Name: ____________________ Page 1 1.018/7.30J Ecology 1 Quiz #2 November 5th, 2009 Please put your name on every page! Space is provided for your answers; if you need more room, use the back of the same page. This exam is worth 100 points, with an additional 6 points of bonus problems. You have 80 minutes to work on it and the value of each question is roughly proportional to the amount of time you should spend answering it. The test will begin at 11:05am and promptly end at 12:25pm. Mean = 83.4, Standard Deviation = 11.0 1. (25 points) a) Explain Liebig’s Law of the Minimum. Describe and provide an example of how limiting factors can make complex systems easier to understand. Liebig’s Law of the Minimum states that the growth of a plant is dependent on the element that is in least supply relative to the needs of the plant. Often one nutrient is limiting, which simplifies complex systems because only the cycling of one nutrient needs to be described thoroughly. For example, in high-nutrient low-chlorophyll areas of the ocean, productivity is determined primarily by the flux of iron into the system. b) Onondaga Lake is located in Syracuse, NY and has experienced extensive cultural eutrophication. Give three potential impacts of cultural eutrophication on the lake ecosystem. Reduced clarity of water Reduced oxygen levels Increased phytoplankton blooms Reduced fish populations (anoxia) Change in food web structure c) Onondaga Lake has two inflows that each contribute 50% by volume: Nine Mile Creek and METRO, Syracuse’s primary sewage treatment plant. Jonathan collected samples from Nine Mile Creek and METRO once a week for six weeks during the summer and plotted it for you below. Draw a line that depicts the approximate concentrations of phosphate and nitrate you’d expect to find in Onondaga Lake. Is this lake nitrogen or phosphorous limited? Phosphorous limitedName: ____________________ Page 2 d) What source is responsible for the eutrophication and why? METRO is responsible. Onondaga Lake is phosphorous limited, therefore the contribution of phosphorous by METRO is causing the eutrophication. e) Sketch one line showing the nutrient (PO43-, NO3-) concentration with ocean depth and another showing the concentration of oxygen with ocean depth. Explain the major features of the nutrient and O2 profiles. Concentration -PO43-, NO3 O2 200 m Depth 400 m In near-surface well-mixed waters, the atmosphere constantly replenishes oxygen. With depth, respiration of heterotrophs and decomposition of organic matter reduces oxygen concentrations. Oxygen levels continue to decrease until the water becomes so deep that respiration and decomposition no longer occur. Nutrients are consumed at the surface and transported to depth by the biological pump where they are regenerated. 2. (25 points) a. Sketch the global carbon cycle using boxes and arrows. Identify major reservoirs (boxes) and their sources and sinks (arrows). Atmosphere, 750 Gt Oceans, 38,000 Gt Recoverable Fossil Fuels, 10,000 Gt Soils and Dead Organic Matter 1,500 Gt Vegetation, 560 Gt 91 Gt 92 Gt60 Gt120 Gt 60 Gt 7.6 GtName: ____________________ Page 3 b. The figure below shows the latitudinal distribution of the global total (land plus ocean) NPP (solid line), land total NPP (dotted line), and ocean total NPP (dashed line). How does NPP relate to the carbon cycle? What features of the Earth system are responsible for the peaks in NPP at A, B, and C? NPP describes the amount carbon (as CO2) removed from the atmosphere by photosynthesis. A – In the Northern Hemisphere, you have production in both the oceans (North Atlantic) and seasonal forests during the spring, summer, and fall. B – Tropical rainforests are productive ecosystems throughout the year. Oceans also contribute, but the signal is controlled by terrestrial NPP. C – Productivity in the Southern Ocean dominates at latitudes south of 30oS. c. Critique the following statement using your knowledge of the carbon cycle and the figure below. “I don’t see any cause for alarm regarding the human contribution of CO2 to the atmosphere. In ppm, it is only slightly larger than the annual cycle and the concentration of CO2 has been much higher on Glacial-Interglacial timescales.” The amplitude is on a log scale, so “slightly larger” is significant in terms of actual carbon concentrations. Additionally, the annual cycle is the Earth “breathing”, so having an effect on that scale is considerable. Dismissing the impact of humans using the argument of higher Glacial-Interglacial fluctuations of CO2 is flawed for two primary reasons. First, humans would have a difficult time adapting to climate changes similar in magnitude to an Ice Age. Second, humans have had a comparable impact on the concentration of CO2 in approximately 100 years that Glacial-Interglacial phenomena have had on timescales of 100,000 years. 60oN 30oN 30oS 60oS01.51.00.50.0ABC10510410310210110010-110-210910810710610510410310210110010-110-210-3Glacial-interglacialHuman perturbationAnnual cycleDiurnal cyclePeriod (years)Amplitude (ppm)Image by MIT OpenCourseWare.Image by MIT OpenCourseWare.Name: ____________________ Page 4 d. Iron ocean fertilization is one geoengineering scheme proposed for removing carbon dioxide from the atmosphere. Briefly describe how, according to this scheme, CO2 is drawn from the air into the ocean, how CO2 is partitioned/cycled after it enters the ocean, and how it is ultimately sequestered in the deep ocean. In high-nutrient low-chlorophyll waters, iron can be used to create phytoplankton blooms, pulling CO2 out of the atmosphere via the process of photosynthesis. Much of this is regenerated in surface waters and released back to the atmosphere. But some, roughly 1/3 (debated number), of that organic carbon sinks through the mixed layer and thermocline to eventually be sequestered in the deep ocean. 3. (20 points) You have managed to escape the confinements of the immediate Boston and Cambridge surroundings to the Greater Boston Area, a.k.a. Suburbia. You spend some time roaming the woods of Suburbia, observing how four species spend their day (% of time spent on the following activities). Rest Competition Eating Rat 30% 15% chasing mice 55% eating seeds Mouse 30% 25% chasing rats 45% eating seeds Raccoon 85% --15% eating rats Coyote 80% --20% eating raccoons a) Construct a food web showing the interactions between the species in this