Nutrient cycles are the intricate pathways through which essential elements move within an ecosystem. These cycles involve complex interactions between living organisms, the atmosphere, and the Earth's crust. Among the vital cycles are the water, carbon, nitrogen, and phosphorus cycles, all of which maintain equilibrium in various ecosystems. Each has a unique structure and flow but can be influenced by human activities, leading to potential disruptions.
Water Cycle
Evaporation
Water from oceans, lakes, and rivers evaporates and turns into water vapour, rising into the atmosphere. The process is driven by the sun's heat.
Condensation
In the cooler upper atmosphere, water vapour condenses, forming clouds. Various weather patterns and conditions influence this phase.
Precipitation
Water returns to the Earth through rain, snow, or other forms of precipitation. It refills bodies of water and moistens the soil.
Runoff and Infiltration
Water either flows over the land (runoff) into rivers and lakes or seeps into the ground (infiltration), replenishing groundwater.
Human Impact
Deforestation, urbanisation, and climate change can significantly alter the water cycle, leading to severe ecological consequences.
Carbon Cycle
Photosynthesis
Plants and algae capture carbon dioxide (CO2) from the air, transforming it into glucose, the basic energy source for life.
Respiration
Organisms release CO2 back into the atmosphere through respiration, balancing the amount absorbed by photosynthesis.
Decomposition
When organisms die, decomposers break them down, returning carbon to the soil, which may eventually release CO2 back into the atmosphere.
Fossilisation and Combustion
Carbon-rich remains of organisms can over time become fossil fuels. Burning these fuels releases large quantities of CO2, contributing to climate change.
Human Impact
Deforestation and burning fossil fuels are significant human activities affecting the carbon cycle, leading to increased atmospheric CO2 levels and global warming.
Nitrogen Cycle
Nitrogen Fixation
Special bacteria convert atmospheric nitrogen into ammonia, making it accessible to plants.
Nitrification
Other bacteria convert ammonia into nitrites and then nitrates, more accessible forms of nitrogen for plants.
Assimilation
Plants absorb nitrates from the soil, converting them into proteins and other organic compounds.
Denitrification
Some bacteria convert nitrates back into nitrogen gas, returning it to the atmosphere.
Human Impact
Excessive use of nitrogen-rich fertilisers can lead to eutrophication, where nutrient runoff causes algal blooms in water bodies, depleting oxygen for other aquatic life.
Phosphorus Cycle
Weathering
Phosphorus is released from rocks into the soil and water bodies through natural weathering processes.
Assimilation and Consumption
Plants take up phosphorus from the soil, and animals obtain it by consuming plants or other animals.
Return to the Soil
Phosphorus returns to the soil through decomposition, where it can be used by plants again.
Human Impact
Mining for phosphorus and excessive use in agriculture can disrupt this cycle, leading to environmental degradation.
Interconnection of Cycles
The nutrient cycles are intertwined, and disturbances in one can affect the others. For example, deforestation can alter both the water and carbon cycles. These changes may have cascading effects on biodiversity, climate, and overall ecosystem health.
FAQ
The phosphorus cycle is unique in that it doesn't involve the atmospheric phase. Unlike carbon and nitrogen, phosphorus cycles through the lithosphere, hydrosphere, and biosphere. The weathering of rocks releases phosphorus into the soil and water, where it is utilised by organisms.
Human activities such as deforestation, urbanisation, and the overuse of water resources can disrupt the water cycle. These actions change the natural flow of water, causing altered precipitation patterns, increased run-off, and reduced infiltration into the ground. Such disruptions can lead to problems like droughts, floods, and degradation of water quality.
Mitigation strategies include responsible agricultural practices, such as reducing the use of fertilisers and implementing proper waste management. Reforestation and afforestation can help in sequestering carbon, and reducing fossil fuel consumption can diminish carbon emissions. Effective water management practices, protection of natural habitats, and education about the importance of maintaining balanced nutrient cycles can also contribute to lessening human impact on these vital ecological processes.
Decomposers play a vital role in nutrient cycles by breaking down dead organic matter into simpler substances. This releases essential nutrients like nitrogen, carbon, and phosphorus back into the soil, making them available for plants. Without decomposers, these nutrients would remain locked within dead organisms, leading to nutrient deficiency in the ecosystem.
Eutrophication is the excessive enrichment of nutrients, particularly nitrogen and phosphorus, in water bodies. It often results from human activities like agriculture and sewage discharge. The surplus nutrients promote algal blooms, which deplete oxygen as they decay, leading to a loss of aquatic life. Eutrophication thus demonstrates how an imbalance in nutrient cycles can negatively impact an ecosystem.
Practice Questions
Nitrogen fixation is a crucial step in the nitrogen cycle where atmospheric nitrogen (N2) is converted into ammonia (NH3) by nitrogen-fixing bacteria. This conversion makes nitrogen accessible to plants, which then use it to synthesise proteins and other vital organic compounds. The importance of this process lies in the fact that atmospheric nitrogen is inert and unusable by most organisms, so nitrogen fixation is essential for the availability of this vital nutrient. Human activities like excessive use of nitrogen-rich fertilisers can lead to a disruption in this cycle, causing issues like eutrophication in water bodies, which depletes oxygen levels and harms aquatic life.
The carbon cycle is a continuous process where carbon is exchanged among the biosphere, lithosphere, hydrosphere, and atmosphere. Photosynthesis plays a key role by absorbing carbon dioxide (CO2) and converting it into glucose, allowing plants to store energy. Respiration reverses this, as organisms release CO2 back into the atmosphere, balancing the amount absorbed by photosynthesis. Together, photosynthesis and respiration maintain equilibrium in the atmospheric CO2 levels. Human activities, especially deforestation and the burning of fossil fuels, significantly affect this cycle. These actions increase atmospheric CO2 levels, leading to global warming and climate change, which can have far-reaching impacts on ecosystems.
