Science Junction

Water What-ifs
Water Quality and Nitrates & Phosphates

Nitrates & Phosphates Reference Desk
 * Teacher Notes, Lesson Extensions and Alternative Assessment Ideas
 * Warning Signs of Pollution
 * Using Lamotte water quality test kit
 * Using CBL equipment

As 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.

Nitrates & Phosphates Lessons 1, 2, and 3 are intended for middle school and high school science students. These lessons focus on the effects of fertilizers and the effect on algae of varying the level of nitrates and phosphates. These lessons highlight several aspects of the following competencies:

Lesson1 Does the increased use of fertilizers effect biodiversity?
Lesson 2 Does an increase in nitrate and phosphate levels effect the growth of algae?
Lesson 3 Does the use of increased amounts of fertilizer accelerate seed germination?

Download PDF version of all three Nitrates & Phosphates lessons.


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Last Modified: 2/24/00

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