Global Change, Fall 2010 A. Biogeochem #1: Carbon Cycle Basics 1. What are the three main processes/timescales that control the atmospheric composition of CO2? What are the corresponding reservoirs of carbon for each of these three processes/timescales? 2. At the multi-million year timescale, the balance of what two processes determines the amount of CO2 in the atmosphere? 3. 400 Million years ago, atmospheric CO2 was 10-15 times higher than today. By 350 Mya, it was within factors of 2-3 of present day. What is believed to have caused the big draw down, and how? 4. Define these terms: pedosphere, lithosphere, hydrosphere, biosphere 5. Why does atmospheric CO2 not increase by the same amount as the CO2 being added by fossil fuel combustion? 6. What is ecosystem ecology? What is biogeochemistry? 7. What is the simplified net chemical reaction known as photosynthesis? What is the net chemical reaction known as respiration? What is the difference between the two? 8. Define the following terms, and be able to relate them to each other mathematically: a. Gross Primary Production (GPP) b. Autotrophic respiration (Rauto) c. Net Primary Production (NPP) d. Heterotrophic respiration (Rhet) e. Net Ecosystem Production (NEP) f. Ecosystem respiration (Reco) 9. What are some of the most important controls on NPP? 10. What does it mean for NPP to be “limited” by factor X (for example, nitrogen)? 11. NPP is the fundamental biological process by which CO2 enters terrestrial ecosystems and is stored as organic carbon. What is the basic loss process by which organic matter leaves terrestrial ecosystems, returning to CO2? B. Biogeochem 2: Ecosystem development and Nitrogen cycling 1. What are the basic ingredients for building an ecosystem? a) in particular, after C, H, and O, which are the most predominant elemental constituents of organic matter, what are the next two most common elements needed to build plants? b) For each of the 5 elements listed in part a, what is their ultimate source (where do plants/ecosystems get these elements?) 2. Describe the simple conceptual model of soil/ecosystem development presented in class and in the Chadwick et al. reading. What nutrients are expected to be limiting early in ecosystem development, and which ones later? 3. What is stoichiometry? 4. What general difference is observed between the C:N:P stoichiometry of marine organisms (called the “Redfield ratio”), and that of terrestrial plants? What is the reason for the difference? 5. What general difference is observed globally between the C:N:P stoichiometry of terrestrial plant litter and that of the comparable foliage from which it derives? What is the reason for the difference?Be prepared to think about how stoichiometric relations constrain biogeochemical cycling. SAMPLE PROBLEM: Consider the figure from Hungate et al. 2003 (discussed in lecture): Fig. The amount of Nitrogen required to support a given amount of model-predicted terrestrial carbon uptake for 6 models (summed from the present to the year 2100). Model runs project terrestrial ecosystem response to elevated atmospheric CO2 by itself (in blue), and to the combined effects of elevated CO2 and climate change (red). Consider the elevated CO2-only model runs (blue markers), and for the time being, don't worry about additional constraints that might limit carbon storage: (a) which 4 models project the most carbon storage? (b) Which 4 are expected to require the most nitrogen to store their carbon? (c) Now, let's consider the nitrogen constraint that limits plausibility of some of the projections shown in the figure. According to this figure's depiction, which models project plausible amounts of carbon storage when only CO2 changes are taken into account, and which are implausible? Which models project plausible carbon storage under scenarios in which the combined effects of CO2 and climate are included? What rules out the other scenarios as implausible? (d)What is the highest amount of Carbon storage that is plausible, according to the above figure? Which model, and how much carbon? Compare your answer to the pre-industrial carbon stock of the atmosphere, which was about 550 PgC. 6. What are some reasons why N is an essential nutrient for plants? 7. In what forms do plants typically take up N? 8. What is N–fixation? What is N mineralization? What is denitrification? (alternative formulation: draw a diagram of a simple Nitrogen cycle that includes the above terms) 9. What are some of the requirements biological nitrogen fixation? 10. What are three activities engaged in by humans that alter the amount of Nitrogen that is fixed globally? 11. What are some ecosystem impacts of Nitrogen cycle alterations caused by human activities? C. Biogeochem #3: Water Cycle & Climate interactions with Ecosystems 1. How big is global average precipitation? Is average precipitation on land greater or less than this global average? 2. Only about 2/3 of the water that falls as precipitation on the land surface is returned to the atmosphere via evapotranspiration. What happens to the rest of the water?3. What is the residence time of water vapor in the atmosphere, and how does it compare to the residence time of other greenhouse gases, such as CO2, CH4, and N2O? 4. What effect is global climate change expected to have on precipitation for: (a) the globe on average? (b) tropical regions? (c) sub-tropical regions, and (d) high latitudes? 5. How can changes in the water cycle affect the temperature of the land surface? 6. How do plants regulate their water loss? 7. What are some of the most important direct controls on evapotranspiration, and what are some of the indirect controls? 8. What is the definition of Water Use Efficiency? What is increased atmospheric CO2 expected to do to Water Use Efficiency, on average? All else being equal, what consequence for the global water cycle is this likely to have? 9. What is potential evapotranspiration? 10. What is a basic indicator of water limitation at the ecosystem-scale? 11. Changes in water cycling may cause droughts and increases in water limitation of vegetation in some ecosystems. Drawing on the homework reading (Adams et al., 2009), what are two main mechanisms by which droughts can cause plant mortality. 12. What is NDVI? How is it defined? What does it measure? 13. Summarize the Zhao and