1. 1 Dynamics of Ecosystems Chapter 57

2. 2 Biogeochemical Cycles Biogeochemical cycles: chemicals moving through ecosystems; biotic and abiotic – Can cross the boundaries of ecosystems (one ecosystem might import or export chemicals to another)

3. 3 Biogeochemical Cycles Water Cycle – All life depends on the presence of water – Amount of water available determines the nature and abundance of organisms present – It can be synthesized and broken down Synthesized during cellular respiration Broken down during photosynthesis

4. 4 Biogeochemical Cycles Basic water cycle – Evaporation – Transpiration: 90% of evaporation is through plants – Condensation – Precipitation – Groundwater Aquifers : provide 95% fresh water used in US

5. 5 Biogeochemical Cycles Water cycle

6. 6 Biogeochemical Cycles Changes in the supply of water to an ecosystem can radically alter the nature of the ecosystem Deforestation disrupts the local water cycle Water that falls as rain drains away Tropical rain forest  semiarid desert

7. 7 Biogeochemical Cycles Nitrogen Cycle – component of proteins and nucleic acids – Usually the element in shortest supply – Availability Most cannot use N 2 (gas) Use NH 3, and NO 3 -

8. 8 Biogeochemical Cycles Nitrogen fixation: synthesis of nitrogen containing compounds from N 2 Nitrification: N 2 --> NH 3 --> NO 3 - Denitrification: NO 3 - --> N 2 – carried out by microbes: free or living on plant roots – Nitrogenous wastes and fertilizer use radically alter the global nitrogen cycle

9. 9 Biogeochemical Cycles Nitrogen Cycle

10. 10 Biogeochemical Cycles Phosphorus cycle – Occurs in nucleic acids, membranes, ATP – Exists as PO 4 3- in ecosystems – Plants and algae use free inorganic phosphorus, animals eat plants to obtain their phosphorus

11. 11 Biogeochemical Cycles Phosphorus cycle

12. 12 Biogeochemical Cycles carbon cycle (important component of bodies ~20% of human body weight)

13. 13 Biogeochemical Cycles Respiration/photosynthesis Methane producers: anaerobic cellular respiration releases CH 4 Decomposition: releases CO 2 Combustion: burning fossil fuels produces CO 2

14. 14 Biogeochemical Cycles Over time, globally, the carbon cycle may proceed faster in one direction – Human burning of fossil fuels is creating large imbalances in the carbon cycle – The concentration of CO 2 in the atmosphere is going up year by year

15. 15 Biogeochemical Cycles Limiting nutrient: weak link in an ecosystem; shortest supply relative to the needs of organisms Fe for algal populations N and P for both terrestrial and aquatic ecosystems

16. 16 Biogeochemical Cycles Biogeochemical cycling in a forest ecosystem-- Hubbard Brook Experiment Undisturbed forests are efficient at retaining nutrients Disturbed (cut trees down) amount of water runoff increased by 40% – Loss of Ca; increased nine fold – Loss of Phosphorus did not increase – Loss of NO 3 - ; 53kg/hectare/yr

17. 17 Biogeochemical Cycles The Hubbard Brook Experiment 38-acre watershed. Orange curve shows nitrate concentration in the runoff water from the deforested watershed. Green curve shows the nitrate concentration in runoff from an undisturbed watershed