Backyard Observation

Exploring Nitrogen in Your Local Watershed

Testing for nitrogen in your local watershed can help identify potential “hot spots” in your community that may be contributing to nutrient loading downstream. With a simple, inexpensive field test kit, you can detect inorganic forms of nitrogen readily available to plants such as nitrate (NO3−), nitrite (NO2−), and ammonium (NH3). Before going out into the field, plan when to sample. For example, if you want to test the effect of crop fertilization on the nitrogen levels in a stream adjacent to a local farm, you’ll need to schedule your sampling according to the farm’s fertilization schedule and after a substantial rainfall. You may also want to sample the same location during a time of relatively low water flow and compare it to a sample from the same location at a time of higher water flow. The number of samples you collect and how often you collect them depends on your interests and the question(s) you have about your local watershed.

Supplies

  • nitrogen (nitrate/nitrite/ammonium) test strips, available from most pet supply stores in the aquarium test equipment section or from science supply companies/as part of full water quality testing kit; (Select online retailers: Omega, Industrial Test Systems, Inc. ($15.99), Hach ($15.89)
  • water collection bottles such as Hach 250 mL Polyethylene collection bottles ($43.55 for 12 pack). Small Nalgene bottles from an outdoor supply store also work well, $2-$5 from Nalgene.
  • Internet connection
  • Google Earth (download here; latest available version is recommended)
  • The Citizen Scientist’s Guide to Earth Observations Water Quality Data Entry Sheet
  • rubber gloves (optional)
  • rubber boots (optional)
  • bucket (optional)
  • rope (optional)

WARNING: Always keep safety in mind when collecting water. If you are collecting water from the edge of a stream, river, or lake, walk carefully along the bank so as not to fall in. For safety, you can also attach a rope to bucket, toss the bucket into the water away from the edge, and bring a water sample back to shore for testing. Do not collect samples in a severe storm or flood or if there is a threat of lightning in the area. Bring a partner when possible, especially if you are planning to collect samples from water in remote areas. If you think your water source is highly polluted or might contain raw sewage, wear rubber boots and rubber gloves to avoid direct contact with the source.

CAUTION: Some experts recommend that you wear rubber boots and gloves to avoid contamination of the water sample. Rinse collection bottles in the water source you are testing to decrease sample contamination.

Procedure

  1. Follow these step-by-step instructions for identifying and exploring your watershed in Google Earth.
  2. With your watershed map open in Google Earth, identify one or more bodies of water in your area from which you would like to collect samples. Choose locations that are publicly accessible or ones at which you have explicit permission from the land owner to collect samples and perform water quality tests.
  3. Place the cursor over your chosen sampling site and write down the latitude and longitude that appears in the bottom left corner of the Google Earth window.
  4. Print copies of the Water Quality Data Entry Sheet to bring with you into the field. Use this data entry sheet to keep track of all your notes and observations to make it easy to share your data with others.
  5. Go to your sampling location. Write down the date, time, and weather. Carefully note and record landmarks or other identifying features near the location in enough detail that you will be able to find the exact same location again for more observations at a later date. If you have a camera, take a picture to help you keep a record of the location and conditions.
  6. Take detailed notes about the condition of the stream or river. What color is the water? Are there any detectable odors? Is the stream/river bottom silt or rock? Are there any visible drainage pipes nearby? NOTE: It is important to be consistent and uniform when taking notes about your data collection so that it is easy to compare your observations between sampling sites and with those made by other scientists.
  7. Take detailed notes about the conditions along the stream/river bank. Is the bank rock or mud? Is it steeply sloped? Are there plants along the bank? If so, what kind are they and how far are they from the water’s edge?

    NOTE: Some plants can slow runoff and limit the amount of nitrogen that enters water at a particular location because they absorb the nutrients for themselves. However, if a body of water borders a field of crops or a lawn, excess nitrogen from fertilizers may make its way into the they were all written by different people, water. Taking careful notes about the conditions around the stream or river may help you determine the source of nitrogen and why nitrogen levels vary over time.

  8. Label your sample bottle with the date, time, and location so that you can easily identify it later.
  9. Rinse the bottle in the stream.

