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What Is the Chemical Makeup of a Pond?

The most important ingredient in any pond is water; without water, you can't have a pond, after all. But dissolved in that water are a variety of other compounds and substances, some of which are very important for life. The precise composition and chemistry of a pond will vary depending on temperature, sources of water that drain into the pond and so forth, but some of the ingredients you'll find are ubiquitous.

Salts
- All pond water contains various salts. Since the salts are dissolved, they have separated into their component ions, so the pond water will contain sodium ions, chloride ions, potassium and magnesium ions, calcium and sulfate ions and various others in even smaller quantities. The pond water is fresh water, so its salt content is very low compared to seawater, but small quantities are present nonetheless. The salt content varies, as does the concentration of the different ions.
Dissolved Gases
- Since the pond is in contact with the atmosphere, its waters will contain dissolved carbon dioxide, oxygen and nitrogen. At higher temperatures, all of these gases become less soluble in pond water, so the amount present in the pond will be less in hot weather. Animals in the pond like fish consume dissolved oxygen, while water plants and algae produce more. An algae bloom is undesirable, however, because the bacteria that decompose dead algae in the pond consume oxygen, and during an algae bloom they can consume so much oxygen the pond no longer has enough to keep the fish alive.
Nitrogen
- Ponds not only contain dissolved nitrogen gas but also nitrogen in other forms -- ammonia, nitrites and nitrates. Ammonia is excreted by fish and at high levels can become toxic to them. Nitrites and nitrates are produced by bacteria in the water. Nitrites are also potentially toxic to fish and hence undesirable, but the obliging bacteria will generally oxidize them to nitrates, which are not harmful to fish. Nitrogen in the form of nitrates is very important for plant and algae life in your pond.
Other Components
- Phosphorus in the form of phosphates is another pond-water nutrient essential to plant and algal life. Another important consideration is the pond pH, the concentration of hydrogen ions in the pond. Low pH indicates an acidic pond, whereas high pH indicates a basic pond, and 7 is neutral. Ponds may also contain organic matter from decaying fish, plants or other life, although the concentration of these also will vary.

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