Pond and Lake Water Quality
Posted: July 23, 2012
Testing your pond or lake can provide an ongoing record of conditions in your lake and is an important step for assessing its quality and helping prevent problems before they occur. Changes in water quality can indicate threats from sources such as failed or inadequate septic systems, agricultural and lawn runoff, burgeoning development, erosion from construction sites. For ponds or lakes with an existing water quality program, testing is an essential tool for diagnosing the cause of the problem and determining suitable treatment options.
Important Test Parameters
Test parameters that are helpful in assessing the quality of your pond or lake water include pH, alkalinity, total dissolved solids, hardness, nitrate-nitrogen, aluminum, iron manganese, phosphorus, sulfate, and E. coli bacteria.
The pH of a pond should generally fall between 6.0 and 9.0. A pH near 7.0 is optimum for most fish, while fish populations can be reduced or even eliminated when the pH drops below 6.0. Some elements like aluminum increase in the water at a pH below 6.0. A healthy pond or lake should also have some measurable alkalinity, which determines how well the water buffers or maintains the pH at a given level.
Total dissolved solids (TDS) is the sum of all chemical ions dissolved in water and is controlled by the natural source of the pond or lake water. Ponds or lakes in limestone areas may have a higher TDS than water bodies in areas underlain by sandstone or shale due to high concentrations of calcium and magnesium (hardness). TDS can also be affected by nearby land-use activities, with a significant increase over time indicating a potential pollution problem. Other test parameters provide important and direct measures of pollutants that may affect the quality of pond and lake water. Elevated levels of nitrate-nitrogen and total phosphorus may be indicative of pollution from fertilizers, manures, or other nutrient-rich wastes and can cause increased growth of aquatic plants and algae.
Iron, manganese, sulfate, and aluminum are most common in water bodies in coal mining areas or as a consequence of acid rain. While iron and manganese are not directly harmful to aquatic life, they may adversely affect pond aesthetics. Similarly, sulfate is not generally harmful to aquatic life but may be problematic if the pond or lake is used for irrigation purposes. In contrast, aluminum is extremely toxic to aquatic life when present at even relatively low levels.
E. coli bacteria is an important test parameter for ponds or lakes used for swimming or other recreation. Elevated levels can come from septic system runoff, barnyards, or wildlife, especially large numbers of waterfowl. The limit for E. coli bacteria in ponds and lakes for swimming is less than 126 colonies per 100 ml.
For more information on testing your pond or lake, visit the following website - http://www.aasl.psu.edu/water_pond.html. Penn State Extension offices have test kits from the Penn State Analytical Laboratory that you can obtain to test your pond or lake.
Peter T. Wulfhorst AICP
Economic & Community Development Educator
Penn State Extension