UCSB EEMB 171 - Quiz 1 2017 Key (5 pages)

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Quiz 1 2017 Key



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Quiz 1 2017 Key

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5
School:
University of California, Santa Barbara
Course:
Eemb 171 - ECOSYSTEM PROCESSES
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Your Name EEMB ES 171 Fall 2017 Quiz 1 Read each question carefully Use the back if you need to True or False If false briefly explain why 1 6 T F Cation exchange capacity is an important characteristic of both clays and organic matter True 2 6 T F Soil texture and structure are effectively the same thing False texture is the proportion of sand silt clay particles Structure is how those particles are packaged in the macro structure of the soil 3 6 T F The main resource limiting the productivity of tropical rainforests is typically nitrogen because the soils are so old and weathered False The main resource limiting in old soils is typically phosphorus Your Name 4 12 If you were considering buying a piece of property to farm the first piece of information you should probably check is the soils map Why Give at least three specifics A soils map would tell you 1 Nutrient status 2 Water holding dynamics 3 Soil depth 4 Are there hard pans that would be a problem for roots 5 10 What is the difference between photosynthesis and net primary production Photosynthesis is the total amount of CO2 fixed by a plant It pays no attention to plant respiration NPP is equal to GPP i e photosynthesis minus plant respiration It is the amount of C accumulated by a plant 6 16 You are doing a water balance on an area The following values are for the summer only PET 1500 mm Rainfall 700 mm Soil water 150 mm this amount of water is in the soil at the beginning of the summer a 5 What is AET for this summer AET will either be equal to PET or to the amount of water available in the system I e PET is the credit card bill AET is the amount you actually pay If you have enough to cover the whole bill you will If you don t you ll pay what you can So Available water is 850 rainfall plus soil water This is less than PET Hence AET 850 b 5 If all this rain comes in two big thunderstorms would AET change Why or why not If all the rain came in two big storms it would almost certainly overwhelm the system s ability to use all that water and some would run off Hence there would be less available for supporting plants Less water would be used for AET more would run off downstream Consider two day long storms Seasonal PET is 1500 So over a 100 day season daily PET would be on the order of 15 mm d If each storm dropped 350 mm of rain in even a few days that would overwhelm PET for those days Your Name c 6 If the plants in this area had roots that went deep enough to reach groundwater do you think AET would change If so how If roots could reach groundwater AET would increase because plants would use that water 7 16 Consider the ecosystem at right You ve established the following measurements 1 A flux tower to measure the net ecosystem exchange of between the ecosystem and the atmosphere 2 Soil flux chambers to measure total soil respiration which includes root respiration 3 A flume on the stream to measure export Assume there are no other important C fluxes N e t flu x in 1 0 g C m F lu x to w e r 2 y 1 CO2 S o il r e s p ira tio n 4 g C m 2 y 1 A 8 What is the value for Net Primary Production NPP is the C gain by the plants via gas exchange The whole system is gaining 10 But it is losing 4 to the atmosphere from soil respiration So the gaseous exchanges are S tr e a m e x p o rt 1 g C m 2 y 1 Net C flux NEE NEE 10 NPP 4 14 g m2y The plants gain 14 the soils lose 4 the net change is 10 B 8 What is the value for Net Ecosystem Productivity NEP is the total net change in C stock in the ecosystem That is inputs minus all outputs NEP 14 4 1 9 g m2 y Alternatively NEP Net gas exchange minus other C losses Hence 10 1 9 Your Name 8 12 You set up a suite of fertilizer trials to test the fertility of a farm soil You set up three plots in which you add either N P or a combination of both Treatment Control N P N P Growth kg 9 9 14 18 From these data would you conclude that Liebig s Law applies in this situation Liebig s Law says that only one resource may be limiting at a time In this case adding N alone does nothing for plant growth Hence it is not independently limiting Adding P alone does increase growth hence it was limiting Adding both increases growth beyond what P does on its own So after you ve eliminated the Plimitation N is the next limiting nutrient So adding N P increases growth beyond what P alone will do In this case Liebig appears to work 9 16 You are evaluating the likely response of an ecosystem to climate warming To do this you measure how much the rate of each process increases as temperature increases You measure the Q10 value which describes how much a reaction speeds up with each 10 C increase in temperature a value of 2 means the rates doubles with a 10 C increase so rate is 1 at 10 2 at 20 4 at 30 etc Process Photosynthesis Plant respiration Soil respiration Q10 2 0 3 0 1 5 A 8 As the temperature increases will NPP increase or decrease Why Simple Answer Plant respiration increases more rapidly with temperature than does photosynthesis Hence NPP will decrease Complex Answer If you assume as I ve said is a common pattern that GPP 2 NPP Your Name Then consider Temp Photo 10 12 14 16 18 20 Resp 2 00 2 30 2 64 3 03 3 48 4 00 NPP 1 00 1 25 1 55 1 93 2 41 3 00 1 00 1 05 1 09 1 10 1 07 1 00 At 10 C photo 2 Resp 1 So NPP 1 At 20 C photo 4 Resp 3 So NPP 1 At temperatures between these NPP actually goes up slightly At 30 C photo 4 Resp 9 So NPP 5 So above 20 C NPP declines increasingly rapidly No one needs to worry about this complex answer since no one did the math to work through what the patterns would look like if you made assumptions about the values of the individual pieces B 8 As temperature increases will this system gain or lose carbon Why Here there is no complex answer At all temperatures total C storage will decline Even in the range from 10 to 20 C where NPP might increase a little and even if you only assume …


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