* Nitrates (NO3-)

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picture by Emily Osman

What are nitrates?

Nitrates are salts that are composed of ions with one Nitrogen atom in the middle and three Oxygen atoms around the outside. Nitrogen exists in many forms including nitrates, nitrites, ammonia, and nitrogen gas. Nitrates are one of the building blocks used by plants and animals to make proteins.
 
Where do nitrates come from?  Because they dissolve easily, nitrates enter the water from many natural sources, including soil and decomposed plant material. Humans add nitrates to the water system through:
 
 - fertilizer runoff from lawns, golf courses and croplands;
 
 - sewage;
 
- domesticated animal wastes.
 
Natural levels of nitrates are usually low, less than 1 mg/L. Higher levels of nitrates than phosphates are needed to have an impact on the aquatic ecosystem.

Why do we care about nitrates?

Too high levels of nitrates in water can greatly increase the rate of plant and algae growth, leading to the gradual choking of the water systems with algae blooms. The plants then take in the dissolved oxygen, making it an unfriendly home for its living organisms.

Vegetables grown in water with high nitrates can make cancer-causing nitrites.

Water becomes toxic for drinking at concentrations of nitrates greater than 10 mg/L. Readings above this amount in your body of water could indicate pollution from fertilizers or sewage.

Nitrates above this level cause blood poisoning in infants, hypertension, gastric cancers, and fetal malformations in humans. High levels of nitrates can lower the level of dissolved oxygen in the blood of mammals. Wastewater treatment plant effluent can range up to 30 mg/L nitrate concentrations.

Investigative Questions:

 - Follow the Nitrogen as it moves through the environment, changing its chemical form. Where is it gas? Where is it liquid?  Where is it solid? 
 
- Nitrogen Levels Measurements – What do they mean? Nitrates are measured in concentrations of mg/L.

- What kinds of fertilizers are used by your local farmers? Do the vegetables show any effects? (Russian and US students found high levels one year in hydroponic vegetables.)

 Do some measurements!

Farmers are required to grow vegetation barriers when their fields go up to the edges of streams. Do they do this in your area? Why would this be important?

Additional Resources:

Some kits include Nitrogen probes. (Check Pasco and Vernier)

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*Nitrogen molecule from Wikipedia: http://en.wikipedia.org/wiki/Nitrate