Intro to Environmental Science Unit 2 Review: Earth Systems & Biogeochemical Cycles

Key Concepts and Definitions

• Earth systems encompass the complex interactions and processes between the planet's major components (atmosphere, hydrosphere, geosphere, and biosphere)
• Biogeochemical cycles describe the movement and exchange of matter (such as water, carbon, nitrogen, and phosphorus) between living organisms and the environment
  • Consist of reservoirs (places where matter is stored) and fluxes (processes that move matter between reservoirs)
• Feedback loops can amplify (positive feedback) or dampen (negative feedback) changes within Earth systems
• Tipping points represent thresholds beyond which a system shifts abruptly and often irreversibly into a new state
• Anthropogenic activities, such as fossil fuel combustion and land-use changes, significantly influence Earth systems and biogeochemical cycles
• Sustainability involves managing human impacts to maintain the stability and resilience of Earth systems for future generations

Earth's Major Systems

• The atmosphere is the gaseous envelope surrounding the Earth, consisting primarily of nitrogen (78%) and oxygen (21%)
  • Plays a crucial role in regulating the Earth's temperature through the greenhouse effect
  • Influences weather patterns and the distribution of heat and moisture across the planet
• The hydrosphere encompasses all water on Earth, including oceans, lakes, rivers, groundwater, and water vapor in the atmosphere
  • Covers approximately 71% of the Earth's surface and is essential for life
  • Participates in various biogeochemical cycles and influences climate through heat storage and transport
• The geosphere comprises the solid Earth, including the crust, mantle, and core
  • Provides the foundation for life and shapes the Earth's surface through processes like plate tectonics and weathering
  • Stores and releases nutrients and minerals that are essential for biological processes
• The biosphere consists of all living organisms on Earth and the environments in which they live
  • Includes ecosystems ranging from tropical rainforests to deep-sea hydrothermal vents
  • Plays a critical role in biogeochemical cycles by assimilating, transforming, and recycling matter

Biogeochemical Cycles Overview

• Biogeochemical cycles involve the transfer of matter between the Earth's major systems (atmosphere, hydrosphere, geosphere, and biosphere)
• The water cycle (hydrologic cycle) describes the continuous movement of water through processes like evaporation, transpiration, precipitation, and infiltration
  • Drives weather patterns and shapes the Earth's surface through erosion and deposition
• The carbon cycle encompasses the exchange of carbon between the atmosphere, oceans, land, and living organisms
  • Plays a crucial role in regulating the Earth's climate and supporting life
• The nitrogen cycle involves the transformation of nitrogen between various chemical forms (such as nitrogen gas, ammonium, and nitrate) by biological and physical processes
  • Essential for the growth and reproduction of living organisms
• The phosphorus cycle describes the movement of phosphorus through the environment, primarily through weathering, biological uptake, and sedimentation
  • Phosphorus is a limiting nutrient in many ecosystems and is essential for the formation of DNA, RNA, and ATP
• Other important biogeochemical cycles include the sulfur cycle, which involves the transformation of sulfur compounds, and the oxygen cycle, which is closely linked to photosynthesis and respiration

Carbon Cycle

• The carbon cycle involves the exchange of carbon between the atmosphere, oceans, land, and living organisms
• Atmospheric carbon dioxide (CO2) is absorbed by plants through photosynthesis and converted into organic compounds
  • Some of this carbon is released back into the atmosphere through respiration by plants and animals
• Carbon is stored in various reservoirs, including the atmosphere (as CO2), oceans (dissolved CO2 and carbonate sediments), land (soil and vegetation), and fossil fuels (coal, oil, and natural gas)
• The burning of fossil fuels and land-use changes (deforestation) have significantly increased atmospheric CO2 levels, leading to climate change
• The oceans absorb a substantial amount of atmospheric CO2, acting as a carbon sink
  • However, increased CO2 absorption leads to ocean acidification, which can have detrimental effects on marine ecosystems (coral reefs)
• The carbon cycle is closely linked to the global climate system, as CO2 is a potent greenhouse gas that traps heat in the atmosphere