    CAUTION: If you do not rinse the collection bottle, the sample may be contaminated and you will not get accurate results with your nitrogen tests.

    WARNING: Be extremely careful when collecting your water sample—the stream/river bank may be slippery. Do not take samples when the National Weather Service has issued a severe storm or flood warning for the region in which you are collecting your sample.

  10. Fill your sample bottle(s) with water from the stream or river. If the water is shallow, be careful not to scrape the bottom. If you take more than one sample at a given location, make sure they are clearly and distinctly labeled. For example, if you want to test the same stream or river along opposite banks, label one bottle “east bank” and the other “west bank.”
  11. Test your sample on-site or bring the collection bottles home for testing. Samples can be refrigerated and tested the following day, but should not be stored for more than 24 hours to ensure the most accurate results. Follow the directions on the test strip kit to record the nitrate and nitrite levels of your water sample. If you do not test the sample immediately, swirl the contents of the collection bottle around before testing to ensure that the water is evenly mixed.
  12. Record the nitrate and nitrite levels for each sample in units of ppm, as well as the uncertainty indicated by the test strip manufacturer. If your tests show nitrogen levels that are considered to be out of the ordinary range (see Interpretation section below), and the source of the nitrogen is not easily identifiable at your sampling location, consider driving upstream to investigate where the origin might be.

Interpretation of results:

Nitrogen test strips are convenient, inexpensive and relatively accurate compared to commercial laboratory analysis. A typical test strip will measure nitrate levels from 1 to 50 parts per million (ppm) and nitrite levels from 0.15 to 3.0 ppm. Any concentration of nitrates in a water source may be cause for concern. If nitrate levels are greater than 10 ppm, you should not drink the water. While there are no national or state standards in place regarding nitrate levels as they relate to aquatic life, the consequences of high nitrate levels can be quite serious. Nitrate is not toxic to plants or animals, but can become toxic during digestion if it is converted to nitrite that binds with hemoglobin and prevents blood from carrying oxygen. High levels of nitrates can also result in increased plant and algae growth in water, which can lead to hypoxia (decreased oxygen). If dissolved oxygen levels in the water get low enough, fish and other aquatic life that require oxygen can die. Bodies of water with oxygen levels too low to support life are known as “dead zones.”

Water should not be consumed if nitrite levels are above 1 ppm. As mentioned above, nitrite can be extremely harmful to both humans and aquatic life. High levels of nitrite are uncommon in water because it is often rapidly converted to other nitrogen compounds such as nitrate, nitrous oxide or nitrogen gas through chemical reactions.

The nitrogen you might detect in the water comes from a variety of sources. Some stems from natural rock or soil deposits, but the majority of it comes from things like wastewater treatment plants, septic systems, and runoff from fields and lawns. For more information about nitrates and nitrites in drinking water, take a look at the EPA’s Consumer Factsheet on Nitrates/Nitrites. To learn more about the ill effects of excess nitrogen on aquatic life, read the Scientific American article Oceanic Dead Zones Continue to Spread.

Going Further

If your research interests are focused on nitrogen contributions to your local water source from runoff, you should consider rainfall when making your observations. Runoff samples will be most revealing after a significant rainfall. To make a quantitative assessment of the relationship between nitrogen levels and rainfall, you will need to collect time series rainfall data from your sampling site. For step-by-step instructions about how to collect rainfall data, see the Precipitation chapter of this guide.

You might also want to test your water sample(s) for other nutrients. In addition to nitrogen, compounds containing phosphorous are also commonly found in fertilizers that make their way into water through runoff. Phosphates can cause algae blooms, which like nitrogen, can lead to hypoxic conditions and dead zones. To test for phosphorous, you will need a phosphate test kit. Like nitrogen test kits, these kits are relatively inexpensive and available from most pet supply companies in the aquarium testing section. Follow the nitrogen testing procedures and any additional manufacturer instructions to test your water sample(s).

For additional water quality monitoring ideas, visit NASA’s Goddard Earth Sciences Data and Information Services Center (GES DISC) Amateur Scientist’s Guide to Water Quality Monitoring Observations. This site has instructions for monitoring a variety of water properties including turbidity, salinity, dissolved oxygen, pH, temperature, and hydraulic flow.

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