The Biogeochemical Cycles Chapter 5 The Biogeochemical Cycles Botkin & Keller Environmental Science 5e

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 Atmosphere Hydrosphere Lithosphere Biosphere Botkin & Keller Environmental Science 5e

Environmental Science 5e Chemical Reactions Ch emical reaction: The process in which new chemicals are formed from elements and compounds through chemical change Botkin & Keller Environmental Science 5e

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: carbon oxygen hydrogen 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

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 Hydrologic Rock Biochemical Botkin & Keller Environmental Science 5e

Environmental Science 5e Tectonic Cycle Tectonic cycle: Involves creation and destruction of the solid outer layer of Earth, the lithosphere Plate tectonics: The slow movement of these large segments of Earth’s outermost rock shell Boundaries between plates are geologically active areas Botkin & Keller Environmental Science 5e

Tectonic Cycle: Plate Boundaries Divergent plate boundary: Occurs at a spreading ocean ridge, where plates are moving away from one another New lithosphere is produced (seafloor spreading) Convergent plate boundary Occurs when plates collide Produces linear coastal mountain ranges or continental mountain ranges Transform fault boundary Occurs where one plate slides past another San Andreas Fault in California Botkin & Keller Environmental Science 5e

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. Includes: Evaporation of water from the oceans Precipitation on land Evaporation from land Runoff from streams, rivers, and sub-surface groundwater Botkin & Keller Environmental Science 5e

Environmental Science 5e 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 Rock is classified as Igneous Sedimentary Metamorphic Botkin & Keller Environmental Science 5e

Environmental Science 5e The Carbon Cycle Carbon is the element that anchors all organic substances The carbon cycle: Carbon combines with and is chemically and biologically linked with the cycles of oxygen and hydrogen that form the major compounds of life Botkin & Keller Environmental Science 5e

Environmental Science 5e Fig 5.15 Idealized diagram illustrating photosynthesis for a green plan (tree) and generalized reaction. Botkin & Keller Environmental Science 5e © 2005 John Wiley and Sons Publishers

The Carbon Cycle: Unanswered Issues The Missing Carbon Sink Substantial amounts of carbon dioxide released into the atmosphere but apparently not reabsorbed and thus remaining unaccounted for Botkin & Keller Environmental Science 5e

The Carbon-Silicate Cycle A complex biogeochemical cycle over time scales as long as one-half billion years. Includes major geological processes, such as: Weathering Transport by ground and surface waters Erosion Deposition of crustal rocks Believed to provide important negative feedback mechanisms that control the temperature of the atmosphere. Botkin & Keller Environmental Science 5e

Environmental Science 5e The Nitrogen Cycle The nitrogen cycle: Cycle responsible for moving important nitrogen components through the biosphere and other Earth systems Extremely important because nitrogen is required by all living things Nitrogen fixation: The process of converting inorganic, molecular nitrogen in the atmosphere to ammonia or nitrate Denitrification: The process of releasing fixed nitrogen back to molecular nitrogen Botkin & Keller Environmental Science 5e

Environmental Science 5e 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 plant growth. Botkin & Keller Environmental Science 5e