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Chapter 5 The Biogeochemical Cycles Botkin & Keller Environmental Science 5e The Geologic Cycle • The Geologic Cycle: – The processes responsible for formation and change of Earth materials – Best described as a group of cycles: • • • • Tectonic Rock hydrologic Biochemical Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Tectonic Cycle Creation and destruction of the Lithosphere Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers The Rock Cycle • The rock cycle: – Numerous processes that produce rocks and soils – Depends on other cycles: • tectonic cycle for energy • Hydrologic cycle for water for erosion – Rock is classified as • Igneous – high heat, volcanic • Sedimentary – weathering & erosion • Metamorphic – compact, melting Botkin & Keller Environmental Science 5e How Chemicals Cycle • Biogeochemical Cycle – The complete path a chemical takes through the four major components – or reservoirs – of Earth’s systems 1. 2. 3. 4. Atmosphere Hydrosphere Lithosphere Biosphere Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Biogeochemical Cycles and Life: Limiting Factors • Macronutrients – Elements required in large amounts by all life – Include the “big six” elements that form the fundamental building blocks of life: hydrogen carbon oxygen phosphorus nitrogen sulfur • Micronutrients – Elements required either in • small amounts by all life or • moderate amounts by some forms of life and not all by others • Limiting factor – When chemical elements are not available at the right times, in the right amounts, and in the right concentrations relative to each other Botkin & Keller Environmental Science 5e Major Chemical Cycles • • • • Water (hydrologic) Carbon Nitrogen Phophorus Botkin & Keller Environmental Science 5e The Hydrologic Cycle • The Hydrologic Cycle: – The transfer of water from the oceans to the atmosphere to the land and back to the oceans. POWERED BY THE SUN !! – Includes: • • • • Evaporation of water from the oceans Precipitation on land Evaporation from land Runoff from streams, rivers, and sub-surface groundwater • Transpiration from plants Botkin & Keller Environmental Science 5e Human Impacts • Withdrawal: – Removal from society & industry faster than recharged (overdraft) • Increased flooding: – Removal of wetlands & creating non-pourous tracts • Deforestation: – Clearing land reduces transpiration, therefore there is a decrease in precipitation. Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Botkin & Keller Environmental Science 5e The Carbon Cycle • 4th most abundant element in the universe • Building block of life • Cycles through the geosphere, biosphere, ocean and atmosphere • Two types of cycling – Geological carbon cycle – Biological carbon cycle Botkin & Keller Environmental Science 5e Geological Carbon Cycle Botkin & Keller Environmental Science 5e How does this work? • CO2 reacts with atmospheric water and minerals to produce calcium carbonate. • Calcium carbonate rock (limestone) weathered by water – dissolves and travels to ocean. • Forms sedimentary layers in the ocean. Through plate tectonics, sediments subduct and melts. • Carbon is released into the atmosphere during volcanic eruption as CO2 Botkin & Keller Environmental Science 5e Biological Carbon Cycle Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Botkin & Keller Environmental Science 5e Carbon Reservoirs • Ocean – dissolved, calcium carbonate of marine organisms shells • Geosphere – soils, fossil fuels • Biosphere –living organisms • Atmosphere – 0.038% of troposphere – (Acts as natural thermostat for Earth) Botkin & Keller Environmental Science 5e Human impacts • Increases Carbon Dioxide in the atmosphere by: – Burning of fossil fuels – Clear cutting of trees Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Botkin & Keller Environmental Science 5e The Nitrogen Cycle • The nitrogen cycle: – Limiting factor for primary productivity – 2 forms as nutrients: NH4 and NO3 – Conversion of N2 gas into nutrients – lightning & nitrogen fixing bacteria • Nitrogen reservoirs: – Atmosphere • 78% of Troposphere Botkin & Keller Environmental Science 5e Common nitrogen compounds • • • • • • • • N2 - nitrogen gas NH4 - ammonium NH3 - ammonia NO3 - nitrate NO2 - nitrite N2O - nitrous oxide NO2 - nitrogen dioxide HNO3 - nitric acid Botkin & Keller Environmental Science 5e Steps in the Nitrogen Cycle • Nitrogen fixation: – N2 converted to NH4 or NH3 by bacteria • Ammonification (mineralization) – Decomposers turn organic material into NH4 or NH3 • Nitrification – Bacteria convert NH4 & NH3 into NO3 for plant uptake • Denitrification – Bacteria convert NH4 & NH3 into N2 & N2O Botkin & Keller Environmental Science 5e Nitrogen fixation • In order to be used by most living organism nitrogen must by in the form of NH3 or NO3. • Nitrogen is ‘fixed’ by lightning or bacteria. • ‘Fixing’ allows nitrogen to be made biologically available. • Can be found on the roots of legumes. Botkin & Keller Environmental Science 5e Nitrification • Soil bacteria convert ammonia (NH4) into a form that plants can use – NO3 Botkin & Keller Environmental Science 5e Assimilation • Plants absorb ammonium (NH3), ammonia (NH4) and nitrate (NO3) through their roots. • Heterotrophs (or organisms that receive energy from consuming other organisms) obtain nitrogen from consuming plant proteins or other animals. Botkin & Keller Environmental Science 5e Ammonification • Decomposing bacteria convert dead organisms and other waste to ammonia (NH3) or ammonium (NH4), which can be reused by plants Botkin & Keller Environmental Science 5e Denitrification • Specialized bacteria (anaerobic) convert ammonia back to nitrates and nitrites THEN back into nitrogen gas and nitrous oxide, where they enter the atmosphere. Botkin & Keller Environmental Science 5e Nitrogen Cycle Botkin & Keller Environmental Science 5e Additional Info • Assimilation: – Plants take up inorganic nitrogen (NH3 & NO3) and convert to organic compounds (amino acids) Botkin & Keller Environmental Science 5e Human Impacts • Excess Nitrates – Animal waste, municipal discharge • Can promote algae growth • Burning of Fossil Fuels – Released NO, NO2 and HNO3 • Use of inorganic fertilizers – Increases denitrification by anaerobic bacteria, and therefore releases more NO2 into the atmosphere. Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers The Phosphorus Cycle • The phosphorus cycle: – Involves the movement of phosphorus throughout the biosphere and lithosphere – Important because phosphorus is an essential element for life and often is a limiting nutrient for Botkin & Keller plant growth. Environmental Science 5e Phosphorus Reservoirs • Ocean sediments • Terrestrial rock layers – Erosion releases PO4 for producers – Limiting factor for primary productivity Botkin & Keller Environmental Science 5e Guano Island Botkin & Keller Environmental Science 5e Human Impacts • Phosphate run-off from – Sewage, mining & fertilizers – Algal blooms Botkin & Keller Environmental Science 5e Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers Botkin & Keller Environmental Science 5e © 2008 John Wiley and Sons Publishers