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.