Forms of Nitrogen
R-NH2 is organically bound form of nitrogen
N2
X
R-NH2
Decomposition
Of O.M.
NH4+
Uptake by
plant
nitrosomonas
NO2-
Uptake by
plant
nitrobacter
NH4+ is exchangeable, NO3- is not
NO3-
Symbiotic Biological Nitrogen Fixation
Symbiosis between plant roots and rhizobium bacteria
Rhizobium
N2
gas
NH4+
mineral
Nodules are packed with Rhizobium
Nitrogen Fixation is Difficult and Specialized
N2 + 6H2
2NH3
Fixing N2 is energetically “expensive”
N N
Triple bond
– Must use energy to break these bonds
Artificial Nitrogen Fixation
Haber - Bosch Process - Artificial Fixation of
Nitrogen Gas:
– 200 atm
– 400-500 oC
yield of 10-20%
– no oxygen
Produces 500 million tons of artificial N fertilizer per year.
1% of the world's energy supply is used for it
Sustains roughly 40% of the world’s population
Nitrogen and Food
Food production has
grown with population
Crop Varieties
Fertilizers
70% of water used
Nitrogen Fertilization
NH4+
NO3-
NO3Negative Exchange
sites
Loss of Productivity
Leaching to groundwater, surface water
Mineral Forms: NH4+ and NO3NO3- is more mobile in the environment than NH4+
_
_
_
_ _
_
_ _
_
NH4+
NO3-
Loss of Productivity
Leaching to groundwater, surface water
Leaching to ground
Or surface water
Some Areas of Florida are Susceptible
Approximately 250 million years ago
Approximately 150 - 200 million years ago
Late Jurassic
Flooded, stable platform
Subject to marine sedimentation
FL platform/plateau
For the next several million years the platform was dominated by carbonate sedimentation
Sedimentation: settling of particles from a fluid due to gravity
Carbonate Deposition/Sedimentation
Marine Calcium and Magnesium Carbonate
CaCO3
MgCO3
Between about 150 Mya and 25 Mya
Florida platform was a flooded, submarine
plateau dominated by carbonate deposition
CaCO3
FL platform
*
The Eocene and Oligocene Limestone
The Eocene and Oligocene limestone forms the
principal fresh water-bearing unit of the Floridan Aquifer,
one of the most productive aquifer systems in the world
Eocene: 55 – 34 million years ago
Oligocene: 34 – 24 million years ago
Marine Carbonates
carbonates
Prior to 24 Mya
Between 150 and 25 Mya, Florida was dominated by carbonate deposition
Continental Influences
highlands
Sediments
Isolation of the Florida Peninsula
Sediments
Georgia Channel
Suwannee Current
Events of the Late Oligocene Epoch, approximately 25 Mya
Raising of the Florida Platform
Lowering of Sea Levels, Interruption of Suwannee Current
Suwannee Current
Exposure of Limestone
The Oligocene marked the
beginning of a world wide
cooling trend and lower sea
Levels.
Erosion cavities
Due to acidity
Miocene Epoch: began approximately 24 Mya
sediments
Rejuvenation of Appalachians, weathering, increased sediment load
Sediments were sands, silts, clays
Filling in the Georgia Channel
Sediments
Early Miocene
(~ 24 Mya)
Sediments
Rising sea levels allow sediments to become
suspended in water and drift over the platform
Siliciclastics Covered the Peninsula
Sands
And
Clays
Summary
Deposition of Eocene/Oligocene Limestone (55 – 24 Mya)
Raising of the Florida platform
Lowering of sea levels, interruption of the Suwannee Current
Infilling of the Georgia Channel with sediments derived from
Appalachian/continental erosion
5. Sea level rise, lack of Suwannee current.
6. Suspended siliciclastic sediments settle over the peninsula
7. These sediments blanket the underlying limestone forming
the upper confining layer for the Floridan Aquifer.
1.
2.
3.
4.
Conductivity: the ease with which water moves through material
Surface Siliciclastics (sandy)
(highly permeable)
Clays and Sands
(low permeability)
55 – 24 million years ago
Unconfined aquifer is
extensive throughout
the state of Florida
Low Conductivity
Confining Unit
(poor water movement)
The Floridan aquifer
is a confined aquifer.
The water-bearing unit
is permeable limestone.
Low permeability rock (confining)
The Water-bearing Unit is Extremely Productive
Calcium Carbonate CaCO3
Magnesium Carbonate MgCO3
limestone
How does this material hold and deliver water?
Carbonate Dissolution
Acid (H+) dissolves calcium carbonate
Carbonates are made porous by acid dissolution
Rainfall is naturally acidic
Carbon dioxide dissolved in water produces carbonic acid
CO2 + H2O = H2CO3 (carbonic acid)
H2CO3 => H+ + HCO3Acid
Acidity from rainfall reacts with CaCO3
and dissolves the carbonate rock.
