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Cole et al. 1994 Science 265:1568-1570. Why this pattern?. Cole et al. 1994 Science 265:1568-1570. Directly measured. Autumn. Full Seasonal Data. Summer. Tropical Africs. Lec 6: Nutrients and Nutrient cycling. I. Storages and cycling II. Nutrient loading (more next lecture) - PowerPoint PPT Presentation
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Cole et al. 1994 Science 265:1568-1570
Why this pattern?
Cole et al. 1994 Science 265:1568-1570
Directly measured
Autumn
Full Seasonal Data
Summer
Tropical Africs
Lec 6: Nutrients and Nutrient cycling
I. Storages and cyclingII. Nutrient loading (more next lecture)
III. PhosphorusIV. NitrogenV. Other elements
1
I. Storages and cycling A. Energy versus nutrients -Energy flows -Nutrients cycle
B. Closed system 1. Rate = cycles/time a. as rate increases, productivity increases b. total N or P versus the amount of inorganically available N or P 2. Pathways - In a closed system all the nutrients cycle within the system
C. Open system
- Boundaries
1. Rate 2. Pathways (e.g. internal cycling vs. nutrient loading) 3. Residence time: time spent cycling before being lost from the system a. residence time = amount of nutrient in the system/amount in output b. in an open system nutrient use depends on recycling rate and retention by the system
(residence time) c. inputs and outputs do not necessarily balance 2
II. Nutrient Loading
A. Estimates of critical amounts of nutrients for eutrophication (especially used for N and P)B. Amount of nutrient input per time and lake area
called aerial loading
C. Used to develop models of nutrient effects in lakes
D. Must determine:1. Volume of inflow and outflow2. Concentration of nutrient in effluents and influents3. Volume of lake4. Loss rates to sediments
3
A. Except under polluted conditions, the only significant inorganic form of Phosphorus is Orthophosphate (PO4
–3)
B. Phosphorus often is a limiting nutrient in freshwater habitats
C. Generally, >90% of Phosphorus is in or adsorbed to living or dead organisms
D. Phosphorus is unique among the major inorganic nutrients in that its oxidation is not an important energy source (P always occurs in the oxidized form)
III. Phosphorus (P)
4
C : N :P106:16:1
100-1000C:10N:1P
6C:4N:1P
1st to become limiting
2nd to become limiting
rarely limiting
III. A. P as a Limiting NutrientElemental composition in plants (w/ balanced growth)
Presence in environment
Composition of sewage effluents
** Luxury Uptake
5
• Weathering of Rock (Apatite)
• P adsorbs to particles
III. B. Phosphorus Cycle
6
A. Particulate P1. Organisms
2. Rocks, soil, sedimentsIgneous rocks are associated with low P
Sedimentary rocks are associated with high P
3. Adsorbed
B. Dissolved P1. Orthophosphate (PO4
–3)
2. Polyphosphates (from detergents)
3. Organic phosphates (mostly colloidal)
Total Phosphorus must take into account all forms of P, including that incorporated into suspended matter and organisms.
III. C. Forms of Phosphorus
7
A. Precipitation (Wet and Dry)Non-populated areas <30 ug/LUrban-Industrial areas >100 ug/L Range 0.01-0.1 g/m2/year
B. Ground Water 20 ug/L
C. Runoff (fertilizers) varies
Lake requirements ~ 0.07 g/m2/year: >0.13 g/m2/year may result in eutrophication if mean depth < 5m
III. D. Sources of Phosphorus
8
Phosphate inliving plant andanimal tissue
Phosphatedissolved in water
CompensationDepth
AphoticZone
PhoticZone
Phosphate in mud
Thermocline
In epilimnion, P rapidly is taken up by algae
In sediments, P is removed by rooted vegetation and benthos
III. E. Distribution of Phosphorus
9
Generalized P Profiles in Lakes of Low and High Productivity
P, oC, O2
O O2
OLIGOTROPHIC EUTROPHIC
O O2
PSPT PS PT
PS = Soluble phosphorus
PT = Total phosphorus
Dep
th
Dep
th
P, oC, O210
Phosphorus in Sediments• Depends on O2 supply
• O2 depends on trophic status and basin morphology
• P is retained by the oxidized microzone• Breakdown of the oxidized microzone releases P
(also Fe, Mn)• P, Fe, and Mn concentrations are related• P released from sediments under anoxic
conditions (+ feedback of internal cycling)• P also may be released from sediments by rooted
vegetation and benthos
11
Productivity Total PUltraoligotrophic <5 ug/LOligo-Mesotrophic 5-10Meso-Eutrophic 10-30Eutrophic 30-100Hypereutrophic >100
P generally is regarded as more important than other nutrients except in marine costal waters and under high P conditions.
