Lake & Watershed Resource Management Associates

P O Box 65; Turner, ME  207-336-2980

LWRMA @megalink.net

 

 

Great Moose Lake Water Quality Report

 

2007

 

Baseline water quality monitoring was conducted for Great Moose Lake on July 10 and August 22, 2007 by LWRMA staff. All parameters and indicators that have been checked during the past several years were measured and sampled, using methods and protocol for lake assessment established by the Maine Department of Environmental Protection. Additional data were gathered throughout the summer monitoring period by certified volunteer lake monitors, John Plummer and Don Childs.

 

Overall, Great Moose Lake experienced a slightly above average year, based on sampling results from the two stations on the lake where monitoring has taken place for the past three decades. This assessment is based on water clarity readings (Secchi transparency), and total phosphorus and chlorophyll-a samples taken at both stations.

 

The 2007 water clarity (transparency) average for Great Moose was 4.9 meters at the deep station (01), compared to 4.5 meters in 2006, 4.3 meters in 2005, 5.3 meters in 2004, and the historical average of 4.5 meters for the station. Water clarity at station 02 averaged 5. 3 meters, compared to 5.0 meters in 2006, 4.4 meters in 2005, 5.3 meters in 2004, and the historical average of 4.8 meters at this station. Note that the average at station 01 (deepest point in the lake) was based on combined readings from John Plummer (May through October) and Scott Williams, whereas the average for station 02 was based solely on the July and August samples from Williams. Additional readings taken by Don Childs were not available at the time that this report was prepared. Those additional data can be calculated to adjust this information, when available.

 

Water clarity (Secchi transparency) is one of three primary indicators of the biological productivity of lake ecosystems, in addition to the nutrient phosphorus (TP) and chlorophyll a (CHL), a pigment that is used to measure the concentration of algae in lake water.

 

The 2007 average total phosphorus (TP) level for station 01 was 9 parts per billion, compared to 13 ppb in 2006, and the historical average of 9 ppb. The July TP concentration was 10 ppb, and the August sample measured 8 ppb. The station 02 average was 7.5 ppb, compared to 10 ppb in 2006 and the historical average of 10 ppb for that area of the lake, based on the July sample concentration of 9 ppb, and 8 ppb in August. This is the first time in three years that the average phosphorus concentration at station 02 has been lower than the historical average for the station.

 

A TP sample taken in August near the bottom sediments at the deepest point in station 01 measured 26ppb, and a similar sample taken at station 02 in August measured 14 ppb. Both samples, especially the one taken at station 01 were substantially higher than samples taken near the surface on the same date. The higher concentrations of phosphorus near the bottom may have been associated with very low dissolved oxygen levels at the time at both stations. Historical bottom grab samples taken during the late summer have also been relatively high, indicating that low oxygen levels may be playing a role in the release of phosphorus from the bottom sediments. Dissolved oxygen levels at station 01 were somewhat lower in 2007 than at the approximate same time in 2006, but were similar to historical oxygen levels in this area of the lake during the months of August and September.

 

The 2007 chlorophyll-a (CHL) average at station 01 was 4.0 ppb, compared to 4.2 ppb in 2006 and the historical average of 4.3 ppb at this station. The station 02 average was 3.5 ppb, compared to 4.0 ppb in 2006 and the historical average at this station, 4.0 ppb.  CHL averages in 2007 were consistent with the total phosphorus and transparency averages.

 

 

Dissolved oxygen profiles taken in July and August were similar to those from the past several years. Moderate oxygen depletion (less than 1-2 parts per million) was documented in the deepest seven meters of water at station 01 in August. Oxygen levels were lower than at a similar time in August, 2006, but were similar to historical conditions documented in this region of the lake.  Severe oxygen depletion was documented at Station 02 in August, with virtually no oxygen found below 7 meters depth. The August, 2007 oxygen profile was similar to ones documented at station 02 for several of the preceding years.

 

Additional water quality indicators monitored in 2007 (pH, total alkalinity, water color and specific conductance) were within normal limits for Great Moose Lake, and generally supported the indicators of primary productivity. Water color was somewhat lower than the historical average for both sampling stations, whereas in 2006 it was somewhat higher. This was very likely related to lower average precipitation during much of the summer period in 2007, compared to higher than average conditions in 2006. Lake color is a function of the concentration of natural humic acids in the water. Humic acids from wetland vegetation and other sources may also have been partially responsible for elevating phosphorus levels in the lake in 2006, and may have played a role in the somewhat lower concentrations in 2007. However, phosphorus concentrations in the lake are very likely primarily related to watershed development.

 

 

PLEASE NOTE: THE FOLLOWING INFORMATION FOR 2007 WAS NOT AVAILABLE WHEN THIS REPORT WAS PREPARED. IT CAN BE ADDED TO THIS REPORT SOMETIME AFTER MAY, 2008.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Source: Maine Volunteer Lake Monitoring Program

 

The illustration above shows that for the past three years, the “average” clarity of Maine lakes has been dropping. This may be related to the fact that much of the state has experienced above average precipitation during the period. Or, it may be related to other natural forces that are not known or easily measurable. It can be seen from this illustration, however, that similar declines have occurred historically, sometimes followed by dramatic recoveries. Some of the “clearest” years have been those during which drought has recently occurred, such as 1985 and 2002 and 2003 (possible delayed effects of the severe 2001-2002 drought).

 

Each lake and pond responds in a unique way to the influences of weather, changes in land use in the watershed, and other forces upon the ecosystem. This is because of the wide range of physical, chemical and biological characteristics of each lake basin and its watershed. Most lakes and ponds experience a moderate amount of natural annual variability. There is little doubt that extreme weather was a significant factor in the 2006 findings for Great Moose Lake. However, stormwater runoff is only the “vehicle” through which pollutants from the watershed travel to the lake.  Given the overall water quality of Great Moose, efforts should be taken to insure that long-term conservation practices in the watershed are sustained, so that conditions can be held constant, and hopefully improved, over time.

 

Prepared by Scott Williams, Aquatic Biologist