Understanding the Water Quality in Your Pond or Lake
July 22nd, 2014
Written by Industry Expert Shannon Junior, Aquatic Ecologist
As an Aquatic Ecologist with SOLitude Lake Management, I visit hundreds of ponds and lakes each year to evaluate them and to provide recommendations for nutrient remediation and long-term management. Our initial assessment typically includes a visual inspection of the pond from the shore, and we are able to gain quite a bit of ecological information about the waterbody during this visit. However, in order to have a more comprehensive understanding of the lake ecosystem, it is important to perform quantitative measurements of the appropriate water quality parameters.
The determination of the most important water quality parameters to sample and the frequency of data collection would be based primarily on the water use and management goals for the pond or lake. There are several general baseline water quality parameters that are helpful to know for every pond. The pH of a waterbody reflects whether it is acidic or basic, and most aquatic organisms thrive at a fairly neutral pH between 6 and 9. Abnormally high or low pH readings can be stressful for fish and other inhabitants of the pond, and extremely acidic conditions can also cause other water quality issues. Alkalinity and hardness are closely related and affect the buffering capacity of the waterbody to fluctuations in pH, which can also be stressful to aquatic organisms. The alkalinity level is particularly important to know for waterbodies with nuisance vegetation issues because there are certain herbicides that can be toxic to fish at low levels. Low alkalinity can be remediated by applying the appropriate amount of lime to the waterbody.
Dissolved oxygen (DO) is another parameter that is especially valuable to know for larger waterbodies and for ponds where recreational fishing is a high priority. Dissolved oxygen is the amount of oxygen gas dissolved in the water column. Small amounts of oxygen enter the water column by direct diffusion at the air/water interface. However, the primary source of oxygen in a pond is production during photosynthesis by aquatic plants and algae. The breakdown of organic matter (i.e. aquatic plants, leaf litter, manure, fish waste) consumes large amounts of oxygen from the water column, so ponds with heavy organic loads may experience low dissolved oxygen conditions, especially during the hottest part of the summer. Fish require oxygen for respiration and become stressed at levels less than 5 mg/L. Dissolved oxygen is typically measured not just at the surface, but in set increments all the way through the water column to the bottom of the pond, along with temperature readings at the same depths. The dissolved oxygen/temperature profile indicates where the thermocline exists in a waterbody (the density gradient between warm surface water and colder bottom waters), and whether anoxic conditions exist near the bottom of the lake. This can have important implications for the health of fish and other aquatic organisms. Submersed diffused air aeration systems or floating aerating fountains can be specified for lakes where low dissolved oxygen is an issue.
Most of the ponds and lakes in the geographic areas that we service have elevated nutrient levels, which are primarily caused by the runoff of fertilizer and sediment from urban and agricultural watersheds. While nutrients are essential to the productivity of the phytoplankton that form the base of the food web, over-enrichment can lead to excessive growth of pond algae and aquatic plants. Nitrogen and phosphorus are the elements most associated with plant growth, although phosphorus is generally the limiting nutrient in fresh waterbodies. With the recent development of a new product called Phoslock that can be used to remediate phosphorus, it has become even more important to understand these parameters. Measuring the numerical values for nutrient parameters can help us to provide a site specific nutrient and algae management program for your pond or lake. We are also able to identify the species of algae that are present in the waterbody in order to determine when potentially harmful blooms of cyanobacteria are present, which also helps us choose the best herbicide to control the target species.
For ponds used for swimming, it is recommended that the E. coli and fecal coliform levels are measured to confirm that the water is safe for humans and pets. These bacteria are indicators of contamination with the fecal matter of humans or other animals, and can be a sign of the presence of pathogens in the water that may cause gastroenteritis or other illnesses.
No matter what your goals are for your pond or lake, baseline water quality testing and periodic monitoring can be a valuable tool for providing long-term management recommendations.
Shannon Junior is an Aquatic Ecologist with SOLitude Lake Management. Since 1998, SOLitude Lake Management has been committed to providing full service lake and pond management services that improve water quality, preserve natural resources, and reduce our environmental footprint. Services are available throughout the Eastern United States. Fisheries management consulting and aquatic products are available nationwide. Learn more about SOLitude Lake Management and purchase products at www.solitudelakemanagement.com.