Flows of Energy and Matter

Significant Ideas Ecosystems are linked together by energy and matter flows. The Sun’s energy drives these flows, and humans are impacting the flows of energy and matter both locally and globally.

Energy Flows, Materials Cycle Almost all ecosystems are driven by energy from the sun. Energy (heat) continually flows through systems Matter (nutrients, oxygen, carbon dioxide, water) are cycled and recycled. Biosphere systems are dependent on amount of energy reaching the ground.  Affected by time of day, season, cloud cover, etc. Most solar energy is not used to power living systems; it is reflected or reradiated as heat (infrared).

Solar Radiation

Solar Radiation Continued A study of a cornfield suggested that only 1.6% of solar energy was used by the corn. So what happened to the rest?  35% is reflected back into space by snow, ice, water, and land  60% is absorbed by the atmosphere  < 5% available at Earth’s surface and is absorbed, heating up land and the ocean (this can be used by plants for photosynthesis)

Pathways of Energy in an Ecosystem Conversion of light energy into chemical energy (photosynthesis) Transfer of chemical energy from one trophic level to another with varying efficiencies (moving up the food chain/food web) Overall conversion of ultraviolet and visible light to heat energy by an ecosystem Re-radiation of heat energy into the atmosphere (infrared)

Biomass and Productivity Productivity: The conversion of energy into biomass over a given period of time. Biomass: Living mass of an organism or organisms (sometimes referred to as dry mass). Gross: Refers to the total amount of something Net: Refers to the amount left over after deductions.  Gross Income: $60,000 per/year  Net Income: $50,000 per/year after taxes, social security, retirement, health care, etc. Primary Production: to do with plants Secondary Production: to do with animals

Gross vs. Net Productivity Gross Productivity: Total gain in energy or biomass per unit area per unit time.  Biomass that can be gained before deductions  But all organisms have to respire to stay alive so some energy is used up to stay alive instead of used to grow. Net Productivity: Gain energy or biomass per unit area per unity time that remains after deductions due to respiration.

Gross Primary Productivity (GPP) All light energy fixed by plants is converted to sugars Can estimate plant’s energy uptake by measuring amount of sugar produced: Gross Primary Productivity. However, measuring sugar produced is difficult because it is used almost as soon as it is produced. Easier to measure Net Primary Productivity (NPP)

Net Primary Productivity (NPP) NPP: An ecosystem’s NPP is the rate at which plants accumulate dry mass (actual plant material). Measured in grams per square meter. It is a measure of potential food for consumers in the ecosystem. Calculation for NPP: GPP – R, where GPP is Gross Primary Productivity (production of sugar) and R is respiratory loss.  In theory, any glucose that’s left over after photosynthesis and respiration should be material deposited in and around cells to form new plant matter.  NPP is Biomass

Gross Secondary Productivity (GSP) The total food ingested including the food not used for energy and is excreted as waste.

Net Secondary Productivity (NSP) Dry mass of plants that is stored in new tissue (the tissue of an animal) Calculate: NSP = GSP – R GSP is equal to food eaten minus energy in waste (feces and urine) R is respiratory loss

Maximum Sustainable Yield Equivalent to the NSP or NPP of system. Important number for farmers who are trying to predict how much money they will get for their product. Farmers are often paid by how much biomass (often measured by weight/acre) that their crop yields. Modern agricultural economists spend many months predicting yields which drives prices of the food you buy.  Corn Futures are a good example. People bet on how much corn will be grown in a particular year…even before it is ever planted!

Matter Flows Matter flows through ecosystems linking them together. The flow of matter involves transfers and transformations. Carbon Cycle Nitrogen Cycle

Carbon Cycle Carbon flows through ecosystems through feeding, death and decomposition, photosynthesis, respiration, dissolving, and fossilization. Carbon is stored in organisms and forests, the atmosphere, soil, fossil fuels, and in the oceans. Places where carbon is stored are called Carbon Sinks The oceans are the largest carbon sinks, holding many times more carbon than all the forests on earth combined. Climate change is affecting how much carbon the ocean can hold.

Nitrogen Cycle Nitrogen flows include nitrogen fixation by bacteria and lightning, absorption, assimilation, consumption, excretion, death, decomposition, and denitrification by bacteria in water-logged soils. Nitrogen is stored in organisms, soil, fossil fuels, atmosphere, and bodies of water. Places where nitrogen is stored are called Nitrogen Sinks

Human Impact on Energy Flows Human activities such as burning of fossil fuels, deforestation, urbanization, and agriculture impact energy flows as well as the carbon and nitrogen cycle. How does the burning of fossil fuels or deforestation affect the carbon cycle? How could urbanization and agriculture affect either the carbon cycle or nitrogen cycle? Take 5 minutes to write down your thoughts

To Do: Calculating Productivity Pg. 67 of Course Companion, Do question 1, a-e. Calculating productivity worksheet