2.3A Biogeochemical cycles Notes

Biogeochemical Cycles

1. Biogeochemical cycles are natural processes that circulate and recycle the chemical elements essential for life through different spheres of the Earth.
2. These cycles link the biotic environment (living organisms) with the abiotic environment (air, water, soil, rocks).

The key biogeochemical cycles include:

1. Carbon cycle: involves the movement of carbon between the atmosphere, biosphere, hydrosphere, and lithosphere.
2. Nitrogen cycle: focuses on nitrogen transformations through atmospheric, terrestrial, and aquatic systems.
3. Phosphorus cycle: a sedimentary cycle involving movement from rocks to living organisms and back.
4. Hydrological cycle: the movement of water through evaporation, condensation, precipitation, and runoff.

Key Spheres Involved in Biogeochemical Cycling

1. Biosphere: all living organisms and their interactions.
2. Lithosphere: the Earth’s crust and upper mantle; includes soils and rocks.
3. Atmosphere: the layer of gases surrounding Earth, containing nitrogen, oxygen, CO₂, and trace gases.
4. Hydrosphere: all forms of water on Earth, including oceans, rivers, lakes, groundwater, and atmospheric water vapour.

Role in Ecosystem Functioning

1. Biogeochemical cycles ensure that key nutrients remain available to living organisms over time.
   1. Carbon is cycled through photosynthesis, feeding, respiration, and decomposition, maintaining a steady supply for biological molecules like carbohydrates, lipids, and proteins.
   2. Nitrogen is fixed by bacteria into forms plants can use, then recycled through food chains and decomposers.
   3. Phosphorus, often derived from weathering of rocks, cycles through soil, water, and organisms, supporting bone formation and DNA synthesis.
2. Disruptions to these cycles can affect nutrient availability, impacting primary productivity, species interactions, and overall ecosystem resilience.

Human Impacts on Biogeochemical Cycles

1. Human activities increasingly disrupt the natural balance of these cycles, often causing excess accumulation or depletion of elements in certain compartments, thereby affecting ecosystem sustainability.
2. Major disruptions include:
   1. Burning fossil fuels → increases atmospheric CO₂, contributing to climate change.
   2. Deforestation → reduces carbon uptake and alters nutrient flows.
   3. Fertilizer overuse → disrupts nitrogen and phosphorus cycles, leading to eutrophication and water pollution.
   4. Urbanization → changes hydrological flows and reduces infiltration.

Stores, Sinks, and Sources

1. Within biogeochemical cycles, elements are held or moved through various reservoirs.
2. These can be classified as stores, sinks, or sources, based on the net balance between inputs and outputs.

Stores (Storages)

1. They are essentially reservoirs or pools of the element, and they maintain equilibrium with the environment.
2. Function: The amount of the element in a store does not change drastically over time because the input and output rates of the element are balanced.

Sinks

1. In other words, a sink is an area that absorbs more of the element than it releases.
2. Function: Sinks contribute to the long-term storage of an element. They act as carbon sinks, nitrogen sinks, etc., by holding and reducing the amount of the element in the atmosphere or other systems.

Sources

1. Sources contribute to the addition of the element to the cycle.
2. Function: Sources drive the movement of elements from one part of the system to another, often due to natural processes (like respiration) or human activities (like burning fossil fuels).

Matter vs. Energy in Ecosystems

1. While energy flows in one direction (entering as sunlight, leaving as heat), matter cycles.
2. Biogeochemical cycles illustrate how elements are stored, transferred, and transformed within and between ecosystems, linking terrestrial, aquatic, and atmospheric systems.