9.1 Biogeochemical Cycles
6 min read•august 14, 2024
Biogeochemical cycles are nature's recycling systems, moving essential elements through Earth's ecosystems. These cycles, including water, , , , and , sustain life by circulating nutrients and energy between living and non-living components.
Understanding these cycles is crucial for grasping how ecosystems function and how human activities impact them. From carbon's role in to nitrogen's influence on soil fertility, these cycles shape our planet's health and .
Biogeochemical Cycles and Ecosystems
The Water Cycle
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- The , also known as the hydrologic cycle, describes the continuous movement of water through processes such as evaporation, , , , , and
- Evaporation occurs when water changes from a liquid to a gas, typically due to heat from the sun (oceans, lakes, rivers)
- Transpiration is the process by which water vapor is released into the atmosphere through the leaves of plants (forests, grasslands)
- Condensation happens when water vapor cools and transforms back into a liquid, forming clouds or fog (dew, mist)
- Precipitation is the falling of water from the atmosphere in the form of rain, snow, sleet, or hail (monsoons, blizzards)
- Infiltration is the process by which water on the ground surface enters the soil (percolation, groundwater recharge)
- Runoff is the flow of water over the surface of the Earth, often into streams, rivers, or other bodies of water (flash floods, erosion)
The Carbon Cycle
- The involves the exchange of carbon among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere
- is the process by which plants and other organisms convert and water into and oxygen using energy from sunlight (forests, phytoplankton)
- is the process by which organisms break down glucose and release carbon dioxide and water (animals, decomposers)
- is the breakdown of organic matter by decomposers, releasing carbon dioxide and other nutrients back into the environment (fungi, bacteria)
- is the burning of organic materials, such as fossil fuels, which releases carbon dioxide into the atmosphere (coal, oil, natural gas)
- Carbon can be stored in various reservoirs, such as the atmosphere, oceans, soil, and living organisms (permafrost, carbonate rocks)
The Nitrogen Cycle
- The is the biogeochemical cycle that converts nitrogen into multiple chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems
- is the process by which atmospheric nitrogen is converted into or other nitrogen compounds that can be used by plants (legumes, cyanobacteria)
- is the conversion of ammonia into and then by bacteria in the soil (Nitrosomonas, Nitrobacter)
- is the reduction of nitrate back into atmospheric nitrogen by bacteria in anaerobic conditions (wetlands, sediments)
- is the conversion of organic nitrogen compounds into ammonia by decomposers (animal waste, decaying plants)
- Plants absorb nitrate from the soil and incorporate it into their tissues, which are then consumed by animals (crops, grasslands)
The Phosphorus Cycle
- The describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere
- Phosphorus is an essential nutrient for plant growth and is often a limiting factor in ecosystems (tropical rainforests, coral reefs)
- Weathering of rocks releases phosphorus into the soil, where it can be taken up by plants (apatite, phosphorite)
- Decomposition of organic matter by microorganisms releases phosphorus back into the soil (leaf litter, animal carcasses)
- Phosphorus can be lost from ecosystems through leaching, soil erosion, and runoff (, algal blooms)
The Sulfur Cycle
- The involves the movement of sulfur between rocks, waterways, and living systems
- Weathering of rocks and volcanic eruptions release sulfur into the environment (pyrite, )
- Sulfur-reducing bacteria convert into hydrogen sulfide in anaerobic conditions (salt marshes, hot springs)
- Hydrogen sulfide can be oxidized by bacteria, forming sulfuric acid, which contributes to (coal combustion, industrial emissions)
- Plants absorb sulfate from the soil and incorporate it into their tissues, which are then consumed by animals (cruciferous vegetables, amino acids)
Human Impact on Biogeochemical Cycles
Disruption of the Carbon Cycle
- Burning fossil fuels releases carbon dioxide into the atmosphere, intensifying the greenhouse effect and contributing to global climate change (industrial revolution, transportation)
- Deforestation reduces the amount of carbon dioxide absorbed by plants through photosynthesis, further exacerbating the greenhouse effect (Amazon rainforest, Indonesian peatlands)
- Ocean acidification occurs when excess atmospheric carbon dioxide dissolves in seawater, lowering the pH and disrupting marine ecosystems (coral bleaching, shellfish dissolution)
Alteration of the Nitrogen and Phosphorus Cycles
- Agricultural practices, such as the use of nitrogen-based fertilizers, can lead to nutrient runoff into waterways (eutrophication, dead zones)
