Nitrogen is an element needed by all living plants and animals to build protein. In aquatic ecosystems, nitrogen is present in many forms and is a much more abundant nutrient than phosphorus in nature. It is most commonly found in its molecular form, which makes up 79 percent of the air we breathe. This form, however, is useless for most aquatic plant growth.

Blue-green algae, the primary algae of algal blooms, are able to use molecular nitrogen and convert it into forms of nitrogen that plants can take up through their roots and use for growth: ammonia and nitrate.  How do aquatic animals obtain the nitrogen they need to from proteins? In two ways: they either eat aquatic plants and convert plant proteins to specific animal proteins, or they eat other aquatic organisms, which feed upon plants.

Excretions of aquatic organisms are very rich in ammonia, although the amount of nitrogen they add to waters is usually small. Ducks and geese, however, contribute a heavy load of nitrogen (from excrement) in areas where they are plentiful. Through decomposition of dead plants and animals, and the excretions of living animals, nitrogen that was previously "locked up" is released..

Because nitrogen, in the form of ammonia and nitrates, acts as a plant nutrient, it also causes eutrophication. As you learned in the Total Phosphate section, eutrophication promotes more plant growth and decay, which in turn increases biochemical oxygen demand. However, unlike phosphorus, nitrogen rarely limits plant growth, so plants are not as sensitive to increases in ammonia and nitrate levels.

Sources of Nitrates

Sewage is the main source of nitrates added by humans to rivers. Sewage enters waterways in inadequately treated wastewater from sewage treatment plants, in the effluent from illegal sanitary sewer connections, and from poorly functioning septic systems. Septic systems are common in rural areas. Unlike large, centralized urban sewer systems that collect waste from many households, septic systems are generally used to treat the waste from only a single household.

Water containing high nitrate levels can cause a serious condition called methemoglobinemia if it is used for infant milk formula. This condition prevents the baby's blood from carrying oxygen; hence the nickname "blue baby" syndrome.

Two other important sources of nitrates in water are fertilizers, and the runoff from cattle feedlots, dairies, and barnyards. High nitrate levels have been discovered in groundwater beneath croplands due to excessive fertilizer use, especially in heavily irrigated areas with sandy soils. Stormwater runoff can carry nitrate-containing fertilizers from farms and lawns into waterways. Similarly, places where animals are concentrated, such as feedlots and dairies, produce large amounts of wastes rich in ammonia and nitrates. If not properly contained, these can seep into groundwater or be transported in runoff into surface waters.

As discussed in the Total Phosphate section, people have created the eutrophication problem that threatens to limit organism diversity, recreational opportunities, and property values. Only we can reverse eutrophication through thoughtful action.

Sampling Procedure

Any sampling device may be used for this water quality test to obtain representative samples. It is  important to have spotless glassware, rinsed with demineralized water. Always use demineralized water during the nitrate test. Distilled water contains ammonia ions that will interfere with the test. Demineralized water comes with many kits if you don't have the facilities to demineralize water yourself.

See the materials section for information on where to obtain materials and supplies to do this test.

HOME                           BACK TO PROCEDURES

For information on the Washington Virtual Classroom or this website contact Sherry Schaaf at sschaaf@esd114.wednet.edu