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ESM 202 Nitrogen Issues Human activities alter the N cycle N fertilization of aquatic systems leads to eutrophication N2O is a major greenhouse gas All of this is linked to our demand for energy and food N: where is it? ATMOSPHERE: 3.9E21 g LAND: 3.4E17 g WATER: 2.3E19 g Nitrogen compounds Gases N2 dinitrogen N20 nitrous oxide NOx = NO2 + NO nitrogen dioxide + nitric oxide NH3 ammonia Inorganic NH4+ ammonium NO2- nitrite (HNO2 nitrous acid) NO3- nitrate (HNO3 nitric acid) Organic N Amino acids, proteins; enzymes Uric acid: C5H4N4O3 Urea: (NH2)2CO (hydrolyzes to CO2 and NH4+) N Reservoirs Source: Biogeochemistry, Schlesinger, 1991 Global N Cycle Source: Biogeochemistry, Schlesinger, 1997 N fixation N2 reactive N (e.g. NH3 , NH4+) Mostly biological symbiotic free- living bacteria (asymbiotic) Synthetic fertilizer • production is considered N fixation • takes N2, reacts it with natural gas, producing NH3 and CO2 Agriculture… (Townsend et al. Frontiers Ecol. Environ. 2003) (Tilman et al. Nature, 2002) Maximum N uptake Source: Biogeochemistry, Schlesinger, 1997 Fixed N: what happens to it? N2 (g) N2O (g) Denitrification N Fixation NO (g) Nitrification NH3/NH4+ NO-2/NO3- Assimilatory Ammonification Nitrate (mineralization) Reduction Ammonia Assimilation & Immobilization Organic N Ammonia Cycle Source: Biogeochemistry, Schlesinger, 1997 Ammonia Cycle Source: Biogeochemistry, Schlesinger, 1997 Ammonia Oxidation In the atmosphere: NH3 + OH· NO/NO2 + H2O NO and NO2 referred to as NOX NO + O NO2 NO converts to HNO2 NO2- NO2 converts to HNO3 NO3- Nitrite and Nitrate deposit as particles or with rain NOx Cycle: Human N Fixation Source: Biogeochemistry, Schlesinger, 1997 NOx Sources Source: Biogeochemistry, Schlesinger, 1997 Spatial location of N Processes Atmosphere Source: Biogeochemistry, Schlesinger, 1997 Factors in Nitrification Ammonium Bicarbonate (HCO3-) alkalinity Oxygen Time While “specialists”, the bacteria are widely distributed… NO3- Nitrate Water soluble, mobile Metabolized (gut) into NO2- Nitrite inactivates hemoglobin, particularly for infants—methemoglobin WHO / US health standard: 10 mg/L As with SO42-, acid rain Groundwater (Townsend et al. Frontiers Ecol. Environ. 2003) Percent Increase in Nitrogen Fluxes in Rivers Source: Millennium Ecosystem Assessment Gulf of Mexico Dead Zone Source: NOAA Source: Principles Env. Sci. & Eng. (Davis & Masten) Oceanic N Processes Source: Biogeochemistry, Schlesinger, 1997 Oceanic N Processes Source: Biogeochemistry, Schlesinger, 1997 Nitrification and Denitrification Factors in Denitrification Nitrate Organic C Lack of dissolved oxygen Wide range of bacteria, widely distributed….. N2O 120 yr residence time in atmosphere Absorbs radiation / greenhouse gas 4th largest contributor more effective than CO2 Depletes stratospheric O3 UV degrades N2O to NO; NO is O3 depleter N2O accumulation in atmosphere Source: Biogeochemistry, Schlesinger, 1997 Source: National Oceanic and Atmospheric Administration, N2O Budget Source: Biogeochemistry, Schlesinger, 1997 (Matson et al. Science 1998) Sources of Nitrogen Fertilizer application Atmospheric Deposition Groundwater irrigation Septic systems Livestock & manure Treated wastewater (Valiela et al. 1997) Sources of N in catchments (Petzoldt & Uhlmann 2006) Sewage 20 to 85 mg/L N untreated (domestic, US) 2º trmt for BOD5 and TSS (30/30 mg/L) Some N removed to biomass: C5H7NO2 Nutrient removal Nitrification , denitrification Total effluent N can be < 5 mg/L Biological nutrient removal Issues Nitrous Oxide (N2O) Is a Greenhouse Gas. Nitrous Oxide Depletes Stratospheric Ozone. Nitrogen Gases Generate Air Pollution. Nitrate Ions in Drinking Water Can Be a Threat to Infant Health. Nitrogen Oxides Emitted into the Atmosphere Contribute to Acid Deposition. High Nitrate Concentrations in Aquatic Ecosystems Can Lead to Eutrophication. Nitrogen Addition to Ecosystems Reduces Biodiversity and Loss of Ecosystem Function. Socolow, 1999, PNAS “Fertilizer is the fossil fuel of food.” “The goal of achieving a constant carbon dioxide concentration in the atmosphere makes future use of fossil fuels hostage to the combined power of natural and engineered carbon sequestration. Similarly, the goal of achieving constant stocks of fixed nitrogen makes future use of nitrogen fertilizer hostage to the strength of natural plus engineered denitrification in the corresponding ecosystems. Globally, until nitrogen fixation is balanced by denitrification, the amount of excess fixed nitrogen in the world will grow relentlessly, with increasing consequences for ecosystems and public health.” “As an alternative to fossil fuel, fast-growing energy crops may be established on dedicated, fertilized plantations.” Socolow, 1999, PNAS (Townsend et al. Frontiers Ecol. Environ. 2003) (Townsend et al. Frontiers Ecol. Environ. 2003) Global N Budget Source: Millennium Ecosystem Assessment
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