2007 Norway Lakes Water Quality Report

The Lakes Association of Norway, with support from the Town of Norway , continued to monitor the health of the four Norway Lakes in 2007. Water quality monitoring was a combined effort of volunteers and lake professionals. Monitoring of the lakes takes place from early May through September, during the time of year when lakes and ponds are the most biologically productive, and water quality problems are most likely to occur. In addition to monitoring lake water quality, LAON also conducted a screening survey for invasive aquatic plants on the four lakes.

The weather that occurs during and preceding lake monitoring can have a strong influence on indicators of lake water quality, and is likely responsible for some of the variability that is measured within individual seasons and from one year to the next. The 2007 monitoring season was characterized by heavy rain and stormwater runoff in the spring and early summer, followed by moderating conditions from July through September.

Pennesseewassee Lake:

2007 was an average year for Pennesseewassee Lake , when compared to historical conditions. Water clarity averaged 5.7 meters (about 18.5 feet) over the five month monitoring period, compared to above average conditions in 2006 (6.56 meters), 5.9 meters in 2005, and the historical average for the lake of 5.8 meters. While 2007 was one of the clearest years on record for the lake (extending back to 1976) the conditions in 2007 were about average for the thirty year water quality data history for the lake.    

The concentration of phosphorus (the nutrient that is responsible for the growth of algae in lakes) averaged 9 parts per billion (ppb) in 2007, compared to 7 ppb in 2006, 8 ppb in 2005, and the historical average of 9 ppb. It is likely that heavy precipitation and runoff from the watershed resulted in higher phosphorus levels and lower water clarity in 2007.  

Chlorophyll-a (CHL) is a pigment that is measured to determine the concentration of algae in lake water. The 2006 average concentration measured 4.3 ppb, compared to 4.4 ppb in 2006, and the 2005 average of 4.1 ppb The 2007 average was very slightly lower than the historical average of 4.4 ppb.  

The three primary indicators of lake health were consistently about average for Pennesseewassee in 2007.

Late August and September dissolved oxygen levels were very low in the deepest region of the lake, as has been the case for a number of years. In August, the deepest six meters of water, measured at the deepest point in the lake, were completely devoid of dissolved oxygen. By September, conditions had improved somewhat, but oxygen levels remained at, or near zero near the bottom of the lake. Low concentrations of late summer dissolved oxygen serve as a warning that the lake is sensitive and vulnerable to a decline in water quality, regardless of conditions near the surface, where wind and wave action keep oxygen levels high throughout the summer.  

Natural water color levels were average in 2007, as were pH and total alkalinity. All were within the normal range of values for the lake.

No invasive aquatic plants were found in the screening survey of Pennesseewassee Lake . A native species of Milfoil is known to occur in this lake. However, this plant is not invasive.

A species of non-native, invasive snail, referred to as the “Chinese Mystery Snail” has been documented in the lake. This snail has now been observed in all four of the Norway lakes, as well as in a number of area waterbodies, including Thompson, the Range Ponds, and others. The ecological significance of this invader has not been determined. However, from a nuisance perspective, the large, dark green snails are offensive to the nose when they wash up on the shoreline, and there has been at least one report of oxygen depletion in a pond when a large number of the snails died over a short period of time.

Gleotrichia is a colonial blue-green algae that occurs naturally in many Maine lakes. Looking down into the water, “Gleo” has the appearance of tiny off-white dots, often likened to tapioca. In recent years, this algae has become problematic on some Maine lakes and ponds, and it may be on the increase throughout Maine . We will continue to carefully monitor the concentration of this algae in Pennesseewassee.

Hobbs Pond (Little Penn):

Hobbs Pond (Little Penn) was very clear again in 2007, averaging 6.1 meters, which was also the 2006 average (nearly 20 feet). The historical water clarity average for Hobbs Pond is 5.2 meters. In 2005, the average was 5.6 meters, and 5.9 meters in 2004. On average, Hobbs was nearly 3 feet clearer in 2007 than it has been historically! Hobbs drains directly into Pennesseewassee.

Phosphorus levels were very low in 2007, averaging 8 ppb for the five month period. This was substantially lower than the historical average of 11 ppb, and the 2006 average of 10 ppb!  In addition, the average concentration of chlorophyll-a (algal concentration in the pond) was even lower in 2007 (4.3 ppb) than the relatively low average in 2006 (4.5 ppb) and notably lower than the historical average of 4.9 ppb, and the 2005 average of 5.1 ppb.  

During the past decade, the water quality of Hobbs Pond has improved quite notably. Back in the late 1970’s and early 80’s, the annual water clarity was nearly always in the mid 4 meter range (about 15 feet). At times, individual water clarity readings were as low as 2.0 meters (about 6 feet). LAON took the initiative to work with landowners in the watershed to implement conservation practices, which resulted in a nearly immediate turnaround in water quality.

