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National Aquatic Resource Surveys

Indicators: Nitrogen

What is nitrogen?

Nitrogen, like phosphorus, is a critical nutrient required for all life. Nitrogen can occur in rivers and streams, lakes, and coastal waters in several forms including ammonia (NH3), nitrates (NO3) and nitrites (NO2). These forms of nitrogen occur naturally in the environment at various points of the nitrogen cycle. Nitrogen is a common ingredient in commercial fertilizers.

Excessive growth of common water hyacinth (Eichhornia crassipes), an introduced nuisance aquatic plant that grows in excess in nitrogen-enriched waters. Photo: Forest and Kim Starr, Starr Environmental.

Why is it important to evaluate nitrogen?

Nitrogen is particularly important as a contributor to coastal and estuarine algal blooms. Increased nitrogen inputs can stimulate excess growth of algae, which leads to low dissolved oxygen levels, potential for harmful algal toxins, blockage of sunlight needed by organisms and plants in the water and degraded habitat conditions for benthic macroinvertebrates and other aquatic life. Sources of excess nitrogen to rivers and streams, lakes and coastal waters include fertilizers, waste water, animal wastes and atmospheric deposition.

What can nitrogen tell us about the condition of water?

In appropriate quantities, nitrogen supports the growth of algae and aquatic plants. Increased nitrogen inputs to a waterbody can stimulate excessive growth of algae and aquatic plants, thereby creating eutrophic conditions that interfere with recreation and the health and diversity of vegetation, insects, fish and other aquatic organisms. Over time, animal and plant species composition may shift as native species decline and are replaced by species that take advantage of high nutrient levels. This change in community composition can cause declines in ecological condition and alter the functions that the waterbody provides to the environment.