Lecture 18 Nitrogen and Groundwater

Lecture 18 Nitrogen and Groundwater - Forms of Nitrogen...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 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 Nitrogen N2 + 6H2 2NH3 Fixing N2 is energetically “expensive” NN Triple bond – Must use energy to break these bonds Artificial Nitrogen Fixation Artificial Haber - Bosch Process - Artificial Fixation of Nitrogen Gas: Nitrogen – 200 atm yield of 10-20% 400-500 C 400-500 – o – roduces 500 million tons of artificial N fertilizer per year. P no oxygen 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 Nitrogen NH4+ NO 3- Negative Exchange sites NO 3- 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 1. 1. 1. 1. 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 1. Sea level rise, lack of Suwannee current. 1. Suspended siliciclastic sediments settle over the peninsula 1. These sediments blanket the underlying limestone forming the upper confining layer for the Floridan Aquifer. 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 CaCO Magnesium Carbonate MgCO 3 3 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 CO + H O = H CO (carbonic acid) 2 H2 CO =2 H3 + HCO > 2 3 + Acid 3- Acidity from rainfall reacts with CaCO3 and dissolves the carbonate rock. CO + H O = H CO H CO => H +2HCO 2 2 3 CaCO3 + H = +HCO3- +- Ca2+ 2 3 3 (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 Phosphorous Importance Importance Essential Macronutrient Limiting Resource Present in Fertilizers, animal wastes, wastewater Availability can be very limited Organic Phosphorous Organic Components of soil organic matter and plant tissue Phosphate sugars Nucleic Acids (DNA/RNA) ATP Phospholipids ATP Fertility 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 Soil Inorganic PO4-3 (Orthophosphate) H3PO4 H2PO4- HPO4-2 The form of available phosphorus is pH-dependent Plant Availablity Plant H2PO 4 pH 3-6 Most Available pH 6-8 HPO4-2 pH 8-11 Optimum pH = 6.5 for mineral soils Acidic Soils Acid Soils (Low pH) Acid 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 Aluminum Form of available P at low pH: H2PO4- (pH 3-6) H PO combines with free Al and Fe 2 (Insoluble)3+ 3+ 4- Al3+ + H2PO4- + 2H20 = Al(OH)2H2PO4 + 2H+ Al(PO4) • H2O simplified Al 3+ + PO = Al(PO4) 4-3 Variscite Basic Soils (High pH) Calcium Binding in Basic Soils Calcium CaCO3 (higher calcium availability) H2(PO4)- is the available form of P CaCO3 + 2H2(PO4)- = Ca [H2(PO4)]2 + CO32CaHPO 4 Ca (PO ) OH (Apatite mineral) 5 43 Availability and pH Availability Formation of insoluble solids Low pH Aluminum and Iron phosphates High pH Calcium Phosphates Reaction with Soil Minerals Reaction 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 Fixation 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 Fixation: OH OH Fe Fe OH + H2(PO4)- H2(PO4)FE Fe OH OH + OH- OH O Fe OH + Fe O- P- OH OH OH OH O O- P- Fe Fe OH OH OH Coatings on Sands and Silicate Clays Coatings 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 ...
View Full Document

This note was uploaded on 07/31/2011 for the course SOS 3022 taught by Professor Staff during the Fall '08 term at University of Florida.

Ask a homework question - tutors are online