Nitrogen in Lakes and Streams

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Nitrogen in Lakes and Streams

• Horne and Goldman Chapter 8

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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

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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

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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 lt10 of light rates

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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

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Inorganic and Organic Nitrogen

• Influents bring significant sources of N into
  lakes and streams
• Common Concentrations in Lakes
• NH4-N, 0 - 5mg L-1 higher in anaerobic
  hypolimnions of eutrophic waters
• NO2-N, 0 - 0.01mg L-1 possibly higher in
  interstitial waters of deep sediments
• NO3-N, 0 - 10mg L-1 highly variable seasonally
  and spatially
• Organic N up to 50 of Total Dissolved N

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• N concentrations can have an effect on algal
  productivity but it is more likely that
  phosphorus is the limiting factor
• Growth rates for algae are higher with more
  reduced forms
• NH4-NgtNO3-NgtN2-N

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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
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Generation and Distribution continued

• Nitrification
• Nitrosomonas biological conversion of nitrogen
  from a reduced state to a more oxidized state
• NH43/2O2?2HNO2-H20
• ?G0-66 k cal mol-1

• Nitrobacter responsible less energy is given
  off by this oxidation, O2 needed.
• NO2-1/2O2?NO3-
• ?G0-18 k cal mol-1

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Overall NH4 2O2 ? NO3- H20 2H

• 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 anaerobic conditions

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Seasonal Distribution

• Interaction of Stratification, Anoxia, and
  Circulation with Biology control distributions

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Seasonal Distribution continued
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Seasonal Distribution continued
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Seasonal Distribution continued
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CarbonNitrogen Ratios

• Indicative of nutrient availability but also of
  relative amount of proteins in organic matter
• Approximate indication of phytoplankton status
• CN gt14.6 nitrogen limitation
• Nitrogen-Fixing phytoplankton become more
  abundant
• CN lt8.3 no N-deficiency

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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)

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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

Gaia !!!
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Phosphorus

• Next to N, generally the primary limiting
  nutrient.
• NP ratio normally 101, higher ratios indicate
  P deficiency
• Most of available P present in biota
• Reserves in rocks and sediments and mostly
  unavailable
• Essential for all living organisms, comprising
  about 0.3 of the biomass.

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• Component of genetic materials DNA, RNA, etc.
• Component of energetic compounds, ATP, NADP
• Component of phospholipids

• Law of the minimum (Liebig)
• Luxury uptake

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Erosion, Sewage, Aerial Deposition, Streams and
Rivers
Bacteria Phytoplankton Zooplankton Fish
Particulate Org-P
PO4-P
P-ase
decay
O2, Fe, Ca
anoxia
Soluble Org-P
Organic Sediments
Inorganic Sediments
P-cycle
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Conclusions

• P is an essential nutrient
• Rock and sediment derived
• Mostly in biota
• Mainly responsible for eutrophication
• Target nutrient for environmental protection