(6) Nitrate contamination

Transcription

1 (6) Nitrate contamination Nitrate (N 3 ) = most stable form of N in environment, in addition to N 2 (g), and is highly soluble #1 Water Quality problem in the U.S. What are the major sources of N 3 contamination? 1) N-based fertilizers 2) Animal manure 3) Leaky septic tanks 4) Effluent from wastewater treatment plants 5) Atmospheric Deposition 6) Geologic sources

2 How is N 3 removed from the environment? (1) Dilution - by mixing with low nitrate waters (e.g. old groundwater, or heavy precipitation) (2) Denitrification in anoxic environments - microbes degrade nitrate Health effects of nitrate contamination Infants below six months who drink water containing nitrate in excess of the maximum contaminant level (MCL) could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue baby syndrome. (epa.gov) Doctors noticed that babies with blue baby syndrome developed symptoms after leaving the hospital, and were not from families using municipal water supplies or being breast feed. Disease linked to babies from rural communities using well water to mix with baby formula. Very few cases reported in the US today, likely because of public education.

3 EPA Water Quality Standards for Nitrate MCL = 45 mg/l nitrate (N 3 ) Calculate MCL as N 3 -N: EPA Water Quality Standards for Nitrate MCL = 45 mg/l nitrate (N 3 ) Calculate MCL as N 3 -N: 45 mg N 3 L 1 mole N 3 62 g 1 mole N 1 mole N 3 14 g 1 mole N 10 mg L N =10 mg/l nitrate as nitrogen (N 3 -N) < 3 mg/l N 3 -N uncontaminated groundwater 3-10 mg/l N 3 -N likely influenced by human activity >10 mg/l N 3 -N highly contaminated groundwater

4 Fingerprinting nitrogen sources in the environment - Isotopes 18 Nitrate N 14 N After Kendall & McDonnell (1998)

5 Fingerprinting nitrogen sources in the environment - Isotopes N N N 15 N 14 N N 3 sample N 15 N 14 N N 3 sample AIR(stan dard ) 1000 AIR(stan dard ) AIR(stan dard ) 1000 AIR(stan dard ) After Kendall & McDonnell (1998) Fingerprinting nitrogen sources in the environment - Isotopes After Kendall & McDonnell (1998)

6 (1) Nitrogen-based fertilizers Under native prairie vegetation, annual N inputs were typically measured in tens of kg/ha With corn & grain crops, annual N inputs are the order of several hundred kg/ha Usually <50% of the N applied as fertilizer is used by the plants Significant amounts of N are left behind in the soils, and can be leached to groundwater by infiltrating water (i.e. precipitation or irrigation)

7 (2) Animal manure homesteading in the midwestern US for several generations has led to build up of N near farmsteads resulting from outdoor toilets and livestock confinement (Stewart et al., 1967) NE US and Great Lakes region - high density of dairy and poultry operations and limited availability of agricultural lands for waste disposal (3) Leaky septic tanks

8 QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. Nx transported during dry season are deposited as dry deposition and particulates at high elevation. Raindrops can also contain N and organic carbon species from uptake of soluble gases and aerosol particles. (4) Effluent from wastewater treatment plants Nogales International Wastewater Treatment Plant releases effluent into the Santa Cruz River at a rate of 12,000 to 15,000 acre-feet/yr Effluent discharge maintains perennial flow in the river for ~20 miles Significant portion of the discharge infiltrates into the aquifer beneath the wash ld WTP = major source of nitrate contamination, E Coli and volatile organic compounds New WTP opened in substantially reduce ammonia (nitrate) in effluent discharge What will the impacts be on riparian communities along the wash and River? (5) Atmospheric sources of nitrate Most atmospheric N comes from combustion; values highest downwind of power plants or industrial areas Sources and transport of nitrogen deposition in sky islands High N (nitrite) levels observed in mountain streams during summertime, likely from atmospheric deposition. 4) 3) 2) Nx rises and is transported to high in the atmosphere. Nx emissions from Tucson 1) urban core during summer monsoon. N containing species (e.g. nitrate and nitrite) are also associated with dust particles that are lifted with wind. Figure 11: Schematic diagram showing sources of nitrogen deposition and transport in sky-island ecosystems.

9 (6) Geologic sources 45 umole/l N 3 = 2.8 mg/l Groundwater is the source of water for ~90% of people living in rural areas in the US 50% of all people living in the US use groundwater for domestic water supplies 75-80% of water used for irrigation comes from groundwater **Maintenance of groundwater quality is a major concern

10 Nitrate in US Groundwater Mitigation Strategies for Nitrate Contamination? Farmers have most control over fertilizer N and animal wastes, so control of groundwater nitrates can be achieved most easily through judicious use of these two inputs Power and Schepers (1989) Best Management Practices for agriculture to hopefully reduce the amount of nitrogen getting into groundwater over time; outreach and education through Groundwater Management Areas and other programs Each year there are 8 billion pounds more N available in farm fields than can be used by crops (NRC, 1993). Conservation programs help farmers account for all sources of nitrogen in fields (fertilizer/manure + nitrogen fixing crops (e.g. legumes)), timing application properly, using nitrogen soil tests, and setting realistic yield goals. In Iowa, farmers have decreased N-fertilizer use by 18% over 4 years, and still are able to grow as much corn as other Corn Belt farming states. Better technology at municipal wastewater treatment plants to reduce nitrate levels in effluent discharge

