The Colby
Environmental Assessment Team (CEAT) investigated the water quality and factors
affecting water quality in the surrounding watershed of Togus Pond in Augusta,
Maine from June through September 2004.
CEAT analyzed several physical, chemical and biological water quality
parameters, land use patterns in the watershed, and the impact of residential
and commercial development on water quality. Data collected were used to produce models of the watershed
that enabled CEAT to identify possible sources of degradation to the current
and future water quality of Togus Pond.
To obtain a historical perspective, all data collected this summer were
compared to data collected in previous years by the Maine Department of
Environmental Protection. Lake
water quality is most affected by the accumulation of external nutrients,
particularly phosphorus, resulting from surface runoff and land erosion. Internal nutrient loading is an
important factor to consider since a large amount of the phosphorus in the lake
comes from internal sediment loading.
When concentrations of phosphorus approach threshold levels (15 ppb), a
lake may experience algal blooms that decrease the aesthetic, recreational,
ecological, and economic value of the lake and land areas surrounding the lake.
A
brief summary of the CEAT findings in the Togus Pond study:
�
Dissolved
oxygen and mean transparency (3 m) readings for Togus Pond were consistent with
other lakes in the surrounding area.
The range of transparency over the summer months was from 6 m in June
decreasing to 2 m in September.
�
The
dissolved oxygen level during the mid-summer months was 0 ppm at 8 m and below
giving a volume of approximately 1,836,000 m3 of the anoxic water in
the lake (12% of the total volume).
This anoxia allows significant phosphorus release from the sediments.
�
Conductivity
was 58 mMHOs/cm, which is well above the means for other
lakes in the area, suggesting that runoff is contributing particulate matter to
Togus Pond.
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Mean
hardness (22.2 mg/L) was very high compared to surrounding lakes in the area.
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Phosphorus
data were collected from June-September 2004 at the surface, mid-depth, and bottom
of the lake, as well as by epicore samples. Mean total phosphorus was found to be 28 ppb in epicore
samples. Phosphorus levels
increased in epicore and bottom samples throughout the course of the
summer. Phosphorus levels peaked
at 401 ppb in the bottom samples at Site 1 at about 14.7 m (48.2 ft) of
depth.
�
A
phosphorus loading model was used to assess the inputs and outputs of
phosphorus in the Togus Pond watershed in 2004. The budget is based on the amount of phosphorus entering the
lake from the different land use types in the watershed. It also takes into account internal
recycling of phosphorus. The model
predicts that the land area in the Togus Pond watershed contributes 410 kg/yr
of phosphorus to the lake and that 328 kg phosphorus/yr is released from the
sediments within the lake. The mean phosphorus concentration predicted by the
model ranged from 19 ppb to 28 ppb, which was similar to actual water quality
data obtained by CEAT.
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The
mean septic suitability of the watershed soil was 5.0 on a scale of 1-9, with 1
being the least suitable and 9 being the most suitable for septic systems.
�
Roads
within the watershed disproportionately contribute to the phosphorus loading of
Togus Pond. Paved state and
municipal roads contribute approximately four percent of the total phosphorus
load entering the lake, and camp roads contribute five percent of the total
phosphorus load. This is a
substantial amount for the relatively small percent of the watershed land use
devoted to roads (1.5%). Because of
the relatively small road area, road improvement would be an easy way to
decrease the total phosphorus load entering the lake to help improve water
quality. Camp roads and driveways
should be a priority for repair because of their proximity to the water.
�
CEAT
found a total of 283 houses in the Togus Pond watershed. 184 of these houses (65%) are
considered shoreline (within 200 feet of the lake) and 99 houses (35%) are
non-shoreline. There are 221
year-round residences (78% of the houses) and 62 seasonal residences (22%) in
the Togus Pond watershed.
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CEAT
found that 43% of the buffer strips on developed residential lots are
inadequate. The majority of buffer
strips need to be enhanced to decrease nutrient runoff. Many of the older homes do not meet current
setback standards, and shoreline septic systems may contribute
disproportionately to high lake phosphorus levels.
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The
little commercial development that exists in the Togus Pond watershed is
primarily found along Route 3 and Route 105. The proposed expansion of the golf course is of potential
concern for lake water quality.
Clusters of shoreline residences exist in the northern and southern
sections of the lake, eliminating the potential for any major future increase
in residences along the shore.
Future increases in the Togus Pond watershed population will likely
occur outside the shoreline zone.
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The
four remediation methods deemed most applicable to Togus Pond are:
-
Alum
treatment to reduce the concentration of phosphorus in the water column
chemically and to seal the sediment to prevent internal recycling of
phosphorus;
-
Fish
stock manipulation to decrease fish that consume zooplankton to attain higher
levels of zooplankton to reduce the intensity of algal blooms. This method will not reduce the level
of phosphorus in the lake;
-
Drawdown
to remove nutrient-rich water from the lake;
-
Vegetative
mats that trap phosphorus in aquatic plant biomass and remove it from the lake.
The Colby Environmental Assessment Team presentation, �A Watershed Analysis of Togus Pond� will be available online at: http://www.colby.edu/biology/BI493/. The complete report will be available in the spring.