Nutrients
Chapter 14
Nitrogen and Phosphorus
Nitrogen
Macronutrient
DNA
RNA
Amino acids, proteins
chlorophyll
Forms of N
N2
N2O
Nitrate (NO3-)*
Nitrite (NO2-)
Ammonium (NH4-)*
NH3
DIN (sum of the ions)
DON (0.45 µm filter)
PON
N sources/sinks
Atmosphere, Atm diffusion, N fixation
Stream flow
Stream outflow
PPT
Dryfall
Epilimnetic cycling
Sediment cycling
Groundwater
Denitrification
Volatilization
N processes
N fixation
– Lightning
– N fixing plants have Rhizobia in nodules
– Haber process (fixing N for fertilizers)
– Burning fossil fuels (re-fixing it)
– Cyanobacteria
Heterocytes and nitrogenase
©2010 Elsevier, Inc.
FIGURE 14.1
Streamers composed of the sulfur-oxidizing bacterium Thermothrix at Mammoth Terrace, Yellowstone National
Park (courtesy of R. W. Castenholz) and a transmission electron micrograph of a heterocyst (the site of nitrogen
fixation in Nostoc and other cyanobacteria) attached to a smaller dividing vegetative cell with a diameter of
approximately 8 μm. (Micrograph courtesy of N. J. Lang).
N processes
Nitrification
– NH4- to NO2
- then to NO3-
– bacteria
Denitification
– Nitrate reduction
– NO3- back to NO2
- and eventually N2
– Low redox, NO3- goes to NH4
-
N processes
Uptake
– NH4-
– NO3-
Excretion
– NH4-
Ammonification
– PON, DON to NH4-
– Decomposition
N Cycle
N2
N fixation (anaerobic, cyanobacteria)BGA
PON
PON
Detrital
PoolDie
PON
Animals
DON
NO2-
PON
Plants
NO3-
PON
Detrital
Pool
PON
Detrital
Pool
PON
Detrital
Pool
Excrete
©2010 Elsevier, Inc.
FIGURE 14.6
A conceptual diagram of the nitrogen cycle.
Nitrogen Dynamics
Sources
– Lakes
– Streams
Sinks/Losses
– Lakes
– Streams
Seasonal N Distribution in Lakes
Seasonal N Distribution in Lakes
FIGURE 14.4
Distribution of nitrate (A) and ammonium (B) in hypereutrophic Wintergreen Lake, Michigan, as a function of depth
and time. Ice cover occurred from January to March. Darker colors represent higher concentrations. Contours are
reported in μg liter21. (Reproduced with permission from Wetzel, 1983).
N in Streams
©2010 Elsevier, Inc.
FIGURE 14.7
Correlation between nitrate intake and rates of gastrointestinal cancer. (After P. E. Hartman. 1983. Reprinted by
permission of Wiley–Liss, Inc., a subsidiary of John Wiley & Sons, Inc.).
Phosphorus
Macronutrient
DNA
RNA
Cell membranes
ATP
Forms of P
Rare
Soluble Particulate
Inorganic PO43- (BAP) Mineral apatites
Organic ATP, phospholipids Detritus, POP
Ca(PO4)2
FePO4
Phosphorus fluxes
Geophysical weathering
Cycling (rapid uptake)
– DOP
– POP
– DIP
Sedimentation (attachment), loss from
epilimnion
– Importance of macrophytes
– Role of P-ase (alkaline phosphatase)
©2010 Elsevier, Inc.
FIGURE 14.9
A diagram of the phosphorus cycle.
P Cycle in a Lake
Rock
Inorganic
sediments
DIP,
BAP
Organic
sediments
Trophic
dynamics
Decay
Organic detritus,
soluble POP,
leaching, lysis
Total P
90% particulate
10% soluble
– 90% Organic
– 10% inorganic
1% is BAP
Very low availability
– Attaches to sediment
– Rapid uptake by biota
P in lakes vs streams
Streams: erosion from surrounding
watershed, soil
Lakes: less for lakes (isolated from soil)
Litter fall in streams
Macrophytes in lakes
NOT groundwater like N
What is more N and P limited?
Streams or lakes? Why?