Ecology PART III Recycling Matter Lesson Objectives • Define biogeochemical cycles. • Describe the water cycle and its processes. • Give an overview of the carbon cycle and the oxygen cycle. • Outline the steps of the nitrogen cycle. BIOGEOCHEMICAL CYCLES bio- biotic components geo- geological and abiotic components WATER CYCLE Evaporation, Sublimation, and Transpiration Sun drives the water cycle. Heats oceans, lakes, and other bodies of water. Heated water evaporates. Evaporation Heats ice and snow. Heated ice and snow turns into water vapor. Sublimation Heat causes plants to release water through their stomata (pores in leaves) Transpiration Condensation and Precipitation Rising air currents carry water from evaporation, sublimation, and transpiration into the atmosphere….eventually forming CLOUDS Groundwater and Runoff Rain falls on land and soaks into ground infiltrating and becomes groundwater Or rain falls on land and flows over it Runoff ends up in bodies of water CARBON CYCLE Carbon in rocks is dissolved by water and ends up in oceans Other carbon from burned fossil fuels or their byproducts ends up in the atmosphere or biosphere Note: fossil fuels are formed from the remains of dead organisms Carbon in the Atmosphere • Living organisms release carbon dioxide as a byproduct of cellular respiration. • Carbon dioxide is given off when dead organisms and other organic materials decompose. • Burning organic material, such as fossil fuels, releases carbon dioxide. • When volcanoes erupt, they give off carbon dioxide that is stored in the mantle. • Carbon dioxide is released when limestone is heated during the production of cement. • Ocean water releases dissolved carbon dioxide into the atmosphere when water temperature rises. • From methane gases released from landfills Carbon in the Ocean Water Most comes from atmospheric carbon dioxide that dissolves in ocean water thus forming carbonic acid. (in cooler water) – The process is reversible in warmer water changing carbonic acid to bicarbonate ions – Bicarbonate ions are also deposited into oceans from runoff Carbonic acid H2CO3 Bicarbonate ions HCO3- Carbon in the Biosphere organic pathway • Photosynthetic algae and bacteria take up bicarbonate ions in the ocean use it to synthesize organic compounds • Terrestrial autotrophs remove carbon dioxide from the atmosphere to synthesize organic compounds • Both recycle it back through a process called cellular respiration • Decomposers release carbon dioxide when they consume dead organisms • They rates of exchange are about equal Carbon in Rocks and Sediments (geological pathway) • Long, slow process through rock formation, subduction, and volcanism • In oceans begins as sedimentary rock; pressure of additional layers forms the rock Oxygen Cycle • Movement of oxygen through the atmosphere, biosphere, and the lithosphere. Oxygen and the Hydrosphere • Failures in this type of movement = development of hypoxic (low oxygen) zones or dead zones • Cause: excessive nutrient pollution from human activities that lead to depletion of oxygen required to sustain marine life Oxygen and the Biosphere/Atmosphere • Free oxygen in the biosphere (0.01%) and atmosphere (0.36%). • The main source of atmospheric free oxygen is photosynthesis. Photosynthesizing organisms include the plant life of the land areas as well as the oceans. • Additional source of atmospheric free oxygen comes from photolysis Oxygen and the Lithosphere • Largest reservoir of Earth's oxygen is within the silicate and oxide minerals of the crust and mantle (99.5%). NITROGEN CYCLE • Most nitrogen is stored in the atmosphere (78% nitrogen gas) • Nitrogen moves through abiotic and biotic components of ecosystems Absorption of Nitrogen • Plants and producers make nitrogencontaining organic compounds (chlorophyll, proteins, nucleic acids) • Plants absorb nitrogen from the soil through their root hairs in the from of nitrate ions – Nitrogen is changed in the soil through nitrogen fixation into nitrate ions Nitrate ions NO3- Nitrogen Fixation Nitrogen-fixing bacteria live in soil or in the root nodules of legumes In aquatic system, some cyanobacteria fix nitrogen Nitrogen gas in the atmosphere can also be fixed by lightning Some nitrogen is converted into fertilizer by humans Ammonification and Nitrification • Decomposers break down organic remains and release nitrogen in the form of ammonium ions – Ammonification • Certain soil bacteria convert the ammonium ions into nitrites. Others convert the nitrites into nitrates that plants can absorb – Nitrification Ammonium ions NH4Nitrites NO2Nitrates NO3 Denitrification and the Anammox Reaction • Denitrifying bacteria in soil convert some nitrates back to nitrogen gas NO2 – Denitrification • In aquatic systems, bacteria in the water convert ammonium and nitrite ions to water and nitrogen gas - Anammox Reaction Lesson Summary • • • • • Chemical elements and water are recycled through biogeochemical cycles. The cycles include both biotic and abiotic parts of ecosystems. The water cycle takes place on, above, and below Earth’s surface. In the cycle, water occurs as water vapor, liquid water, and ice. Many processes are involved as water changes state in the cycle. The atmosphere is an exchange pool for water. Ice masses, aquifers, and the deep ocean are water reservoirs. In the carbon cycle, carbon passes among sedimentary rocks, fossil fuel deposits, the ocean, the atmosphere, and living things. Carbon cycles quickly between organisms and the atmosphere. It cycles far more slowly through geological processes. The oxygen cycle produces most available oxygen through photosynthesis by plants on land and phytoplankton on the ocean’s surface. Some oxygen is made in the atmosphere when sunlight breaks down atmospheric water. Oxygen is used by both biotic and abiotic factors in ecosystems: plants, animals, bacteria, decomposition, fire, and oxidizing agents The nitrogen cycle moves nitrogen back and forth between the atmosphere and organisms. Bacteria change nitrogen gas from the atmosphere to nitrogen compounds that plants can absorb. Other bacteria change nitrogen compounds back to nitrogen gas, which re-enters the atmosphere.