Nutrient Dynamics in Lakes

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Nutrient Dynamics in Lakes
Nutrient a chemical element essential for
life Limiting nutrient plant growth is limited
by that nutrient that is least abundant relative
to the needs of the plant
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Nitrogen
Forms of nitrogen 1. Organic nitrogen DON PON
2. Elemental nitrogen N2 3. Nitrate
NO3-1 Most oxidized form of nitrogen 4. Nitrite
NO2-1
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• Ammonium NH41
• NH41 is the most reduced form of N
• Nitrate from geologic sources
• Ammonium from biological sources
• Nitrate usually more abundant except in eutrophic
  lakes
• NO, N2O, NOx oxides
• Anthropogenic pollutants

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Oxidation states NO3-1 5 NO2-1 3 NO 2 N2O
1 N2 0 ? NH41 -3
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Processes transformations among forms of
nitrogen
1. Nitrogen fixation N2 ? NH4, NO3, organic
N A. Abiotic B. Biotic fixation Aquatic N
fixers Importance of N-fix in lakes is highly
variable
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2. Nitrification oxidation of ammonium
NH41 ? NO2-1 ? NO3-1 reduced 3
3 5 oxdized

• Autotrophic immobilization -- nitrogen uptake by
  plants
• DIN ? PON
• Either NH4 or NO3 ? living algae

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4. Heterotrophic immobilization -- nitrogen
uptake by fungi or bacteria DIN ?
PON

• 5. Ammonification -- mineralization of organic
  nitrogen
• ON ? NH4

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• 6. Denitrification - oxidation of organic
  matter using NO3 as the oxidizing agent
• e.g., C6H12O6 4NO3 ?
• 6CO2 6H2O 2 N2 574 kcal/mole

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Diffusion
Diffusion
Nitrogen fixation Nitrification
(Nit) Immobilization (I) Autotrophic Heterotroph
ic Ammonification (A) Denitrifiction Runoff Diffu
sion Sedimentation
N
N
Runoff
Runoff
2
2
Denitrification
Denitrification
N
-
fixation
N
-
fixation
Nit
Nit
NO
NH
NO
NH
3
4
3
4
I
I
I
I
I
I
Plant N
Plant N
Excreation (A)
I
Excretion (A)
I
Death
Death
A
A
Animal
Animal
N
N
PON DON
PON DON
Death
Death
Detritus
Detritus
A
Mineralization
Sedimentation
Sedimentation
Sediments
Sediments
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Nitrogen distribution in an oligotrophic lake Mid
summer, thermally stratified Orthograde oxygen
curve
Figure 12-4
Nitrogen distribution in a eutrophic lake Mid
summer, thermally stratified Clinograde oxygen
curve
Seasonal pattern of nitrate Oligotrophic lake --
low throughout the year Eutrophic lake --
depleted in summer due to immobilization
and denitrification
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Phosphorus
Forms Essentially all phosphate,
PO4-3 Problems 1. PO4-3 combines with many
things 2. Define forms based on function or
analytical techniques
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Functional forms -- what we think is in the
water I. Dissolved a. dissolved inorganic
PO4-3 b. dissolved polyphosphates c.
dissolved organic PO4 II. Particulate a.
Organic living and detritus b. PO4 adsorbed
to organic particles c. PO4 adsorbed to
inorganic particles d. Particles of insoluble
P compounds III. Gaseous -- phosphene
PH3
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• Light spectrophotometry
• Combine target chemical with another chemical
  that produces a color
• Measure the intensity of the color

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Analytical forms
SRP -- soluable reactive phosphorus
Filterable
TDP -- total dissolved phosphorus
Dissolved organic phosphorus -- DOPTDP-SRP
Sample
Non-filterable
Particulate phosphorus -- PP
Total phosphorus -- TP
PPTP-TDP
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Major questions SRP PO4? TP all
phosphorus?
What are the most abundant forms of P in
freshwaters?
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Phosphorus reactions (see figure) I. Reactions
with cations (A) a. Calcium b. Redox metals
Fe, Mn, Al II. Adsorption to particles (A,
B) III. Autotrophic immobilization (C) IV.
Heterotrophic immobilization (B) V.
Mineralization of P (D)
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Precipitation (P) Adsorption and Heterotrophic
Immobilization (H) Autotrophic Immobilization
(A) Mineralization (M) Excretion (E) Death and
Feeding (F) Leaching (L)
Runoff
N
-
M
L
A
L
L
I
L
E
F
Death
H
A
F
F
F
M
M
P
Sedimentation
Sediments
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Phosphorus distribution Thermally
stratified Oligotrophic Orthograde O2 curve
Figure 13-1
Phosphorus distribution Thermally
stratified Eutrophic Clinograde O2 curve
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Phosphorus in sediment Sediment concentrations
may be much higher than concentrations in the
overlying water
Microzone prevents release of P from sediments
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Phosphorus in sediment -- rooted
macrophytes Terrestrial plants move nutrients up
from soil. Can aquatic plants do the same thing?
The role of animals on the phosphorus cycle 1. A
source of P 2. Form of P 3. Bioturbation 4.
Diel migration