NUTRIENT CYCLES AND HUMAN IMPACT NOTES

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1 NUTRIENT CYCLES AND HUMAN IMPACT NOTES I. Nutrient Cycles Unlike energy in an ecosystem, which flows in one direction and decreases as it flows, matter is recycled within the biosphere. Matter passes through organisms and through various abiotic factors. As matter passes through biotic and abiotic factors, it can be changed, but never created anew or destroyed. These flows of different types of matter are called biogeochemical cycles. Biogeochemical cycles are made up of four processes: Biological Processes: Activities performed by living things. These include eating, breathing, respiration, and waste elimination Geological Processes: These include volcanic eruptions, formation and erosion of rock. Chemical Processes: Formation of clouds, precipitation, flow of running water and the action of lightning. Human Activity: Mining, burning of fossil fuels, clearing of land, burning of forests, and the manufacture and use of fertilizers and other compounds 1. The Water Cycle Water continuously moves between the oceans, the atmosphere and land, sometimes passing through living things on the way. Water is split apart during photosynthesis to form Oxygen gas, Hydrogen and electrons. Water is put together during aerobic respiration from inhaled Oxygen gas and Hydrogen and electrons from the Electron Transport Chain. Water enters the atmosphere as water vapor (a gas) when it evaporates from bodies of water or from living things. Plants are an important component of the water cycle as they can take up water trapped deep in the earth and have it evaporate from the surface of their leaves. Wind can transport water vapor over large distances and as the water vapor cools it can fall as precipitation, thus bringing new water to new locations.

2 2. The Carbon Cycle Plants use CO 2 from the atmosphere to make glucose (high-energy carbon molecules) via photosynthesis Primary consumers, after consuming plants, make ATP by breaking the glucose down into CO 2 via aerobic respiration All of the complex compounds in living things contain carbon: Carbohydrates, Proteins, Lipids, and Nucleic Acids. When organisms die and decay, the carbon molecules in them enter the soil. Microorganisms break down the molecules, releasing CO 2 Plants use the CO 2 again to make glucose. Lather, rinse, repeat. Carbon Pool: A reservoir with the capacity to store and release carbon. Carbon is stored on our planet in the following major carbon pools: As organic molecules in living and dead organisms found in the biosphere As gaseous CO 2 in the atmosphere As organic matter in soil In the earth as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk In the oceans as dissolved atmospheric CO 2 & as calcium carbonate shells in marine organisms The Carbon Cycle

3 3. The Nitrogen Cycle All organisms require Nitrogen, which is used to make Amino Acids (monomers of Proteins) and Nucleotides (monomers of Nucleic Acids). Nitrogen occurs in many different forms in the biosphere: Nitrogen gas (N 2 ) makes up 78% of the Earth's atmosphere Ammonia (NH 3 ), Nitrate (NO 3 ) and Nitrite (NO 2 ) are found in soil as wastes produced by many organisms. Even though most of the Nitrogen on Earth is in the form of Nitrogen gas, very few organisms (called Nitrogen-Fixing Bacteria) can access Nitrogen in that form. In order for Nitrogen in the form of Nitrogen gas to be available to other organisms, these Nitrogen-Fixing Bacteria must first convert Nitrogen Gas into Ammonia. The Ammonia is then converted via Nitrification into Nitrites and Nitrates which can be utilized by a much wider range of organisms to make amino acids and nucleotides. Nitrates can be converted into Nitrogen Gas via Denitrification. Humans add nitrogen to the biosphere through the manufacture and use of fertilizers. Lightning is also able to convert Nitrogen gas into other forms via a process called Atmospheric Nitrogen Fixation.

4 4. The Phosphorus Cycle Phosphorus is an essential component of phospholipids (which make up cell membranes) and nucleic acids. While phosphorus is of great biological importance, it is not abundant in the biosphere. Unlike carbon, nitrogen and oxygen, phosphorus does not enter the atmosphere in significant amounts. Most phosphorus remains on land, in the form of phosphate rocks and soil minerals, and in the oceans, as dissolved phosphate and phosphate sediments. As rocks and sediments wear down, phosphate is released, becoming available to living organisms.

