts of the Earth’s climate system — air, clouds, the ocean, lakes, vegetation, snowpack, and glaciers offsite link.
The water cycle shows the continuous movement of water within the Earth and atmosphere. It is a complex system that includes many different processes. Liquid water evaporates into water vapor, condenses to form clouds, and precipitates back to earth in the form of rain and snow. Water in different phases moves through the atmosphere (transportation). Liquid water flows across land (runoff), into the ground (infiltration and percolation), and through the ground (groundwater). Groundwater moves into plants (plant uptake) and evaporates from plants into the atmosphere (transpiration). Solid ice and snow can turn directly into gas (sublimation). The opposite can also take place when water vapor becomes solid (deposition).
–> energy from the sun is the basis of the cycle of water.
Unique properties of water:
- strong forces of attraction between molecules of water
- water exists as a liquid over a wide temperature range
- liquid water changes temperature slowly
- it takes a large amount of energy for water to evaporate
- liquid water can dissolve a variety of compounds including rock
- water expands when it freezes
Effects of humans on water cycle:
- withdrawing of large amounts of freshwater from the ground causing salt water to contaminate reservoirs
- withdrawing large amounts from rivers and streams changes flow of nutrients
- clearing vegetation causes eroding soils that clog streams
- polluting surface and underground water
All these changes contributes to climate change.
Explain the carbon cycle
Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. The carbon cycle, one of the most complex cycles on Earth, describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration to and release from carbon sinks.
On Earth, most carbon is stored in rocks and sediments, while the rest is located in the ocean, atmosphere, and in living organisms. These are the reservoirs, or sinks, through which carbon cycles. Carbon is released back into the atmosphere when organisms die, volcanoes erupt, fires blaze, fossil fuels are burned, and through a variety of other mechanisms. In the case of the ocean, carbon is continually exchanged between the ocean’s surface waters and the atmosphere, or is stored for long periods of time in the ocean depths.
Main characteristics of the carbon cycle:
- carbon just like all other nutrients cycles from one reservoir to another through many years.
- carbon enters plants as CO2 which is incorporated into organic molecules by the process of photosynthesis.
- when organisms respire, a portion of this carbon is returned to the atmosphere as CO2.
- carbon reservoir pools are: organic molecules (living and dead organisms), CO2 in the atmosphere, organic matter in soil, fossil fuels and sedimentary rock like limestone, CO2 in ocean/water bodies, calcium carbonate in the shells of marine organisms.
Effects of humans on the carbon cycle:
- -> burning of fossil fuels
- -> clearing vegetation faster than it is replaced
- -> breathing (we are too many)
Explain the Nitrogen cycle
Nitrogen is the second largest nutrient cycle o the planet, second only to carbon. Although 78% by volume of the atmosphere is nitrogen gas, this abundant reservoir exists in a form unusable by most organisms. Through a series of microbial transformations, however, nitrogen is made available to plants, which in turn ultimately sustain all animal life. The steps, which are not altogether sequential, fall into the following classifications: nitrogen fixation, nitrogen assimilation, ammonification, nitrification, and denitrification.
Nitrogen fixation: nitrogen gas is converted into inorganic nitrogen compounds, is mostly accomplished by certain bacteria and blue-green algae. A much smaller amount of free nitrogen is fixed by abiotic means (e.g., lightning, ultraviolet radiation, electrical equipment) and by conversion to ammonia.
Nitrates and ammonia resulting from nitrogen fixation are assimilated into the specific tissue compounds of algae and higher plants. Animals then ingest these algae and plants, converting them into their own body compounds.
The remains of all living things are decomposed by microorganisms in the process of ammonification, which yields ammonia and ammonium. Ammonia can leave the soil or be converted into other nitrogen compounds, depending in part on soil conditions.
Nitrification, a process carried out by nitrifying bacteria, transforms soil ammonia into nitrates, which plants can incorporate into their own tissues. Nitrates also are metabolized by denitrifying bacteria, which are especially active in water-logged anaerobic soils. The action of these bacteria tends to deplete soil nitrates, forming free atmospheric nitrogen.
Effects of human activities on nitrogen cycle:
- -> adding gases to atmosphere that contribute to acid rain
- -> adding nitrous oxide to the atmosphere through faring practices which can warm the atmosphere and deplete ozone
- -> contaminating groundwater from nitrate ions in inorganic fertilizers
- -> releasing nitrogen into the troposphere trough deforestation
Fertilizers now “fix” more nitrogen than all natural sources combined.
Explain the phosphorous cycle
phosphorus cycle, circulation of phosphorus in various forms through nature. Of all the elements recycled in the biosphere, phosphorus is the scarcest and therefore the one most limiting in any given ecological system. It is indispensable to life, being intimately involved in energy transfer and in the passage of genetic information in the deoxyribonucleic acid (DNA) of all cells.
Much of the phosphorus on Earth is tied up in rock and sedimentary deposits, from which it is released by weathering, leaching, and mining. Some of it passes through freshwater and terrestrial ecosystems via plants, grazers, predators, and parasites, to be returned to those ecosystems by death and decay. Much of it, however, is deposited in the sea, in shallow sediments, where it circulates readily, or in ocean deeps, whence it wells up only occasionally. Phosphorus is brought back to the land through fish harvests and through collection of guano deposited by seabirds. Although there are seasonal pulses of availability, there appears to be a steady loss of phosphorus to the ocean deeps.
Because of the steady diversion of phosphorus into the oceans, the element must be added (in fertilizers) to soils to maintain fertility and agricultural productivity.
Effects of humans on phosphorus cycle:
- -> we remove large amounts of phosphate from the earth to make fertilizers
- -> we reduce phosphorus in tropical soils by clearing forests
- -> we add excess phosphate to aquatic systems from runoff animal wastes and fertilizers
Explain the sulfur cycle
All living things require sulfur to make proteins. Sulfur reserves are found in the lithosphere and are released by weathering. In addition hydrogen sulfide is released in the atmosphere by volcanic eruptions, hot springs and the decay of biological material in swamps. Marine algae produce dimethyl sulfide that is released into the atmosphere in droplets. When Dimethyl sulfide reacts with water it forms sulfur dioxide gas. Burning of fossil fuels also release sulfur dioxide into the atmosphere.
Sulfur dioxide reacts with oxygen in the atmosphere and creates sulfur trioxide, which reacts with water in the atmosphere to create sulfuric acid. Sulfur trioxide also reacts with ammonia in the atmosphere and creates sulfate salts.
Sulfate salts and sulfuric acid fall down on the earth with precipitations. The soil absorbs sulfate salts, plants absorb it and animals do as well by eating the plants. Animals then release sulfur when they decay.
Effects of humans on the sulfur cycle:
- -> burning of coal and oil
- -> refining sulfur containing petroleum
- -> converting sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.
