Lecture 28 HUMAN ALTERATIONS OF NUTRIENT CYCLESHow are humans altering water cycle? 23.4- Depletion from overuse- Fossilized vs. re-chargeable aquifers- Overpopulation- Used to produce crops to produce meat Irrigation salt buildup in soil 578-9; 27.10, 27.11- Land-use changes lower local cycling 514; 24.13 50% of water in the Amazon Basin is internally recycled. Predict how deforestation there might be affecting the hydrological cycle and the tropical forest.- Links to other cycles:- Water carries solutes (e.g. N, P, K, H+)- C cycle – link to global warming - precipitation changes worldwide- glacial melt loss of water sourceWhat are consequences of human changes in C cycle? 583-5 23.6Production of CO2 by burning of fossil fuels and deforestation has increased greatly. 27.16Production of plastic products from oil has increased greatlyGreenhouse gases and other human inputs add to the heat budget of the atmosphere = (radiative forcing) 27.17Global warming Lower snowpack colder soil temp kill roots greater leaching More drought wildfires more frequent/severe alter several cycles positive feedback fires generate more CO2 570-1 27.1 Accelerate decomposition, especially in N biomes (boreal; tundra) 515-16 24.14, 24.15 positive feedback faster decomposition generates more CO2How are humans altering the N cycle? 23.11Humans fix as much nitrogen industrially as occurs naturally. Through what processes are we altering the N-cycle?- Nitrogen-fixing crops- Fossil fuel burning- Nitrogen fertilizer- Animal feed lots + manure - Invasive species fix N- What are some major consequences of our alterations of the N cycle? Nitrous oxide, a greenhouse gas, is produced. N-run-off from excess fertilizer and feedlots gives excess N to aquatic systems change algae relative abundances + lower water quality; causes eutrophication (see below) Saturate soils with N in forests initially increases leaf N and NPP; but then alters soil chemistry, eventually causing heavy leaching of nitrates.Biodiversity and species mix are alteredWhat is the major way in which humans are altering the P cycle? 23.14 Mining for P to add to fertilizer for crops run-off into aquatic communities 24.20 increases algal abundance eutrophication (see below); lower water quality. Moves P to geologic time scale if sedimentation in bottom of lakes/ocean occursHow do human activities affect input from land to water?- runoff/seepage- agriculture land, especially NPK- animal feedlots, especially N- sewage input, C, N- into ground water/aquifers/streams/oceansHuman eutrophication (overproduction of organic matter in aquatic systems) is harmful.- Added nutrients stimulate algal GPP, BUT- Too much overwhelms intrasystem regeneration- Increase in dead organic matter- Energy flows to bacteria, not higher trophic level- Increase in decomposition + respiration- depletes oxygen (hypoxia + anoxia)- kills aerobes, including fish- lower quality of drinking water- change freshwater aquatic communities- create ‘dead zones’ in oceans 522 24.23What are consequences of human activities on sulfur cycle? 23.17 Burning of fossil fuels containing H2S puts SO4 into air SO4 reacts with H20 to form sulfuric acid acid rain 505-6; 579-80; 24.1 Of what consequence is S presence in coal? Strip-mine - sulfuric acid directly into streams lowers pH and disrupts aquatic community 23.18 Acid rain Lowers Ca in soilslowers forest productivity. Lowers pH in lakes disrupts aquatic community.Ozone (O3) + UV radiation 582-3 27.151. at surface-O2 with N2O with light O3-N2O from burning gas in cars-Ozone = oxidant of organic molecules-SOYFACE: elevated O3 lowers crop productivity2. CFCs destroy ozone in upper atmosphere and creates ‘black hole’ increase damage from UV radiation; Montreal treaty banned
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