Nitrogen in Our Watersheds

This blog is part of a feature on Harmful Algal Blooms. To learn more about this topic, visit our Harmful Algal Blooms page, read our blog on Phosphorus, HABs 101 Blog, and read HABS FAQ.  

What is Nitrogen? 

Nitrogen (N) is a chemical element that is found in our environment. The most common inorganic forms of nitrogen, or those lacking carbon-hydrogen bonds, include nitrogen gas (N2), nitrate (NO3-), nitrite (NO2-), and ammonium (NH4 +). Nitrogen gas is the most abundant form of nitrogen; it makes up 78% of the Earth’s atmosphere and readily dissolves into water. Similar to phosphorus, it is an essential element for plant and animal growth and development. However, it also can have adverse effects on lakes and ponds in excess. It is worth noting that nitrogen does not typically receive the focus that phosphorus does, as it is more abundant and has several sources in a watershed. 

Sources of Nitrogen 

In the Adirondacks, nitrogen has historically entered Adirondack lakes and ponds through acid deposition, otherwise known as acid rain. Acid rain primarily occurred when large scale industry in the midwestern United States released excessive amounts of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) as a byproduct of production. Although the impacts of acid rain have been greatly reduced over recent decades, N can still be found in high quantities in our watersheds due to fertilizers, animal operations, sewage, and other human uses.   

Nitrogen is naturally occurring in our environment but can be introduced to our waterbodies through sewage or lack of wastewater treatment, fertilizers, or atmospheric pollution/deposition. N is used as a fertilizer in both a residential and an agricultural setting to improve the growth and development of home gardens, lawns, or large-scale food production. As precipitation occurs, especially heavy-precipitation events, runoff collects N and delivers into waterbodies, often leading to acute loading events. Other sources of nitrogen include the products of chemical reactions from the combustion of fossil fuels, such as from vehicles or large-scale industrial production – causes of acid rain. In the Lake Champlain watershed, these inputs can lead to additional challenges in our watersheds. Inorganic forms of nitrogen are continuously cycled through bacterial decomposition of organic matter.  

How does Nitrogen impact our lakes and ponds? 

Similar to excess levels of phosphorus, excess nitrogen can give a boost to cyanobacteria growth. Nitrogen acts as a nutrient source for cyanobacteria, and can lead to Harmful Algal Blooms. Harmful Algal Blooms occur when cyanobacteria, capable of producing toxins, grow to extremely high numbers and are concentrated at the surface of a lake. Some species of cyanobacteria are capable of producing powerful cyanotoxins, which can be harmful to people and pets. In the Lake Champlain watershed, less of an emphasis is placed on nitrogen than phosphorus as a driver of these blooms, however, consideration for N should still be made. The ratio of nitrogen to phosphorus can be helpful in determining cyanobacteria nitrogen fixing – a process that allows cyanobacteria to convert atmospheric nitrogen to ammonia or bioavailable forms of nitrogen. 

Too much nitrogen can lead to or intensify Harmful Algal Blooms and consequences for pets, livestock, and people. Additional outcomes could include the loss of oxygen in the waterbody, a process known as hypoxia – which has cascading impacts for an aquatic ecosystem. Although these changes can occur in our lakes and ponds, it’s widely accepted that with frequent monitoring, elevated levels of nitrogen can be caught early and mitigated. Updating sewage treatment practices, such as septic systems, and limiting fertilizer use can go a long way in reducing the impacts that excess levels of nitrogen or phosphorus can have on a waterbody.  

Our team at the Adirondack Watershed Institute monitors lakes and ponds for nitrogen levels. To learn more about our water quality monitoring efforts, visit the publications or lake & stream monitoring webpages.