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?