(6) Nitrate contaminationweb.sahra.arizona.edu/education2/wrtt/lecs/McIntosh... · (6) Nitrate...

(6) Nitrate contamination

J. McIntosh UA-HWR (2012)

Nitrate (NO3) = most stable form of N in environment, in addition to N2(g), and is highly soluble

#1 Water Quality problem in the U.S.

What are the major sources of NO3 contamination?

1) N-based fertilizers2) Animal manure3) Leaky septic tanks4) Effluent from wastewater

treatment plants5) Atmospheric Deposition6) Geologic sources


How is NO3 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.


EPA Water Quality Standards for Nitrate

MCL = 45 mg/L nitrate (NO3)

Calculate MCL as NO3-N:


EPA Water Quality Standards for Nitrate

=10 mg/L nitrate as nitrogen (NO3-N)

MCL = 45 mg/L nitrate (NO3)

45mg NO3

L

1 mole NO3

62 g

1 mole N

1 mole NO3

14 g

1 mole N10 mg

L N

< 3 mg/L NO3-N uncontaminated groundwater3-10 mg/L NO3-N likely influenced by human activity>10 mg/L NO3-N highly contaminated groundwater

Calculate MCL as NO3-N:



After Kendall & McDonnell (1998)

Fingerprinting nitrogen sources in the environment - Isotopes

Nitrate

18O

16O

18O

16O

18O

16O

15N

14N




18O

18O 16O

15N

16O

16O 16O

15NNO3

15N14N

sample

15N14N

AIR(s tan dard )

15N14N

AIR(s tan dard )

1000

18ONO3

18O16O

sample

18O16O

AIR(s tan dard )

18O16O

AIR(s tan dard )

1000




(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)


(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


(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

Old WTP = major source of nitrate contamination, E Coli and volatile organic compounds

New WTP opened in 2009 -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

QuickTime™ and a decompressor

are needed to see this picture.



NOx emissions from Tucsonurban core during summermonsoon. N‐containing species(e.g. nitrate and nitrite) are alsoassociated with dust particlesthat are lifted with wind.

2)

1)



NOx rises and istransported to high in theatmosphere.



NOx and particulates

transported during dry season

are deposited as dry deposition

at high elevation. Raindrops can

also contain N and organic

carbon species from uptake of

soluble gases and aerosol

particles.

3)

Sources and transport of nitrogen deposition in sky islands

4)



High N (nitrite) levelsobserved in mountainstreams during summer-time, likely fromatmospheric deposition.

Figure 11: Schematic diagram showing sources of nitrogen deposition and transport in sky-island ecosystems.


(6) Geologic sources

45 umole/L NO3 = 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


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


Natural removal of nitrate via denitrification:

NO3- + 5/4CH2O 1/2N2(g) + 5/4HCO3

- + 1/4H+ + 1/2H2O

Denitrification primarily driven by microbes (nitrate reducing bacteria) that live under ANOXIC conditions

Need organic matter (carbon) as an electron donor to reduce NO3 to N2


McMahon & Chapelle (2007)

High amounts of organic carbon in sediments promotes anoxic conditions in groundwater

ANOXIC = no oxygenOXIC = lots of oxygen

Nitrate (NO3) may be removed by microbes via denitrification under anoxic conditions

Oxygen content of groundwater across US

McMahon & Chapelle (2007)

Basin & Range alluvial aquifers (incl. S AZ) contain low amounts of organic carbon

Mostly OXIC

High NO3 waters can persist for a long time because there is no mechanism for nitrate removal

Oxygen content of groundwater across US

Dr. Brad Esser, Lawrence Livermore National Laboratory

Removal of nitrate by denitrification in CA wells

*No NO3 detected

USGS studies of the Delmarva Peninsula, Maryland

Bohlke and Denver (1995)

Groundwater discharging into Morgan Creek has lower nitrate because of percolation through organic-rich sediments (Hornerstown unit) which enhanced denitrification.

Influence of organic-rich sediments on groundwater nitrate levels


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

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

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 1992–2001.

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

Pesticide Occurrence 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

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

Raw meat: E. Coli can get into meat during processing; bacteria can survive if meat isn’t cooked to 160oF; 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)

E. Coli contamination - vectors

(1) Food

(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.

Not washing hands properly.

(3) Person to person

Symptoms: bloody diarrhea; stomach cramps, nausea & vomiting

CDC

Transport pathways of pathogens in urban environments

Stormwater is a major contributor to pathogen transportSome urban areas have combined sewer systems (waste and stormwater are carried in the same pipe systemDuring heavy rain events, runoff can exceed pipe capacity and result in overflowDuring 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. Only carry human, pet, and maybe industrial waste.Overflows 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.

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.

“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”

Storm sewers oozing human fecal bacteria to beaches, rivers, study finds

Milwaukee Journal Sentinel

Transport of pathogens on farms

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