Science Junction

Water What-ifs
Nitrates and Phosphates Mini-workshop
Introduction

A s decomposition of plant and animal material occurs, dissolved oxygen levels decrease and nitrate levels increase. In addition, bacteria break down large protein molecules into ammonia which combines with oxygen to form nitrates and nitrites. Of these, nitrate is usually the most important to consider when determining water quality. Normally only small amounts are found naturally, but an increase in nitrate levels can come from many man-made sources such as septic systems, fertilizer runoff and improperly treated wastewater. As nitrates increase, they act as a plant nutrient and cause an increase in plant growth. As the plant material dies and decomposes, dissolved oxygen levels decrease.

An increase in nitrates may be followed by an increase in phosphates. As phosphates increase and the growth of aquatic plants is encouraged, algal blooms can occur. With the increase in algae growth and decomposition, the dissolved oxygen levels will decrease.

Sources of phosphates include septic tanks, runoff from feedlots, runoff from agriculture and waste water treatment plants. In addition, detergents with phosphates were a prime source before manufacturers developed phosphate-free alternatives.

 
Goals and Objectives

Nitrates and Phosphates Objectives

A fter completing the tutorial you should be able to

  • explain the reasons for measuring nitrates and phosphates and describe how they are measured and determined.
  • interpret nitrate and phosphate levels and analyze their meaning using LaMotte Nitrate/Phosphate test kits.
Learn the skills

Nitrate & Phosphate Test Kit (LaMotte)

Nitrate

  1. Fill the test tube (0844) to the 2.5 ml mark with the water sample.
  2. Add Mixed Acid Reagent (V-6278) to the water sample to the 5 ml mark.
  3. Cap and invert three times. Wait 2 minutes.
  4. Using the 1.0 gram measuring spoon (0699) provided with the test kit, add one level spoon of Nitrate Reducing Reagent (V-6279). Cap and invert 30-40 times in a one minute period. Wait 10 minutes.
  5. Mix after the 10 minute waiting period and remove the cap.
  6. Insert the tube into the Nitrate-N and Phosphate Comparator (3120) with the Axial Reader (2071).
  7. Match the sample color to a color standard.
  8. If no color change is apparent to the unaided eye, the result must be recorded as <0.2 ppm rather than 0. The color change might be so slight that it may not be visible to the unaided eye, but actually may be more than a 0 ppm reading.
  9. Read the number off the Nitrate-N and Phosphate Comparator and record as Nitrate-Nitrogen in parts per million (ppm).
  10. To convert to Nitrate, multiple by 4.4.

NOTE: Reading the number off the Nitrate-N and Phosphate Comparator x 4.4 = mg/L or ppm Nitrate.

If more than one nitrate reading is taken, take the average of all the readings and record this number.

This test will measure a range of Nitrate-Nitrogen from 0.2-1.0 ppm.

Phosphates

NOTE: This test should be run on clear samples only. Filter sample if necessary.

  1. Fill the test tube (0844) to the 10 ml mark with sample water.
  2. Use the 1.0 ml pipet (0354) provided with the water test kit to add 1.0 ml to Phosphate Acid Reagent (V-6282).
  3. Cap the test tube and invert three times.
  4. Use the 0.1 gram spoon (0699) to add one level measure of Phosphate Reducing Reagent (V-6283). Cap and invert until the reagent is dissolved. Wait 5 minutes.
  5. Remove the cap. Place the test tube in the Nitrate-N and Phosphate Comparator (3120) with the Axial Reader (2071).
  6. Match the sample color to the color standard.
  7. If no color change is apparent to the unaided eye, the result must be recorded as <0.2 ppm rather than 0. The color change might be so slight that it may not be visible to the unaided eye, but actually may be more than a 0 ppm reading.
  8. Record the result as ppm Total Phosphate.

NOTE: If more than one phosphate reading is taken, take the average of all the readings and record that number.

Total phosphate levels of non-polluted waters are usually less than 0.1mg/L or ppm.

For review, click here

Check yourself

Describe three possible sources of nitrates in a body of water.

If excess phosphates are present, what phenomenon may occur?

 
Post-test

Workshop Wrap-up

Once you have completed the mini-workshops, test your knowledge with the Water Quality Post-test. Once your completed post-test is submitted, you will receive a password which will give you and your students complete access to all areas of the Water What-ifs web site. Thanks for taking part in this research project on water quality.
 
| Water What-ifs Home | Teacher Tutorial | next mini-workshop (macroinvertebrates) |

e-mail the author
©1998-2001 April J. Cleveland for Science Junction, NC State University.
All rights reserved.
page design by Lisa Leonor Grable and April J. Cleveland
URL: http://www.ncsu.edu/sciencejunction/depot/experiments/water/tutorial/tutorialnp.html
Last Modified: 8/15/01

| Data Depot  | Science Junction  | NC State |