Ecosystems and Biogeochemical Cycles: Comprehensive Study Notes

1. Introduction to Environmental Science

  • Environmental Science: An interdisciplinary field combining biology, chemistry, geology, and social sciences to study how the natural world works, how our environment affects us, and how we affect our environment.

  • Environmentalism: A social movement dedicated to protecting the natural world.

  • Sustainability: Living on Earth in a way that allows us to use its resources without depriving future generations of those resources.

    • Ecological Footprint: Quantifies the area of land and water needed to provide all the resources a person consumes and absorb all the wastes produced.

    • IPATS Model: Describes environmental impact (I) as a function of population (P), affluence (A), and technology (T). I=P×A×TI = P \times A \times T

2. Earth Systems and Resources
2.1. Earth's Structure and Plate Tectonics

  • Layers of the Earth:

    • Core: Innermost layer, dense iron and nickel; solid inner core, liquid outer core.

    • Mantle: Thickest layer, molten rock (magma), convection currents drive plate tectonics.

    • Crust: Outermost layer, thinnest; oceanic (dense, basalt) and continental (less dense, granite).

  • Plate Tectonics: Earth's lithosphere (crust and uppermost mantle) is divided into plates that move slowly over the asthenosphere.

    • Types of Plate Boundaries:

    1. Divergent: Plates move apart (e.g., mid-ocean ridges, rift valleys).

    2. Convergent: Plates move together (e.g., subduction zones forming volcanoes/trenches, mountain ranges).

    3. Transform: Plates slide past each other horizontally (e.g., San Andreas Fault).

    • Consequences: Earthquakes, volcanoes, tsunamis, mountain formation.

2.2. Rock Cycle

  • Three Rock Types:

    1. Igneous: Formed from cooling magma/lava.

    2. Sedimentary: Formed from compaction/cementation of sediments.

    3. Metamorphic: Formed when existing rocks are subjected to heat and pressure.

  • Weathering: Breakdown of rocks (physical, chemical, biological).

  • Erosion: Transport of weathered material (wind, water, gravity).

2.3. Soil Formation and Properties

  • Soil: A complex mixture of weathered rock, organic matter, water, and air.

  • Soil Horizons: Layers (O, A, E, B, C, R).

    • O Horizon: Organic matter (humus).

    • A Horizon: Topsoil, rich in organic matter and minerals.

    • B Horizon: Subsoil, accumulation of clays and nutrients.

  • Soil Properties:

    • Texture: Proportions of sand, silt, and clay (loam is ideal for agriculture).

    • Porosity: Amount of space between soil particles.

    • Permeability: How easily water flows through soil.

    • pH: Affects nutrient availability; optimal range is generally 6−7.56-7.5.

2.4. Water Resources

  • Hydrologic Cycle: Evaporation, condensation, precipitation, runoff, infiltration, transpiration.

  • Groundwater: Water held underground in aquifers.

    • Aquifer: Underground layer of water-bearing permeable rock.

    • Water Table: Upper surface of saturated zone.

  • Surface Water: Rivers, lakes, streams, wetlands.

2.5. Atmosphere

  • Layers of the Atmosphere:

    1. Troposphere: Where weather occurs, densest layer, cools with altitude.

    2. Stratosphere: Contains ozone layer, warms with altitude.

    3. Mesosphere: Colder layer, burns up meteors.

    4. Thermosphere: Hottest layer, contains ionosphere.

  • Atmospheric Composition: Nitrogen (78%), Oxygen (21%), Argon (0.9%), Carbon Dioxide (0.04%).

  • Role of Ozone Layer: Filters harmful UV radiation.

3. Biogeochemical Cycles
3.1. Carbon Cycle

  • Reservoirs: Atmosphere (CO2), oceans (dissolved CO2, bicarbonates), fossil fuels, rocks, biomass.

  • Processes: Photosynthesis (removes CO2), respiration (releases CO2), decomposition, combustion, ocean exchange.

3.2. Nitrogen Cycle

  • Nitrogen Fixation: N2 to NH3/NH4+ (bacteria, lightning).

  • Nitrification: NH4+ to NO2- to NO3- (bacteria).

  • Assimilation: Plants absorb NO3- and NH4+.

  • Ammonification: Organic N to NH4+ (decomposers).

  • Denitrification: NO3- to N2 (bacteria, anaerobic conditions).

3.3. Phosphorus Cycle

  • No Atmospheric Phase: Primarily sedimentary.

  • Reservoirs: Rocks, soil, water, biomass.

  • Processes: Weathering of rocks, runoff, absorption by plants, decomposition.

  • Limiting Nutrient: Often limits primary productivity in ecosystems.

4. The Living World: Ecosystems
4.1. Energy Flow

  • Producers (Autotrophs): Photosynthesis/chemosynthesis; form base of food web.

  • Consumers (Heterotrophs):

    • Primary: Herbivores.

    • Secondary: Carnivores/omnivores that eat herbivores.

    • Tertiary: Carnivores/omnivores that eat secondary consumers.

  • Decomposers/Detritivores: Break down dead organic matter, nutrient recycling.

  • Trophic Levels: Energy transfer from one level to the next.

  • 10% Rule: Only about 10% of energy is transferred to the next trophic level; the rest is lost as heat.

  • Food Chains/Webs: Illustrate energy flow.

4.2. Productivity

  • Gross Primary Productivity (GPP): Total amount of solar energy converted to chemical energy by producers.

  • Net Primary Productivity (NPP): GPP minus energy used by producers for respiration (NPP=GPP−RNPP = GPP - R); represents energy available to consumers.

  • Factors Affecting NPP: Sunlight, water, nutrients, temperature.

4.3. Biomes

  • Biomes: Large regions characterized by distinct climate patterns and dominant plant/animal life.

  • Key Determinants: Temperature and precipitation.

  • Terrestrial Biomes: Tundra, Boreal Forest (Taiga), Temperate Deciduous Forest, Temperate Grassland, Chaparral, Desert, Savanna, Tropical Rain Forest.

  • Aquatic Biomes: Freshwater (rivers, lakes, wetlands) and Saltwater (oceans, coral reefs, estuaries).

5. Biodiversity

  • Biodiversity: The variety of life on Earth.

    • Genetic Diversity: Variation within a species.

    • Species Diversity: Number and abundance of species in an ecosystem.

    • **Ecosystem Diversity