What does it tell us about a lake?

pH
By measuring the pH of lake water, it can help us understand the conditions that organisms in the lake are experiencing, and like any other long term water quality measurement, we can tell if conditions are staying the same or if they are changing.

Alkalinity
By measuring the alkalinity of lake water, we can determine the lake’s ability to react to acid inputs. Alkalinity is important to aquatic life because it buffers against changes in pH that could have drastic effects on animals and plants.

The Connection to other Processes in a Lake
pH and the process of photosynthesis in a lake are linked. In photosynthesis, plants use the energy from the sun to convert CO 2 to oxygen and sugar. The use of CO 2 alters the equilibrium in the water, and causes an uptake of hydrogen, increasing the pH of the water. CO 2 removal reduces the acidity of the water and so pH increases. On the other hand, the process of respiration where sugars and oxygen are processed and CO 2 is produced, releases hydrogen ions, leading to lower pH.

Because photosynthesis happens during daylight hours, pH levels may fluctuate from day to night, as well as with growing season. Because photosynthesis happens only in the upper waters of a lake, pH may change with depth as well.

A reduction in pH, which lead to more acidic conditions, has a negative effect on the reproduction of may aquatic organisms, such as crayfish, mollusks, insects, and many zooplankton and fish species. Aquatic species have different tolerances for life in low pH conditions, and although conditions may not lead to death for an individual, it may mean reduced ability in reproduction or growth, which may cause another species to out-compete for resources, and cause the population to be reduced.

The pH of water determines the amount of chemicals and heavy metals that can be dissolved in the water and the amount that are available to aquatic organisms. The pH of water can determine how these chemicals such as phosphorus, nitrogen and carbon can be used by aquatic animals. pH of water can effect how toxic heavy metals such as lead, copper and cadmium are. These metals are generally more toxic at lower pH because they are more soluble in more acidic conditions.

Resources:

Bronmark, Christer and Lars-Anders Hansson. 1998. The Biology of Lakes and Ponds. New York. Oxford University Press.

Kalff, Jacob. 2002. Limnology. Upper Saddle River, N.J. Prentice Hall.

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