phosphorus and nitrogen
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Phosphorus and Nitrogen
PhosphorusHow is P used in organisms?Biomolecules
ADP and ATPnucleic acidsphospholipids (cell membranes)apatite (bones and tooth enamel)
Forms of PhosphorusPhosphorus 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)
Limiting nutrientsTheoretically, phosphorus is usually the
most limiting nutrient in freshwater systems as determined by Liebig’s Law of the Minimum and Ecological stoichiometry
Liebig’ LawLiebig’ LawGrowth is limited by the nutrient that is in shortest supply.
P N FeC
Limiting nutrientsEcological stoichiometry
Ratios of elements in plankton and other organisms
Important in addition to Liebig’s law
Stoichiometry gives the “recipe” for phytoplankton
Cake Example2 1/4 cups sifted cake flour2 teaspoons baking powder1/2 teaspoon salt1/2 pound Butter2 cups sugar4 large egg yolks2 teaspoons vanilla1 cup sour cream4 large egg whites
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?
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 >100X the weight of added P in algae
C H O N P S Fe 106 263 110 16 1 0.7 0.01
2 1/4 cups sifted cake flour2 teaspoons baking powder1/2 teaspoon salt1/2 pound Butter2 cups sugar4 large egg yolks2 teaspoons vanilla1 cup sour cream4 large egg whites
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?
The Burglar BakerThe Burglar Baker
2 1/4 cups sifted cake flour2 teaspoons baking powder1/2 teaspoon salt1/2 pound Butter2 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.
Phosphorus and Lake Classification
The productivity of a lake is often determined by its P loading and its volume (mean depth)
Lake Productivity Classification
Total Phosphorus g/L
Ultra-oligotrophic <5
Oligotrophic 5-10
Mesotrophic 10-30
Eutrophic 30-100
Hypereutrophic >100
Sources of PhosphorusWeathering 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 watershedsSewage, agriculture, etc.
Sources of PhosphorusIncreased 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)
Point and Nonpoint sources
thinkquest.org
External vs. Internal P Loading
“Loading” refers to input of a nutrient per unit timeUsually 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
Lake sediments can trap P under oxic conditions or release P under anoxic conditions
0
5
10
15
20
25
0 1 2 3 4 5
DO (mg/L)
Se
dim
en
t d
ep
th (
mm
)
P diffusion
Diffusion Barrier
Oxygen profile of sediments in oxic conditions
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)
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
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.
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
phytoplankton
decomposition
hypoxia
regeneration of P from sediments
external P loading
Positive Feedback LoopPositive Feedback Loop
Bioturbation
Physical re-suspension by organisms living in oxic sediments may also increase the regeneration of Phosphorus from sediments into the overlying water
J. Chaffin
Without Mayflies
With Mayflies
Phosphorus RemediationEutrophication can be ugly: high algal biomass
(sometimes toxic), hypoxia, fish kills, foul smellsOne 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 PUsing buffer strips to trap agricultural runoffUsing pumps to aerate the hypolimnion
Wastewater Treatment
www.defra.gov.uk
Addition of alum to precipitate P
Buffer Strips
www.epa.gov/owow/nps/Section319III/OH.htm
NRCS
content.cdlib.org/xtf/data
Hypolimnion Aeration
The importance of the Maumee River watershed in phosphorus loading to Lake Erie
http://web2.uwindsor.ca/lemn/LEMN2010.htm
D. Dolan, LEMN conf. 2010
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.
Both river flow and DRP concentration have increased, therefore much greater DRP loading
The Maumee River watershed is causing a high degree of stress to Lake Erie
J. Kelly, LEMN Conf. 2010
Where is the dissolved P coming from?Investigation by the Ohio Phosphorus Task Force
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
Stratification of P in soils
Conservation Tillage may have unintentional side effects
Where is the dissolved P coming from?Investigation by the Ohio Phosphorus Task Force
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
MunicipalitiesCombined 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/lakeerie/ptaskforce/Task_Force_Final_Report_April_2010.pdf
• The The Microcystis-Microcystis-AnabaenaAnabaena bloom of 2009 was the bloom of 2009 was the largest in recent years in our sampling region largest in recent years in our sampling region
2011
• ……until 2011until 2011
Phosphorus loading is important, but what about Nitrogen?
Phosphorus remains high Phosphorus remains high throughout the growing season.throughout the growing season.
Nitrogen loading and Nitrogen loading and concentration drop during the concentration drop during the summer, leading to summer, leading to Nitrogen-Nitrogen-limited limited conditions.conditions.
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