evsc lec 4 deck

Main drivers of biogeochemical cycles on Earth

Microorganisms

Metabolic Processes:

The life-sustaining chemical reactions which occur in organisms, with three main functions

three main functions of metabolic processes

1. Conversion of the energy in food to energy available to run cellular processes → think ATP

2. Conversion of food (matter) to building blocks for proteins, lipids, nucleic acids, and some carbohydrates

3. Elimination of wastes.

4 steps of the nitrogren cycle

1. Nitrogen Fixation

2. Nitrification

3. Ammonification

4. Denitrification

1. Nitrogen Fixation

Atmospheric nitrogen must be processed, or "fixed", into a usable form to be taken up by plants - fixation results in Ammonia (NH3 ) and can occur by bacteria and lightning.

• Industrial fixation – humans artificially convert atmospheric nitrogen into ammonia for fertilizers.

what can "Fixed" also be thought as?

as "combining"

• Nitrogen is combined with hydrogen by breaking the triple N2 bond with ATP in the presence of water and free electrons.

where does fixing occur

"Fixing" in the soil occurs in root nodules of nitrogen fixing plants, and in the soil where bacteria are found. Fixing in the soil occurs under anoxic (oxygen free) conditions

processes through which Nitrogen is "fixed" into a reactive form that can be used by organisms.

1. Biological fixation

2. Atmospheric fixation

Biological fixation

carried out by nitrogen-fixing bacteria (often in root nodules or soil) that convert N₂ into ammonia (NH₃).

Atmospheric Fixation

lightning breaks the strong N₂ triple bonds, combining nitrogen with oxygen to form reactive nitrogen compounds.

2. nitrification

the process where bacteria convert Ammonia (NH3) to Nitrite (NO2) and then to Nitrate (NO3-), which is then used by plants. 

What do bacteria convert Ammonia (NH3) into during nitrification?

Bacteria convert Ammonia (NH3) into Nitrite (NO2).

What do bacteria convert Nitrite (NO2) into during nitrification?

Bacteria convert Nitrite (NO2) into Nitrate (NO3-).

What type of conditions are required for nitrification to occur?

oxygenated conditions.

What is the role of oxygen in the nitrification process?

Oxygen acts as an electron acceptor in the oxidation of Ammonia and Nitrite.

3. ammonification

the process that occurs when a plant or animal dies, or when an animal expels waste, leading to the release of nitrogen as ammonia.

What role do bacteria and fungi play in ammonification?

break down organic molecules, releasing nitrogen as ammonia during ammonification.

What happens to ammonia after ammonification?

becomes available for uptake by plants and microorganisms, or it can undergo nitrification and denitrification before being released back to the atmosphere.

4. Denitrification

Anaerobic bacteria turn nitrates back into nitrogen gas.

• occurs under anoxic (oxygen-free) conditions.

• often occurs deep in the soil, or in wet environments where mud keeps oxygen at bay.

why the Phosphorus cycle is the "slowest" of all the matter cycles

because it has no gaseous phase and relies mainly on the slow weathering of rocks to release phosphates. Much of its phosphorus also becomes trapped in sediments, only re-entering the cycle through geological processes that take millions of years.

one example of how human activities can alter the Phosphorous and Nitrogen biogeochemical cycles

• Industrial fixation of nitrogen and mining of phosphorus increase the amount of reactive nitrogen and speed up the release of phosphorus in the environment.

another example of the Human Impacts to the N and P Cycles

Combustion of oil, natural gas and coal releases N → greenhouse gas, produces smog, eutrophication & acid rain.

what are the control variables and planetary boundaries for biogeochemical flows

Control variables are the amounts of phosphorus (P) and nitrogen (N) that enter the environment from water sources and the amounts applied to farmland, which can then wash into rivers and lakes.

• The flow of phosphorus (PO₄³⁻) into freshwater systems.

• The flow of nitrogen (NH₄⁺, NH₃, NO₃⁻) into the environment

Quantified boundaries (safe operating limits

• Phosphorus (P): 11 Tg P per year globally, 6.2 Tg P per year regionally.

• Nitrogen (N): 62 Tg N per year globally.

process of eutrophication

Eutrophication - Algal Blooms → O2 depletion → CO2 production → pH drop → Aquatic stress

Eutrophication

excessive richness of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and death of animal life from lack of oxygen.

eutrophication sequence?

1. algal blooms occur due to increased nitrates into water

2. they consume co2 and release o2 during daylight photosynthesis

3. at night the algae consumes o2 to make food (sugar) - causing a lack of oxygen

4. when the algae dies more oxygen is consumed

5. at the same time co2 is produced which forms acids in the water and lowers the ph - affects shells

drivers of eutrophication

• excess inputs of nitrogen (N) and phosphorus (P) into aquatic systems, primarily from fertilizer runoff, sewage, wastewater, and fossil fuel combustion (NOx emissions).

• These human activities speed up natural biogeochemical cycles

why does hypoxia occur

• When nutrients fuel algal blooms, the algae eventually die and sink.

• Microorganisms decompose the dead algae, and in doing so they consume large amounts of dissolved oxygen.

What is hypoxia?

low oxygen levels in a body of water.

two control measures that can reduce the amount of P and N entering waterways

1. Regenerative farming practices

2. Runoff treatment systems

Regenerative farming practices

crop rotation, soil regeneration, and reducing reliance on industrial fertilizers can lower nutrient runoff.

Runoff treatment systems

designing farmlands to include treatment wetlands or buffer zones can filter excess P and N before they reach rivers and lakes.

one action i can take to reduce my individual N footprint

eat less food produced with industrial fertilizers, such as reducing meat consumption or choosing crops grown with sustainable/regenerative farming practices.

• This works because industrial agriculture and nitrogen-based fertilizers are major sources of reactive nitrogen that can runoff into waterways and contribute to eutrophication.