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Phosphorus and Nitrogen

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Title: Phosphorus and Nitrogen


1
Phosphorus and Nitrogen
  • But firsta few more examples of stratification
    and hypoxia

2
Phosphorus
  • Why study P?
  • Biomolecules
  • ADP and ATP
  • nucleic acids
  • phospholipids (cell membranes)
  • apatite (bones)     

3
Central Basin
Eastern Basin
Western Basin
ZAVG 6 m
Thermocline
18 m
24 m
4
Central Lake Erie Observation Buoy
www.glerl.noaa.gov
5
Temporary Stratification in Western Lake Erie
S
Dissolved Oxygen (mg/L)
6
Forms of Phosphorus
  • Total P DIP DOP PP
  • DIP (lt5) dissolved inorganic phosphorus
  • PO43- polyphosphates
  • DOP dissolved organic phosphorus -- often
    organic colloids less quickly available
  • PP particulate phosphorus -- often largest
    percentage of P in lakes (gt70)
  • Algae, animals, detritus, suspended sediments
  • We usually measure soluble reactive phosphate
    (SRP) which is DIP and some DOP

7
Phosphorus and Lake Classification
The productivity of a lake is often determined by
its P loading and its volume (mean depth)
8
(No Transcript)
9
Limiting nutrient
  • Theoretically, phosphorus is usually the most
    limiting nutrient in freshwater systems as
    determined by Ecological stoichiometry
  • Ratios of elements in plankton and other organisms

10
Stoichiometry gives the recipe for
phytoplankton
2 1/4 cups sifted cake flour2 teaspoons baking
powder1/2 teaspoon salt1/2 pound Butter 2 cups
sugar4 large egg yolks2 teaspoons vanilla1 cup
sour cream4 large egg whites
11
Recipe for phytoplankton is the Redfield Ratio
  • In the 1950s Alfred Redfield found in the deep
    ocean an average phytoplankton composition (by
    number of atoms) of 
  •  C       H      O      N     P    S Fe
    106    263   110   16    1     0.7 0.01

Note that C, H, O, and N are required in greater
proportion than P. Why then are these NOT the
generally nutrient limiting?
12
C       H      O      N    P     S Fe
106    263   110   16    1     0.7 0.01
  • In freshwater systems P is usually limiting
    because the amount of P available to primary
    producers is much less than the amount required
    relative to the other elements.
  • P makes up only 1 of organic matter which
    implies that if nothing else is limiting, then
    increasing P can theoretically generate gt100X the
    weight of added P in algae

13
The Thieving Baker
Suppose you were a baker and wanted to sabotage a
rival baker by stealing supplies from his
storehouse. You can carry 50 lbs. of any
ingredient with you. What do you steal in order
to prevent him from making the most cakes?
2 1/4 cups sifted cake flour2 teaspoons baking
powder1/2 teaspoon salt1/2 pound Butter 2 cups
sugar4 large egg yolks2 teaspoons vanilla1 cup
sour cream4 large egg whites
14
2 1/4 cups sifted cake flour2 teaspoons baking
powder1/2 teaspoon salt1/2 pound Butter 2 cups
sugar4 large egg yolks2 teaspoons vanilla1 cup
sour cream4 large egg whites
i.e. If you have plenty of everything else, then
with only ½ teaspoon of salt, you can bake a cake.
15
Sources of Phosphorus
  • Weathering of calcium phosphate minerals,
    especially apatite Ca5(PO4)3OH from sediments
    of ancient oceans. There are no important
    gaseous sources of P.
  • Anthropogenic P is now often much greater than
    natural inputs of P in many watersheds
  • Sewage, agriculture, etc.
  • Increased production of algae due to increased
    Anthropogenic P input is cultural
    eutrophication               
  • Anthropogenic P may come from
  • point sources (think of a pipe)
  • nonpoint sources (diffuse, like agriculture
    runoff)

16
Point and Nonpoint sources
thinkquest.org
17
External vs. Internal P Loading
  • Loading refers to input of a nutrient per unit
    time
  • External loading refers to sources outside the
    lake (as in previous slide)
  • If all external sources of P were removed, a lake
    would continue to grow algae for many years.
    This is because P is recycled within the lake.
    This recycling is termed Internal Loading

18
Sediment Oxygen profile
Diffusion Barrier
P diffusion
19
Internal P Loading
  • P may be recycled in the food web several times
  • Phytoplankton are extemely efficient at absorbing
    any P that is released by excretion or
    decomposition
  • Eventually P will be lost from lake either by
    outflow or by sedimentation to the lake bottom.
  • P is bound in lake sediments under oxic
    conditions, but may be regenerated from sediments
    under anoxic conditions (iron and microbes play
    an important role)
  • Deep lakes with oxic hypolimnia and long WRT may
    retain 70-90 of incoming P in the sediments
  • Lakes with Anoxic hypolimnia retain only half as
    much P as lakes with oxic hypolimnia
  • Therefore external loading may result in a
    positive feedback loop that multiplies
    eutrophication.

lakes.chebucto.org/DATA/PARAMETERS/TP/popup.html
20
?phytoplankton
?external P loading
? decomposition
? regeneration of P from sediments
? hypoxia
21
Bioturbation
With Mayflies
Without Mayflies
J. Chaffin
Physical resuspention by organisms living in oxic
sediments may also increase the regeneration of
Phosphorus from sediments into the overlying water
22
Phosphorus Remediation
  • Eutrophication can be ugly high algal biomass
    (sometimes toxic), hypoxia, fish kills, foul
    smells
  • One answer is to reduce P loading by
  • Removing P from waste water (tertiary treatment)
  • Diverting waste water (see Lake Washington)
  • Using natural or constructed wetlands to trap P
  • Using buffer strips to trap agricultural runoff
  • Using pumps to aerate the hypolimnion

