1. Nutrient Cycles in Ecosystems

2. What are Nutrients?
Nutrients are chemicals required for growth and other life processes.
Nutrients move through the biosphere in nutrient cycles or exchanges.

3. Nutrient Cycle AKA Biogeochemical Cycle
The flow of a nutrient from the environment to living organisms and back to the environment
Main reservoir for the nutrient is in the environment

4. geochemical cycle Fig. 47-14, p.852
Main nutrient reservoirs in the environment
geochemical cycle
fraction of nutrient available to ecosystem
herbivores, carnivores, parasites
primary producers
detritivores, decomposers
Fig , p.852

5. Three Categories Hydrologic cycle Atmospheric cycles
Water
Atmospheric cycles
Nitrogen and carbon
Sedimentary cycles
Phosphorus and sulfur

6. Carbon Cycle
Carbon moves through the atmosphere and food webs on its way to and from the ocean, sediments, soil and rocks
Sediments and rocks are the main reservoir (AKA carbon stores or sinks)

8. Carbon in the Oceans
Most carbon in the ocean is dissolved carbonate or decaying organic matter.
Ocean currents carry dissolved carbon
It becomes layers of shells deposited on the ocean floor or carbonate rocks such as limestone

9. Carbon in Atmosphere Atmospheric carbon is mainly carbon dioxide
Carbon dioxide is added to atmosphere
cellular respiration, volcanic action, burning fossil fuels
Removed by photosynthesis

11. Human Effects
CO2 levels have risen by more than 30% since the start of the Industrial Revolution due to burning of fossil fuels
CO2 is a Greenhouse gas which absorbs heat in the atmosphere and contributes to global climate change.
Clearing land for agriculture and urban development reduces plants that can absorb and convert CO2.

12. Clearing Land for Burning Fossil Fuels Urban Expansion
Agriculture

13. Nitrogen Cycle Nitrogen is used in making proteins in the body and DNA
Main reservoir is nitrogen gas in the atmosphere

15. Nitrogen Fixation and Uptake
Plants cannot use nitrogen gas
Nitrogen-fixing bacteria convert nitrogen gas into ammonium (NH4+)
Ammonium can be taken up by some plants

16. Nitrification and Uptake
Nitrifying bacteria convert ammonium to nitrites (NO2–), and then to nitrates (NO3-) which are taken up by plants

17. Nitrogen Loss Nitrogen is often a limiting factor in ecosystems
Nitrogen is lost from soils via leaching and runoff
Denitrifying bacteria convert nitrates and nitrites back to nitrogen gas

18. Human Effects
Humans increase rate of nitrogen loss in soil by clearing forests and grasslands
Humans increase nitrogen in water by using fertilizers which cause algae blooms (eutrophication) that use up O2 in the water and block sunlight

19. Human Effects
Humans increase nitrogen in the air by burning fossil fuels which leads to acid precipitation.
Too much or too little nitrogen can compromise plant health

21. Phosphorus Cycle
Phosphorus is essential for life processes in plants and animals
Main reservoir is Earth’s crust; no gaseous phase

22. Phosphorus Cycle Weathering releases these phosphates from rocks.
- chemical weathering, via acid precipitation or lichens
- physical weathering, including wind, water and freezing
Phosphates are then absorbed by plants, which are then eaten by animals.

23. Phosphorus Cycle
Figure 47-27, Page 862

24. Human Effects
In tropical countries, clearing lands for agriculture may deplete phosphorus-poor soils
In developed countries, phosphorus runoff is causing eutrophication of waterways