- Excessive nitrogen and phosphorus in aquatic ecosystems stimulate algal growth, depleting oxygen levels and harming aquatic life (Gulf of Mexico, Lake Erie)
- Wastewater discharge and sewage leaks introduce additional nutrients into water bodies, further contributing to eutrophication (urban areas, septic systems)
Impact on the Sulfur Cycle and Acid Rain
- Mining activities and fossil fuel combustion release sulfur compounds into the atmosphere (coal, oil refineries)
- Sulfur dioxide and other sulfur oxides react with water vapor to form sulfuric acid, a major component of acid rain (Appalachian Mountains, Black Forest)
- Acid rain can harm plant and animal life, degrade infrastructure, and leach nutrients from the soil (forest decline, corroded buildings)
Urbanization and Land-Use Changes
- Urbanization and land-use changes alter the water cycle by increasing surface runoff and reducing groundwater recharge (impervious surfaces, stormwater management)
- Modification of local precipitation patterns can occur due to changes in surface albedo and heat island effects (urban microclimates, flash flooding)
- Habitat fragmentation and destruction disrupt the flow of nutrients and energy through ecosystems (wildlife corridors, biodiversity loss)
Plastic Pollution and Biogeochemical Cycles
- The production and disposal of plastics introduce microplastics into marine ecosystems (nurdles, plastic bags, synthetic fibers)
- Microplastics can be ingested by marine organisms, potentially disrupting food chains and biogeochemical cycles (zooplankton, fish, seabirds)
- Plastic debris can also serve as a substrate for the growth of microorganisms and the transport of invasive species (great Pacific garbage patch, rafting communities)
Interconnectedness of Biogeochemical Cycles
Cascading Effects of Cycle Disruptions
- Biogeochemical cycles are interconnected, and a disruption in one cycle can have cascading effects on other cycles and ecosystem processes
- Changes in the carbon cycle affect the nitrogen and phosphorus cycles, as carbon is essential for the growth and development of organisms that participate in these cycles (plant productivity, microbial activity)
- Alterations in the water cycle can influence the availability and distribution of nutrients, impacting the functioning of terrestrial and aquatic ecosystems (drought, flooding)
Climate Regulation and Greenhouse Gases
- Biogeochemical cycles play a crucial role in regulating Earth's climate by controlling the concentrations of greenhouse gases in the atmosphere
- The carbon cycle helps maintain the Earth's temperature within a habitable range by regulating the amount of carbon dioxide in the atmosphere (photosynthesis, ocean absorption)
- Feedback loops between the climate system and biogeochemical cycles can amplify or mitigate the effects of climate change (permafrost thaw, ocean carbon uptake)
Nutrient Cycling and Ecosystem Productivity
- Nutrient cycling through biogeochemical processes supports primary productivity and the growth of organisms at the base of food webs (phytoplankton, plants)
- The availability of essential nutrients, such as nitrogen and phosphorus, can limit the productivity of ecosystems (oligotrophic lakes, desert soils)
- Efficient nutrient cycling sustains higher and maintains the stability and of ecosystems (predator-prey interactions, keystone species)
Soil Health and Ecosystem Functioning
- Biogeochemical cycles contribute to the formation and maintenance of soil health, which is essential for supporting plant growth and ecosystem productivity
- The decomposition of organic matter by microorganisms releases nutrients back into the soil, improving fertility and structure (humus, mycorrhizal fungi)
- Healthy soils provide ecosystem services, such as water filtration, carbon sequestration, and erosion control (wetlands, grasslands)
Global Redistribution of Nutrients and Energy
- The coupling of biogeochemical cycles and physical processes, such as ocean circulation and atmospheric transport, helps redistribute nutrients and energy across the globe
- Ocean currents transport nutrients and dissolved organic matter, supporting the diversity of marine life (Gulf Stream, upwelling zones)
- Atmospheric circulation patterns, such as the Hadley cell, influence the distribution of moisture and nutrients on a global scale (Intertropical Convergence Zone, dust storms)
Key Terms to Review (38)
Acid rain: Acid rain refers to precipitation that has a higher acidity than normal due to the presence of sulfuric and nitric acids formed from pollutants released into the atmosphere. This phenomenon results from the interaction of water vapor with sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) which are emitted by industrial processes, vehicles, and other sources. Acid rain can have detrimental effects on ecosystems, water sources, and built environments, highlighting its connection to atmospheric composition and the cycling of elements within the environment.
