Nutrients as Pollutants

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Nutrients as Pollutants
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Major Determinants of Water Quality and the
Impact or Availability of Water Pollutants
Organisms Solubility Oxygen pH
Nutrients (N, P) Metals (Hg, Pb, As) Organic
Chemicals (PCBs, Dioxins)
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Nutrients Nitrogen and Phosphorus
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Nutrients Nitrogen and Phosphorus
Sources fertilizers, manures, wastewater
discharge
Availability in the environment is controlled
by Oxygen pH Organisms
Both are limiting to primary productivity
Excess amounts can severely alter ecosystems
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Eutrophication
Nutrient addition increases primary productivity
(algae)
Sunlight is limited at greater depth
Photoautotrophs die and become food for aerobic
heterotrophs
Aerobic autotrophs consume O2 Oxygen content in
water is reduced
bacteria
If oxygen is reduced sufficiently, aerobic
microbes cannot survive, and anaerobic microbes
take over
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Nitrogen
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Nitrogen
NH4 and NO3-
Forms are controlled by organisms NH4 is
converted to NO3- by aerobic bacteria The process
is called nitrification
These bacteria, therefore, are controlled by
oxygen levels
Nitrifying bacteria do not function well at low
pH.
Organisms Oxygen pH
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Dominant Forms NH4 and NO3-
Sources fertilizers, manures, wastewater
discharge
NO3- is more mobile in the environment than NH4
NH4
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NO3-
_
Soil particles possess a negative electrical
charge
Leaching to ground Or surface water
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Groundwater and Nitrates (NO3-)
Nitrates do not interact significantly with
soil material and can move rapidly to
groundwater.
What areas are particularly vulnerable?
1. The unconfined, surficial aquifer
2. Areas where natural groundwater recharge occurs
3. Areas where the aquifer confining unit is
thin are also particularly vulnerable.
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Unconfined Aquifers
Sandy Materials
Unconfined aquifer is extensive throughout the
state of Florida
Low Permeability Confining Unit (poor water
movement)
Miocene Clays (Hawthorne Formation)
The Floridan aquifer is a confined aquifer. The
water-bearing unit is permeable limestone.
Low permeability rock (confining)
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Recharge
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Where the Confining Layer is Thin
Groundwater
Thin sandy overburden
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Lower Suwannee River Watershed

• residential and commercial septic systems in
  rural areas
• about 300 row crop and vegetable farms
• 44 dairies with more than 25,000 animals
• 150 poultry operations with more than 38 million
  birds

Nitrates
NO3 Drinking water standard 10 ppm
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Groundwater Nitrate Discharge to Rivers
Possible sources of nitrate in the ground water
in the vicinity of the river include fertilizer,
animal wastes from dairy and poultry
operations, and septic-tank effluent.
Flow
Nitrate concentrations were higher in the
measured springs than in the river.
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Environmental and Health Hazard
Methemoglobinemia
Nitrate is converted to nitrite in infants (pH,
organisms)
Nitrite converts iron in the hemoglobin of red
blood cells to form methemoglobin which cannot
bind oxygen
Adults possess an enzyme that reverses the
conversion
Infants possess 60 less of the enzyme
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Phosphorus
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Phosphorus
Present in Fertilizers, animal wastes, wastewater
Limiting Element to Primary Productivity
Chlorophyll ATP Phospholipids
Additions increase Productivity
ATP
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Fertility
Most phosphorus is unavailable to plants
Only 10-15 of applied fertilizer phosphorous is
used by plants The rest is bound to soil
particles or forms insoluble solids
This leads to excess application
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Plant Availablity and pH
Most Available
H2PO4-
HPO4-2
pH 6-8
pH 3-6
pH 8-11
Optimum pH 6.5 for plant availability
At low pH, P binds to iron and aluminum At high
pH, P binds to calcium
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Acidic Conditions (low pH)
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Acid Conditions (Low pH)
Aluminum and Iron availability is increased at
low pH
solids
FeOOH
Al(OH)3
Solubility increased at low pH (Acids dissolve
Metals)
Al3
Fe3
example
Al(OH)3 3H Al3 3H2O
In solution
solid
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Aluminum Precipitation at Low pH
H2PO4-
(pH 3-6)
Form of available P at low pH
H2PO4- combines with free Al3 and Fe3
time
simplified
Al3
PO4-3 Al(PO4)
Fe3 PO43- FePO4
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Basic Conditions (High pH)
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Calcium Binding in Basic Conditions
Calcium is often present at high pH
H (PO4)-2 is the available form of P at high pH
time
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Binding of Phosphorus
Low pH High pH
Aluminum and Iron phosphates
Calcium Phosphates
Insoluble solids
There is a limited ability to immobilize
phosphorus
If the capacity is exceeded, phosphorus becomes
more mobile
Mobile phosphorus can contaminate surface and
groundwater
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Unimpacted
P-impacted