5 II. Humans in the Biosphere 1. Human Population Growth Like the populations of other organisms, the human population tends to increase over time. The rate of that increase has changed dramatically over time. For most of human existence, food was hard to find, winters/summers were harsh and predators and diseases were common and life-threatening. Until fairly recently, only half of the children in the world survived until adulthood. As civilization advanced, food became more plentiful, and sanitation and medicine led to lower death rates. These lower death rates led to an exponential growth in the human population. Recently, the growth of the world human population has been slowing. It took 123 years for the population to double from 1 billion in 1804 to 2 billion in Then, it took a mere 33 years for it to grow by another 1 billion people to 3 billion in To reach 4 billion people in 1974, it only took 14 years. To reach 5 billion in 1987, it only took 13 years. It only took 12 years for the next 1 billion people to be added to reach 6 billion in In 2012, the next billion was added to bring the total human population to 7 billion. It is expected to take 15 years for the next billion to be added, bringing the human population to 8 billion in 2027, and then 19 years for us to reach 9 billion in The reason for this slowing of the human population growth is due mostly to a drop in birth rates and a leveling off of death rates in developed countries. 2. Human Effects on the Biosphere Humans affect regional and global environments through agriculture, development, and in industry in ways that have an impact on the quality of Earth's natural resources, including soil, water and the atmosphere. 3. Agriculture Having a dependable supply of food that can be stored for later use is what fueled the movement of humans from small settlements to towns and large cities. Over the last 50 years, modern agriculture practices have allowed farmers to double world food production. Monoculture: The practice of clearing large areas of land to plant a single highly productive crop year after year. Monoculture can lead to the rapid spreading of pests and disease through the uniformly planted crops. Fertilizers: The use of industrially produced fertilizers have allowed farmers to add back lost nutrients to soil to help maintain the productivity of the soil. Excess fertilizer use leads to run off into lakes, rivers and oceans, which in turn leads to an excess of nutrients which fuels algal growth. This algal growth uses huge amounts of oxygen, thus depleting the oxygen from the water causing many other organisms to die. Pesticides: The use of pesticides have helped farmers increase their crop output by limiting the damage done by a large variety of pests. Many pesticides are toxic not only to their intended target, but to other species as well, including humans. 4. Development As societies developed, many people opted to live in cities. As cities fill up, people move to, and build up, suburbs. Dense human communities produce lots of wastes. If these wastes are not disposed of properly, they can affect the quality of the air, water and soil. In addition, human developments uses up farmland and partitions natural habitats into fragments.

6 5. Industrial Growth The advent of the Industrial Revolution in the 1800s has provided us with a higher quality of life and modern conveniences. The production of these modern conveniences requires a tremendous amount of energy (provided by fossil fuels) and large amounts of natural resources that must be mined from the earth, some in ecologically or politically sensitive areas. In addition, many of our modern electronic devices have short life spans, and once disposed of, many of the components end up polluting the air, soil and water. 6. Water Pollution and Biomagnification Pollutants are harmful materials that can enter the biosphere. Single source pollutants: Pollutants that enter water supplies from a single source, such as from a factory or an oil spill. Nonpoint source pollutants: Pollutants that enter water supplies from many smaller sources, such as grease and oil washed off streets by rain, or the chemicals released into the air by factories and automobiles. Once contaminants are present in a part of the ecosystem, they can be very hard to get rid of. DDT was a pesticide used to control agricultural pests and disease-carrying mosquitoes. DDT can be picked up by an organism in the environment, but it is not broken down or eliminated from its body. Instead, DDT builds up in the body tissues of organisms. Plants (primary producers) picked up DDT from the direct spraying of the compound. Herbivores (primary consumers) then ate the plants which lead to the storage and concentration of DDT in their body tissues. Carnivores then eat the herbivores, thus leading to further storage and concentration of DDT in their body tissues. As DDT moves up the food chain, it becomes more and more concentrated until it leads to severe problems in apex predators (tertiary and quaternary consumers). DDT causes female birds such as pelicans, falcons and bald eagles to lay eggs with thin, fragile shells. When the female tries to incubate those eggs, she ends up crushing them. The widespread use of DDT in the 1950s led to a dramatic drop in the population of avian predators. Since DDT was banned in the 1970s, bird populations have recovered. 7. Air Pollution Smog: A gray-brown haze formed by chemical reactions among pollutants released into the air by industrial processes and automobile exhaust. Ozone is one component of smog. While ozone in high atmosphere helps to protect living things from UV light, ozone at ground level can lead to respiratory problems in humans. Acid rain: When fossil fuels are burned, nitrogen and sulfur compounds are released into the air. When these compounds combine with water vapor in the air, they form nitric and sulfuric acids. This acidified rain can fall many miles from where they are produced, thus damaging plants and changing the chemistry of soil on farms. Greenhouse Gases: Burning fossil fuels releases stored carbon into the air as CO 2. Raising cattle and farming rice releases methane into the air. CO 2 and methane are greenhouse gases that trap heat and contribute to rising global temperatures and climate change.