Ammonia: Ammonia is a colorless gas with a distinct odor, composed of nitrogen and hydrogen (NH₃). It plays a crucial role in various biogeochemical cycles, particularly in the nitrogen cycle, where it serves as an important nutrient for plants and as a product of the decomposition of organic matter.
Ammonification: Ammonification is the process by which organic nitrogen from decomposing plant and animal matter is converted into ammonia (NH₃) or ammonium ions (NH₄⁺) by microorganisms. This crucial step in the nitrogen cycle allows nitrogen to be made available to plants and other organisms, playing a vital role in maintaining ecosystem health.
Biodiversity: Biodiversity refers to the variety of life forms on Earth, including the different species of plants, animals, fungi, and microorganisms, as well as the ecosystems they form and the genetic diversity within those species. This concept is crucial for maintaining ecosystem stability and resilience, influencing how organisms interact with each other and their environments. A rich biodiversity supports essential ecological processes, such as nutrient cycling, pollination, and climate regulation, which are interconnected with biogeochemical cycles, terrestrial biomes, and aquatic ecosystems.
Biomagnification: Biomagnification refers to the process by which certain harmful substances, such as heavy metals and persistent organic pollutants, become more concentrated as they move up the food chain. As smaller organisms absorb these substances, predators that consume them accumulate even higher concentrations, leading to potentially toxic levels in top predators, including humans. This phenomenon highlights the interconnectedness of ecosystems and the potential for pollutants to have far-reaching effects on both wildlife and human health.
Carbon: Carbon is a chemical element with the symbol 'C' and atomic number 6, known for its ability to form a vast array of organic compounds, making it essential for life on Earth. In the context of biogeochemical cycles, carbon is a crucial element that circulates through different reservoirs, such as the atmosphere, hydrosphere, lithosphere, and biosphere, influencing global processes like climate change, energy production, and ecosystem dynamics.
Carbon cycle: The carbon cycle is a natural process that describes the movement of carbon among the Earth's atmosphere, oceans, soil, and living organisms. This cycle is crucial for regulating Earth's climate and supporting life, as carbon is a key component of biological molecules and plays a significant role in energy transfer within ecosystems.
Carbon dioxide: Carbon dioxide (CO₂) is a colorless, odorless gas that is naturally present in Earth's atmosphere in trace amounts. It plays a critical role in various processes, including photosynthesis and the greenhouse effect, which are essential for maintaining life and regulating Earth's climate.
Climate change: Climate change refers to significant and lasting changes in the average temperature, weather patterns, and other atmospheric conditions on Earth, largely driven by human activities such as burning fossil fuels and deforestation. This term encompasses both global warming, which is a rise in Earth's average surface temperature due to greenhouse gas emissions, and the broader changes in climate systems that result from these increases in temperature.
Combustion: Combustion is a chemical reaction that occurs when a substance, typically a fuel, reacts rapidly with oxygen to produce heat and light. This process not only generates energy but also results in the formation of various products, including gases like carbon dioxide and water vapor, which play significant roles in environmental processes and cycles.
Condensation: Condensation is the process by which water vapor in the air cools and transitions into liquid water, forming droplets. This process is vital in many natural cycles and influences weather patterns, as it contributes to the formation of clouds and precipitation.
Decomposition: Decomposition is the natural process by which organic matter breaks down into simpler substances, returning essential nutrients to the environment. This process plays a crucial role in recycling matter and energy within ecosystems, contributing to biogeochemical cycles and the carbon cycle specifically. As organic materials decompose, they release carbon dioxide back into the atmosphere, which is vital for maintaining ecological balance.
