1. Nutrient Cycles Ecosystems have an essentially inexhaustible supply of energy But chemical elements are available in limited amounts Life therefore depends on the recycling of these essential chemical elements Nutrient cycles involve abiotic and biotic components and are often referred to as biogeochemical cycles

2. The Nutrient Cycle Matter cycles between the biotic environment and in the abiotic environment. Simple inorganic molecules (CO 2, N 2 and H 2 O) are assimilated (or fixed) from the abiotic environment by producers and microbes, and built into complex organic molecules (carbohydrates, proteins and lipids). These organic molecules are passed through food chains and eventually returned to the abiotic environment again as simple inorganic molecules by decomposers. Without either producers or decomposers there would be no nutrient cycling and no life.

3. Nutrient Cycles A chemicals specific route through a cycle varies depending on: –Element –Trophic structure Generally 2 categories –Global –Local Reservoirs defined by 2 characteristics –Organic or inorganic –Directly available for use by organisms or not

4. General Nutrient Cycle Available inorganic matter (soil, atmosphere, water) Available organic materials (in living organisms or detritus) Unavailable organic materials (Coal, Oil, Peat) Unavailable inorganic materials (minerals in rocks) Photosynthesis Assimilation Respiration Decomposition Excretion Fossilisation Erosion Burning of fossil fuels Weathering Erosion Formation of sedimentary rocks

5. Organic nutrients in producers Organic nutrients in Primary consumers Organic nutrients in Secondary consumers Decomposers Inorganic nutrients General Nutrient Cycle

6. Carbon 4 th most abundant element Essential for life on earth Every organism requires it for structure, energy or both Discounting water we are 50% carbon Found in a variety of forms, from gaseous states (CO 2 ) to solid states (limestone, graphite, diamonds, coal) The Cycle Carbon moves between the atmosphere, oceans, geosphere and biosphere Much of this recycling occurs during an animals lifetime and not just after its death Contains large pools of carbon (sinks or sources) Has biological and geological components

7. The Carbon Cycle: Geological Components Accumulation of detritus often occurs more quickly than it can be broken down Remain stable and unavailable for longer periods These ‘stores’ can lock carbon up for millions of years These include: –Coal –Oil –Peat –Carboniferous rocks –Wood Eventually released as carbon dioxide

8. The Carbon Cycle: Biological Components Important role in movement of carbon between the land, sea and air Mainly through the processes of photosynthesis and respiration Photosynthesis bridges the gap from air to land (moving carbon from CO 2 to organic compounds) Respiration moves carbon in the other direction Occurs at timescales of days to 1000s of years

9. Carbon compounds in producers Carbon compounds Primary consumers Carbon compounds in Secondary consumers Detritus Atmospheric CO 2 The Carbon Cycle 2 2 Carbon compounds in decomposers 3 4 5 1 5 Carbon locked up in fossil fuels, peat and limestone 6 7

10. Fluctuations in atmospheric CO 2 The concentration of CO 2 in the atmosphere is not constant but is always fluctuating On a local scale there are highs and lows that occur daily

11. Taken from www.mlo.noaa.gov On a global scale the fluctuations occur on an annual basis, in response to the seasons BUT….. On top of these fluctuations the CO 2 levels over the last few hundred years have been consistently rising, with this rise accelerating at an ever increasing rate What are the causes of all these fluctuations?

12. There are potential conflicts between the need/wish to produce things useful to humans in the short term and the conservation of ecosystems in the long term. Forests Contain large stores of carbon in plant tissues Often hundreds of years old Fossil fuels (coal, oil, peat) Huge stores of carbon Carbon has been ‘locked-up’ for millions of years Limestone Huge store of calcium carbonate So how has the use of these resources by man lead to increases in atmospheric CO 2 ? Human Activities and the Carbon Cycle

13. Poster and Presentation Task Group 1 –What are the causes of the daily fluctuations in local atmospheric CO 2 concentrations? Group 2 –How has mans activities effected the carbon stored in fossil fuels and carboniferous rocks? Group 3 –How has deforestation caused an increase in atmospheric CO 2 concentrations?

14. Daily CO 2 fluctuations Due to an imbalance between photosynthesis and respiration What happens: Photosynthesis and occurs at a faster rate than respiration during the day but at night only respiration takes place Result: More CO 2 is taken up than is released by the plant during the day but at night CO 2 is not taken up at all Consequence: Local atmospheric CO 2 concentration falls during the day and increases at night

15. Seasonal CO 2 fluctuations Due to a seasonal variation in the rate of photosynthesis on a global scale What happens: Photosynthesis occurs at its maximum rate during the summer Result: More CO 2 is taken up during the summer Consequence: The northern hemisphere has more land and therefore more vegetation than the southern hemisphere so global CO 2 levels are lower during the northern hemispheres summer

16. Burning of fossil fuels The concentration of CO 2 in the atmosphere has been increasing as a result of the combustion of fossil fuels and burning of wood removed during deforestation Long-term perspective: –Just a return to atmosphere of the CO 2 that was removed by photosynthesis millions of years ago BUT in the millions of years since: –New equilibrium has developed in the global carbon cycle –This balance is now being disrupted with uncertain consequences

17. Limestone Contains carbon locked up as calcium carbonate All materials that are exposed to the outdoor environment are subject to degradation caused by natural weathering processes releasing CO 2 as a result Since the mid-19th century, air pollution (and acid rain in particular) has been suspected of accelerating the degradation of natural and man-made materials. The use of limestone and marble in the construction of buildings and monuments exposes a greater surface area to weathering This all results in a greater amount of CO 2 being released into the atmosphere from geological components

18. Humans have been clearing areas of forest for thousands of years, using the land for buildings or agriculture – leading to deforestation over large areas of Europe, Asia and North America. Growth in the world population continues to increase demand for land for farming and more recently deforestation has affected tropical rain forests. Tropical rain forests are particularly important because: Contain 50% of the world’s standing timber Huge store of carbon Sink for carbon dioxide Deforestation

19. Large scale destruction of rainforests greatly reduces the biomass of plants on the planet This results in a huge reduction in photosynthetic activity As a consequence less CO 2 is removed from the atmosphere resulting a global trend of increasing atmospheric CO 2 concentration Major contributory factor of global warming Rainforest destruction may increase atmospheric concentrations of carbon dioxide by up to 50% Affect of Deforestation on the Carbon Cycle

20. The Greenhouse Effect Major implication of increased atmospheric CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 CO 2 Results in a warmer atmosphere

21. But is it all bad? An increase in CO 2 levels in the atmosphere has obvious positive implications for plant growth CO 2 is a limiting factor for photosynthesis in bright conditions Therefore an increase in CO 2 should theoretically increase photosynthesis Which plants in particular will benefit from increased CO 2 concentration? –C3 plants are affected more by an increase CO 2 than C4 plants Could lead to change in agricultural practices Could effect species composition in non agricultural communities