Biogeochemical Cycles Biology 20

Chemicals Cycle Inorganic nutrients are cycles through natural ecosystems repeatedly. Biogeochemical cycles are the pathways by which chemicals circulate. –Water Cycle –Phosphorus Cycle –Nitrogen Cycle –Carbon Cycle Chemicals Cycle, Energy Flows

Water Cycle Saltwater evaporates from sun’s energy producing fresh water in clouds; leaves salt in the ocean Water vapor cools and condenses to precipitation over oceans and land. Runoff forms fresh water lakes, streams, ponds, ground water, and is held in plants and transpired.

Water cycle Gravity returns water to oceans but some moves slowly through water table and porous aquifers between rock layers. Although the water cycle shows water to be a renewable resource, the 3% of water that is fresh may be polluted or inadequate for human populations concentrated in specific areas.

Percolation

Acid Deposition and the Water Cycle Sulfur dioxide is released by the burning of substances that contact sulfur such as fossil fuels and metal ores. Nitrous oxides are produced by the burning of fossil fuels. These combine with water droplet in the air to produce “acid rain”, which can be 40X more acidic than acid rain. Minimized in Alberta because of the limestone from the mountains

Acid Deposition

Phosphorus Cycle Weathering of rocks makes phosphates ions available to plants through soils. Runoff returns phosphates to aquatic systems and sediments; called a sedimentary cycle. Widely used in organisms for: phospholipids, ATP, teeth, bones, etc Humans Influence the Phosphorus Cycle –We mine phosphate ores for fertilizers, animal feed supplements, detergents –Detergents, untreated human and animal waste, fertilizers from crops, all add excess phosphates to water often causing algae blooms. When the algae die it increases the bacteria in the water. The bacteria then consume large amounts of oxygen, decreasing oxygen levels in the water.

Human Influence Humans Influence the Phosphorus Cycle –We mine phosphate ores for fertilizers, animal feed supplements, detergents –Detergents, untreated human and animal waste, fertilizers from crops, all add excess phosphates to water often causing algae blooms. When the algae die it increases the bacteria in the water. The bacteria then consume large amounts of oxygen, decreasing oxygen levels in the water.

Spring runoff of nitrogen and phosphorus fertilizers promotes the growth of algea.

Nitrogen Cycle Atmospheric nitrogen gas (N 2 ) is unavailable to plants. Plants therefore depend on various types of bacteria to take up nitrogen gas and make it available to them in the form of nitrates. This is done in four ways:

Nitrogen Cycle The first way is Nitrification which is the production of nitrates. In soil, bacteria convert ammonium to nitrate in a two-step process –First, nitrite producing bacteria convert ammonia to nitrites –The nitrate producing bacteria convert nitrite to nitrates. –These two groups of bacteria are called nitrifying bacteria.

Nitrogen Gas becomes Nitrates The third way is Nitrogen gas becomes fixed –Nitrogen fixation occurs when nitrogen gas is reduced and nitrogen is added to organic compounds –Atmospheric nitrogen is converted to ammonium (NH 4 + ) by some nitrogen-fixing bacteria in the nodules on roots of legume plants. –The ammonia is then converted to nitrates to be used by plants.

Nitrogen Gas becomes Nitrates The third way is by the use of fertilizers. The fourth way is Nitrogen gas is converted to nitrates by lightning in the atmosphere. Denitrification is conversion of nitrates to nitrogen gas, which is returned to the atmosphere by denitrifying bacteria.

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The Carbon Cycle Relationships exist between photosynthesis and respiration –Respiration releases carbon dioxide, which is used in photosynthesis –Photosynthesis releases oxygen used in respiration –Therefore animals depend on green organisms for organic food, energy and oxygen

Carbon Cycle In the carbon cycle, organisms exchange carbon dioxide with the atmosphere –On land, plants take up carbon dioxide, via photosynthesis, incorporate it into food used by themselves and heterotrophs –When organisms respire, a portion of the carbon is returned to the atmosphere as carbon dioxide

Carbon Cycle Inorganic carbon is found in three places: the atmosphere, the oceans and the earth crust Organic carbon is held in the bodies of living things. The organic carbon may eventually be converted to fossil fuels

Humans and the Carbon Cycle Humans burning of fossil fuels and wood has increased amount of carbon dioxide released into the atmosphere. Increased CO2 may increase the greenhouse effect, where such gases allow the sun’s rays to pass through to earth where it is absorbed and emitted as heat, but heat is then reflected back to earth, causing global warming.

Greenhouse Effect

Human Impacted Ecosystems Natural ecosystems tend to be stable. –Size of populations are held in check by competition, predation, etc –Energy input-output is balanced; cycles are sustainable –Pollution, and undesirable change in the environment harmful to humans and life; does not normally occur.

Good or bad?? Human beings replace ecosystems with their own.

The Solution ?