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Reminder about EEOB 698.02

Reminder about EEOB 698.02. Still spaces available on the Lake Guardian for EEOB 698.02 – Great Lakes Limnology Week-long cruise on Lake Erie; June 23-30 See course website for more information. Finishing up Inorganic Carbon. Hall Lake Free CO2, pH, HCO3 Distribution in time and space

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Reminder about EEOB 698.02

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  1. Reminder about EEOB 698.02 • Still spaces available on the Lake Guardian for EEOB 698.02 – Great Lakes Limnology • Week-long cruise on Lake Erie; June 23-30 • See course website for more information

  2. Finishing up Inorganic Carbon • Hall Lake Free CO2, pH, HCO3 • Distribution in time and space • Effect of turnover and stratification • Changes in pH associated with photosynthesis and reduction

  3. Nitrogen in Lakes and Streams Wetzel Chapter 12 pp. 205-237

  4. Introduction • Where does the Nitrogen come from? • Biological Fixation • By bacteria and Cyanobacteria • Lightning Fixation • Reduction of N2 in the atmosphere • Human Fixation • Crop production • Energy Production

  5. Forms: Dissolved N2 Oxidation State = 0 Ammonia NH4+ Oxdn State = -3 Nitrate NO3- Oxdn State = +6 Nitrite NO2- Oxdn State = +3 Organic Nitrogen Various States Sources Precipitation Fixation Surface/Groundwater Drainage Losses Effluent Outflow Reduction with loss of gaseous N2 Adsorption with Sedimentation Sources and Forms of N in Water

  6. Nitrogen Fixation • Bacterial • Cyanobacterial • Only forms with heterocysts are capable of N-fixation • N-fixation mainly light-dependent • Requires reducing power and ATP • Both of these come from photosynthesis • Expensive energetically – 12-15mol ATP: 1mol N2 reduced • Dark rate <10% of light rates

  7. Nitrogen Fixation continued • N-fixation curve follows the same path as the photosynthesis curve • Photosynthetic and Heterotrophic bacteria may also contribute to the fixed N pool • Fixation by shrubs on wetland, river, and lake shores can also contribute to N in water

  8. Inorganic and Organic Nitrogen • Influents bring significant sources of N into lakes and streams • Common Amounts in Lakes • NH4 – 0-5mgL-1; higher in anaerobic hypolimnions of eutrophic waters • NO2-N – 0-0.01mgL-1; possibly higher in interstitial waters of deep sediments • NO3-N – 0-10mgL-1; highly variable seasonally and spatially • Organic N – up to 50% of Total Dissolved N

  9. Inorganic and Organic N continued • N concentrations can have an effect on algal productivity but it is more likely the phosphorus is the limiting factor • Growth rates for algae are higher with more reduced forms: NH4-N>NO3-N>N2-N

  10. Generation and Distribution of Various Forms of Nitrogen • Ammonia • End product of deamination of organic material • Present in non-oxygenated areas – highly reduced • Used rapidly in trophogenic zone • Sorbs quickly to particles and can sediment out • Can be higher at sediment interface due to reduced adsorptive properties of sediments under anoxic conditions or due to excretion products of benthic heterotrophs Variation by lake status

  11. Generation and Distribution continued • Nitrification – biological conversion of nitrogen from a reduced state to a more oxidized state NH4++3/2O22H++NO2-+H20 G0=-66kcalmol-1 - Nitrosomonas also methane-oxidizing bacteria capable of producing this reaction

  12. Nitrification cont. NO2-+1/2O2NO3- G0=-18kcalmol-1 Nitrobacter responsible – NOTE: less energy is given off by this oxidation Overall: NH4++2O2NO3-+H20+2H+ Need oxygen for this reaction Denitrification – biochemical reduction of oxidized nitrogen anions with concomitant oxidation of organic matter Occurs in both aerobic and anaerobic areas but is highly important under anerobic conditions Examples: C6H12O6+12NO3-12NO2-+6CO2+6H20 G0=-46kcalmol-1 Generation and Distribution continued

  13. Seasonal Distribution • Interaction of Stratification, Anoxia, and Circulation with Biology control distributions

  14. Seasonal Distribution continued

  15. Seasonal Distribution continued

  16. Seasonal Distribution continued

  17. Carbon:Nitrogen Ratios • Indicative of nutrient availability but also of relative amount of proteins in organic matter • Approximate indication of phytoplankton status • C:N >14.6 – nitrogen limitation • Nitrogen-Fixing phytoplankton become more abundant • C:N <8.3 – no N-deficiency

  18. Nitrogen Cycle

  19. Nitrogen Cycle

  20. Nitrogen Cycle in Streams and Rivers • Nutrient Spiraling – net flux downstream of dissolved nutrients that can be recycled over and over while moving downstream • Spiraling Length (S) – average distance a nutrient atom travels downstream during one cycle through the water and biotic compartments • S = distance traveled until uptake (Sw uptake length) + distance traveled within biota until regenerated (SB turnover length)

  21. Conclusions • Nitrogen is very important to aquatic ecosystem function • Different forms occur at different times and depths • Occurrence controlled by the interaction between Biology, Chemistry, and Physics

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