27 Nitrogen and Phosphorus

27 Nitrogen and Phosphorus - Nutrients as Pollutants Major...

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: 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 Photosynthetic life Nutrient addition increases primary productivity (algae) Sunlight is limited at greater depth Photoautotrophs die and become food for aerobic heterotrophs Aerobic autotrophs consume O If oxygen is reduced sufficiently, Oxygen content in water is reduced aerobic microbes cannot survive, and anaerobic microbes take over 2 O2 bacteria Nitrogen Nitrogen NH4+ and NO3Forms are controlled by organisms NH is converted to NO by aerobic bacteria 4+ These bacteria, therefore, are 3controlled by oxygen levels The process is called nitrification 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+ __ 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 Unconfined aquifer is extensive throughout the state of Florida Low Permeability Confining Unit (poor water movement) Miocene Clays (Hawthorne Formation) 55 – 24 million years ago 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 Phosphorus Present in Fertilizers, animal wastes, wastewater Limiting Element to Primary Productivity Chlorophyll ATP Phospholipids Additions increase Productivity ATP Fertility 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 Plant H PO pH 3-6 2 4Most Available HPO pH 8-11 4-2 pH 6-8 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) Acid Aluminum and Iron availability is increased at low pH solids Al(OH)3 FeOOH 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 Aluminum Form of available P at low pH: H2PO4H PO combines with free Al and Fe (pH 3-6) Al3+ + H2PO4- + 2H20 = Al(OH)2H2PO4 + 2H+ simplified time 2 4- 3+ (solid)3+ Al 3+ + PO 4-3 = Al(PO ) = FePO 4 Al(PO4) Solid Fe3+ + PO Basic Conditions (High pH) Calcium Binding in Basic Conditions Calcium 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)] CaHPO (solid) time 4 Ca (PO ) OH (Apatite mineral) 5 43 Binding of Phosphorus Binding Low pH Aluminum and Iron phosphates High pH 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 * 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 Low Soil P Celery Endive Escarole 260 200 200 200 175 175 140 150 150 80 125 125 20 100 100 0 75 75 0 50 50 V. High Soil P 0 25 25 0 0 0 Lettuce (Head) Radish Romaine 200 100 200 175 40 175 150 0 150 125 0 125 100 0 100 75 0 75 50 0 50 25 0 25 0 0 0 Sugar Cane 120 100 80 40 20 0 0 0 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 Fe high oxygen 3+ Fe low oxygen 2+ Forms insoluble solids with Phosphate Phosphorus compounds become soluble Fe + PO 3+ 43- = FePO solid 4 Internal Loading Fe high oxygen Fe low oxygen Dissolved phosphorus combines with oxidized iron (Fe3+) to create 3+ 2+ an insoluble compound that becomes buried in lake sediments. Simplified: Fe3+ + PO43- = Fe(PO4) solid Fe 3+ If oxygen contents are reduced (anoxic bottom sediments) the converts to Fe which solubilizes the compound returning P to water. 2+ Fe (PO4) 2+ 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 ...
View Full Document

Ask a homework question - tutors are online