Transcript raven ch5
Chapter 5 Ecosystems and the Physical Environment Cycling of Materials within Ecosystems Basics of biogeochemical cycling Energy flows one way through ecosystems Matter cycles continuously through biotic and abiotic components. MATERIAL CYCLES • Carbon Cycle – Begins with intake of CO2 during photosynthesis. Carbon atoms are incorporated into glucose and then: • Remain in plant material until death. – Eaten by predator – Respiration – Excretion » Death (Decomposers) Cycling of Materials within Ecosystems Carbon cycle: Carbon Cycle Nitrogen Cycle • Plants uptake inorganic nitrogen from the environment and build protein molecules which are later eaten by consumers. – Nitrogen-fixing bacteria change nitrogen to a less mobile, more useful form by combining it with hydrogen to make ammonia - used to build amino acids. • Members of bean family (legumes) have nitrogenfixing bacteria living in their root tissue. Nitrogen Cycle – Nitrogen re-enters the environment: • Death of organisms • Excrement and urinary wastes – Nitrogen re-enters atmosphere when denitrifying bacteria break down nitrates into N2 and nitrous oxide (N2O)gases. • Humans have profoundly altered nitrogen cycle via use of synthetic fertilizers, nitrogen-fixing crops, and burning fossil fuels. Cycling of Materials within Ecosystems Nitrogen cycle: Atmospheric nitrogen (N2) Biological nitrogen fixation Nitrogen fixation by humans Decomposition Denitrification NH3 & NH4- Internal cycling Plant & animal proteins Assimilation Nitrification NO3- Nitrogen Cycle Phosphorous Cycle • Phosphorous compounds are leached from rocks and minerals and usually transported in aqueous form. – Taken in and incorporated by producers. • Passed on to consumers. – Returned to environment by decomposition. Cycling of Materials within Ecosystems Phosphorus cycle: Phosphate rocks Excretion / decomposition Phosphate mining Erosion Internal cycling Marine organisms Marine sediments Fertilizer containing phosphates Animals, crops Dissolved phosphates Erosion Internal cycling Soil phosphates Phosphorous Cycle Sulfur Cycle • Most sulfur tied up in underground rocks and minerals. Inorganic sulfur released into air by weathering and volcanic eruptions. – Cycle is complicated by large number of oxidation states the element can assume. – Human activities release large amounts of sulfur, primarily by burning fossil fuels. • Important determinant in rainfall acidity. Cycling of Materials within Ecosystems Sulfur cycle: Hydrologic Cycle • Describes the circulation of water as it: – Evaporates from land, water, and organisms. (Transpires from plants) • Enters the atmosphere. –Condenses and precipitates back to the earth’s surfaces. »Moves underground by infiltration or overland runoff into rivers, lakes and seas. Cycling of Materials within Ecosystems Hydrologic cycle: Hydrologic Cycle Hydrologic Cycle • Solar energy drives the hydrologic cycle by evaporating surface water. – Evaporation - Changing liquid to a vapor below its boiling point. – Sublimation - Changing water between solid and gaseous states without ever becoming liquid. Solar Radiation • Visible light passes through atmosphere undiminished. • Ultraviolet light is absorbed by ozone in the stratosphere. • Infrared radiation is absorbed by carbon dioxide and water in the troposphere. – Albedo - Reflectivity • Fresh clean snow • Dark soil • Net average of earth 90% 3% 30% Solar Radiation Solar Radiation – Solar energy is unevenly distributed. • Sun strikes the equator directly all year. • Earth’s axis is tilted. – Also rays of light entering the atmosphere at the poles must pass through a deeper envelope of air than light entering at the equator. – This causes the sun’s energy to be scattered at the pole, producing lower temperature. Solar Radiation Temperature Changes with Latitude Like equator Like at poles Solar Radiation Temperature Changes with Season •Seasons are a result of the tilt of the earth. •During half of the year, the northern hemisphere tilts towards the sun, and during the other half away from the sun. The Atmosphere Composition Nitrogen Oxygen Carbon dioxide Argon Water vapor Pollutants Helium Etc. 78% 21% 1% The Atmosphere Troposphere •Ranges in depth from 12.5 km over the equator to 8.0 km over the poles. •All weather occurs here. •Composition is relatively uniform. •Air temperature drops rapidly with increasing altitude. The Atmosphere • Stratosphere – Extends from troposphere to about 45 km. • Air temperature is stable • -45deg C to -75 degC (part