Summary - Great Pond Watershed Report


Colby College - Problems in Environmental Science (Biology 493) - 1998


This brief summary gives a capsule view of some of the findings from the study to be published this winter, entitled "Land Use Patterns in Relations to Lake Water Quality in the Great Pond Watershed"

Water Quality of Great Pond and Tributaries


General Chemistry and Tributaries


An overall assessment of general water chemistry was important in developing a comprehensive evaluation of the present water quality of Great Pond. Transparency levels classified the lake as mesotrophic, indicating that it is moderately productive concerning algae growth. The transparency levels are decreasing over time, indicating possible nutrient increases. This trend indicates a gradual shift, which, if not halted, could move towards a eutrophic status in which nutrient concentrations are high enough to cause algal blooms. The level at which anoxia occurs in late fall is becoming shallower over time. This could also be evidence of increasing productivity.
Other chemical data indicates that Great Pond has better water quality than many other Maine Lakes. The color value of Great Pond was low compared to other Belgrade Lakes, indicating negligible concentrations of natural dissolved acids such as tannins and lignins. Low levels could allow primary production to occur at a lower depth, increasing primary production overall. The pH of the lake was normal and the alkalinity tests indicated that Great Pond is well buffered against acid inputs. The conductivity levels found in the lake were also classified as normal for Maine lakes, although this value has increased slightly over time.
Conductivity levels were higher in the tributaries than in the lake. Tributaries also had higher turbidity levels than the lake. Trout Brook (8T) had the highest level. This is of concern since high turbidity and high conductivity can indicate sediments bringing nutrients into the lake. The color values of the tributaries were variable and Robbins Mill Stream (9T) and Pinkhams Cove Tributary (12T) showed high levels. Great Meadow Stream (10T), the main input into the lake, had a low pH.

Phosphorus and Water Budget


The water budget is used to determine the amount of water entering Great Pond and the flushing rate of the lake. Great Pond has a low flushing rate of 0.52 flushes per year. The low flushing rate can allow nutrients to build up in the water column and bottom sediments, which can lead to an increased rate of eutrophication for the lake. Movement of water within the lake can also affect water quality. Great Pond has a number of bays and deep holes in which the water can become trapped and not easily mix with water in the rest of the lake. Nutrients can build up in these bays because the water may not be mixing with the water in the rest of the lake. Managing the level of water in the lake can also affect water quality. Opening the dam at the outlet of Great Pond allows some of the water and nutrients to be flushed out of the lake. Lowering the water level in the fall also reduces the probability of flooding in the spring due to increased runoff and tributary inputs from snowmelt.

Land Use


Residential Land


The quality of septic systems in the Great Pond Watershed is relatively good, with low risk of contamination or nutrient loading from individual systems. It is estimated that only a small number of pre-1974 septic systems are still in use due to high replacement rates over the last decade. Better constructed components of the new septic systems reduce the risk of contamination through leakage and stricter regulations for the site design of shoreline septic systems have reduced the potential for high phosphorus loading from septic systems. Improvements in septic systems in the Great Pond Watershed have not been limited to residential systems. The septic systems of summer camps on Great Pond have all had recent repairs or replacements as well. As a result, phosphorus loading from individual systems is probably not a major concern.
While individual systems may release little phosphorus, the aggregate effect of subsurface wastewater disposal systems is a major source of concern. Great Pond is highly developed, and in many cases the development is concentrated in small areas along the shoreline. This is a problem for two reasons. First, no regular inspection schedule exists, so malfunctioning systems are not recognized until the problem is large enough for a neighbor to notice obvious leaks or odors. Once a problem of this magnitude arises, it has already affected residences surrounding it and water quality in the area. The second cause for concern is that concentrated areas of development tend to have smaller lots which reduce the area for soil infiltration. This effect is magnified on properties that have poor septic suitability but have received variances (special permission from MDEP) and continue producing high sewage volume.
The Sub-Surface Waste Water Disposal Act, and the State of Maine Guidelines for Shoreland Zoning protect Great Pond by reducing the potential for nutrient loading from each system. Great Pond is still at risk because of the large number of systems currently in use.

Roads


Roads make up a total of 230 acres or 1.1 percent of the land in the watershed. One hundred and nineteen roads are dirt, while 30 roads are paved. The majority (77) of the roads in the watershed are found in Belgrade. Rome has the second largest number of roads (62), while Smithfield and Mercer have a total of ten roads in the watershed. One hundred and one of these dirt roads can be defined as camp roads, which are the closest roads to the lake. Fifty-seven of these camp roads were classified as being in Needing Work or Poor conditions, indicating the potential to load large amounts of phosphorus into the lake. The number of the camp roads in acceptable conditions for Great Pond is low compared to the number of acceptable camp roads for other Belgrade Lakes.

Managed Land


Cleared and municipal/industrial land did not exhibit similar changes between 1965/66 and 1998. Total cleared land area decreased while municipal/industrial land area increased. Cleared land decreased by 834.4 acres (3.1 percent). Cropped land composed 68.6 percent and grazed land composed 38.0 percent of this total decline. In 1965/66 and 1998 cropped land was the dominant type of cleared land. Municipal/industrial land increased by 183.25 acres (1.1 percent) between 1965/66 and 1998. The majority of this growth was due to the increase of gravel pits. Also contributing to the increase was the addition of an 18-hole golf course along Rt 27 in Belgrade.

Natural Land


Mature forest decreased in the Great Pond Watershed by 1771.75 acres (8.5 percent) from 1965/66 to 1998. Transitional forest increased in the watershed by 2522.95 acres (12.2 percent) from 1965/66 to 1998. Wetlands decreased in the watershed by 981.01 acres (4.7 percent) from 1965/66 to 1998. Some of the forested land has been converted to transitional forest because of selective logging. Forested land has also been the victim of increased development. Some of the wetlands have become transitional forest due to succession along edges. The total area of natural land has decreased as the area of managed land has increased over the past 30 years.