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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
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
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
nitrogen in lakes and streams

Nitrogen in Lakes and Streams

Wetzel Chapter 12

pp. 205-237

introduction
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
sources and forms of n in water
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
nitrogen fixation
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
nitrogen fixation continued
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
inorganic and organic nitrogen
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
inorganic and organic n continued
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

generation and distribution of various forms of nitrogen
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

generation and distribution continued
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

generation and distribution continued12
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
seasonal distribution
Seasonal Distribution
  • Interaction of Stratification, Anoxia, and Circulation with Biology control distributions
carbon nitrogen ratios
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
nitrogen cycle in streams and rivers
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)
conclusions
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