closest to Earth) • Fraction ozone is 1000x more than in the troposphere. • Absorbs UV • Steady wind • Relatively calm The Atmosphere • Mesosphere – Middle Layer. • Minimum temperature is about - 138o C. • Thermosphere – Extends from 80-500 km. • Ionized and thin air –Ionosphere - Lower Thermosphere »Aurora borealis (northern lights) • high temperatures. (-1000 deg C+) • Absorbs UV and X-ray The Atmosphere Atmospheric Circulation Circulation spawned by heating / cooling Prevailing winds Generated by pressure differences and Coriolis effect The Atmosphere The Coriolis Effect The influence of Earth’s rotation which tends to turn fluids towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere. Coriolis effect How does the airplane fly? Coriolis effect • Deflects air in North hemisphere to right • Deflects air in South hemisphere to left • Currents flow clockwise in the North and counter-clockwise in the South. • Most noticed in higher latitudes. Other Winds • • • • Prevaling winds Polar easterlies Westerlies Trade The Global Ocean Patterns of Circulation in the Ocean •Surface winds cause ocean currents (gyres). The Global Ocean Patterns of Circulation in the Ocean Influenced by: 1) Coriolis Effect 2) Land Masses (freer to move in the S. Hemisphere) The Global Ocean Vertical Mixing of Ocean Water •Cold salty water is more dense that warmer water. •As a result, warm less salty water floats above the colder water. Ocean Conveyor Belt El Nino Southern Oscillation (ENSO) • Large pool of warm surface water in Pacific Ocean moves back and forth between Indonesia and South America. – Most years, the pool is held in western Pacific by steady equatorial trade winds. • Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east. The Global Ocean Ocean Interactions with the Atmosphere ENSO alters the climate in many areas remote from the Pacific Ocean. The Global Ocean Ocean Interactions with the Atmosphere Coastal Upwelling – deep waters come to the surface due to strong trade winds bringing nutrients. This decreases during El Niño Increases during La Niña El Nino Southern Oscillation – Weak trade winds, expand warm mass of water, currents slow, prevents upwells – Devastates S. Hemi fishing industry – Nutrient poor waters – Some species thrive, ie shrimp and scallops – During an El Nino year, the northern jet stream pulls moist air from the Pacific over the US. • Intense storms and heavy rains. – During intervening La Nina years, hot, dry weather is often present. – Pacific Decadal Oscillation - Very large pool of warm water moving back and forth across the North Pacific every 30 years. Weather and Climate • Weather - A description of physical conditions of the atmosphere. • Climate - A description of the long-term weather pattern in a particular area. – Weather and climate are primary determinants of biomes and ecosystem distribution. Weather and Climate Precipitation: any form of water that falls from the atmosphere • Driest place on earth – Atacama Desert in Chile = 0.05 cm / year • Wettest place on earth – Mount Waialeale in Hawaii = 1200 cm / year Weather and Climate Rain shadows Mountains cause air to rise . As the air rises it takes moisture with it, which forms a cloud when temperatures decreases (with greater elevation), and precipitation occurs. As the air moves down the other side of the mountain it is warmed. This decreases the chance of precipitation. Insert Fig 5.19 b Weather and Climate Severe weather events: 1) Tornados: form when a mass of cool dry air collides with warm moist air Frequency of tornados annually per 100,000 km2 Tornado Alley (US) 40 Sydney, Australia 8 United Kingdom 1 Bangledesh 0.6 Source: University of Wyoming, Department of Atmospheric Science Weather and Climate Severe weather events: 2) Tropical cyclones Atlantic Ocean = hurricanes Pacific Ocean = typhoons Indian Ocean = cyclones Weather and Climate But, all are the same severe weather event: • hurricane • typhoon • cyclone Internal Planetary Processes Plate tectonics: study of the movements of plates Internal Planetary Processes Plate boundaries Internal Planetary Processes Plate boundaries Internal Planetary Processes Volcanoes Most volcanoes occur along subduction zones Internal Planetary Processes Volcanoes Some occur along spreading zones Few, such as Hawaiian Islands, not associated with plates. Internal Planetary Processes Earthquakes • caused by release of built up stress, typically along faults • movement releases seismic waves Typical side effects include: 1) Landslides 2) Tsunamis