How Does pH Affect Ponds?

Ponds, home to numerous varieties of aquatic animals and plant life, depend on a set of interacting factors to maintain a good environment. One element that can easily become upset by both natural and man-made influences is the pH balance of the water. A healthy pond requires a fairly narrow range of pH levels. A pH level that has fallen out of balance can have adverse effects on the pond.

  1. pH

    • The pH scale, which measures the acidity or alkalinity of a solution by counting the hydrogen ions present, ranges from 0 to 14, with 7 being neutral. A change of one unit changes the ion concentration by a factor of 10. A pH of 8 is 10 times higher than a 7, and a level of 9 is 100 times higher than 7. A higher pH number means fewer ions. If the pH is less than 7, the substance is acidic. Conversely, a pH of more than 7 indicates that the substance is a base.

    pH Changes

    • Several factors, both natural and man-made, affect the pH level in a pond. Photosynthesis by water plants causes the pH to increase during bright times of the day. The levels drop again in the evening. Heavy rains may overwhelm the geographic "buffers" --- formations that absorb chemicals --- and allow more chemicals that change pH into the water. Acid rain, rainfall that has absorbed chemicals while falling, can cause major changes in the pH level of a body of water.

    Effects on Animals

    • Most water animals require a pH level in a relatively narrow range. Even small pH changes can affect aquatic life. Amphibians are most susceptible to minor changes --- especially lower pH levels --- because their skin absorbs pollutants easily. Low pH can also affect fish in different ways, preventing eggs from hatching and irritating gills and sensitive membranes. Levels higher than 10 or lower than 4 can kill fish and deaden a pond.

    Effects on Plants

    • Like aquatic animals, pond plant life is also susceptible to changes in pH levels. Again, an optimum range of pH levels promotes healthy plants. Absorption of many minerals necessary for growth becomes compromised if pH levels fall too far. Additionally, certain heavy metals are more toxic when dissolved in water, and many dissolve more easily in low-pH water. Other chemicals, such as ammonia, are not toxic at normal pH ranges but become increasingly toxic as levels drop. Alternatively, high pH levels may cause extreme algae growth, which can overtake and choke a pond.