BL 103 Basic Ecology Lectures 12 and 13 Dynamics of Ecosystems-Chemical Cycling.pdf

Biogeochemical Cycles The pathways by which chemical...

Biogeochemical Cycles The pathways by which chemicals circulate through ecosystems involve both living (biotic) and nonliving (geologic) components BIO 1032 Basic Ecology Therefore, they are known as biogeochemical cycles Chemical Cycling: Biogeochemical Cycles References: Mader, S. S. and Windelspecht, M. 2016. Biology. 12th Ed. McGraw Hill Education, New York, NY. Raven, P., Johnson, G., Mason, K., Losos, J. and Duncan, T. 2020. Biology. 12th Ed. McGraw Hill Education, New York, NY. 2 Biogeochemical Cycles Biogeochemical Cycles Each organism assembles its body from atoms that previously have been in The atomic constituents of matter are cycling (unlike the soil, the atmosphere, other parts of the abiotic environment, or other energy, which flows one way) organisms Because of this cycling of matter, your body is likely When the organism dies, its atoms are released unaltered to be used by during your life to contain a carbon or oxygen atom… other organisms or returned to the abiotic environment … that once was part of Julius Caesar’s body or Cleopatra’s! 3 4 Biogeochemical Cycles Biogeochemical Cycles In this lesson, we will look at four major biogeochemical cycles: A biogeochemical cycle may be sedimentary or gaseous water, carbon, phosphorus, and nitrogen cycles The phosphorus cycle is a sedimentary cycle: the chemical is absorbed from the soil by plant roots, passed to heterotrophs, and eventually returned to the soil by decomposers. 5 6 Biogeochemical Cycles Water Cycle The carbon and nitrogen cycles are gaseous: The water (or hydrologic) cycle is probably the most familiar of all biogeochemical cycles This means that the chemical returns to and is withdrawn from the atmosphere as a gas All life depends on the presence of water: even organisms that can survive without water in resting states require water to regain activity The bodies of most organisms consist mainly of water: E.g., adult human body is about 60% water by weight 7 8 Water Cycle Water Cycle Each type of biogeochemical cycle has distinctive features Water is synthesized during aerobic A distinctive feature of the water cycle is that… cellular respiration … water is a compound, not an element Therefore it can be synthesized and broken down Aerobic respiration in the mitochondria 9 10 Water Cycle Water Cycle Water is chemically split during The rates of these processes are usually about equal photosynthesis ? A relatively constant amount of water cycles through the biosphere Overview of photosynthesis 11 12 Water Cycle Water Cycle During the water cycle, fresh water is first distilled Next, condensation occurs from salt water through evaporation During condensation, a gas is converted into a During evaporation, liquid water changes to gaseous liquid state (water vapor) in the atmosphere E.g., vaporized fresh water rises into the atmosphere, The sun’s rays cause fresh water to evaporate from the seawater, and the salts are left behind and stored in clouds, cools, and falls as rain over the oceans and the land 13 14 Water Cycle Water Cycle Water evaporates from: Because land lies above sea level, gravity eventually returns all fresh water to the sea Land In the meantime, water is contained within and from plants (evaporation from plants is called transpiration) standing waters (lakes and ponds), flowing water (streams and rivers), and and also from bodies of fresh water groundwater 15 16 Water Cycle Some of the water from precipitation sinks, or percolates, into the ground and saturates the Earth to a certain level The top of the saturation zone is called the groundwater table, or simply, the water table The Water Cycle Water circulates from the atmosphere to the surface of the Earth and back. 17 The Sun provides much of the energy required for evaporation. 18 Carbon Cycle Carbon Cycle In this cycle, organisms in both terrestrial and These nutrients are used by autotrophs and aquatic ecosystems exchange carbon dioxide heterotrophs alike (CO2) with the atmosphere When organisms, including plants, respire, ? CO2 in the atmosphere is the exchange pool carbon is returned to the atmosphere as for the carbon cycle CO2 On land, plants take up CO2 from the air and, CO2 then recycles to plants by way of the through photosynthesis, they incorporate atmosphere carbon into nutrients 19 20 Carbon Cycle Carbon Cycle In aquatic ecosystems, the exchange of CO2 Similarly, when aquatic organisms respire, the CO2 they give off becomes with the atmosphere is indirect HCO3− Carbon dioxide from the air combines with The amount of bicarbonate in the water is in equilibrium with the amount water to produce bicarbonate ion (HCO3−) of CO2 in the air This becomes a source of carbon for algae that produce food for themselves and for heterotrophs 21 22 Carbon Cycle Carbon Cycle Living and dead organisms contain organic carbon and serve as one of the Ordinarily, decomposition of organisms returns CO2 reservoirs for the carbon cycle to the atmosphere The world’s biotic components, particularly trees, contain 800 billion tons Some 300 mya* plant and animal remains were of organic carbon transformed into coal, oil, and natural gas And an additional 1,000–3,000 billion metric tons are estimated to be held These materials are called fossil fuels in the remains of plants and animals in the soil *million years ago 23 24 Carbon Cycle Carbon Cycle Another reservoir for carbon is the inorganic carbonate that accumulates in At present, more CO2 is being deposited in the atmosphere than is being limestone and in calcium carbonate shells removed Many marine organisms have calcium carbonate shells that remain in This is largely due to the burning of fossil fuels and the destruction of forests bottom sediments long after the organisms have died to make way for farmland and pasture Geologic forces change these sediments