The Global Ecosystem

1. 46 The Global Ecosystem

2. Chapter 46 The Global Ecosystem • Key Concepts • 46.1 Climate and Nutrients Affect Ecosystem Function • 46.2 Biological, Geological, and Chemical Processes Move Materials through Ecosystems • 46.3 Certain Biogeochemical Cycles Are Especially Critical for Ecosystems

3. Chapter 46 The Global Ecosystem Key Concepts 46.4 Biogeochemical Cycles Affect Global Climate 46.5 Rapid Climate Change Affects Species and Communities 46.6 Ecological Challenges Can Be Addressed through Science and International Cooperation

4. Chapter 46 Opening Question How did Keeling’s research contribute to our understanding of the global ecosystem?

5. Concept 46.1 Climate and Nutrients Affect Ecosystem Function Ecosystem—an ecological community plus the abiotic environment with which it exchanges energy and materials. Ecosystems are linked by processes and material movements. It impossible to understand a local ecosystem completely without considering it in the context of the larger systems of which it is a part.

6. Concept 46.1 Climate and Nutrients Affect Ecosystem Function One aspect of ecosystem function: Net primary productivity (NPP)—rate at which an ecosystem produces primary-producer biomass. NPP can be estimated by instruments on satellites that measure wavelengths of light reflected from the Earth’s surface.

7. Concept 46.1 Climate and Nutrients Affect Ecosystem Function NPP varies among ecosystem types, mostly due to variation in climate and nutrient availability. Tropical forests, swamps, and marshlands are the most productive. Cultivated land is less productive than many natural ecosystems.

8. Figure 46.1 NPP Varies among Ecosystem Types

9. Concept 46.1 Climate and Nutrients Affect Ecosystem Function NPP varies with latitude, as solar input and climate vary with latitude. Tropics are very productive; high latitudes and dry regions are less productive.

10. Figure 46.2 Terrestrial NPP Corresponds to Climate

11. Concept 46.1 Climate and Nutrients Affect Ecosystem Function Terrestrial NPP tends to increase with temperature and moisture. Activity of photosynthetic enzymes increases with temperature (up to the point at which they denature). At very high moisture levels, productivity may be inhibited by cloud cover or lack of oxygen in saturated soils.

12. Figure 46.3 Terrestrial NPP Varies with Temperature and Precipitation (Part 1)

13. Figure 46.3 Terrestrial NPP Varies with Temperature and Precipitation (Part 2)

14. Concept 46.1 Climate and Nutrients Affect Ecosystem Function Aquatic NPP is strongly affected by nutrient availability and light penetration. Nutrients are most abundant in near-shore areas and upwellings. Hydrothermal vents are productive areas in the deep oceans, where chemolithotrophs use chemical energy rather than sunlight.

15. Figure 46.4 Marine NPP Is Highest around Coastlines

16. Concept 46.2 Biological, Geological, and Chemical ProcessesMove Materials through Ecosystems Earth is an open system with respect to energy, but a closed system with respect to matter. The sun provides a steady input of energy. There is a fixed amount of each element of matter, but biological, geological, and chemical processes can transform it and move it around the planet in biogeochemical cycles.

17. Concept 46.2 Biological, Geological, and Chemical ProcessesMove Materials through Ecosystems Different chemical forms and locations of elements determine whether they are accessible to living organisms. The different forms and locations can be represented as compartments.

18. Figure 46.5 Chemical Elements Cycle among Compartments of the Biosphere

19. Concept 46.2 Biological, Geological, and Chemical ProcessesMove Materials through Ecosystems Pool—total amount of an element or molecule in a compartment. Flux—movement of an element or molecule between compartments.

20. Concept 46.2 Biological, Geological, and Chemical ProcessesMove Materials through Ecosystems All the materials in the bodies of living organisms are ultimately derived from abiotic sources. Primary producers take up elements from inorganic pools and accumulate them as biomass. Trophic interactions pass the elements on to heterotrophs. Decomposers break down the dead and waste matter pool into elements that are available again for uptake by primary producers.

21. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems The global water (hydrological) cycle: Water is essential for life; makes up 70% of living biomass. Flowing water is an erosion agent and transports sediment—moves material around the planet. Because of high heat capacity, water redistributes heat as it circulates through the oceans and atmosphere.

22. Figure 46.6 The Global Water Cycle

23. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Solar-powered evaporation moves water from ocean and land surfaces into the atmosphere. The energy is released again as heat when water vapor condenses.

24. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Humans affect the water cycle by changing land use: Reduced vegetation (deforestation, cultivation, etc.) reduces precipitation retained in soil and increases amount that runs off. Groundwater pumping depletes aquifers, brings water to surface where it evaporates. Climate warming will melt ice caps and glaciers and cause sea level rise and increased evaporation. Water vapor is a greenhouse gas.

25. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems The global nitrogen cycle: Involves chemical transformations. N2 gas is 78% of the atmosphere, but most organisms cannot use this form. Nitrogen fixation: some microbes can break the strong triple bond and reduce N2 to ammonium (NH4+).

