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Lecture 21.docx

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University of Toronto St. George
John Stinchcombe

BIO220 Lecture 21: March 28 Nuclear research also gave ecology tools and a model  Radioactive tracers allowed following fates of chemicals in natural communities  Manhattan Project was the classic model for collaborative ‘Big Science,’ a model that ecologists tried to follow with limited success. Aspects of some selected biogeochemical cycles:  Carbon cycle (will revist later)  Nitrogen cycle (a gaseous cycle) o Human intervention: N fertilizer for crops  Phosphorus cycle ( a sedimentary cycle) Chemistry of the Natural World  Anything that’s sugar based compound (anything with carbon) will be synthesized primarily by plants. Consumed by omnivores/carnivores.  Overall cycle we refer to as pools and fluxes are transitions in between (ex. Carbon cycle is the pool, and one flux is from human activity fossil fuels which accelerate fossil fuel pollution back into the atmosphere pool) C, N and P cycles  Usually first Nitrogen limitation and then P limitation The carbon cycle  Imitating steps governing the carbon cycle  the transfer by combustion/respiration from burning from fuel. Humans have land clearance, combustion of fossil fuels, extraction of fossil fuels  There’s a naturally recurring cycle where Co2 from some communities, some run offs. Humans are just accelerating this natural set of pools. Agricultural impacts on carbon: Man makes grass  Humans turn forests into grasses, or grasslands, or less forests. Some of it is for agriculture (clear jungle, a rain forest ) to cultivate plants  Some burn to have some visibility for predators  In N. America  maintained by fire.  This has been going on since humans have developed stone and bone calibre tools.  There are in this volume of this transition has been expanding  We need to consider per rate and capital issues and the number of people imposing that rate Before history: effect of forest clearance by Neolithic humans indicated by the relative abundances of pollen from lake sediments  can take the top layer off and you can see that things that used to be woodland, there was a clearing phrase and it moved more tewards grasslands. We can date it by isotope discomposition by mud of these cores. We can access how much humans hve facilitated these processes by looking at charcoal in ash Acceleration in modern times: Deforestation in North America Cleared woodslands to try and grow crops People clearing redwood forests (Clifornia), the size of the trees in respective to the train (really ancient big trees) Recovery in some places (Rhode Island)  trying to farm when soil isn’t good for farming and so the climate isn’t good, they abandoned farms. What we have are the old stone walls for what marked the boundaries of those fields. So there were rapid forests, clearing, destruction, abandonment of the farms and forests growing back Current deforestation mostly in the tropics  Equador (from 1938  all the black areas are forests and then going to 1988, have a lot less forests) Some tropic al clearing is subsistence ‘slash and burn’f or garden plots Clear the jungle, plant things, the soil tends to give out quickly. This system only works if there are human pops are low enough so that forests revert back to forest. Other is for lumber, growing plantations, etc. Logging in Sarawak, Borneo  anything that’s brown is cleared Tropical forests contain great stores of carbon:  Really efficient in taking carbon out of the atmosphere and bringing it into the terrestrial food level  Usually too wet to burn, bt this peat horizon was in the understory and moist, and shielded from wind and direct sunlight will start to dry up.  One of the kinds of characteristics of whiskey they have a smoked flavour. Burning peat, it has to be harvested and dried up. People in Scotland and Ireland use it to make whiskeys in the context of tropical forests. If you log the forest, and peat dries up and it gets smokey (look at Asian fires picture) Industrial Revolution: powered by fossil fuel combustion  dramatically changed the carbon cycle in the course of the earth (previously things were drawn and pushed by muscle power by humans and animals, except for water power and mills) After revolution, muscle power was replaced with fossil fuel consumption -Driven by cars in the US, Canada, Western Europe and increasingly in the developing world. -Cars are consuming a ton of fossil fuels it’s being burned and pushed into the atmosphere Human effects on carbon budget:  Carbon compounds oxidized to Co2 and released into atmosphere  Fossil fuel burning ~6 billion tonnes  Deforestation ~ 1.6 billion tonnes  Atmospheric Co2 from baseline l
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