CO2 + H2O = H2CO3
H2CO3 => H+ + HCO3-
CaCO3 + H+ = HCO3- + Ca2+
(solid)
(acid)
(solution)
(solution)
Dissolution Cavities
Dissolution Cave
Acid dissolves calcium carbonate
Caves and
Solution Cavities
CaCO3 + H+ = HCO3- + Ca2+
Clayey Deposits
Carbonates
Channels and Caves
Karst Topography
Characterized by sinkholes, springs, depressions, lakes
Sinkhole Lakes
Florida is Dominated
by Karst Topography
Sinkhole formation depends on the material
overlying the carbonate water-bearing unit
Very thick clays
> 200ft.
Thin, sandy covering
Cohesive clays up to 200ft
Thick sands up to 200 ft
thick and some clays
Miocene clays have been eroded and shaped throughout their history
resulting in extreme variability in thickness across the state.
The Importance of Sinkholes and Sinkhole Lakes
Hydrologic connections between the surface
and the underlying limestone are maintained.
Florida: 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.
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.
Phosphorous
Importance
Essential Macronutrient
Limiting Resource
Present in Fertilizers, animal wastes, wastewater
Availability can be very limited
Organic Phosphorous
Components of soil organic matter and plant tissue
Phosphate sugars
Nucleic Acids (DNA/RNA)
ATP
Phospholipids
ATP
Fertility
-Total soil phosphorous is low
-Most of the total is unavailable to plants
-Much of soil P forms insoluble solids
(limiting to availability)
-10-15% of applied fertilizer phosphorous used by plants
- the rest is bound to soil particles or forms insoluble solids
=>excess application
=>saturation of soil capacity
Soil Phosphorous
Inorganic
PO4-3
(Orthophosphate)
H3PO4
H2PO4-
HPO4-2
The form of available phosphorus is pH-dependent
Plant Availablity
H2PO4
-
Most Available
HPO4-2
pH 6-8
pH 3-6
pH 8-11
Optimum pH = 6.5 for mineral soils
Acidic Soils
Acid Soils (Low pH)
Aluminum and Iron availability increased at low pH
FeOOH
Al(OH)3
Solubility increased
Al3+
Fe3+
example
Al(OH)3 + 3H+ = Al3+ + 3H2O
Aluminum Precipitation at Low pH
Form of available P at low pH: H2PO4-
(pH 3-6)
H2PO4- combines with free Al3+ and Fe3+
(Insoluble)
Al3+ + H2PO4- + 2H20 = Al(OH)2H2PO4 + 2H+
simplified
Al3+ + PO4-3 = Al(PO4)
Al(PO4) • H2O
Variscite
Basic Soils (High pH)
Calcium Binding in Basic Soils
CaCO3
(higher calcium availability)
H2(PO4)- is the available form of P
CaCO3 + 2H2(PO4)- = Ca [H2(PO4)]2 + CO32CaHPO4
Ca5(PO4)3OH (Apatite mineral)
Availability and pH
Formation of insoluble solids
Low pH
Aluminum and Iron
phosphates
High pH
Calcium Phosphates
Reaction with Soil Minerals
Anion Exchange
It is possible for clays to develop
positive change at their edges
when they are broken during weathering
+
+
H2PO4-
+
+
Small quantities of P
Fixation on Iron and Aluminum
A dominant interaction between Phosphorus and
soils is strong interaction with Iron and Aluminum Oxides
OH
Al
OH
Fe
OH
Al
OH
Fe
OH
OH
Fixation: Aluminum/Iron oxides
OH
OH
Fe
Fe
OH
H
(PO
)
+ 2
4
H2(PO4)FE
Fe
OH
OH
+
OH-
OH
O-
Fe
OH
+
O-
P
OH
Fe
OH
OH
OH
O-
O-
P
Fe
Fe
OH
OH
OH
Coatings on Sands and Silicate Clays
OH
Fe
H2(PO4)Fe
OH
Fe coating
Organic Matter
Organic matter does not typically
bind strongly with phosphorus.
Organic matter covers fixation sites
Organic matter reacts with free Fe and Al
Organic matter competes for anion exch. sites
Organic Matter tends to increase P availability
Inorganic Soil Phosphorous
Inorganic
-Plant Available
H2PO4-
HPO4-2
(low)
-Fe, Al bound
-Calcium bound
-exchangeable
- Fixed on oxides
Al(PO4) • H2O
Ca3(PO4)2
H2PO4H2PO4-
+
Next: Phosphorus and South Florida