Nitrogen Cycle – What it is & Why it is Important

The Nitrogen cycle is one of the most vital processes occurring in freshwater ponds. This procedure breaks down toxic ammonia derivatives by beneficial bacteria into less toxic versions that eventually maintains a healthy ecosystem for fish and plants.

There are several steps to the cycle which is summarized as the following:

1. Ammonification (Ammonia Production): the cycle begins with the production of ammonia (NH3) from organic debris - plant matter, uneaten fish food and fish waste (urine excreted from the gills and their fecal matter)- decomposed by bacteria and fungi. This production of ammonia is highly toxic to fish, especially in alkaline water (above pH of 7).

2. Nitrification (Ammonia to Nitrate): this 2 step process converts ammonia (NH3) into nitrites (NO-2) by Nitrosomonas aerobic bacteria. Nitrites are toxic to fish causing “brown blood disease” that binds red blood cells, impeding oxygen production. High nitrite levels can cause fish gills to turn a brownish color.  The second part involves the conversion of nitrites (NO-2) into nitrates (NO-3)  by Nitrobacter bacteria (and similar species).

3. Assimilation (Nitrate Consumption): Nitrate is the final product in the cycle and the main source of fertilizer consumed by algae and aquatic plants.

4. Denitrification (Nitrogen to Nitrogen Gas): in areas where oxygen is low- deep in the sediment and other anaerobic areas- denitrifying bacteria convert nitrate back into nitrogen gas (N2). Nitrogen gas escaping into the atmosphere completes the nitrogen cycle.  

There are many factors that indicate an imbalanced nitrogen cycle in ponds.  Some issues that you may encounter that can signify problems are the following:

Fish Behavior Indicators:

Gasping at the Surface- this indicate fish are struggling for oxygen, often caused by high nitrite levels causing brown blood disease.

Physical Distress -clamped fins, red streaks on fins, rapid gill movement

Lethargy & Isolation- fish behavior is subdued, they may hide or isolate themselves away from other fish   

Erratic Swimming Behavior- fish may dart from one side of the other in an erratically or rub on rocks or the bottom of the pond.

Fish gasping at the surface for air is an indicator of serious ditress

Physical Indicators (visual and olfactory):

Cloudy Water- high ammonia levels can cause water to appear murky.

Excessive Algae Blooms- sudden, rapid algae blooms that cause a “pea soup” appearance or excessive carpet algae on rocks indicating high nutrient levels that plants are not consuming fast enough.

Unpleasant Odors- the presence of strong sulfur-like or “fishy” smells can be a sign of excess fish waste and debris.  

Water Quality Indicators. use a reliable kit to determine your water quality factors:

High Ammonia and Nitrite Levels- in a healthy pond, these levels should be zero. Levels of .25ppm or higher is concerning, and an indicator that the bacteria cannot keep up with the high nutrient load.   

High Nitrate Levels- although this is the least toxic form of ammonia, consistently high levels of nitrates (80ppm or higher) indicate that the pond needs maintenance and can lead to fish distress and illness in fish.

Unstable pH- stable pH levels are important to a healthy nitrogen cycle. Changes in carbonate hardness can cause the Nitrosomonas to go dormant leading to a “pH cycle crash”.

In order to maintain a healthy nitrogen cycle there are many factors to consider, and remeber that Healthy Ponds = Healthy Nitrogen Cycle. There are several key factors that can contribute to a healthy cycle. These include:

Beneficial Bacteria- are the champions of the pond that colonize on rocks, liner, filters and gravel. They are crucial to the health of the nitrogen cycle as they facilitate important chemical processes. A new pond takes 4-8 weeks to mature and high levels are needed to maintain a healthy functioning nitrogen cycle.

Oxygen- another crucial component is dissolved oxygen levels. Oxygen is important for filtration, aquatic life to respiration and enables aerobic beneficial bacteria functions.

Plants- vital partners to bacteria, aquatic plants absorb nitrates and completes with algae for nutrients.

Regular Maintenance- a schedule that removes debris, performs partial water changes and  adding beneficial bacterial treatments on a regular basis  will contribute to a healthy nitrogen cycle. Water changes of 10% - 20% monthly (more less) during late spring through early fall can decrease ammonia levels by diluting the water. Physically removing debris and sludge waste also decreases the ammonia levels.

Reaching and maintaining balance in your pond can take time and a bit of patience. Stop by for a visit and we can discuss how we can help you achieve a healthy pond for your plants and fish. At Nature Perfect Pond & Supply Store located in Tumwater, WA we carry a variety of beneficial bacterial products, water treatments, plants, fish and pond supplies. And we also have classes during the spring and summer if you would like that type of experience. You may also email me with questions and images of your pond at: Kerri.B@NaturePerfect.net Happy Pondering!