into limestone By cutting down forests, we reduce a reservoir and also the very organisms that take up excess carbon dioxide 25 26 Carbon Cycle Carbon Cycle Today, the amount of CO2 released into the atmosphere is about twice the In addition to CO2, other gases are excessively emitted into the atmosphere amount that remains in the atmosphere due to human activities Much of the CO2 dissolves into the ocean These other gases include: nitrous oxide (N2O) from fertilizers and animal wastes, and methane (CH4) from bacterial decomposition that takes place particularly in the guts of animals, in sediments, and in flooded rice paddies 27 28 Carbon Cycle These gases are known as greenhouse gases This is because, just like the panes of a greenhouse, they allow solar radiation to pass through but obstruct the escape of infrared rays (heat) back into space This phenomenon is known as the greenhouse effect 29 30  The greenhouse gases are contributing significantly to an overall rise in the Earth’s ambient temperature This trend is called global warming The global climate has already warmed about 0.6°C since the Industrial Revolution It is predicted that the Earth’s temperature may rise 1.5–4.5°C by 2100 if greenhouse emissions continue at the current rates 31 The Carbon Cycle 32 Nitrogen Cycle Nitrogen Cycle Nitrogen gas (N2) makes up about 78% of the atmosphere N2 (nitrogen) fixation occurs when nitrogen gas (N2) is converted to ammonium (NH4+) However, plants cannot make use of nitrogen in its gaseous form Ammonium is a form of nitrogen that plants can ? Nitrogen can be a nutrient that limits the amount of growth in an use ecosystem Some cyanobacteria in aquatic ecosystems and some free-living bacteria in soil are able to fix atmospheric nitrogen in this way 33 34 Nitrogen Cycle Nitrogen Cycle Other nitrogen-fixing bacteria live in nodules on the Plants can also use nitrates (NO3−) as a source of nitrogen roots of legumes, such as beans, peas, and clover The production of nitrates during the nitrogen cycle is called nitrification They make organic compounds containing nitrogen available to the host plants Therefore the host plant can form proteins and nucleic acids 35 36 Nitrogen Cycle Nitrogen Cycle Nitrification can occur in two ways: 2. Ammonium (NH4+) in the soil from various sources is converted to nitrates (NO3−) by 1. Nitrogen gas (N2) is converted to nitrates nitrifying bacteria in soil (NO3−) in the atmosphere The sources of ammonium include This happens when cosmic radiation, meteor trails, decomposition of organisms and animal wastes and lightning provide the high energy needed for nitrogen to react with oxygen 37 38 Nitrogen Cycle Nitrogen Cycle Specifically, NH4+ (ammonium) is converted to NO2− (nitrite), and then Finally, denitrification is the conversion of NO2− is converted to NO3− (nitrate) nitrate back to nitrogen gas, which then enters the atmosphere During the process of assimilation, plants take up NH4+ and NO3− from the soil… Denitrifying bacteria living in the anaerobic mud of lakes, bogs, and estuaries … and use these ions to produce proteins and nucleic acids carry out this process as a part of their own metabolism 39 40 Nitrogen Cycle Nitrogen Cycle In the nitrogen cycle, denitrification would counterbalance nitrogen fixation Fertilizer, which also contains phosphate, runs if not for human activities off into lakes and rivers Humans significantly alter the transfer rates in the nitrogen cycle by This results in an overgrowth of algae and producing fertilizers from N2 rooted aquatic plants In fact, they nearly double the fixation rate When the algae die off, enlarged populations of decomposers use up all the oxygen in the water This results is a massive fish kill 41 42 Nitrogen Cycle Nitrogen Cycle Acid deposition occurs because nitrogen oxides (NOx) and sulfur dioxide Acid deposition has drastically affected forests (SO2) enter the atmosphere from the burning of fossil fuels and lakes in northern Europe, Canada, and the northeastern United States Both these gases combine with water vapor to form acids This is because their soils are naturally acidic These acids eventually return to the Earth and their surface waters are only mildly alkaline (basic) 43 44 Nitrogen Cycle Acid deposition reduces agricultural yields and corrodes marble, metal, and stonework 45 The Nitrogen Cycle 46 Phosphorus Cycle Phosphorus Cycle Phosphorus, trapped in oceanic sediments, moves onto land due to a Animals eat producers and incorporate some of the geologic uplift phosphate into their teeth, bones, and shells On land, the very slow weathering of rocks places phosphate ions (PO3− and These structures take many years to decompose HPO4+) in the soil However, eventually the death and decay of all organisms Some of these become available to plants and the decomposition of animal wastes make phosphate ions available to producers once again Plants use phosphate in a variety of molecules, including phospholipids, ATP, and the nucleotides that become a part of DNA and RNA 47 48 Phosphorus Cycle Phosphorus Cycle The available amount of phosphate is usually being used within food chains Some phosphate naturally runs off into aquatic ecosystems Because of this, phosphate is usually a limiting inorganic nutrient for plants In these, the algae acquire phosphate from the water before it becomes trapped in sediments That is, the lack of phosphate limits the size of populations in ecosystems Phosphate in marine sediments does not become available to producers on land again until a geologic upheaval exposes sedimentary rocks on land Now, the cycle begins again 49 50 Phosphorus Cycle Human beings boost the supply of phosphate by mining phosphate ores for producing fertilizer and detergents Runoff of phosphate and nitrogen due to fertilizer use, animal wastes from livestock feedlots, and discharge from sewage treatment plants results in eutrophication (overenrichment) of waterways 51 The Phosphorus Cycle 52