Nutrient Cycles

1. Nutrient Cycles

2. Matter Cycling in Ecosystems • Nutrient – any atom, ion, or molecule an organism needs to live, grow, or reproduce • Some (such as C, O, H, N, P, S, and Ca) are needed in fairly large amounts • Some (such as Na, Zn, Cu, and I) are only needed in trace amounts.

3. Nutrient Cycles • Compartment – represents a defined space in nature • Pool – amount of nutrients in a compartment • Flux rate – the quantity of nutrient passing from one pool to another per unit time.

4. Major Nutrient Cycle Pathways Flux rate Pool

5. Plants Herbivores Water Hypothetical Phosphorus Nutrient Cycle 126 81 1.4 9 133 7 45 19 100 9.5 Flux rate and pool size together define the nutrient cycle within any particular ecosystem

6. Two Broad Types of Nutrient Cycles • Local Cycle – operates within an ecosystem • Nonvolatile elements • No mechanism for long-distance transfer • Global Cycle – involve exchanges (gaseous) between the atmosphere and the ecosystem • Volatile elements: Water, oxygen, carbon, and nitrogen • Easy exchange among ecosystems

7. Hydrologic Cycle • Collects, purifies, and distributes the Earth’s fixed supply of water – powered by the sun. • Distribution of Earth’s Water Supply: • Salt water (oceans) = 97.4% • Freshwater = 2.6% • 80% in glaciers and ice caps • 20% in groundwater • 0.4% in lakes and rivers (0.01% of all water!) • Anytime of year, the atmosphere holds only 0.0001% of water on the planet. • Although large quantities are evaporated and precipitated each year • About 84% of water vapor comes from the ocean

8. Main Processes of the Hydrologic Cycle • Evaporation – conversion of water into water vapor • Transpiration – evaporation from leaves of water extracted from soil by roots • Condensation – conversion of water vapor into droplets of liquid water • Precipitation – rain, sleet, hail, and snow • Infiltration – movement of water into soil • Percolation – downward flow of water through soil and permeable rock formations to groundwater storage areas called aquifers • Runoff – downslope surface movement back to the sea to resume cycle

9. 3 4 2 1 5 6 Hydrologic Cycle 7

10. Nutrient Cycles in Forests • Inputs – outputs = storage • Nutrients accumulate in the leaves and wood over time

11. Nutrient Storage in Trees is Temperature and Vegetation Type Related In cold climates nutrients are tied up in the soil.

12. Nutrient Turnover Time is Temperature Related Turnover time – the time an average atom will remain in the soil before it is recycled into the trees or shrubs

13. Net Primary Production and Nutrient Cycling • In general, NPP is closely related to the speed of nutrient cycling. • Tracking the decay of a leaf and the cycling rate of nutrients provides an indicator of biome productivity. * Mean residence time is the time for one cycle of decomposition.

14. A Closed System • The speed of nutrient cycling in the humid tropics promotes high productivity, even when soils are poor in nutrients. • Nutrients are cycled so quickly there is little opportunity for them to leak from the system! • Because there is virtually no loss of nutrients, many tropical forests have virtually closed nutrient cycles. • The opposite would be an open system, in which nutrients are washed out rapidly

15. Rapid Cycling in the Tropics • Reasons for rapid cycling in the tropics: • Warm climate • No winter to retard decomposition • An army of decomposers • Abundant mycorrhizal fungi on shallow roots • Fungi that grow symbiotically with plant roots • Facilitate water and nutrient uptake • Waters in local streams and rivers can have as few nutrients as rain water!

16. Tropical Rain Forest Paradox • Most tropical rain forests are poor in nutrients – especially oxisol. • When the forests are cleared for farmland, the land can only support three or four harvests. • Well, how can they support the amount of primary production we find in a tropical rain forest?

17. Standing Biomass • Standing Biomass - all the plant matter in a given area. • Nutrients are either found in the soil or in the standing biomass. • In a temperate forest system, recycling is slow. • Consequently, at any given time, a large proportion of nutrients are in the soil. • So when the land is cleared, it is fertile and can support many years of agriculture

18. Tropical Soils • In the humid tropics, as little as 10% of the total nutrients are in an oxisol (soil) at any given time. • Hence, when the logging trucks take the trees, they are carrying the majority of the nutrients! • An increase in soil acidity often follows timber removal to the point that available phosphorous is transformed to an insoluble form.

19. Normal Nutrient Loss • Rain runoff is the major vector of nutrient loss from most ecosystems a Not determined, but very low; b Watershed 4 only

20. Stream Nitrite Concentration Note Scale Change Deforestation Can Increase Loss of Nutrients From Areas Due to Runoff Other stream nutrient increase two years after the deforestation: Calcium 417%, Magnesium 408%, Potassium 1,558%, Sodium 177%

21. Carbon Cycle • Carbon is the basic building block of organic compounds necessary for life. • The carbon cycle is a global gaseous cycle • Carbon dioxide makes up 0.036% of the troposphere and is also dissolved in water • Key component of nature’s thermostat • Too much taken out of the atmosphere, temp’s decrease • Too much added to atmosphere, temp’s increase

22. CO2 Uptake and Release • Terrestrial producers remove CO2 from the atmosphere and aquatic producers remove CO2 from water via photosynthesis. • The cells in oxygen-consuming producers, consumers, and decomposers break down the organic compounds and release CO2 back to the atmosphere or water. • The link between photosynthesis and respiration is a major part of the global carbon cycle

23. Primary Productivity Heat Energy Chemical Energy (ATP) Solar Energy CO2 Respiration Photosynthesis C6H12O6 O2 Available to Consumers Biomass (g/m2/yr) GPP NPP

24. Other Links of the Carbon Cycle • Fossil Fuels – large stores of carbon which are not released as CO2 unless extracted and burned. • In only a few hundred years, we have extracted and burned fossil fuels that took millions of years to form. • Limestone (CaCO3) – largest storage for the earth’s carbon is in sedimentary rocks such as limestone. • Carbon reenters the cycle as some of the rock releases dissolved CO2 back to the atmosphere. • Geologic processes can bring sediments to the surface and expose carbonate rock to the atmosphere.

