🍂Environmental Chemistry II Unit 9 – Biogeochemical Cycles: C, N, P, and S

Key Concepts and Definitions

• Biogeochemical cycles involve the movement and exchange of elements between the biosphere, atmosphere, hydrosphere, and geosphere
• Reservoirs are places where elements are stored for varying lengths of time (atmosphere, oceans, sediments)
• Fluxes are the movement of elements between reservoirs
• Residence time is the average length of time an element remains in a reservoir before moving to another
• Limiting nutrients are essential elements that limit biological productivity when in short supply (nitrogen, phosphorus)
• Eutrophication is the excessive growth of algae and aquatic plants due to an overabundance of nutrients, often leading to oxygen depletion
• Anthropogenic influences are human activities that alter biogeochemical cycles (fossil fuel combustion, agriculture, deforestation)

Cycle Overview and Importance

• Biogeochemical cycles are essential for maintaining the balance and availability of elements in ecosystems
• These cycles regulate the flow of elements through living organisms, soil, water, and the atmosphere
• Understanding biogeochemical cycles helps predict and mitigate the impacts of human activities on the environment
• Disruptions in these cycles can lead to environmental problems (climate change, air and water pollution, ecosystem degradation)
• The carbon, nitrogen, phosphorus, and sulfur cycles are interconnected and influence each other
• Studying biogeochemical cycles provides insights into the sustainability and resilience of ecosystems
• Knowledge of these cycles is crucial for developing strategies to manage natural resources and address environmental challenges

Carbon Cycle

• The carbon cycle involves the exchange of carbon between the atmosphere, biosphere, hydrosphere, and geosphere
• Photosynthesis is the primary process that removes carbon dioxide from the atmosphere and incorporates it into organic compounds
• Cellular respiration and decomposition release carbon dioxide back into the atmosphere
• The atmosphere, oceans, and terrestrial ecosystems are major reservoirs of carbon
• Carbon dioxide is a greenhouse gas that contributes to global warming when its atmospheric concentration increases
• Fossil fuel combustion and deforestation are anthropogenic sources of carbon dioxide emissions
• The ocean absorbs carbon dioxide from the atmosphere, leading to ocean acidification as carbonic acid forms
• Weathering of rocks and formation of carbonate sediments are long-term carbon sinks

Nitrogen Cycle

• The nitrogen cycle involves the transformation and movement of nitrogen through the environment
• Nitrogen fixation converts atmospheric nitrogen (N2) into biologically available forms (ammonia, nitrates)
  • Biological nitrogen fixation is carried out by certain bacteria and archaea
  • Lightning and industrial processes (Haber-Bosch) also contribute to nitrogen fixation
• Nitrification is the conversion of ammonia to nitrites and then to nitrates by bacteria
• Assimilation is the uptake of nitrates and ammonia by plants and microorganisms to form organic nitrogen compounds
• Ammonification is the decomposition of organic nitrogen compounds into ammonia
• Denitrification is the reduction of nitrates to atmospheric nitrogen (N2) by bacteria under anaerobic conditions
• Human activities (fertilizer use, fossil fuel combustion) have significantly altered the nitrogen cycle, leading to environmental issues (eutrophication, acid rain)

Phosphorus Cycle

• The phosphorus cycle involves the movement of phosphorus through the environment
• Phosphorus is a limiting nutrient in many ecosystems, essential for biological processes (DNA, ATP)
• Weathering of rocks releases phosphorus into soils and water bodies
• Plants and microorganisms assimilate phosphorus from the environment and incorporate it into organic compounds
• Decomposition of organic matter releases phosphorus back into the environment
• Phosphorus can be adsorbed onto soil particles or form insoluble compounds, limiting its availability
• Runoff from agricultural lands and wastewater discharge can lead to excessive phosphorus in aquatic systems, causing eutrophication
• Unlike other biogeochemical cycles, the phosphorus cycle lacks a significant atmospheric component

Sulfur Cycle

• The sulfur cycle involves the transformation and movement of sulfur through the environment
• Sulfur is an essential element for living organisms, found in amino acids and other biomolecules
• Weathering of rocks releases sulfur into the environment
• Assimilatory sulfate reduction incorporates sulfur into organic compounds in plants and microorganisms
• Decomposition of organic matter releases sulfur back into the environment
• Dissimilatory sulfate reduction by bacteria produces hydrogen sulfide (H2S) under anaerobic conditions
• Oxidation of hydrogen sulfide forms sulfates, which can be assimilated by organisms or deposited as sediments
• Volcanic eruptions and fossil fuel combustion release sulfur dioxide (SO2) into the atmosphere, contributing to acid rain
• Acid mine drainage can occur when exposed sulfide minerals react with water and oxygen, releasing sulfuric acid

Interactions Between Cycles

• The carbon, nitrogen, phosphorus, and sulfur cycles are interconnected and influence each other
• Photosynthesis in the carbon cycle requires nitrogen and phosphorus for the synthesis of organic compounds
• Decomposition releases nutrients (nitrogen, phosphorus, sulfur) back into the environment, making them available for uptake by plants and microorganisms
• Nitrogen fixation by legumes is coupled with the carbon cycle, as the process requires energy from photosynthesis
• Eutrophication, caused by excessive nitrogen and phosphorus, can lead to increased carbon dioxide emissions from aquatic ecosystems
• Acid rain, resulting from nitrogen and sulfur emissions, can affect the weathering of rocks and alter the availability of nutrients in soils
• Changes in one biogeochemical cycle can have cascading effects on the others, emphasizing the need for a holistic understanding of these processes

Environmental Impacts and Human Influence

• Human activities have significantly altered biogeochemical cycles, leading to various environmental impacts
• Fossil fuel combustion and deforestation have increased atmospheric carbon dioxide levels, contributing to climate change
• Agricultural practices (fertilizer use, livestock farming) have disrupted the nitrogen and phosphorus cycles, causing eutrophication and water pollution
• Wastewater discharge and runoff from urban and agricultural areas can introduce excess nutrients into aquatic systems
• Acid rain, resulting from nitrogen and sulfur emissions, can harm ecosystems and degrade infrastructure
• Land-use changes (deforestation, urbanization) can alter the cycling of elements and disrupt natural habitats
• Sustainable management practices (precision agriculture, wastewater treatment, reforestation) can help mitigate the negative impacts of human activities on biogeochemical cycles
• Addressing the challenges posed by human influence on biogeochemical cycles requires a multidisciplinary approach, involving scientific research, policy development, and public awareness