Nitrogen is a critical elemental food source for all plants, including aquatic plants. Some aquatic plants absorb nitrogen from the water, while others absorb it through roots buried in the soil along banks or the bottom of water bodies. Excess nitrogen from agricultural or other local runoff or groundwater leeching can cause imbalances in aquatic systems that affect aquatic plants and other organisms.
Role of Nitrogen
Atmospheric nitrogen accounts for 78 percent of the air we breathe. Chemical and organic sources of nitrogen help aquatic plants produce foliage, convert sunlight to energy, and build proteins. Many aquatic plants absorb large amounts of nitrogen, and can help reduce nitrogen surpluses in water bodies. The roots of floating plants absorb nitrogen directly from water, which is especially useful when the nitrogen content in water builds up faster than it can filter down into the ground for soil-rooted plants, as in the case of storm runoff.
Proper Aquatic Fertilization
Soil-rooted aquatic plants in decorative water features should be fertilized with slow-release tablets buried under the soil so that they do not float into the water, where they upset the ecological balance of the water supply. Liquid fertilizers should be added sparingly, if at all. Often the nitrogen content of the water is more than sufficient to support free-floating aquatic plants. Test the soil and the water before adding any fertilizers, and never add more than is recommended.
When nitrogen runoff or nitrogen that has leeched into groundwater rises past the ability of the aquatic ecosystem to keep it in balance, the nitrogen is no longer a source of food, but becomes a source of contamination. The excess nitrogen can cause algae blooms. An abundance of aquatic plants can manage high nitrogen levels in water systems, but most waterways and lakes lack sufficient aquatic plants.
Excess nitrogen in waterways often spurs aquatic weed growth and algae blooms rather than a balanced growth of aquatic plants. Aquatic weeds multiply readily in the presence of extra food and can choke waterways and out-compete beneficial aquatic plants. Algae blooms absorb high amounts of dissolved oxygen, which leads to the suffocation of fish and other aquatic life. The algae mats also block sunlight to submerged aquatic plants, often causing them to die as well.
When aquatic weed plants die, they add sediment and organic material to water systems, encouraging the growth of microbes, bacteria and algae. These microbes can cause disease or use up dissolved oxygen in the water. Proper fertilization practices on farms, at the home and in commercial areas reduce fertilizer runoff. Animal and human wastes also contain high amounts of nitrogen, and should be composted for terrestrial vegetative growth rather than being dumped into water sources, where they become pollutants.