However, the same words of caution apply with Hobbs as with Penn and Sand: Late summer oxygen levels near the bottom of the pond were very low, and phosphorus samples taken near the bottom of the lake were moderately high (19 ppb) compared to surface concentrations. This means that, despite the fact that things look good near the surface, this pond is sensitive and vulnerable, and water quality could easily decline if continued efforts are not taken to protect the very good water quality that has been documented in recent years.

Other water quality indicators that are measured to help support the primary data (color, pH, and total alkalinity) were within the normal range of readings for Hobbs in 2007.

No invasive aquatic plants were detected in Hobbs Pond in the 200 screening survey, however, as indicated above, the Chinese Mystery Snail was documented in the pond.

Sand Pond:

Sand Pond experienced a slightly below average year, especially when compared to 2006 and the spectacular conditions in 2005. Water clarity averaged 7.0 meters (~23 feet), compared to 7.7 meters in 2006, 8.5 meters in 2005, and the historical average of 7.4 meters. Sand Pond is the clearest of the four Norway Lakes , and in general, the water quality of this small pond is above average, compared to other Maine lakes.

The average total phosphorus concentration in Sand Pond last summer was 6 ppb, compared to 6 ppb in both 2006 and 2005, and the historical average of 7 ppb. Chlorophyll-a averaged 3.0 ppb, compared to 2.7 ppb in 2006, 2.5 ppb in 2005 and the historical average of 2.6 ppb. It is interesting that while water clarity was lower in 2007 (but still very good, compared to many area lakes), the phosphorus level has been relatively steady for three years running.

Late summer dissolved oxygen levels were actually improved in 2007, at least compared to conditions in late August, 2006. However, by September 21, there was virtually no oxygen in the water below 10 meters depth. The maximum depth of Sand Pond is approximately 17 meters (56 feet). Phosphorus samples taken near the bottom of the deepest area of the pond in late summer were four times as high as samples from the surface. This suggests that the pond is in a very sensitive state, and that water quality could change if conservation measures are not employed for both existing and new development in the watershed.  

All additional support indicators of water quality were within normal ranges in Sand Pond during the 2006 monitoring season.

No invasive aquatic plants were detected in the 2006 screening survey of Sand Pond. However, the Chinese Mystery Snail was documented for the first time in this pond, and Gleotrichia (discussed above) was observed in the water in September. We will continue to closely monitor the pond for the presence of these two potentially troublesome species.

North Pond:

North Pond is relatively shallow, having a maximum depth of less than 15 feet. The shallow depth can limit the value of water clarity readings that are taken with a Secchi disk, because often the disk reaches the bottom of the pond before it disappears from view. In the 1970’s and 1980’s, the Seechi disk was nearly always visible on the bottom of North Pond. However, when the pond started to experience algal blooms, the situation changed. Often the disk would disappear in the algae-laden water before it reached the bottom at only 12-13 feet.

In 2007, the Secchi disk was visible on the bottom of North Pond in May, June, July and September, but not in August. In 2006, the disk was visible on the bottom throughout the five month monitoring period. The average phosphorus concentration for the year was 15 ppb, compared to the low average of 13 ppb in 2006 and16 ppb in 2005. The historical average for North Pond is 18 ppb, so 2007 levels were definitely lower (better) than average. The concentration of algae in the water, as indicated by chlorophyll-a levels, was higher than it has been for the past two years, averaging 5.2 ppb, compared to 3.8 ppb in 2006, and  4.1 ppb in 2005. However, it was still lower (better) than the historical average of 6.6 ppb.

North Pond experienced a mixed year in 2007, but overall good, especially when compared to the historical average for the pond. But it was not as good as in 2006, which was the best in more than two decades for the pond. This may have been, in part,  the result of nearly constant flushing of the pond from heavy rains throughout the summer. The weather can certainly have a very strong influence on variations in lake and pond water quality from one year to the next. But the improvement  in North Pond in recent years may also be attributed in part to conservation practices that have been implemented in the watershed through the efforts of LAON. North Pond drains into Pennesseewassee Lake .

No invasive aquatic plants were detected in the 2006 screening survey of North Pond, which included the extensive attached wetland areas that drain to Pennesseewassee. The Chinese Mystery Snail has existed in North Pond for more than a decade. The snail popula

Summary:

2007 was an average year for the Norway Lakes , except for Hobbs Pond (Little Penn), which was very clear. Weather conditions during the early summer were similar to those in 2006, but lake systems are complex, and it is possible that the declines observed in 2007 were the result of cumulative conditions from two wet summers.

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.

The following is a summary of findings for Pennesseewassee Lake , and Hobbs (Little Penn), Sand and North Ponds.  

Special thanks are due to certified volunteer lake monitors Patti Ann Douglas on Sand Pond, and Warren Bryant on Pennesseewassee, who contributed additional Secchi disk transparency (water clarity) data in 2007. Their efforts substantially improve our confidence in the monitoring results on the two bodies of water last summer.

TO BE ADDED: Statewide perspective on Maine lakes in 2007.

Prepared by Scott Williams, Aquatic Biologist