III. F. Epilimnetic Phosphorus and Lake Productivity
*Note areal loading rate; influence of depth
12
Jan 2004
0.01
0.10
1.00
10.00
FR
R01
0F
RR
020
FR
R03
0N
EC
010
FR
R04
0C
HC
010
FR
R05
0F
RR
060
PE
C01
0M
IC01
0
FR
R07
0C
RC
010
CG
C01
0F
RR
080
CG
C02
0F
RR
090
CG
C03
0
FR
R10
0C
GC
040
FR
R11
0H
EL0
10 1
mH
EL0
10 4
mH
EL0
20 1
mH
EL0
20 3
mH
EL0
30 1
mH
EL0
30 4
mH
EL0
40 1
mH
EL0
40 4
m
TN
or
TP
(m
g/L
)
0
20
40
60
80
N:P
Rat
io
TN TP TN:TP
Generalized relationship between water clarity (Secchi depth) and algal concentration (Chl a). (OECD 1982).
Hensley Reservoir and Fresno River Data
A. P levels often positively correlated
with aquatic productivity
B. Noxious algal blooms
C. Hypolimnetic Oxygen Deficits
D. P is difficult to remove from water
III. G. Phosphorus and Water Quality
13
P Loading & OxygenP Loading & Phytoplankton(Lake Washington, Seattle)
Hypolimnetic O2 deficit
14
A. Generally considered to be the 2nd most important nutrient in lakes in terms of limiting the rate of primary production (Phosphorus being 1st)
B. Occurs in many forms and energy states (gas, organic and inorganic)
Lithosphere 97.6%
Atmosphere 2.3%
Hydrosphere + Biosphere 0.1%
C. Important both as a nutrient and
(in some forms) for its toxicity to organisms
IV. Nitrogen
15
A. Dissolved molecular Nitrogen (N2)
B. Organic Nitrogen•Proteins Highest Energy•Amino acids•Amines•Humic compounds
C. Inorganic Nitrogen•NH4
+ Ammonium
•NO2– Nitrite
•NO3– Nitrate Lowest Energy
IV. A. Forms of Nitrogen
16
IV. B. Nitrogen Sources and Losses
A. Sources1. Precipitation (wet & dry)2. Nitrogen Fixation3. Runoff
B. Losses1. Outflow2. Denitrification (NO3 => N2)3. Sediments
17
IV. B. Nitrogen FixationA. N2 gas to ammonium, very expensive energetically (Chemical “fixation” of molecular nitrogen (breaking the
triple covalent bond) in the laboratory requires 500OC and 100+ atmospheres of pressure)
B. Only bacteria known to fix nitrogen
C. Nitrogenase sensitive to O2, a variety of adaptations protect it
D. Lightning also fixes N2 to NO3- in the atmosphere
E. Nitrogen-fixing cyanobacteria can be very important in lake N cycles 18
A. Nitrification- oxidation of ammonium to nitrite (Azotobacter) and nitrite to nitrate (Nitrobacter)
B. Denitrification- using NO3- as an electron
acceptor for oxidation of carbon, yields N2O and N2. Drives N loss from environment. Under very low redox, can go to ammonium
C. Remineralization (ammonification)OrgN => NH4
+
IV. C. N Cycling
19
Jan Mar May Jul Sep Nov
5
4
3
2
1
0
1 1
1 10
10
10
10
100
100
250
500
500
1000
100
0 125
0 125
0
A
Jan Mar May Jul Sep Nov
Month
5
4
3
2
1
0
Dep
th (
m)
1
20
100
500 500
500 1
000 1000
1000
150
0
1500
1500 3000
B
Nitrate(NO
3)
Ammonium(NH
3)
IV. D. N Distribution in a Lake
20
N, o C, O2
NH4+ NO3
–O O2 NH4
+ NO3– O
O2
OLIGOTROPHIC EUTROPHIC
N, o C, O2
Dep
th
Dep
th
Generalized N Profiles in Lakes of Low and High Productivity
21
pH NH4+ : NH4OH
6 3000:1 7 300:1 8 30:1 9.5 1:1
Least toxic
Most toxic
IV. E. Toxic Forms of Nitrogen A. Nitrate/Nitrite – concentrations in drinking water >10 mg/l can cause the disease Methemoglobinemia in infants (a problem in some agricultural areas) (NO2 binds to hemoglobin more strongly than O2)
-Can be converted to carcinogenic nitrosamines in the stomach
B. Ammonia (especially in the form NH4OH) is toxic to many organisms
• Amount of NH4+
vs. NH4OH is pH dependent:
22
A. Silicon1. Key element in diatom frustules
2. Can become limiting in lakes
B. Iron1. Ferric, Fe3+, oxidized; ferrous, Fe2+ reduced
2. Iron oxidation by microorganisms important chemoautotrophic pathway, but also will happen abiotically, so must occur at oxic/anoxic interface
3. Oxidized iron precipitates with phosphate, but dissociates again in anoxic conditions
V. Silicon, Iron, etc.
23
0
1
2
3
Sili
ca (
mg
L-1)
1953 1954 1955 1956
Year
1
10
100
1000
Ast
erio
nella
(ce
lls m
L-1)
Annual Silicon Cycle in a Lake
24