Nitrogen Cycle

• The nitrogen cycle involves the transformation of nitrogen between various chemical forms, primarily through biological processes
• Nitrogen gas (N2) makes up 78% of the Earth's atmosphere but is unavailable to most organisms
  • Nitrogen fixation converts atmospheric N2 into biologically available forms (ammonia, NH3) through lightning, industrial processes (Haber-Bosch), and nitrogen-fixing bacteria (root nodules of legumes)
• Nitrification is the process by which ammonia is converted to nitrite (NO2-) and then to nitrate (NO3-) by bacteria in the soil
  • Plants absorb nitrate and incorporate it into organic compounds (amino acids, proteins)
• Denitrification is the process by which nitrate is converted back into atmospheric N2 by bacteria in anaerobic conditions (waterlogged soils)
• Human activities, such as the use of nitrogen fertilizers and the burning of fossil fuels, have significantly altered the nitrogen cycle
  • Excess nitrogen can lead to environmental problems like eutrophication (algal blooms) in aquatic ecosystems and groundwater contamination

Phosphorus Cycle

• The phosphorus cycle describes the movement of phosphorus through the environment, primarily through weathering, biological uptake, and sedimentation
• Phosphorus is a limiting nutrient in many ecosystems and is essential for the formation of DNA, RNA, and ATP
• The main reservoir of phosphorus is sedimentary rocks, which release phosphorus through weathering and erosion
  • Dissolved phosphorus is taken up by plants and incorporated into organic compounds
• Unlike the carbon and nitrogen cycles, the phosphorus cycle does not have a significant atmospheric component
• Phosphorus is returned to the environment through the decomposition of organic matter and the excretion of waste products by animals
• Human activities, such as the use of phosphate fertilizers and the discharge of wastewater, have altered the natural balance of the phosphorus cycle
  • Excess phosphorus can lead to eutrophication in aquatic ecosystems, causing algal blooms and oxygen depletion (dead zones)
• The limited availability of phosphorus and its importance for agriculture has raised concerns about the future sustainability of phosphorus resources (peak phosphorus)

Human Impacts on Earth Systems

• Anthropogenic activities have significantly altered Earth systems and biogeochemical cycles, often with unintended consequences
• The burning of fossil fuels and deforestation have increased atmospheric CO2 levels, leading to climate change and ocean acidification
  • Climate change impacts include rising sea levels, more frequent and intense extreme weather events (hurricanes, droughts), and shifts in species distributions
• Land-use changes, such as urbanization and agricultural expansion, have led to habitat loss and fragmentation, contributing to the ongoing biodiversity crisis (sixth mass extinction)
• The widespread use of nitrogen and phosphorus fertilizers has disrupted nutrient cycles, causing eutrophication and dead zones in aquatic ecosystems
• The release of pollutants, such as plastics, pesticides, and heavy metals, has contaminated air, water, and soil, with detrimental effects on human health and ecosystems
• The overexploitation of natural resources (overfishing, deforestation) has led to the degradation and collapse of ecosystems, threatening the livelihoods of communities that depend on them
• Addressing these challenges requires a transition towards sustainable practices, such as renewable energy, sustainable agriculture, and ecosystem-based management

Practical Applications and Case Studies

• The Chesapeake Bay, the largest estuary in the United States, has suffered from nutrient pollution (nitrogen and phosphorus) due to agricultural runoff and urban development
  • Efforts to restore the bay include implementing best management practices (cover crops, riparian buffers) and setting nutrient reduction targets (Total Maximum Daily Load)
• The Amazon rainforest, the largest tropical rainforest in the world, plays a crucial role in the global carbon cycle by absorbing CO2 and regulating regional climate
  • Deforestation and land-use changes have reduced the Amazon's carbon storage capacity and biodiversity, with implications for global climate change
• The Sahel region of Africa has experienced desertification and land degradation due to a combination of climate change, overgrazing, and unsustainable agricultural practices
  • Initiatives to combat desertification include planting trees (Great Green Wall), promoting sustainable land management, and supporting local communities
• The Arctic region is experiencing rapid warming and sea ice loss due to climate change, with consequences for local communities, wildlife (polar bears), and global climate patterns
  • Efforts to mitigate and adapt to these changes include reducing greenhouse gas emissions, supporting Indigenous knowledge and practices, and enhancing international cooperation (Arctic Council)
• The Gulf of Mexico has been affected by nutrient pollution from the Mississippi River, leading to the formation of a large dead zone (hypoxic area) each summer
  • Strategies to address this issue include implementing nutrient reduction strategies in the Mississippi River Basin (precision agriculture, wetland restoration) and improving wastewater treatment
• The Great Barrier Reef, the world's largest coral reef system, is under threat from climate change, ocean acidification, and water quality issues (agricultural runoff)
  • Conservation efforts include improving water quality, reducing greenhouse gas emissions, and supporting research and monitoring programs