Forms of Nitrogen N2N2 X R-NH 2 R-NH 2 is organically bound form of nitrogen NH 4 + Decomposition Of...

Forms of Nitrogen

N2

XR-NH2R-NH2

R-NH2 is organically bound form of nitrogenR-NH2 is organically bound form of nitrogen

NH4+

DecompositionOf O.M.

Uptake byplant

Uptake byplant

NO2- NO3

- nitrosomonas nitrobacter

NH4+ is exchangeable, NO3

- is not

Rhizobium

Symbiotic Biological Nitrogen Fixation

Symbiosis between plant roots and rhizobium bacteria

Nodules are packed with Rhizobium

N2 NH4+

gas mineral

Nitrogen Fixation is Difficult and SpecializedNitrogen Fixation is Difficult and Specialized

NN22 + 6H + 6H22 2NH 2NH33

Fixing NFixing N22 is energetically “expensive” is energetically “expensive”

NN NN Triple bondTriple bond– Must use energy to break these bondsMust use energy to break these bonds

Artificial Nitrogen FixationArtificial Nitrogen Fixation

Haber - Bosch ProcessHaber - Bosch Process - Artificial Fixation of - Artificial Fixation of Nitrogen Gas:Nitrogen Gas:– 200 atm200 atm– 400-500 400-500 ooCC– no oxygenno oxygen

yield of 10-20%

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

70% of water used

Food production hasgrown with population

Crop VarietiesFertilizers

Nitrogen FertilizationNitrogen Fertilization

NO3- Negative Exchange

sites

Loss of ProductivityLeaching to groundwater, surface water

NO3-NH4

+

Mineral Forms: NH4+ and NO3

-

NO3- is more mobile in the environment than NH4

+

_ ___

___

__

NH4+

NO3-

Leaching to groundOr surface water

Loss of ProductivityLeaching to groundwater, surface water

Some Areas of Florida are Susceptible

Approximately 250 million years ago

Approximately 150 - 200 million years ago

Flooded, stable platformSubject to marine sedimentation

FL platform/plateau

For the next several million years the platform was dominated by carbonate sedimentation

Late Jurassic

Sedimentation: settling of particles from a fluid due to gravity

Carbonate Deposition/Sedimentation

Marine Calcium and Magnesium Carbonate

CaCO3

MgCO3

Florida platform was a flooded, submarineplateau dominated by carbonate deposition

FL platform

CaCO3

Between about 150 Mya and 25 Mya

*

The Eocene and Oligocene limestone forms theprincipal 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

The Eocene and Oligocene Limestone

carbonates

Prior to 24 Mya

Marine Carbonates

Between 150 and 25 Mya, Florida was dominated by carbonate deposition

Continental Influences

highlands

Sediments

Isolation of the Florida Peninsula

Suwannee Current

Georgia Channel

Sediments

Lowering of Sea Levels, Interruption of Suwannee Current

Suwannee Current

Events of the Late Oligocene Epoch, approximately 25 Mya

Raising of the Florida Platform

Exposure of Limestone

The Oligocene marked thebeginning of a world wide cooling trend and lower seaLevels.

Erosion cavitiesDue to acidity

Rejuvenation of Appalachians, weathering, increased sediment load

sediments

Miocene Epoch: began approximately 24 Mya

Sediments were sands, silts, clays

Sediments

Filling in the Georgia Channel

Early Miocene(~ 24 Mya)

Sediments

Rising sea levels allow sediments to becomesuspended in water and drift over the platform

Siliciclastics Covered the Peninsula

Sands And

Clays

1. Deposition of Eocene/Oligocene Limestone (55 – 24 Mya)2. Raising of the Florida platform3. Lowering of sea levels, interruption of the Suwannee Current4. Infilling of the Georgia Channel with sediments derived from Appalachian/continental erosion5. Sea level rise, lack of Suwannee current.6. Suspended siliciclastic sediments settle over the peninsula7. These sediments blanket the underlying limestone forming the upper confining layer for the Floridan Aquifer.

Summary

55 – 24 million years ago

Clays and Sands(low permeability)

Surface Siliciclastics (sandy)(highly permeable)

The Floridan aquifer is a confined aquifer.The water-bearing unitis permeable limestone.

Low ConductivityConfining Unit(poor water movement)

Unconfined aquifer isextensive throughoutthe state of Florida

Low permeability rock (confining)

Conductivity: the ease with which water moves through material

Calcium Carbonate CaCO3

The Water-bearing Unit is Extremely Productive

Magnesium Carbonate MgCO3

How does this material hold and deliver water?

limestone

Carbonate Dissolution

Acid (H+) dissolves calcium carbonate

Carbonates are made porous by acid dissolution

Carbon dioxide dissolved in water produces carbonic acid

CO2 + H2O = H2CO3 (carbonic acid)

H2CO3 => H+ + HCO3-

Acid

Rainfall is naturally acidic

CaCO3 + H+ = HCO3- + Ca2+

Acidity from rainfall reacts with CaCO3

and dissolves the carbonate rock.

