Are limnologists obsessed with P

1
Are limnologists obsessed with P?

• Highest demandsupply ratio- 80,000
• O, H 1, Si 2000, C5000, N30,000
• Positive correlation between P and chlorophyll
• Schindlers ESA P-addition experiment
• Why is P so limiting?
• comes from rocks, not atmosphere, not very
  soluble or volatile
• Lost to sedimentation
• Biologically essential (ATP, DNA, RNA)

2
Phosphorus and chlorophyll- observational
evidenceD.W. Schindler 1978 Limnology and
Oceanography 23478
3
Observational evidence is inconclusiveSmith 2006
Limnology and Oceanography 51377
4
Phosphate addition experiment, Experimental Lakes
Area, OntarioDavid Schindler 1977 Science 195
260
Ca
C
N
Se
Mg
P
Mo
Fe
Ca
C
N
Se
Mg
Mo
Fe
5
Routes of non-point source pollution Carpenter et
al. 1998 Ecological Applications 8559
6
P and O2

• Oxic sediments store 2X more P than anoxic ones
• positive feedback- eutrophication leads to
  anoxia, more P recycling from sediments
• Internal loading

7
Recycling by consumers

• Zooplankton excrete 10 of body P per day
• If zooplankton have more P than phytoplankton,
  can reduce P availability
• Recycled P may be more important than new P

8
Biological uses of PhosphorusElser et al.
Ecology Letters 3540

• RNA, DNA
• ATP
• Involved in growth, synthesis of new tissues
• Organisms with lots of P have high growth rates

9
Agricultural eutrophication in the Okanagan
10
The foul stench of Lake Mendota, Wisconsin
11
Oligotrophic vs. eutrophic lakes of B.C.
Cultus Lake, Okanagan Valley Chlorophyll-a 1200
µg/L
Gwendoline Lake, UBC Research Forest Chlorophyll-a
5 µg/L
12
Effects of eutrophication through P pollution

• increased primary productivity
• decreased light availability
• changes in O2 availability
• Increased fish production (unless anoxia occurs)
• decreased species diversity

13
What about grazers? Elser et al. 2000 Nature
408 578
Pieris rapae
Daphnia magna
14
Phytoplankton become less edible at high
productivity Watson, McCauley and Downing 1997
Limnology and Oceanography 42487
15
P and cyanobacteria (N-fixers)Smith 1983 Science
221669
16
What about Nitrogen?

• 2nd highest demandsupply ratio 30,000
• Used mainly for proteins
• Comes from atmosphere and land
• Comes in reduced (NH4), oxidized (NO3/NO2) and
  inert (N2) forms

Burning fossil fuels puts NO2 into the
atmosphere, produces Acid Rain AND Nitrogen
Deposition (fertilization with nitrogen)
17
Transformations between different forms of N-
microbes at work
Pseudomonas friends
Cyanobacteria
C6H12O6 4HNO3? 6CO2 10H2O 2N2
NH4 2O2?NO3- H2O 2H
picky phytoplankton prefer amonium
Nitrosomonas Nitrobacter
18
N-transformations and O2

• Nitrification (NH4-gtNO3)- needs O2
• Denitrification (NO3-gtN2)- needs anoxia (mostly)
• N-fixation- needs anoxia
• heterocysts (cell walls in cyanobacteria)

19
Nitrogen forms by depthin a eutrophic lake
Nitrification (NH4 -gt NO3)
N-fixation (N2-gt NH4)
Denitrification (NO3 -gt NO2 -gt N2)
20
Humans are responsible for 50 of global
N-fixation(from fossil fuels and
fertilizers)Vitousek et al. 1997 277494
Humans have increased biologically-available N
and P by 100 and 400, respectively Falkowski
et al. 2000 Science 290 291
21
What determines N-loading?

• Erosion (deforestation)
• Atmospheric deposition (rain)

What happens to N once deposited?

• retained (soils, sediments)
• runoff to the ocean

22
Hubbard Brook experimentLikens et al. 1970
Ecological Monographs 40 23
23
Nitrogen is increasing due to N-deposition from
atmosphereeven in pristine Lake Superior
Spring nitrate concentration in Lake Superior
(ugN/L)
24
Atmospheric Nitrogen deposition is concentrated
near industrial activity
25
Effects of N-deposition in Sweden shift to P
limitationBergström et al. 2005 Limnology and
Oceanography 50 987
26
Is P-limitation of primary productivity a recent
phenomenon?Were Schindlers lakes historically
N-limited, but N-deposition flipped them to
P-limitation?
27
Comparison between N and P
28
What about other limiting nutrients?