Denitrification: Denitrification is the microbial process by which nitrates (NO₃⁻) and nitrites (NO₂⁻) in the soil are converted into nitrogen gas (N₂) or, to a lesser extent, nitrous oxide (N₂O), which is released into the atmosphere. This process plays a crucial role in the nitrogen cycle, helping to regulate nitrogen levels in ecosystems and reducing excess nitrogen that can lead to environmental issues like eutrophication.
Eutrophication: Eutrophication is the process by which a body of water becomes overly enriched with nutrients, leading to excessive growth of algae and other aquatic plants. This phenomenon can cause significant ecological impacts, including oxygen depletion and disruption of aquatic ecosystems. As nutrient inputs from sources like fertilizers, sewage, and runoff increase, they stimulate algal blooms that can harm water quality and marine life.
Food web: A food web is a complex network of interconnected food chains that illustrates the feeding relationships among various organisms within an ecosystem. It provides a more realistic representation of how energy and nutrients flow through different levels of producers, consumers, and decomposers, highlighting the interdependence of species and their roles in maintaining ecological balance.
Glucose: Glucose is a simple sugar, or monosaccharide, that serves as a primary source of energy for living organisms. It plays a crucial role in the process of photosynthesis, where plants convert sunlight into chemical energy, and it is also vital in cellular respiration, which allows cells to extract energy from organic compounds. Essentially, glucose is the backbone of energy metabolism in both plants and animals.
Hydrogen sulfide: Hydrogen sulfide is a colorless gas with a characteristic odor of rotten eggs, commonly produced in natural processes such as the decomposition of organic matter. It plays a vital role in biogeochemical cycles, particularly in sulfur cycling, and can significantly impact ecosystems due to its toxicity and interactions with other chemical compounds.
Infiltration: Infiltration is the process by which water on the ground surface enters the soil. This crucial part of the water cycle plays a key role in recharging groundwater supplies and supporting ecosystems, as it determines how much water can be absorbed by the soil and ultimately affects plant growth and water quality. Understanding infiltration is important for managing water resources and mitigating issues like flooding and drought.
Nitrate: Nitrate is a chemical compound made up of one nitrogen atom and three oxygen atoms, represented by the formula NO₃⁻. It plays a critical role in the nitrogen cycle, acting as a key nutrient for plants and a vital component in the biogeochemical processes that cycle nutrients through ecosystems. In addition to being essential for plant growth, nitrates can also have environmental implications, particularly when found in excess due to agricultural runoff.
Nitrification: Nitrification is a two-step biological process in the nitrogen cycle where ammonia is converted into nitrites and then into nitrates by specific bacteria. This process is crucial for transforming nitrogen into forms that are usable by plants, thereby playing a key role in nutrient cycling and ecosystem health.
Nitrite: Nitrite is a chemical compound with the formula NO2-, formed when nitrogen undergoes oxidation. It plays a crucial role in various biogeochemical cycles, particularly in the nitrogen cycle, where it acts as an intermediary between ammonia and nitrate, facilitating the conversion of nitrogenous compounds in ecosystems.
Nitrogen: Nitrogen is a colorless, odorless gas that makes up about 78% of the Earth's atmosphere by volume. It is a key element in the biogeochemical cycles and plays a crucial role in the formation of proteins, nucleic acids, and other essential biological compounds. The presence of nitrogen in the atmosphere influences various environmental processes, including the growth of plants and the health of ecosystems.
Nitrogen cycle: The nitrogen cycle is the series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms. This cycle is crucial for life, as nitrogen is a key component of amino acids, proteins, and nucleic acids, linking it to the overall health of ecosystems, including both terrestrial and aquatic environments. Through various transformations, such as nitrogen fixation, nitrification, denitrification, and ammonification, nitrogen moves between the atmosphere, soil, and living organisms, maintaining ecosystem balance.
Nitrogen fixation: Nitrogen fixation is the process through which atmospheric nitrogen (N₂) is converted into a form that can be utilized by living organisms, primarily ammonia (NH₃). This process is crucial for the nitrogen cycle, allowing nitrogen to move from the atmosphere into the soil and subsequently into the biological systems of plants and animals, making it an essential component of biogeochemical cycles.
Nutrient uptake: Nutrient uptake refers to the process by which plants, algae, and some microorganisms absorb essential nutrients from their environment to support growth and metabolic functions. This process is crucial for the cycling of nutrients within ecosystems, impacting soil health, plant productivity, and overall ecological balance.