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Extra Credit

1. Indicate one of the dominant forms of N in the
   environment
2. Methemoglobinemia is caused by what nutrient?
3. At low pH phosphorus binds to ____________________
   __
4. At high pH phosphorus binds to ___________________
   __

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South Florida and Phosphorus
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Phosphorus loading to S. Florida Ecosystem
Dairy/Beef
Inputs North and South of Okeechobee
Crop production
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Crops Everglades Agricultural Area
EAA
Sugar, Rice, Veg.
700,000 ac
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Phosphorus Fertilization (lbs/ac)
Based on how much P is already in soils
V. High Soil P
Low Soil P
Celery 260 200 140 80 20 0 0 0 0
Endive 200 175 150 125 100 75 50 25 0
Escarole 200 175 150 125 100 75 50 25 0
Lettuce (Head) 200 175 150 125 100 75 50 25 0
Radish 100 40 0 0 0 0 0 0 0
Romaine 200 175 150 125 100 75 50 25 0
Sugar Cane 120 100 80 40 20 0 0 0 0
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Phosphorus loading to S. Florida Ecosystem
Agriculture
Overstimulation of primary productivity
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Dairy and Beef
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Kissimmee drainage basin 12,000 km2
Dairy and Beef
In 1521 Ponce de Leon brought horses and cattle
to Florida.
(1947)
No other part of our country had cattle until
the Pilgrims brought cattle in the early 1600's
Florida's ranchers now raise the third largest
number of cattle of any state east of the
Mississippi
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Phosphorus
Solid Manure 5.5 g / kg total Phosphorus
One cow can excrete between 40 and 60 g of
phosphorus per day
Subject to movement via runoff, stream flow,
soil water movement, and groundwater movement
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Cattle and Dairy
Okeechobee, Highlands, and Glades Counties
328,000 head (19 of total)
Okeechobee County is ranked number one for all
cattle in the state
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Kissimmee Okeechobee - Everglades
The Lower Kissimmee River Basin is among largest
sources of external phosphorus loading to Lake
Okeechobee
The Kissimmee river alone contributes about 20
of the phosphorus flowing into Lake Okeechobee
urban
Okeechobee, in turn, is a source of phosphorus to
the Everglades
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Surface Water Improvement Management Act SWIM
(1987)
Mandated phosphorus load level of 397 tons/yr
urban
Clean Water act 154.3 tons per year DEP 140
tons per year
SWIM Plan priority basins
Lake
Target level of 40 ppb in Lake Okeechobee
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Some Strategies
The Dairy Rule (1987)
creating lagoons to capture and contain dairy
waste
Implement Best Management Practices (BMPs)
buffer areas around places animals congregate,
eliminating phosphorus fertilization near
tributaries to the lake, reducing phosphorus
imports in animal feeds, reducing animal density
Works of the District Rule
permits are required for all discharges into
waterways
Dairy Buy-Out Program
to facilitate removal of animals from dairies not
able to comply
19 of 45 Dairies Remain
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2007 146 ton reduction of P entering Okeechobee
From a baseline of 433 tons/yr
The target level is 40 ppb.
Phosphorus concentrations in the Lake remain at
about 117 ppb
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Internal Loading
Two Sources
Decomposition of submerged aquatic
vegetation releasing phosphorus back into the
water column
Dissolution of Iron and Aluminum compounds in
sediments which bind and store phosphorus.
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Internal Loading
Phosphorus and Iron
Phosphorus has a strong affinity for iron
FePO4
Solid Precipitate
Readily incorporates into bottom sediments
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Iron Exists in Two Different Forms Depending on
Oxygen Content
Fe3 high oxygen
Fe2 low oxygen
Phosphorus compounds become soluble
Forms insoluble solids with Phosphate
Fe3 PO43- FePO4
solid
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Internal Loading
Fe3 high oxygen
Fe2 low oxygen
Dissolved phosphorus combines with oxidized iron
(Fe3) to create an insoluble compound that
becomes buried in lake sediments.
Fe3 PO43- Fe(PO4)
Simplified
solid
If oxygen contents are reduced (anoxic bottom
sediments) the Fe3 converts to Fe2 which
solubilizes the compound returning P to water.
2
3-
(PO4)
Fe
to water
P released by sediments is taken up by
photosynthetic algae faster than it can be
returned to the sediments
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Lake Okeechobee Action Plan Developed by the Lake
Okeechobee Issue Team December 6, 1999
RECOMMENDATION Control Internal Phosphorus
Loading. Phosphorus-rich mud sediments need to
be removed from the lake to the maximum extent
that is practical, in order to reduce internal
phosphorus loading. Unless this internal loading
is substantially reduced, it may take as long as
100 years for the lake to respond to watershed
phosphorus control programs.
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