Phosphorus and Nitrogen

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Phosphorus and Nitrogen
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Phosphorus

• How is P used in organisms?
• Biomolecules
• ADP and ATP
• nucleic acids
• phospholipids (cell membranes)
• apatite (bones and tooth enamel)   

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Forms of Phosphorus

• Phosphorus in aquatic systems is usually
  categorized how we measure it.
• Dissolved P Any P that goes through a 0.45um
  filter
• PO43- polyphosphates
• Dissolved organic phosphates
• Particulate P Any P that is retained on the
  filter
• in algae, zooplankton, detritus, attached to
  sediment particles.
• Total P Dissolved P Particulate P
• Reactive P P that reacts with molybdenum to
  form a blue color.
• The most commonly measured forms of P are Total
  Phosphorus (TP) and Dissolved Reactive Phosphorus
  (DRP)

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Limiting nutrients

• Theoretically, phosphorus is usually the most
  limiting nutrient in freshwater systems as
  determined by Liebigs Law of the Minimum and
  Ecological stoichiometry

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Liebig Law
Growth is limited by the nutrient that is in
shortest supply.
P
N
Fe
C
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Limiting nutrients

• Ecological stoichiometry
• Ratios of elements in plankton and other
  organisms
• Important in addition to Liebigs law

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Stoichiometry gives the recipe for
phytoplankton
Cake Example 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
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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?
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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

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The Burglar 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
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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.
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Phosphorus and Lake Classification
The productivity of a lake is often determined by
its P loading and its volume (mean depth)
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Lake Productivity Classification Total Phosphorus mg/L
Ultra-oligotrophic  lt5
Oligotrophic 5-10
Mesotrophic 10-30
Eutrophic 30-100
Hypereutrophic  gt100
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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.

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Sources of Phosphorus

• 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)

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Point and Nonpoint sources
thinkquest.org
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External vs. Internal P Loading

• Loading refers to input of a nutrient per unit
  time
• Usually calculated for rivers as concentration x
  flow
• 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

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Lake sediments can trap P under oxic conditions
or release P under anoxic conditions
Oxygen profile of sediments in oxic conditions
Diffusion Barrier
P diffusion
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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)

lakes.chebucto.org/DATA/PARAMETERS/TP/popup.html
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Internal P Loading

• 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 amplifies
  eutrophication.

lakes.chebucto.org/DATA/PARAMETERS/TP/popup.html
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Positive Feedback Loop
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Bioturbation
With Mayflies
Without Mayflies
J. Chaffin
Physical re-suspension by organisms living in
oxic sediments may also increase the regeneration
of Phosphorus from sediments into the overlying
water
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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

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Wastewater Treatment
Addition of alum to precipitate P
www.defra.gov.uk
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Buffer Strips
www.epa.gov/owow/nps/Section319III/OH.htm
NRCS
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Hypolimnion Aeration
content.cdlib.org/xtf/data
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The importance of the Maumee River watershed in
phosphorus loading to Lake Erie
http//web2.uwindsor.ca/lemn/LEMN2010.htm
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D. Dolan, LEMN conf. 2010
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A look at P in the Maumee River(from P. Richards
and D. Baker, NCWQR)
Study completed in 1995 showed almost all trends
improving, now they are getting worse.
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Both river flow and DRP concentration have
increased, therefore much greater DRP loading
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The Maumee River watershed is causing a high
degree of stress to Lake Erie
J. Kelly, LEMN Conf. 2010
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(No Transcript)
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Where is the dissolved P coming
from?Investigation by the Ohio Phosphorus Task
Force

• Agriculture
• Conservation Tillage
• Reduces soil erosion, but
• Fertilizer remains near the soil surface and is
  more easily washed into tributaries

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Stratification of P in soils
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Conservation Tillage may have unintentional side
effects
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Where is the dissolved P coming
from?Investigation by the Ohio Phosphorus Task
Force

• Agriculture
• Conservation Tillage
• Fertilizer is not incorporated into the soil and
  is more easily washed into tributaries
• Fall application of fertilizers
• Continuation of old P-building practice
• CAFOS (concentrated animal feeding operations)
• Produce large amounts of animal waste with poor
  waste treatment practices
• Municipalities
• Combined sewer overflows (CSOs)
• Addition of P to water supply as anti-corrosive
• See Ohio Lake Erie Phosphorus Task Force Final
  Report http//www.epa.state.oh.us/portals/35/lakee
  rie/ptaskforce/Task_Force_Final_Report_April_2010.
  pdf

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• The Microcystis-Anabaena bloom of 2009 was the
  largest in recent years in our sampling region

• until 2011

2011
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Phosphorus loading is important, but what about
Nitrogen?
Nitrogen loading and concentration drop during
the summer, leading to Nitrogen-limited
conditions.
Phosphorus remains high throughout the growing
season.