Ohio State University

Measures of Nutrients in Water


Availability of Nitrogen

Nutrients are elements (or substances) that are necessary for plant growth. Both nitrogen and phosphorus are two such elements, but large amounts of these elements in water systems can become burdensome by promoting excessive aquatic algal growth. Prime nitrogen sources, eroded soils and sewage sludge, are found in suspended sediments and range from 0.02 to 10%. These concentrations can exist in a variety of forms: organic N (dissolved or particulate), ammonia (dissolved or adsorbed on sediments), nitrate and nitrite N, and dissolved nitrogen gas (N2). Available N is the fraction of the total N that can be readily assimilated by either macrophytes or phytoplankton.

Availability of Phosphorus

Phosphorus is essential to all life, but is naturally scarce in most systems. This element is added to stream systems primarily as animal and human waste, detergents, fertilizers, and as a product of soil erosion. Phosphorus, found in two major forms, inorganic and organic, is readily removed from aquatic environments when fine-grained particles and organic phosphorus compounds settle in the water. Inorganic P (from fertilizers and detergents) can lead to an overload of nutrients, eutrophication. Organic P eventually breaks down into inorganic orthophosphates and becomes readily available to plants.

Testing Information

There are many different laboratory techniques used to assess the quantity and type of nitrogen and phosphorus in water and sediment samples. These analyses are quite complex and require a knowledgeable technician and the ability to isolate the desired form of the investigated element.

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