Transcript Slide 1

Nutrients as Pollutants
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)
Nutrients: Nitrogen and Phosphorus
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
Eutrophication
Nutrient Additions
Nutrient addition increases
primary productivity (algae)
Sunlight is limited at greater depth
Photosynthetic life
O2
bacteria
Photoautotrophs die and become
food for aerobic heterotrophs
Aerobic autotrophs consume O2
Oxygen content in water is reduced
If oxygen is reduced sufficiently,
aerobic microbes cannot survive,
and anaerobic microbes take over
Nitrogen
Nitrogen
NH4+ and NO3Forms 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
Dominant Forms: NH4+ and NO3Sources: fertilizers, manures, wastewater discharge
NO3- is more mobile in the environment than NH4+
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NH4+
NO3-
Soil particles possess
a negative electrical charge
Leaching to ground
Or surface water
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.
Unconfined Aquifers
Sandy Materials
Miocene Clays
(Hawthorne Formation)
55 – 24 million years ago
Unconfined aquifer is
extensive throughout
the state of Florida
Low Permeability
Confining Unit
(poor water movement)
The Floridan aquifer
is a confined aquifer.
The water-bearing unit
is permeable limestone.
Low permeability rock (confining)
Recharge
Where the Confining Layer is Thin
Groundwater
Thin sandy
overburden
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
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.
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
Phosphorus
Phosphorus
Present in Fertilizers, animal wastes, wastewater
Limiting Element to Primary Productivity
Chlorophyll
ATP
Phospholipids
Additions increase Productivity
ATP
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
Plant Availablity and pH
H2PO4
-
Most Available
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
Acidic Conditions (low pH)
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
solid
In solution
Aluminum Precipitation at Low pH
Form of available P at low pH: H2PO4-
(pH 3-6)
H2PO4- combines with free Al3+ and Fe3+
(solid)
Al3+ + H2PO4- + 2H20 = Al(OH)2H2PO4 + 2H+
simplified
Al3+ + PO4-3 = Al(PO4)
Fe3+ + PO43- = FePO4
time
Al(PO4)
Solid
Basic Conditions (High pH)
Calcium Binding in Basic Conditions
Calcium is often present at high pH
H (PO4)-2 is the available form of P at high pH
Ca2+ + 2H (PO4)-2 = Ca [H (PO4)]
CaHPO4 (solid)
time
Ca5(PO4)3OH (Apatite mineral)
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
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 _____________________
South Florida and Phosphorus
Phosphorus loading to S. Florida Ecosystem
Dairy/Beef
Inputs North
and South of
Okeechobee
Crop production
Crops: Everglades Agricultural Area
EAA
Sugar, Rice, Veg.
700,000 ac
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
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
Escarole
0
Phosphorus loading to S. Florida Ecosystem
Agriculture
Overstimulation of primary productivity
Dairy and Beef
Dairy and Beef
In 1521 Ponce de Leon
brought horses and cattle
to Florida.
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
Kissimmee drainage basin 12,000 km2
(1947)
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
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
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
Okeechobee, in turn, is a source
of phosphorus to the Everglades
urban
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
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
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
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.
Internal Loading
Phosphorus and Iron
Phosphorus has a strong affinity for iron
FePO4
Solid Precipitate
Readily incorporates into bottom sediments
Iron Exists in Two Different Forms
Depending on Oxygen Content
Fe3+ high oxygen
Forms insoluble solids with Phosphate
Fe3+ + PO43- = FePO4
solid
Fe2+ low oxygen
Phosphorus compounds become soluble
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.
Simplified: Fe3+ + PO43- = Fe(PO4)
solid
Fe3+
If oxygen contents are reduced (anoxic bottom sediments) the
converts to Fe2+ which solubilizes the compound returning P to water.
2+
Fe (PO4)
3-
to water
P released by sediments is taken up by photosynthetic
algae faster than it can be returned to the sediments
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.
Next: Arsenic, Fluoride, Mercury