1/27/25 - Systems and Cycles: Are We Harming Earth's Life Support Systems?

What are systems?:

Environmental systems are components interacting to produce outcomes each could not achieve on its own
In terms of energy flow, Earth is an open system powered almost entirely by the rays of the sun
In terms of matter, Earth is a closed system in which matter is used and reused in different places/states
Emergent properties are outcomes arising from the function of a system as a whole

How can we show how a system works?:

Scientists use models, simplified representations of the real world to investigate how aspects of a system interact
A stock is a supply of something we observe and measure over time
Flows are the mechanisms and rates by which a stock changes
Inflows increase stock and outflows decrease stock

Feedback:

Feedback: a loop in a system responds to and produces changes in level of stocks by affecting inflows/outflows of that stock
Reinforcing feedback: loop that responds to a change in a stock by enhancing that same direction of change
Balancing feedback: negative feedback that counteracts the direction in which a stock is changing

How do earth’s life support systems work?:

Biogeochemical cycles show how matter on earth flows through different parts of the environment
A cycle shows a complete path of a particular element with “bio” representing living spheres and “geo” representing nonliving spheres like water and rocks
Oxygen and phosphorus cycle through all the spheres and are considered macronutrients which are elements that organisms use in large amounts

Oxygen cycle:

Phosphorus cycle:

Phosphorus is one of the building blocks of all living cells
Phosphorus doesn’t enter the atmosphere, but slowly cycles through the lithosphere and hydrosphere
Phosphorus is mined for use of fertilizer
Eutrophication: process where nutrients like phosphorus/nitrogen from agricultural runoff cause rapid growth, death, and decomposition of algae and phytoplankton in marine/freshwater environments
- Decomposition process consumes and depletes oxygen levels in the water

Nitrogen cycle:

Plant roots take up nitrogen compounds dissolved in water through their roots
Nitrogen fixation is a process where bacteria use free nitrogen to produce ammonium and nitrate ions that plants, algae, and bacteria can take and use
Nitrogen fixation can also occur through the power of lightning that results in nitrate ions falling back into earth’s surface in precipitation
Ammonification is when bacteria breaks down nitrogen compounds and release ammonia
Most ammonia undergoes nitrification where microorganisms convert ammonia to nitrogen compounds
Other organisms use nitrogen compounds undergo denitrification

Human impact on nitrogen cycle:

Dissolved ammonium and nitrate from fertilizers are leading contaminant affecting public drinking water
Excess nitrogen and phosphorus that run into freshwater systems result in dead zones due to eutrophication'

Carbon cycling:

Photosynthesis pulls CO2 from the atmosphere converting it into sugar and O2
Organisms use the resulting organic molecules for energy and eventually return CO2 back to the atmosphere through respiration and decomposition
Many decomposers are methanogens that release methane as a byproduct
Methanogens live in wetlands, hot sprints, hydrothermal vents in the ocean, and in animal digestive tracts
Cattle release methane from their guts through belching, flatulence, etc.

Humans and the carbon cycle:

Extracting/burning fossil fuels that have been beneath earth’s surface for millions of years into the atmosphere
Cement production transforms CaCO3 in limestone into calcium oxide releasing CO2 into the atmosphere