• Si
• especially for diatoms
• Fe
• a big deal in the ocean
• limiting in some lakes

29
Whats the big deal about nutrient limitation?

• Effects on competitive dominance, diversity
• maximal when species are most different
• Effects on trophic efficiency
• maximal when species are most similar
• Multiple vs. single limitation
• homeostasis vs. flexibility

30
Ecological Stoichiometry

• The chemical formula for a human
  H400O100C90N6Ca2P1S0.2Na0.2K0.2Cl0.1Mg0.04Si0.04Fe
  0.03Zn0.02Cu0.08Mn0.013F0.013Cr0.007Se0.004Mo0.003
  Co0.001
• Feeding is a chemical reaction
• Consumer Food ? More consumer waste
• H3C3O1 3H1C5O5 ? 2 H3C3O1 12C 14O
• Animals are not molecules, not always homeostatic
  (have the same formula)
• Wastes can be recycled

31
Animals are more homeostatic than plants
NP ratio in algae
NP ratio in food (dissolved nutrients)
P in Daphnia
P in food (algae)
32
The Redfield Ratio

• C106N16P1
• Very constant in marine phytoplankton, more
  variable in lakes
• Why? Is there something magical about these
  numbers?
• What about terrestrial plants?

33
Is Redfield really a constant?
34
Phytoplankton are more nutritious than
terrestrial plants (eat your algae)Elser et al.
2000 Nature 408 578
35
Zooplankton and insects have more N and P than
their food Elser et al. 2000 Nature 408 578
36
Do limiting nutrients vary between
ecosystems?Elser, Bracken, Cleland, Gruner,
Harpole, Hillebrand, Ngai, Seabloom, Shurin,
Smith 2007. Ecology Letters 10 1135
wild Jim Elser
Phosphorus is much more important as a
limiting nutrient in aquatic systems (than
terrestrial) -Wikipedia (Eutrophication)
37
Do limiting nutrients vary between
ecosystems?Elser, Bracken, Cleland, Gruner,
Harpole, Hillebrand, Ngai, Seabloom, Shurin,
Smith 2007. Ecology Letters 10 1135

• Meta-analysis of 1,069 N and P field addition
  experiments
• 653 freshwater
• 243 marine
• 173 terrestrial

Phosphorus is much more important as a
limiting nutrient in aquatic systems (than
terrestrial -Wikipedia (Eutrophication)
38
N and P are equally important in terrestrial and
freshwater ecosystems
N is more important in the ocean
39
N and P limitation vary by habitat within
ecosystems
40
How far can multiple limitation go?Harpole and
Tilman 2007 Nature 446791
41
Does this work in lakes?Interlandi and Kilham
2001 Ecology 821270
Measured phytoplankton diversity and resource
availability (N, P, Si, light) over two years in
three lakes
42
Phytoplankton diversity is highest in Yellowstone
Lakes when more resources are limitingInterlandi
and Kilham 2001 Ecology 821270
43
How flexible is plant chemistry?
44
What about light as a resource?

• Fertilization with light
• happens when mixing layer is shallow
• Increases C-fixation, photosynthesis
• Too much of a good thing?

45
What does light do to phytoplankton?Urabe and
Sterner 1996 PNAS 938465
algal biomass
PC
100
10
Lab experiment
46
High light lakes have high CP phytoplanktonStern
er et al. 1997 American Naturalist 150663
47
What determines light level?
mixing depth (m)
All in the epilimnion Means lots of low quality
algae
mixing depth (m)
48
Depth distribution of C, N and P in
algaeMatthews and Mazumder 2006 Ecology 872800
49
What happens to trophic efficiency when we add
nutrients vs. light?Dickman et al. 2008 PNAS
50
What happens to trophic efficiency when we add
nutrients vs. light?Dickman et al. 2008 PNAS
51
The lesson

• adding light increases primary production, but
  algae are low quality, zooplankton cant keep up
• adding nutrients makes zooplankton yummier for
  fish, fish grow more and control zooplankton
• How does fish abundance change with light and
  nutrient availability?

52
Nutrients limit production, but most lakes have
very low nutrientsKarlsson et al. 2009 Nature
53
More fish in clearer lakes (low DOC) with lots of
lightKarlsson et al. Nature 2009
54
Why is that? Answer benthic production goes up
with light Karlsson et al. Nature 2009
Benthic/pelagic production
55
The point about light

• mixing depth determines light in the epilimnion
• Algal food quality (CN, CP) decreases with
  light
• BUT primary and secondary production can increase
  with light
• High light means more benthic production -gt more
  fish