Discharge of clay and fine silt into Sebago Lake due to high water
levels, Long Point, Standish. Summer 2002.
5. Analysis of impacts
of lake-level management on water quality of Sebago Lake.
FOSL requests that the relationship between lake level management and water
quality be addressed in the EIS.
FOSL requests that the Secchi disc, lake level and storm data be reviewed
and scientifically analyzed in an EIS.
FOSL believes that in the late spring and early summer of 1998 the 15 foot
clarity readings lakewide were primarily caused by the erosion of shoreline
sediments and resuspension of previously eroded material.
The Portland Water District has mentioned that the poor Secchi disk readings
in 1998 were caused by brown stained water flushed into the lake from adjacent
bogs and wetlands. FOSL believes the causes and impacts of the reduced clarity
are complicated and deserve more study. FOSL requests the EIS analyze the
effects of lake regulation on the input of brown stained water generated
from adjacent wetlands and bogs.
Brown stained water greatly increases light attenuation and significantly
reduces the depth of the euphotic zone. This can greatly degrade the resilience
of the lake ecosystem to resist pollution. FOSL believes the recent shoreline
erosion is a significant contributor to the reduction of water clarity.
Portland Water District has stated that riverine inputs from the watershed
are the major source of phosphorus to the lake. FOSL believes the timing
of the greatest runoff occurs in the snow pack melt and the early spring.
At this time the lake is generally unstratified and sediments can rapidly
sink to the deeper depths where they are safely deposited in the profundal
zone (Perry and Stanford 1982).
The present water level regime maintains higher lake levels into the summer
allowing for a high potential for erosion and sediment resuspension. This
is the time when the lake stratifies. Little attention has been given to
the direct nutrient of phosphorus laden sediment from shoreline erosion.
Sediments and organics can remain in the top layer of the lake until the
lake becomes unstratified in the fall. This phosphorus input is increasing
the growth of phytoplankton, periphyton and aquatic macrophytes, especially
in the littoral areas. FOSL underwater pictures show a siltated littoral
zone with an increase in biomass. We request that FERC include in the EIS
an investigation of these changes in the quality of the littoral zone because
these changes did not occur until the lake water level management became
highly unnaturally regulated in 1987.
In the early 1990s a lifelong resident of North Sebago asked FOSL to observe
the water clarity through the winter ice from an ice shack. This ice shack
was located about 150 yards from Spider Island and offshore from Nason's
Beach. The resident explained he had never seen what he was about to FOSL
observers in the many decades he had ice fished in this area. The water
clarity was poor and a greenish haze (algae bloom) made it difficult to
see the bottom in about 15 to 20 feet of water. This area, like much of
the west shore, had suffered significant erosion during the late 1980s.
Clay exposed embankments south of Nason's Beach had been observed to pollute
the lake with clay plumes during high water and wind direction from the
northeast. The owner of Spider Island has lost substantial land area from
his property due to sedimentation and recession. FOSL believes winter monitoring
is necessary in the littoral zone of Sebago Lake. FOSL suspects this type
of winter algae bloom was related primarily to the shoreline erosion caused
by post-1987 lake regulation. FOSL requests that winter water clarity be
analyzed in the EIS and that FERC requests the licensee begin a winter monitoring
of water clarity. To understand what is happening to the biota and food
web of Sebago Lake it is very important that monitoring through the winter
months occur. FOSL believes this is another case where the littoral area
lake bottom and waters have been negatively impacted by unnatural rates
of shoreline erosion since 1987.
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