26. Figure 46.7 The Global Nitrogen Cycle

27. Figure 46.8 Where Does the Extra Nitrogen Come From? (Part 1)

28. Figure 46.8 Where Does the Extra Nitrogen Come From? (Part 2)

29. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Other microbial species convert ammonium into nitrate (NO3−) and other oxides of nitrogen. N-fixing reactions are reversed by yet another group of microbes in denitrification, which returns N2 gas to the atmosphere.

30. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Human activities affect the nitrogen cycle: Burning fossil fuels, rice cultivation, and raising livestock releases oxides of nitrogen to the atmosphere. These oxides contribute to smog and acid rain. Humans fix nitrogen by an industrial process to manufacture fertilizer and explosives.

31. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Topsoil and dissolved nitrates are lost from farm fields and deforested areas by wind and water runoff. The nitrates are deposited in aquatic ecosystems and result in eutrophication— increased primary productivity and rapid phytoplankton growth. Decomposition of the phytoplankton can deplete oxygen; other organisms can not survive, and dead zones form offshore in summer.

32. Figure 46.9 High Nutrient Input Creates Dead Zones

33. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Excess nitrogen in terrestrial ecosystems can change plant species composition. Species adapted to low nutrient levels grow slowly, even when fertilized, and can be easily displaced by faster-growing species that take advantage of additional nutrients. In the Netherlands, this has caused 13% of the recent loss of plant species diversity.

34. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems The global carbon cycle: Movement of carbon is linked to energy flow through ecosystems; biomass is an important pool. The largest pools occur in fossil fuels and carbonate rocks. Photosynthesis moves inorganic carbon from the atmosphere and water into the organic compartment; respiration reverses this flux.

35. Figure 46.10 The Global Carbon Cycle

36. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Dissolved CO2 in the oceans: some is converted by primary producers, and enters the trophic system. Organic detritus and carbonates continually drift down to the ocean floor. Some organic detritus in ocean sediments is converted to fossil fuels. Carbonates can be transformed into limestone.

37. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Human activities affect the global carbon cycle: Any activity that impacts primary productivity can alter fluxes. Runoff brings carbon to aquatic ecosystems. Deforestation and fossil fuel burning increase atmospheric CO2. Atmospheric CH4 is increased through livestock production, rice cultivation, and water storage in reservoirs (microbes in water-logged soils produce CH4).

38. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Biogeochemical cycles are interconnected. If carbon uptake by primary producers increases, uptake of P, N, and other elements also increases. If decomposition rates increase, flux of elements back to inorganic compartments increases. Any nutrient can limit biological functions; the limiting one is the one that is in lowest supply relative to demand.

39. Concept 46.3 Certain Biogeochemical CyclesAre Especially Critical for Ecosystems Biogeochemical cycles can interact in hard-to-predict ways. Increased atmospheric CO2 can increase water- use efficiency by terrestrial plants; In a high CO2 environment, the plants have stomata open less, which reduces loss of water vapor.

40. Concept 46.4 Biogeochemical Cycles Affect Global Climate All objects that are warmer than absolute zero emit electromagnetic radiation. Most of the incoming solar radiation is in the visible range of wavelengths. Some is absorbed in the atmosphere, some is reflected back to space, and some is absorbed by the Earth’s surface.

41. Concept 46.4 Biogeochemical Cycles Affect Global Climate Greenhouse effect: Earth’s surface re-emits energy in longer, less energetic infrared wavelengths. Some of this infrared radiation is absorbed by gas molecules in the atmosphere (greenhouse gases). The molecules are warmed and radiate photons back to Earth’s surface, keeping the energy within the Earth system as heat.

42. Figure 46.11 Earth’s Radiation Balance

43. Concept 46.4 Biogeochemical Cycles Affect Global Climate Greenhouse gases include H2O, CO2, CH4, N2O. Without the atmosphere, Earth’s average surface temperature would be about 34°C colder than at present. Keeling’s measurements from atop Mauna Loa in Hawaii show a steady increase in CO2 since 1960.

44. Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are Increasing (Part 1)

45. Concept 46.4 Biogeochemical Cycles Affect Global Climate Analyses of air trapped in glacial ice demonstrate that CO2 and other greenhouse gases began increasing after about 1880. Average annual global temperature has also increased.

46. Figure 46.12 Atmospheric Greenhouse Gas Concentrations Are Increasing (Part 2)

47. Figure 46.13 Global Temperatures Are Increasing

48. Concept 46.4 Biogeochemical Cycles Affect Global Climate Higher global temperatures are affecting climate: Hotter air temperatures A more intense water cycle, with greater overall evaporation and precipitation. Hadley cells are expected to expand poleward; warmer tropical air will rise higher and expand farther toward the poles before sinking. Precipitation will increase near the equator and at high latitudes and decrease at mid-latitudes.

49. Concept 46.4 Biogeochemical Cycles Affect Global Climate Warming is spatially uneven, so precipitation changes will be season- and region-specific. In general, wet regions are expected to get wetter and dry regions drier. Precipitation trends in the twentieth century support these expectations.

50. Figure 46.14 Global Precipitation Patterns Have Changed