Upload
gavin-matthews
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
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