25. The Ocean and CO2 • The oceans are the second largest storage reservoir in the carbon cycle. • Some is dissolved as CO2 and some reacts with seawater to form carbonate (CO32-) and bicarbonate (HCO3-). • As water warms, more CO2 is squeezed out of the water into the atmosphere (like a hot coke). • Ions can react with Ca++ to form CaCO3 to build the shells and exoskeletons of marine organisms. • When these organisms die, tiny particles of their shells and bone settle to the oceans bottom and may be buried for eons. • May eventually be converted to limestone rock

26. Carbon Cycle Atmospheric / Aquatic CO2 Photosynthesis Respiration Combustion of wood / fossil fuels Food Web Weathering Sedimentation Limestone Rocks Volcanic Action

27. The Carbon Cycle (Terrestrial) Atmosphere (mainly carbon dioxide) volcanic action combustion of wood (for clearing land; or for fuel photosynthesis aerobic respiration Terrestrial rocks sedimentation weathering Land food webs producers, consumers, decomposers, detritivores Soil water (dissolved carbon) Peat, fossil fuels death, burial, compaction over geologic time leaching runoff Fig. 4.29, p. 93

28. The Carbon Cycle (Aquatic) diffusion between atmosphere and ocean combustion of fossil fuels Carbon dioxide dissolved in ocean water photosynthesis aerobic respiration Marine food webs producers, consumers, decomposers, detritivores uplifting over geologic time incorporation into sediments death, sedimentation sedimentation Marine sediments, including formations with fossil fuels Fig. 4.29, p. 92-93

29. Nitrogen Cycle • Nitrogen is used to make essential organic compounds such as amino acids, proteins, DNA, and RNA. • Normally in short supply and often limits the rate of primary production. • Why most commercial fertilizers contain biologically useful compounds such as ammonium nitrate (NH4NO3). • However, nitrogen is the atmosphere’s most abundant element • 78% of the volume is chemically un-reactive nitrogen gas N2.

30. Nitrogen Fixation • The nitrogen cycle is a global gaseous cycle. • Atmospheric nitrogen must be ‘fixed’ or combined with H or O to provide compounds that plants can use. • Lightning stimulates production of nitrogen oxides: N2 + O2 2NO • Certain bacteria in the soil and aquatic systems can convert nitrogen gas into compounds that can enter food webs.

31. Nitrogen Cycle • Nitrogen fixation – specialized bacteria convert gaseous nitrogen to ammonia (N2 + 3H2 2NH3) which can be used by plants. • Done mostly by cyanobacteria in water and soil and Rhizobium bacteria living in small nodules of some plants

32. Nitrification and Assimilation • Nitrification - Two-step process in which ammonia is converted first to NO2- (toxic to plants) and then to NO3- (easily taken up by plants). • Assimilation – A process by which plants roots absorb inorganic ammonia, ammonium ions, and nitrate ions to make nitrogen containing organic molecules (DNA, RNA, Proteins). • Animals then get their nitrogen by eating plants.

33. Ammonification • Ammonification – the conversion (by decomposer bacteria) of nitrogen-rich organic compounds, wastes, cast-off particles, and dead bodies into: • Simpler nitrogen-containing inorganic compounds such as ammonia (NH3) • Water-soluble salts containing ammonium ions (NH4+)

34. Denitrification • Other specialized bacteria (mostly anaerobic bacteria in waterlogged soil or in the bottom sediments of a water body) convert NH3 and NH4+ back to nitrite (NO2- ) and nitrate (NO3-) ions and then into nitrogen gas (N2) and nitrous oxide gas (N2O) to complete the cycle.

35. Nitrogen Cycle Gaseous N2 Nitrogen Fixation Ammonification Ammonia: NH3, NH4+ 1. Nitrification Nitrogenous Waste Food Web Nitrite: NO2- 2. Nitrification Nitrate: NO3- Denitrification Loss by Leaching

36. Biochemical Transition of Nitrogen NITROGEN OXIDATION STATE

37. Nitrogen Cycle

38. Phosphorous Cycle • The phosphorous cycle is a sedimentary cycle. • Circulates through the earth’s crust and living organisms • Bacteria are less important here than in the nitrogen cycle • At the temperature’s and pressures normally found on the earth, phosphorous and its compounds are not gases. • The phopsphorous is slow, and on a human time scale much phosphorous flows from the land to the sea.

39. Phosphorous • Phosphorous is usually found as phosphate salts containing phosphate ions (PO43-) in terrestrial rock formations and ocean bottom sediments. • Most soils contain very little phosphorous, so it is often the limiting factor for plant growth on land unless added as fertilizer. • Phosphorous also limits primary producer growth in aquatic ecosystems.

40. Phosphorous Cycle

41. Sulfur Cycle • The sulfur cycle is a gaseous cycle. • Although much of the earth’s sulfur is stored underground in rocks and minerals. • Sulfur is important in some amino acids • Sulfur enters the atmosphere from several natural sources. • Hydrogen sulfide (H2S) is released by volcanic activity and by the breakdown of organic matter in swamps, bogs, and tidal flats (you can smell this at low tide in the salt marsh). • Sulfur dioxide (SO42-) enters from volcanoes. • Particles of sulfate (SO42-) salts, such as ammonium sulfate, enter as seas spray.

42. Sulfur Cycle All values are 1012 g S/yr