Just as rocks can cycle between igneous , sedimentary and metamorphic , carbon and water can exist in different forms at different times. Nitrogen in soil is absorbed by plants which are then eaten by animals. Animals release nitrogen through processes such as excretion and egestion. Animal waste and dead animals are broken down by bacteria which returns nitrogen to the soil. Many humans eat protein in the form of meat from other animals. Our bodies break down this protein into its constituent parts, called amino acids.
The biosphere includes all life, from the single-celled organisms in a pond to the mighty grizzly bear, and from tiny lichens to Douglas-fir trees. These four spheres are interconnected. As an example, a bull trout part of the biosphere swims upstream part of the hydrosphere to spawn. Some water from the stream hydrosphere trickles through the rock and soil part of the lithosphere. Changes to spheres can be natural earthquake or human caused air pollution , and changes in one sphere often result in changes in another.
The four spheres work together to create our environment and sustain life on earth. Within the environment are the smaller systems called ecosystems. A very small amount of free oxygen exists in either the biosphere or atmosphere.
The greatest source of atmospheric oxygen is plant photosynthesis which produces sugars and oxygen from carbon dioxide and water. Photosynthesizing organisms include plants on land and in the water. Photosynthesis maintains the level of oxygen in the atmosphere and provides energy to all life forms—either directly for the plants themselves or indirectly as the food source for organisms that consume the plants, and, ultimately the organisms that consume them. Additional atmospheric oxygen is the result of photolysis , a breaking down by ultraviolet radiation of atmospheric water and nitrite into component atoms.
The atmosphere loses oxygen as organisms respire and decay, methods by which bacteria and animal life consume oxygen and release carbon dioxide.
Carbon Cycle One of the most important cycles on earth, the carbon cycle is the process through which the organisms of the biosphere recycle and reuse carbon. Carbon moves through four interconnected reservoirs: the atmosphere, the terrestrial biosphere including non-living organic materials and freshwater systems , the oceans, and sediments including fossil fuels.
Carbon moves between these reservoirs as a result of biological, chemical, physical, and geological processes. Carbon is released into the atmosphere through plant and animal respiration; the decay of plant and animal material; the burning of fossil fuels such as coal, oil, and natural gasses; volcanic eruptions; and in reactions at the surface of the oceans. Nitrogen Cycle Nitrogen, the most abundant element in the atmosphere, is essential to all life.
It is necessary for numerous biological processes, and is a critical component of Deoxyribonucleic Acid DNA , the genetic instructions for all living things and Ribonucleic acid RNA , biologically important molecules. This nitrogen and nitrogenous waste from animals is then processed back into gaseous nitrogen by soil bacteria, which also supply terrestrial food webs with the organic nitrogen they need. Human activity can release nitrogen into the environment by two primary means: the combustion of fossil fuels, which releases different nitrogen oxides, and the use of artificial fertilizers in agriculture, which are then washed into lakes, streams, and rivers by surface runoff.
A major effect from fertilizer runoff is saltwater and freshwater eutrophication: a process whereby nutrient runoff causes the excess growth of microorganisms, depleting dissolved oxygen levels and killing ecosystem fauna. A similar process occurs in the marine nitrogen cycle, where the ammonification, nitrification, and denitrification processes are performed by marine bacteria.
Although the movement of nitrogen from rock directly into living systems has been traditionally seen as insignificant compared with nitrogen fixed from the atmosphere, a recent study showed that this process may indeed be significant and should be included in any study of the global nitrogen cycle. Phosphorus is an essential element of living things, but, in excess, it can cause damage to ecosystems. Phosphorus is an essential nutrient for living processes.
It is a major component of nucleic acid, both DNA and RNA; of phospholipids, the major component of cell membranes; and, as calcium phosphate, makes up the supportive components of our bones. Phosphorus is often the limiting nutrient necessary for growth in aquatic ecosystems. In addition to phosphate runoff as a result of human activity, natural surface runoff occurs when it is leached from phosphate-containing rock by weathering, thus sending phosphates into rivers, lakes, and the ocean.
This rock has its origins in the ocean. Phosphate-containing ocean sediments form primarily from the bodies of ocean organisms and from their excretions. However, in remote regions, volcanic ash, aerosols, and mineral dust may also be significant phosphate sources. Weathering of rocks and volcanic activity releases phosphate into the soil, water, and air, where it becomes available to terrestrial food webs. Phosphate enters the oceans via surface runoff, groundwater flow, and river flow.
Phosphate dissolved in ocean water cycles into marine food webs. Some phosphate from the marine food webs falls to the ocean floor, where it forms sediment. Phosphorus is also reciprocally exchanged between phosphate dissolved in the ocean and marine ecosystems.
The movement of phosphate from the ocean to the land and through the soil is extremely slow, with the average phosphate ion having an oceanic residence time between 20, and , years. Excess phosphorus and nitrogen that enters these ecosystems from fertilizer runoff and from sewage causes excessive growth of microorganisms and depletes the dissolved oxygen, which leads to the death of many ecosystem fauna, such as shellfish and finfish.
