Material Cycles + Extinctions

Water, carbon, nitrogen, and phosphorous cycles, + extinctions

Define an ecosystem:

Communities of organisms together with the abiotic environment.

What flows through ecosystems, and what tends to be recycled in ecosystems?

• Energy flows through ecosystems 

• Matter tends to be recycled within the system 

Why are aquatic biomass pyramids inverted?

The lower level organisms e.g. phytoplankton have an incredibly high turnover rate, which reduces as you travel up the pyramid. 

Give some examples of carbon stores:

• >99% in the lithosphere

• Frozen moss + methyl clathrates in the cryosphere

• 800GtC in the atmosphere

• The oceans have 38,000 GtC, mostly at intermediate depth

• Most carbon in the biosphere is in temperate and boreal forests

Give some examples of fast carbon flows:

Fast flows transfer 1000 times more carbon e.g. respiration, combustion, and photosynthesis 

Give some examples of slow carbon flows:

Slow flows transfer carbon over millions of years between litho, hydro, and pedosphere e.g. sedimentation and tectonic activity 

Why is nitrogen key to organic life?

It is essential for protein and DNA formation, as well as in fertiliser.

Describe the nitrogen cycle:

Atmospheric nitrogen is fixed by bacteria into ammonia, which can be used by plants (assimilation). Or, it can be further fixed by bacteria, into nitrates (nitrification), also used by plants.  

Decomposing living matter release ammonia back into the soil (ammonification). 

Bacteria can also release nitrogen gas, N2, into the atmosphere from nitrates (denitrification). 

Give some positives and negatives of human nitrogen use:

• Nitrogen fertiliser is credited with feeding ~1/4 of the world population

• Nitrogen oxide pollution causes acid rain, respiratory issues, and further global warming

Describe the phosphorus cycle:

1. Phosphorus is released by rock weathering into soil 

2. Producers take in P through the roots 

3. Consumers take in P from plants 

4. Decomposers take in P from consumers + producers 

5. Decomposers release P waste back into the soil 

Why is phosphorus so essential to organic life?

Phosphate is essential for DNA formation, energy transfer (Adenosine triphosphate), and cell membranes. 

Give a case study of phosphorus pollution:

• At Monmouth in the Wye Valley, 74% of their phosphorus comes from agriculture, and 21% from sewage treatment. 

• The UK buys ~175,000 tonnes a year, and wastage costs ~£39.5 billion. 

• In the Wye valley the soil leaks P a lot, and produces 60% more waste than the national average because of the large amounts of livestock (e.g. chickens) being farmed.

• This can contribute to eutrophication

Describe the distribution of water across the globe:

• 97.5% of water is saltwater – only 2.5% is fresh, and 68% is frozen in glaciers, ice sheets, and permanent snow 

• Groundwater composes 30% of all freshwater 

Give some examples of water flows:

Flows include evaporation, transpiration, condensation, precipitation, infiltration, and many more 

Give some problems that arise from water scarcity:

• 1 in 4 people don’t have access to safe drinking water 

• 1.4m deaths could be prevented each year by safe water access 

• Tackling diarrhoea can cost US$86bn each year in health and productivity costs 

Define ecosystem services:

The benefits that living things enjoy from the rate and scale at which ecosystem functions are delivered.

Name the 5 major mass extinctions:

• Ordovician

• Devonian

• Permian

• Triassic

• Cretaceous-Triassic

Define the Holocene Extinction:

The 6^th major extinction, caused by anthropogenic activity such as:

• Habitat destruction 

• Climate disruption 

• Toxification 

• Species invasions 

• Disease 

Define extinction debt:

Some populations show "extinction debt" where they persist for a long time despite being below the minimum viable size.