23
Wastewater Treatment
Addition of alum to precipitate P
www.defra.gov.uk
24
Buffer Strips
www.epa.gov/owow/nps/Section319III/OH.htm
NRCS
25
Hypolimnion Aeration
content.cdlib.org/xtf/data
26
A look at P in Ohios L. Erie Tributaries (from
P. Richards)
Study completed in 1995 showed almost all trends
improving
27
20 year trends 1975-1995
28
Water flow has not changed in Maumee R., has
increased in some others
29
Decreased SS in Maumee River may be due to
Conservation tillage, other rivers have
increasing suburban development
30
TP unchanged in Maumee R. Increasing in others
31
SRP loading has increased in all rivers
32
SRP/TP ratio has increased in all rivers.
33
The Nitrogen Cycle
  • Sources of Nitrogen
  • N is abundant on earth, but only about 2 is
    available to organisms as reactive nitrogen
    (NOx, NHx, Org N)
  • N is made available by Nitrogen-fixation and by
    fertilizer production
  • Gaseous N2 ? NO3
  • Reactive N can be recycled through the biota
    until it is eventually lost to the atmosphere
    through denitrification

34
K. Schulz
35
  • Nitrogen inputs to lakes
  • Atmospheric deposition from combustion of fossil
    fuels dryfall (NO3,NH4, Organic N)
  • Atmospheric deposition has doubled every 34 yrs
  • Watershed inputs
  • Terrestrial systems are generally N-limited,
    therefore most N is retained on land and not
    exported to via streams to lakes

36
Nitrogen Transformations
  • NH4 (ammonium) uptake by algae.
  • NH4 ? PON (Particulate Organic Nitrogen)
  • No ? in oxidation state - not a redox reaction.
  • takes least amount of energy, therefore preferred
    by algae.
  • High concentrations of NH4 in aerobic aquatic
    conditions are usually an indication of pollution
    by sewage or feedlot runoff.
  • Most other reactions are mediated by bacteria
  • Ammonification NH4 production
  • decomposition of PON ? NH4

37
Nitrogen Transformations
  • Nitrification
  • NH4 (ammonium) 3/2 O2 ? NO2 (nitrite) 2H
    H2O then,
  • NO2 1/2 O2 ? NO3 (nitrate)
  • NO2 usually does not build up
  • NO3 is the final product of nitrification. It
    may build up in conditions where there is much
    NH4 being produced, oxygen is present, but there
    is little vegetation to take up NO3
  • (fish aquaria)
  • Assimilative nitrate reduction
  • NO3- uptake by algae
  • algal uptake of N to make more cells. NO3 ORG-N
    (NH3)
  • needs light, done with O2 present.

38
Nitrogen Transformations
  • Denitrification (dissimilatory nitrate reduction)
  • CHO NO3- H ? CO2 N2 H2O
  • must be anaerobic
  • sediments, anoxic hypolimnia.
  • Nitrogen fixation
  • N2 ? ORG-N (NH3).
  • Difficult to break triple bond of N2 therefore
    energetically expensive
  • May be conducted by Cyanobacteria (Bluegreen
    algae) under bright sunlight
  • Or by bacteria in sediments, coupled with other
    reactions.
  • Both cases require anoxic conditions for reaction
    to occur

39
Nitrogen fixation in Cyanobacteria
  • Nitrogen fixation occurs in special cells called
    heterocysts, but
  • Not all cyanobacteria have heterocysts or can fix
    nitrogen
  • Some cyanobacteria can fix nitrogen without
    heterocysts

www.bio.purdue.edu/people/faculty/sherman/ShermanL
ab
www.micrographia.com/specbiol/bacteri/bacter/bact0
200/anabae03.jpg
40
Nitrogen Cycle in Lakes
41
  • Redfield ratios of ocean phytoplankton (by number
    of atoms)
  •  C       H      O      N     P    S Fe
    106    263   110   16    1     0.7 0.01
  • Hecky et al. compiled data from lakes around the
    world to see if the ratios held true for lakes
    (as well as the ocean)

42
NP ratio
Lakes with NP ratio gt 22 are considered to be
P-limited
Note also CN and CP ratios. If they are higher
than the Redfield ratio it means that algal cells
are making do with less N or P than they would
like.
Mean NP ratio 24
43
NP 13, 11 for Lakes Victoria and Albert
Some large tropical lakes can be severely
nitrogen limited
44
Most lakes are P deficient relative to N
45
What about CP ratios? CP is usually above the
Redfield ratio meaning that algae is usually
P-limited relative to C
46
What about NP ratios? NP is also usually above
the Redfield ratio meaning that algae is usually
N-limited relative to C
Therefore, freshwater phytoplankton is usually
both N and P limited. Ie. The cells are making
do with less than optimal N and P. But, P is
more limiting than N
47
Finally, recent studies show that the Redfield
NP ratio of 16 is not a universal biochemical
optimum for phytoplankton, but rather an average
of ratios for many different species.
Christopher A. Klausmeier, Elena Litchman, Tanguy
Daufresne and Simon A. Levin Nature 429,
171-174(13 May 2004)
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