This process is responsible for dead zones in lakes and at the mouths of many major rivers. Dead zones : Dead zones occur when phosphorus and nitrogen from fertilizers cause excessive growth of microorganisms, which depletes oxygen, killing flora and fauna.
Worldwide, large dead zones are found in coastal areas of high population density. A dead zone is an area within a freshwater or marine ecosystem where large areas are depleted of their normal flora and fauna. These zones can be caused by eutrophication, oil spills, dumping of toxic chemicals, and other human activities. The number of dead zones has been increasing for several years; more than of these zones were present as of One of the worst dead zones is off the coast of the United States in the Gulf of Mexico, where fertilizer runoff from the Mississippi River basin has created a dead zone of over 8, square miles.
Phosphate and nitrate runoff from fertilizers also negatively affect several lake and bay ecosystems, including the Chesapeake Bay in the eastern United States, which was one of the first ecosystems to have identified dead zones.
Sulfur is deposited on land as precipitation, fallout, and rock weathering, and reintroduced when organisms decompose. Sulfur is an essential element for the macromolecules of living things. As a part of the amino acid cysteine, it is involved in the formation of disulfide bonds within proteins, which help to determine their 3-D folding patterns and, hence, their functions.
Sulfur cycles exist between the oceans, land, and atmosphere. Sulfur cycle : Sulfur dioxide from the atmosphere becomes available to terrestrial and marine ecosystems when it is dissolved in precipitation as weak sulfuric acid or when it falls directly to the earth as fallout.
Weathering of rocks also makes sulfates available to terrestrial ecosystems. Decomposition of living organisms returns sulfates to the ocean, soil, and atmosphere. On land, sulfur is deposited in four major ways: precipitation, direct fallout from the atmosphere, rock weathering, and decomposition of organic materials. Atmospheric sulfur is found in the form of sulfur dioxide SO 2.
As rain falls through the atmosphere, sulfur is dissolved in the form of weak sulfuric acid H 2 SO 4 , creating acid rain. Sulfur can also fall directly from the atmosphere in a process called fallout. The weathering of sulfur-containing rocks also releases sulfur into the soil. These rocks originate from ocean sediments that are moved to land by the geologic uplift.
Upon the death and decomposition of these organisms, sulfur is released back into the atmosphere as hydrogen sulfide H 2 S gas. Sulfur may also enter the atmosphere through geothermal vents. Sulfur vents : At this sulfur vent in Lassen Volcanic National Park in northeastern California, the yellowish sulfur deposits are visible near the mouth of the vent.
Sulfur enters the ocean via runoff from land, fallout, and underwater geothermal vents. Some marine ecosystems rely on chemoautotrophs, using sulfur as a biological energy source. This sulfur then supports marine ecosystems in the form of sulfates. Human activities have played a major role in altering the balance of the global sulfur cycle. The burning of large quantities of fossil fuels, especially from coal, releases large amounts of hydrogen sulfide gas into the atmosphere, creating acid rain.
Acid rain is corrosive rain that causes damage to aquatic ecosystems and the natural environment by lowering the pH of lakes, which kills many of the resident fauna; it also affects the human-made environment through the chemical degradation of buildings. For example, many marble monuments, such as the Lincoln Memorial in Washington, DC, have suffered significant damage from acid rain over the years. These examples show the wide-ranging effects of human activities on our environment and the challenges that remain for our future.
Privacy Policy. Skip to main content. Search for:. Biogeochemical Cycles. Biogeochemical Cycles The elemental components of organic matter are cycled through the biosphere in an interconnected process called the biogeochemical cycle.
Learning Objectives Summarize the concept of biogeochemical cycles. Materials are recycled via erosion, weathering, water drainage, and the movement of tectonic plates.
Water is essential to all living processes, while carbon is found in all organic macromolecules. Nitrogen and phosphorus are major components of nucleic acids and play major roles in agriculture. Sulfur plays a role in the three-dimensional folding of proteins and is released into the atmosphere by the burning of fossil fuels. Key Terms hydrosphere : combined mass of water found on, under, and over the surface of a planet biogeochemical cycle : cycling of mineral nutrients through ecosystems and through the non-living world.
The Water Hydrologic Cycle Water has a large effect on climate, ecosystems, and living organisms and is continuously cycled through the environment. Learning Objectives Explain the path of the hydrologic cycle and its importance. Key Takeaways Key Points Water cycling affects the climate, transports minerals, purifies water, and replenishes the land with fresh water.
Water with a longer residence time, such as water in oceans and glaciers, is not available for short-term cycling, which occurs via evaporation. Surface water evaporates water to water vapor or sublimates ice to water vapor , which deposits large amounts of water vapor into the atmosphere. Rain percolates into the ground, where it may evaporate or enter bodies of water.
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