Title: Phosphorus and Nitrogen
1Phosphorus and Nitrogen
- But firsta few more examples of stratification
and hypoxia
2Phosphorus
- Why study P?
- Biomolecules
- ADP and ATP
- nucleic acids
- phospholipids (cell membranes)
- apatite (bones)Â Â Â Â Â
3Central Basin
Eastern Basin
Western Basin
ZAVG 6 m
Thermocline
18 m
24 m
4Central Lake Erie Observation Buoy
www.glerl.noaa.gov
5Temporary Stratification in Western Lake Erie
S
Dissolved Oxygen (mg/L)
6Forms 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
7Phosphorus and Lake Classification
The productivity of a lake is often determined by
its P loading and its volume (mean depth)
8(No Transcript)
9Limiting 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
10Stoichiometry 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
11Recipe 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
106Â Â Â Â 263Â Â 110Â Â 16Â Â Â Â 1Â Â Â Â 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?
12CÂ Â Â Â Â Â HÂ Â Â Â Â OÂ Â Â Â NÂ Â Â PÂ Â Â Â S Fe
106Â Â Â Â 263Â Â 110Â Â 16Â Â Â Â 1Â Â Â Â 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
13The 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
142 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.
15Sources 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)
16Point and Nonpoint sources
thinkquest.org
17External 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
18Sediment Oxygen profile
Diffusion Barrier
P diffusion
19Internal 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
21Bioturbation
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
22Phosphorus 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
23Wastewater Treatment
Addition of alum to precipitate P
www.defra.gov.uk
24Buffer Strips
www.epa.gov/owow/nps/Section319III/OH.htm
NRCS
25Hypolimnion Aeration
content.cdlib.org/xtf/data
26A look at P in Ohios L. Erie Tributaries (from
P. Richards)
Study completed in 1995 showed almost all trends
improving
2720 year trends 1975-1995
28Water flow has not changed in Maumee R., has
increased in some others
29Decreased SS in Maumee River may be due to
Conservation tillage, other rivers have
increasing suburban development
30TP unchanged in Maumee R. Increasing in others
31SRP loading has increased in all rivers
32SRP/TP ratio has increased in all rivers.
33The 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
34K. 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
36Nitrogen 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
37Nitrogen 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.
38Nitrogen 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
39Nitrogen 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
40Nitrogen Cycle in Lakes
41- Redfield ratios of ocean phytoplankton (by number
of atoms) - Â CÂ Â Â Â Â Â HÂ Â Â Â Â OÂ Â Â Â NÂ Â Â Â PÂ Â Â Â S Fe
106Â Â Â Â 263Â Â 110Â Â 16Â Â Â Â 1Â Â Â Â 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)
42NP 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
43NP 13, 11 for Lakes Victoria and Albert
Some large tropical lakes can be severely
nitrogen limited
44Most lakes are P deficient relative to N
45What about CP ratios? CP is usually above the
Redfield ratio meaning that algae is usually
P-limited relative to C
46What 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
47Finally, 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)