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Lecture 4

EESA01 UTSC Lecture 4- Finish Biogeo Chemical Cycles Global Energy Balance

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Environmental Science
Carl Mitchell

EESA01 Lecture 4- Finish Global Biogeochemical Cycles, Global Energy Balance Importance of Nitrogen  Bunch of biogeochemical cycles that run the important elements in our earth system between the lithosphere, biosphere, hydrosphere, atmosphere aka and how they move into reservoirs  Certain parts of these spheres are reservoirs, eg hydrosphere- lakes  Have elements that move by different chemical processes as a flux between these reservoirs o Need to multiply the concentration and how quickly it is moving to get flux estimates Nitrogen  78% of atmosphere  The most abundant elements on earth, a key ingredient in living things (amino acids)  Essential nutrient for plant growth  Inert, not reactive, quite scarce in lithosphere, hydrosphere and biosphere  Global nitrogen cycle o Massive amount for atm, much less in water and soil o In addition to transfer between atm and water, there is an intricate n cycle in aquatic ecosystems, changes the chemical structure (ammonia, nitrate, nitrite)  Nitrogen fixation- a key process that fixes nitrogen o N fixation- combo of N gas (N2) with h to form ammonia (NH3) and subsequenty, the biologically available and soluble ammonium ion (NH4+) o We have massive pool of n in atm, and very unreactive o Need ways to pull the n out or we would have no N to use in our system o Driving processes  Lightning  Nitrogen fixing bacteria- live in root/tuber systems of legumes and other plants, harbour the bacteria in roots eg soybeans o Farmers rotate crops with soybeans, get n fixing bacteria to build up the nitrogen in soil o Bacteria pulls dinitrogen gas from atmosphere to form ammonia and that gets mineralized into ammonium ion that can be used by organisms o Once have ammonium, plants like nitrate , are the important ones o Other bacteria converts ammonium into nitrate, which is easily taken up by plants o Nitrification  Conversion of NH4+ (ammonium ion) to NO2- (nitrite ion) and then NO3- (nitrate) by specialised bacteria, plants take up nitrite o Denitrification  At some point, need that nitrogen to go back into atmosphere to complete cycle  Denitrification- conversion of nitrate back to N2 bas by specialized bacterial communities o Denitrification bacteria- mostly live in wet areas, because are facultative anerobes, are adaptive but would rather not have oxygen. Often see denitrification in swamps, pond bottoms,  Bacteria uptakes the nitrate and excretes dinitrogen gas Human alteration of n cycle  Used technology to take advantage of dinitrogn gas for mass production of fertilizer o Haber-Bosch process o Doubled nitrogen fixation through haber-bosch process and also from the increase of legumes  Increased atm nitrogen based gases, from fossil fuel burning, and animal waste decomposing o NOx- smog o No2 very potent gas o N2O- intermediate of denitrification  Depletion of micronutrients (Ca, K) from soils, N fertilizers make them more mobile and they flush out  Acid rain- o Sulfuric acid o Nitric acid- nitrogen gasses converted into nitric acid and brings pH of rain down to low 4-5  Eutrophication- overabundance of nutrients. N is noted for its effect on marine systems. Not a base issue in fresh water system- limited by phosphorus instead.  Increases plant growth o More nutrients make plants and algae grow more by photosynthesis, more biomass Eutrophication  The process of nutrient over enrichment, blooms of algae, increased production of organic matter and ecosystem degradation  Algae blooms die, massive increase of organic matter that floats to the bottom, the bacteria eat the algae, the bacteria consume massive amounts of oxygen. The oxygen levels in water drop and all the fish and aquatic organisms start to suffer  The algae is not doing the consumption of the oxygen  The blooms are going to die, they fall, get consumed and oxygen levels bomb  Gulf of Mexico- huge dead zone because of the run off drain from the Mississippi river. All the farms that are adding to much N fertilizer. Accumulates, flow into local streams, to gulf of Mexico. Massive stream of nutrients, huge algae bloom they die, no oxygen Importance of phosphorus  For fresh water  Very different from n cycle  Key component of cell membranes, DNA, and ATP  Big limiting nutrient for autotrophic growth especially in fresh water  Almost no phosphorous in the atm, little ways to get p outside of sea spray o Cycle Restricted to lithosphere and hydrosphere  Driven by aquatic reactions o Solubilisation- takes precipitated p and brings it into solution o Precipitation- puts it back into solid form o Assimilation- uptake by plants and people o Accumulation in organisms o Decomposition- as they die and p is released  Fig 3.18 o No number for atm, before where it was high for N  1 for transport of dust and sea spray o Main storage for p is in sedimentary rocks o Other storage in soil, plants and the water o Main way we get p is by mining  Mineable rock amount is going down almost as bad as running out of oil  Need p to grow food  run out in 50 years  huge stores way down but it is very hard to get it Human alteration of the p cycle  Mining for p bearing rock for fertilizer o Run off into fresh water systems  Waste water, sewage water  Phosphate detergents o Big push in 80’s to get phosphates out of detergents  Lake erie used to be dead, very shallow, massive amounts of over fert runoff, huge algael bloom o That’s when regulations came in o Experimental lakes- place to manipulate large environments and see how they react to environmental factors  Took a lake system, put a curtain in the middle, same types of processes on 2 halves  In one half, kept on putting detergent in it  Side with detergent, huge algae bloom, fish were dying  P is still a massive issue Mercury cycling  Minor in quantity, only need a little to get very sick  Mercury cycle before people on left  On right, human influence  See that our impact is similar to our impact on the carbon cycle o We mined carbon out of the lithosphere as oil and coal and burned it, so a flux of carbon as co2, taken lithosphere and shoved it into the atmosphere o Same as mercury o From burning of coal in electrical facilities, there is mercury in coal, it is very difficult to control, o It is moving from lithosphere into atm through industrial activities o Mining of mercury for gold mining  Low scale gold mining  Get pan, fill with mercury, gold and it will react and stick to each other  Waste incineration, mercury in batteries, thermostats, old industrial things o Numbers are smaller but similar to c because of industrial and anthropogenic activities  Mercury accumulation in water, thermometers etc not such a big of a deal  Inorganic mercury (silver liquid) is not bioaccumulative, so if ingested, it will be excreted  There are some transformations in environment that make it into an organic methylmercury o Very bioaccumulative o Inputs tend to be much quicker than it
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