Phosphorus: Phosphorus is a vital chemical element represented by the symbol 'P' and atomic number 15. It plays a crucial role in biological systems, particularly in energy transfer, DNA synthesis, and cellular function. As a key component of nucleic acids and ATP (adenosine triphosphate), phosphorus is essential for life and is a major player in biogeochemical cycles, particularly the phosphorus cycle, which describes its movement through the lithosphere, hydrosphere, and biosphere.
Phosphorus cycle: The phosphorus cycle is the biogeochemical process through which phosphorus moves through the environment, including soil, water, and living organisms. Unlike other biogeochemical cycles, phosphorus does not have a significant gaseous phase and primarily cycles through geological and biological processes. This cycle plays a crucial role in ecosystems, influencing plant growth and the health of aquatic ecosystems.
Photosynthesis: Photosynthesis is the biological process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, using carbon dioxide and water as raw materials. This process is crucial as it not only provides the energy needed for growth and development in plants but also contributes significantly to the composition of the atmosphere and supports life on Earth.
Precipitation: Precipitation refers to any form of water, liquid or solid, that falls from the atmosphere and reaches the Earth's surface. This process plays a crucial role in replenishing water sources, influencing river systems, and impacting climate patterns.
Resilience: Resilience is the ability of a system, community, or ecosystem to absorb disturbances and still retain its basic structure and function. This concept is crucial for understanding how natural systems respond to environmental changes and stresses, including climate change, human activities, and natural disasters. Resilience highlights the capacity for recovery, adaptation, and transformation, playing a key role in maintaining ecosystem health and stability.
Respiration: Respiration is the biochemical process through which organisms convert nutrients, primarily glucose, into energy, while releasing waste products like carbon dioxide and water. This process is crucial for maintaining life as it provides the energy necessary for various cellular activities and plays a key role in biogeochemical cycles that connect living organisms with the environment.
Runoff: Runoff refers to the movement of water, usually from precipitation, over the land surface towards rivers, lakes, and oceans. This process plays a crucial role in the hydrological cycle, influencing water availability and quality, while also contributing to various environmental phenomena, including floods and droughts. Runoff can transport sediments, nutrients, and pollutants, impacting ecosystems and biogeochemical cycles.
Sulfate: Sulfate is a chemical compound that contains the sulfate ion, represented as SO₄²⁻, which consists of one sulfur atom surrounded by four oxygen atoms. It plays a crucial role in various biogeochemical cycles, particularly in the sulfur cycle, influencing both ecosystem health and atmospheric chemistry. Sulfate can be found in natural water bodies, soils, and can also be produced through human activities, impacting air quality and contributing to acid rain.
Sulfur: Sulfur is a non-metallic element represented by the symbol 'S' and atomic number 16. It is a vital component in various biogeochemical cycles, particularly in the sulfur cycle, where it plays a key role in the transformation and movement of sulfur through the environment, impacting both ecosystems and human activities.
Sulfur cycle: The sulfur cycle is the series of processes by which sulfur moves through the Earth's atmosphere, lithosphere, hydrosphere, and biosphere. It involves the transformation of sulfur in various forms, including sulfates and hydrogen sulfide, and plays a crucial role in nutrient availability and environmental health.
Transpiration: Transpiration is the process by which water vapor is released from the surfaces of plants, primarily through small openings called stomata. This process plays a crucial role in the movement of water within the water cycle, contributing to the overall balance of Earth's water resources. Transpiration also influences local and regional climates by affecting humidity and precipitation patterns.
Trophic levels: Trophic levels are the hierarchical layers in an ecosystem that categorize organisms based on their feeding relationships and energy transfer. These levels typically include producers at the base, followed by primary consumers, secondary consumers, and tertiary consumers, with each level representing a step in the food chain. Understanding trophic levels is essential for grasping energy flow, nutrient cycling, and the interactions between various species within an ecosystem.
Water cycle: The water cycle is the continuous process through which water moves through the Earth's atmosphere, surface, and subsurface. This cycle involves several key processes including evaporation, condensation, precipitation, and infiltration, which work together to regulate water distribution on our planet. Understanding the water cycle is crucial as it connects various natural systems and influences climate, weather patterns, and ecosystems.