Modeling Phosphorus Luxury Uptake in Lake Biwa, Japan

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Modeling Phosphorus Luxury Uptakein Lake Biwa,
Japan

• Ferdi L. Hellweger
• American Society of Limnology and Oceanography
  (ASLO)
• Summer Meeting
• Savannah, GA
• June 14, 2004

Present address
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Typical Lake Ecological Model Schematic
See Thomann and Mueller (1987) Schnoor (1996)
Chapra (1997)
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Phytoplankton Composition
Redfield Model
Most ecological models assume fixed (Redfield)
composition 106C16N1P Composition varies
significantly, especially in lakes (e.g. Lake
Biwa, later) Composition changes when (net
specific) uptake ? (specific) growth
Algal P
Cell Quota Model
Algal P
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Phosphorus Uptake
PO4
PO4
PO4
Phosphate (PO4) is absorbed against a steep
concentration gradient across the cell
membrane. Uptake is mediated by transport sites
(enzymes) located on the cell membrane. Uptake
rate depends on (1) external concentration, (2)
number activity of transport sites, (3)
internal concentration.
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
PO4
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Effect of Internal Concentration
P-limited
P-replete
P-starved
Uptake Rate
Luxury Uptake
Starved Uptake
Normal Uptake
Internal Concentration (Cell Quota)
Luxury uptake is due to an up-regulation of the
uptake rate.
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Luxury Uptake in Continuous Culture
Rhee, J Phycol 9 (1973) Rhee, J Phycol 10 (1974)
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Luxury Uptake in Batch Culture
Data from Hasegawa et al., Chemosphere 43 (2001)
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Luxury Uptake in Batch Culture
Hellweger et al., Limnol Oceanogr 48 (2003)
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Luxury Uptake on a Michaelis-Menten Plot
Data from Hasegawa et al., Chemosphere 43 (2001)
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Ecological Model
a
(SO4)
ox
DO
Phyto- plankton
Herbivorous Zooplankton
Carnivorous Zooplankton
H2S
POM
DOM
POC
PC
DOC
HZC
CZC
(CO2)
h
zg
ox
p/r
zp
d
PON
NH4
NO3
DON
PN
HZN
CZN
ox
u
h
m
zg
zp
d
u/e
POP
PO4
DOP
PP
HZP
CZP
zp
d
h
m
zg
u/e
SiO2
PSi
BSi
u
d
d/z
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Temperature DO Concentrations

• Temperature
• Monomictic (gt4C)
• Typhoons
• DO
• Surface follows saturation
• Supersaturated during blooms
• Bottom decreases during stratification

Hellweger and Lall, Environ. Sci. Technol. (2004,
in review)
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Chlorophyll Phosphate Concentrations

• Chlorophyll
• Spring and fall blooms
• More productivity in first year
• Bottom is lower less dynamic
• PO4
• Surface is low no obvious pattern
• Bottom increases during stratification
• Chlorophyll PO4
• Luxury uptake

Hellweger and Lall, Environ. Sci. Technol. (2004,
in review)
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PhytoplanktonComposition

• P cell quota is always below Redfield
• P cell quota is very high during overturn
• P-status not just a function of P cell quota

Hellweger and Lall, Environ. Sci. Technol. (2004,
in review)
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Concluding Thoughts
1. The model has a discontinuity and positive
feedback, which makes it difficult to
calibrate. 2. The model is non-linear, which
means scaling is an issue.
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Thank You for your attention! Questions?
Lake Biwa Photo S. Endoh (2000)
More info Hellweger et al., Limnol Oceanogr 48
(2003) Hellweger and Lall, Environ Sci Technol,
in review www.columbia.edu/flh23 (model code
documentation)
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Modeling Uptake Basic Equations
Regular Uptake
Starved Uptake
Luxury Uptake
Rhee, J Phycol 9 (1973) Rhee, J Phycol 10
(1974) Hellweger et al., Limnol Oceanogr 48
(2003)
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Modeling Uptake This Model
Uptake
Limitation
Droop, J Mar Biol Assoc UK 54 (1974) Droop, J
Mar Biol Assoc UK 55 (1975) Hellweger et al.,
Limnol Oceanogr 48 (2003)
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Nomenclature
V Uptake rate (mol P mol C-1 day-1) VMAX
Maximum uptake rate (mol P mol C-1 day-1) S
Substrate concentration (mol P L-1) KM
Half-saturation constant for limited conditions
(mol P L-1) KM Half-saturation constant for
replete conditions (mol P L-1) i inhibitor
concentration (mol P mol C-1) Ki inhibition
constant (mol P mol C-1) ? specific growth rate
(day-1) q cell quota (mol P mol C-1) q cell
quota for non-limited conditions (mol P mol
C-1) q0 subsistence cell quota (mol P mol
C-1) LH growth limitation threshold ()