11 Natural removal of nitrate via denitrification: N /4CH 2 1/2N 2(g) + 5/4HC /4H + + 1/2H 2 Denitrification primarily driven by microbes (nitrate reducing bacteria) that live under ANXIC conditions Need organic matter (carbon) as an electron donor to reduce N 3 to N 2 xygen content of groundwater across US High amounts of organic carbon in sediments promotes anoxic conditions in groundwater ANXIC = no oxygen XIC = lots of oxygen Nitrate (N 3 ) may be removed by microbes via denitrification under anoxic conditions McMahon & Chapelle (2007)

12 xygen content of groundwater across US Basin & Range alluvial aquifers (incl. S AZ) contain low amounts of organic carbon Mostly XIC High N 3 waters can persist for a long time because there is no mechanism for nitrate removal McMahon & Chapelle (2007) Removal of nitrate by denitrification in CA wells *No N 3 detected Dr. Brad Esser, Lawrence Livermore National Laboratory

13 USGS studies of the Delmarva Peninsula, Maryland Influence of organic-rich sediments on groundwater nitrate levels Groundwater discharging into Morgan Creek has lower nitrate because of percolation through organic-rich sediments (Hornerstown unit) which enhanced denitrification. Bohlke and Denver (1995)

14 If we stop polluting the environment with nitrates, will the problem go away?

15 No change in Mississippi River and tributaries over past 20 years, despite decreases in N use from improved WTP and farming practices N has gone up in a few rivers Slow release of nitrates from groundwater discharge into rivers (7) Pesticides & Bacteria

16 What are Pesticides? Pesticides are chemicals that are used to control weeds, insects and other pests Herbicides (weeds) Insecticides (insects) Fungicides (fungi) Nematocides (nematodes = roundworms) Rodenticides (vertebrate poisons) Environmental effects of pesticide use Water quality (more of an issue for aquatic species and predators than humans) A decadal assessment by the National Water-Quality Assessment (NAWQA) Program of the United States Geological Survey (USGS) provides the most comprehensive national-scale analysis to date of pesticide occurrence and concentrations in streams and ground water, based on results from studies completed during Among the major findings are that pesticides are frequently present in streams and ground water, are seldom at concentrations likely to affect humans, but occur in many streams at concentrations that may have effects on aquatic life or fish-eating wildlife. USGS NAWQA program

17 Pesticide ccurrence in the Environment Pesticides typically present in streams draining watersheds with large agricultural or urban areas Less common in groundwater Degradates (products that come from degradation of pesticides) also an issue USGS NAWQA program Bioaccumulation of pesticides with increasing trophic level

18 Total Coliform Bacteria Group of closely related bacteria that are (with few exceptions) not harmful to humans These bacteria naturally live in soil and waters (lake and streams), and in the gastrointestinal tracts of animals E. coli is a type of fecal coliform bacteria commonly found in animal and human intestines; gets into the environment via human and animal waste; these waste products maybe washed into rivers and/or infiltrate into groundwater with precipitation, ending up in drinking water supplies E. Coli contamination - vectors (1) Food Raw meat: E. Coli can get into meat during processing; bacteria can survive if meat isn t cooked to 160 o F; most common food source of contamination Raw milk or dairy products: bacteria can spread from cow s udders to milk; make sure products have been pasteurized (heated up to kill bacteria) Raw fruits and vegetables (e.g. lettuce, unpasteurized juice) (2) Water Human or animal feces may get into lakes, pools, and water supplies. People can become infected when city water supplies haven t been decontaminated with chlorine properly, or when accidentally drinking contaminated pool water, etc. (3) Person to person Not washing hands properly. Symptoms: bloody diarrhea; stomach cramps, nausea & vomiting CDC

19 Transport pathways of pathogens in urban environments Stormwater is a major contributor to pathogen transport Some urban areas have combined sewer systems (waste and stormwater are carried in the same pipe system During heavy rain events, runoff can exceed pipe capacity and result in overflow During overflow events, raw or partially treated sewage is dumped into nearby waterways Transport pathways in urban environments Urban areas may also have separate sewer systems, which are not designed to carry stormwater. nly carry human, pet, and maybe industrial waste. verflows maybe caused by broken pipes, undersized pipes, mechanical failures, blockages (tree roots), etc. Sewage may spill into streets, back up into basements, or spill into waterways.

20 Transport pathways in urban environments Septic systems - may leak pathogens directly to groundwater. Non-point source pollution; e.g. rainfall or snowmelt running off surfaces with fecal contamination from manure, pet feces, wildlife feces. Storm sewers oozing human fecal bacteria to beaches, rivers, study finds Milwaukee Journal Sentinel Most likely sources [of fecal coliform] in rivers include broken sanitary sewers that leak into storm-water pipes, or sanitary pipes misconnected to storm sewers

21 Transport of pathogens on farms