2009 Worthley Pond Water Quality Summary
Prepared by Scott Williams, Aquatic Biologist
Lake & Watershed Resource Management Associates
P.O. Box 65
Turner, ME 04282
Although the overall water quality of Worthley Pond continues to be good, conditions documented during the past two years suggest that the pond is vulnerable to a negative change under certain circumstances. While the extreme weather for the summer may have caused unusual conditions to occur in Worthley Pond, the demonstration provided by mother nature shows us how precipitation, stormwater runoff and watershed development have caused a two year decline in the pond. Unless similar weather occurs in 2010, it is likely that the pond will recover the very good water quality that it has had historically.
However, some of the changes observed during the past two years may be part of a longer-term trend. Although historical sampling is somewhat limted, the concentration of chlorophyll a in the lake appears to be rising - an indication that algae levels in the water are increasing. This possibility is cause for concern.
Late summer oxygen levels continue to be low in Worthely, and while this phenomenon does not appear to pose a threat to water quality at this time, any worsening of this condition could seriously impact water quality, as well as the health of the coldwater fishery.
The most effective strategy for protecting the lake against increasing algae growth in the lake, resulting in additional dissolved oxygen loss during the summer, is to implement water quality conservation practices in the watershed to minimize the amount of phosphorus that flows into the lake from areas that are developed. This includes roads, residential lots, timber harvest areas, and any locations where the natural forest cover has been altered. Proposals for new development in the watershed should always be assessed for the potential of the project to impact water quality, and specific conservation practices should be required to protect Worthley Pond.
2006 Worthley Pond Water Quality Report
Lake & Watershed Resource Management Associates
P O Box 65; Turner, ME 207-336-2980
LWRMA @megalink.net
The Water quality of Worthley Pond was assessed through baseline monitoring and sampling of the pond on August 10, 2006. The sampling entailed water clarity readings, a dissolved oxygen and temperature profile from the surface to the bottom of the deepest point in the pond, total phosphorus samples taken near the surface and bottom of the pond, a chlorophyll-a sample to determine the concentration of algae in the water, a check of the natural background color, pH measurement, and a measurement (total alkalinity) of the ability of the pond to buffer (resist) changes in pH.
The indicators used to assess lake water quality are highly dynamic, in that most are in a state of constant change, due to a wide range of factors that include the influence of weather, natural daily (circadian) rhythms of the physical, chemical and biological elements of the lake ecosystem, and human influences that, over time, can alter water quality in a number of ways.
This “natural variability” of lake systems presents challenges to our ability to characterize water quality, and to identify changes, or trends, over time. For this reason, many years of data are generally required to be able to discuss the water quality of individual lakes with a degree of confidence. Fortunately, water quality data have been collected for Worthley Pond since 1980 (Maine DEP and Maine VLMP database). A large percentage of the basic information has been obtained by trained volunteers, with the remainder provided by lake water quality professionals, including Maine DEP and LWRMA biologists.
Worthley Pond was very clear on August 10, 2006, measuring 6.82 meters (22.2 feet). While only a single reading, this is considerably above the average for Maine lakes (approximately 5.5 meters). The historical average for Worthley Pond is 6.7 meters, and the average in 2005 was 6.6 meters. Water clarity is an indirect indication of the growth of algae in the water. User perception surveys in Maine have indicated that clear water is highly valued by the public.
Phosphorus is the nutrient that most influences the growth of algae in lakes and ponds. The concentration of total phosphorus (organic and inorganic forms) near the surface of Worthley Pond last August measured 5 parts per billion (ppb). This is a relatively low concentration that is consistent with the excellent water clarity of the pond. The historical phosphorus average for Worthley is 7 ppm, and the 2005 concentration measured 6 ppm. All of these readings are lower than the average for Maine lakes.
Chlorophyll-a (CHL) is a pigment that occurs in plant cells. Its measurement is a direct means of determining the concentration of algae in lake water. The 2006 concentration of CHL in Worthley Pond measured 3.6 ppb, compared to the historical average of 3.1 ppb, and the 2005 average of 4.3 ppb. Although the number of historical CHL samples from Worthley Pond is limited, there is some indication that the concentration of CHL has increased since sampling first started in 1980. This should be monitored closely in the future, since an increase in CHL levels in lake water may indicate not only an increase in algal growth, but possibly a decline in water quality.
The temperature and dissolved oxygen profiles taken on August 10 showed moderate oxygen loss in the deepest area of the pond. Readings below 7 meters depth showed progressive depression, then depletion of oxygen levels, similar to what has been documented in the past.
The loss of dissolved oxygen in late summer is associated with thermal stratification, in which cold, dense water in the deepest area of the lake loses oxygen because it is unable to mix with the warmer, well-oxygenated water near the surface. The degree to which oxygen is lost during the summer period may be an indication of the extent to which a body of water is “stressed”. Although Worthley Pond presently experiences above average water quality, based on water clarity and phosphorus and chlorophyll levels, the persistent late summer oxygen loss suggests that the pond is vulnerable to change.
A phosphorus sample taken near the bottom of the pond, where the dissolved oxygen concentration was very low, was nearly three times as high as the phosphorus level near the surface. This may indicat that the low level of oxygen is triggering the release of phosphorus from the bottom sediments. This sample was consistent with results obtained in previous years.
Natural color, pH and total alkalinity levels were within the normal historical range for Worthley Pond in 2006.
Overall, 2006 was a good year for Worthley Pond. With continued conservation efforts on the part of the watershed community, the future of this pond is hopeful. Compared to other lakes and ponds in the region, the water quality of Worthley is certainly above average.