(solid) (solution)(acid) (solution)

CO2 + H2O = H2CO3

H2CO3 => H+ + HCO3-

Dissolution Cave

Dissolution Cavities

Caves andSolution Cavities

Acid dissolves calcium carbonate

CaCO3 + H+ = HCO3- + Ca2+

Carbonates

Clayey Deposits

Channels and Caves

Karst Topography

Characterized by sinkholes, springs, depressions, lakes

Sinkhole Lakes

Florida is Dominatedby Karst Topography

Sinkhole formation depends on the material overlying the carbonate water-bearing unit

Thin, sandy covering

Thick sands up to 200 ft thick and some clays

Cohesive clays up to 200ft

Very thick clays> 200ft.

Miocene clays have been eroded and shaped throughout their historyresulting in extreme variability in thickness across the state.

The Importance of Sinkholes and Sinkhole Lakes

Hydrologic connections between the surfaceand the underlying limestone are maintained.

Florida: Nitrates (NO3-)

Nitrates do not interact significantly with soilmaterial and can move rapidly to groundwater.

3. Areas where the aquifer confining unit is thin are also particularly vulnerable.

What areas are particularly vulnerable?

2. Areas where natural groundwater recharge occurs

1. The unconfined, surficial aquifer

• 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

Lower Suwannee River Watershed

Nitrates

NO3 Drinking water standard: 10 ppm

Possible sources of nitrate in the ground water in the vicinity of the riverinclude fertilizer, animal wastes from dairy and poultry operations, and septic-tank effluent.

Nitrate concentrations were higher in the measured springs than in the river.

Flow

Groundwater Nitrate Discharge to Rivers

PhosphorousPhosphorous

ImportanceImportance

Essential Macronutrient Limiting ResourcePresent in Fertilizers, animal wastes, wastewaterAvailability can be very limited

Organic PhosphorousOrganic Phosphorous

Components of soil organic matter and plant tissue

Phosphate sugarsNucleic Acids (DNA/RNA)ATPPhospholipids

ATP

FertilityFertility

-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

-Total soil phosphorous is low-Most of the total is unavailable to plants-Much of soil P forms insoluble solids (limiting to availability)

Soil PhosphorousSoil Phosphorous

PO4-3

Inorganic

H2PO4- HPO4

-2H3PO4

(Orthophosphate)

The form of available phosphorus is pH-dependent

Plant AvailablityPlant Availablity

H2PO4- HPO4

-2

pH 3-6 pH 8-11pH 6-8

Optimum pH = 6.5 for mineral soils

Most Available

Acidic Soils

Acid Soils (Low pH)Acid Soils (Low pH)

Aluminum and Iron availability increased at low pH

Al(OH)3FeOOH

Solubility increased

Al3+ Fe3+

Al(OH)3 + 3H+ = Al3+ + 3H2Oexample

Aluminum Precipitation at Low pHAluminum Precipitation at Low pH

H2PO4- (pH 3-6)

Al3+ + H2PO4- + 2H20 = Al(OH)2H2PO4 + 2H+

(Insoluble)

Al(PO4) • H2OVariscite

Al3+ + PO4-3 = Al(PO4)

simplified

Form of available P at low pH:

H2PO4- combines with free Al3+ and Fe3+

Basic Soils (High pH)

Calcium Binding in Basic SoilsCalcium Binding in Basic Soils

CaCO3

CaCO3 + 2H2(PO4)- = Ca [H2(PO4)]2 + CO32-

CaHPO4

Ca5(PO4)3OH (Apatite mineral)

(higher calcium availability)

H2(PO4)- is the available form of P

Availability and pHAvailability and pH

Low pH High pH

Aluminum and Iron phosphates

Calcium Phosphates

Formation of insoluble solids

Reaction with Soil MineralsReaction 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 AluminumFixation on Iron and Aluminum

A dominant interaction between Phosphorus andsoils is strong interaction with Iron and Aluminum Oxides

Al

Al

OH

OH

OH

Fe

Fe

OH

OH

OH

Fixation: Aluminum/Iron oxidesFixation: Aluminum/Iron oxides

Fe

Fe

OH

OH

OH

H2(PO4)-+

Fe

FE

OH

OH

H2(PO4)-

OH-

+

Fe

Fe

OH

OH

OH

P OH

O-

OH

O-+

Fe

Fe

OH

OH

P OH

O-

OH

O-

Coatings on Sands and Silicate ClaysCoatings on Sands and Silicate Clays

Fe coating

Fe

Fe

OH

OH

H2(PO4)-

Organic Matter

Organic matter does not typically bind strongly with phosphorus.

Organic matter covers fixation sitesOrganic matter reacts with free Fe and Al

Organic matter competes for anion exch. sites

Organic Matter tends to increase P availability

-Plant Available

-Fe, Al bound -Calcium bound -exchangeable - Fixed on oxides

H2PO4- HPO4

-2

Al(PO4) • H2O

Ca3(PO4)2

H2PO4- +

H2PO4-

Inorganic Soil PhosphorousInorganic Soil PhosphorousInorganic

(low)

Next: Phosphorus and South Florida