8. Analysis of impacts of lake-level management on wetland resources
of Sebago Lake.
Based on available literature of wetland, FOSL believes the present lake
level management plan may adversely affect Sebago Lake's wetlands. This
contention is supported by a report titled, "Living with the Lakes:
Challenges and Opportunities. A Progress Report to the International Joint
Commission. July 1989" which states in part:
pp. 27-28 "There are many types of wetland configurations on the Great
Lakes (Figure 16), but they share an immediate dependency on the actions
of the lake levels for their cyclical transformations. Fluctuating water
levels increase wildlife diversity. During high water periods, waterfowl,
muskrats, terns and herons and many reptiles and amphibians flourish. Fish
populations increase through their access to the lake from the spawning
grounds provided in the wetlands. Low water levels allow for different populations,
such as redwinged blackbirds, marsh wrens, rails, deer, rabbits and smaller
mammals, to be nurtured. The important thing to note here is that neither
flooded wetlands nor dry wetlands are most suitable to wildlife, but rather
the changes themselves seem to be most effective in sustaining and balancing
populations (Annex B Section 3.3)."
p.28 "The role of wetlands in water purification is also of critical
importance in attempting to gain an overview of the interconnectedness of
the elements of the natural ecosystem and the implications for human beings
in the Basin. Recent studies have indicated that the role of the wetlands
in water purification needs to be given serious consideration. Not only
do the wetlands slow down the movement of sediments and thereby trap pollutants,
but the plant life absorbs many of the more persistant pollutants, such
as heavy metals. All these functions are, of course, in addition to the
uses which humans make of the wetlands for sport, recreation, commercial
activities and aesthetic enjoyment."
p. 28: "The relationship of water levels, wildlife and vegetation is
the basis for the support of life in the Great Lakes Basin. Although not
all aspects of this relationship are known and understood, it is clear that
changes in any part of it will have very wide implications for the others.
For some wildlife, such as migratory waterfowl, the wetlands of the Great
Lakes are critical to their survival."
We do know that other lake wetlands in Maine have been altered by lake regulation.
China Lake is one example. In the early 1970s China Lake regulation changed
from a more naturally fluctuating regime to an increased lake level management
with reduced annual water level fluctuation. Dramatic changes in wetland
vegetation occurred, as evidenced in aerial photographs. Constant inundation
of the wetlands adjacent to China Lake has eliminated the ability of the
lake wetlands to dry out, preventing nutrients from being oxidized and safely
reduced. The story of China Lake is available on the web site http://www.depu.org/
FOSL believes the present water level management has reduced the habitat
values of Sebago Lake wetland. Sebago Lake wetlands need periods of drying
out to allow organic nutrient oxidation and reduction. Natural, seasonal
drying of the wetland bottom also serves to create more biodiversity and
a more healthy wetland (Wilcox 1991,1992,1993, 1995). Many of the Sebago
Lake wetlands under the present water level management will never be dry
during the growing season. This is a great change for the Sebago Lake wetlands.
FOSL requests the Commission review pertinent wetland literature and conduct
an analysis of the impacts of lake level regulation on the ability of Sebago
Lake wetlands to oxidize and filter out nutrients and prevent them from
reaching the lake.
Normandeau Associates (1994) provided additional support for the importance
of of natural water level fluctuations to the health and maintenance of
Sebago Lake's wetlands:
p. 23: "Research on the Great Lakes and elsewhere has shown that fluctuating
water levels play critical roles in developing and maintaining wetlands.
Periodic flooding and drying maximizes the areal extent of the wetland development,
increases diversity of wetland species and generally improves overall wetland
value as habitat for fish and wildllife. Of course, the range, duration
and periodicity of water level fluctuations are all important in influencing
wetland development -- not all water level fluctuations are beneficial.
However, it has been generally concluded that fluctuations that more or
less duplicate natural fluctuations usually provide the greatest benefits
and create wetlands of the greatest overall ecological value"
p.23-24: "On the Great Lakes, most of which are largely unregulated,
it has been concluded that periodic water level fluctuation by as much as
2 meters (6 plus feet) are not only acceptable, but necessary to maintain
riparian wetlands in their current state. Reductions in fluctuations, of
either extreme highs or lows would be expected to result in negative impacts
to the wetlands. As discussed previously, water level fluctuations on Sebago
are similar to those on the Great Lakes when evaluated over 20 years or
more. Therefore, it seems reasonable to assume that water level fluctuations
on Sebago would be desirable and necessary to maximize wetland values. Although
detailed wetland evaluations have not been made on Sebago, it is known that
there are several hundred acres of wetlands associated with the lake (Pierce
and Eldridge, 1992). Using the Great Lakes example, it seems logical to
conclude that these wetlands have developed because of, not in spite of,
historic water level fluctuations and that those fluctuations play an integral
role in maintaining the wetlands in their current conditions. One might
also conclude that a permanent reduction in the range of fluctuations could
be expected to have negative impacts to the wetlands."
P.24: "Although the optimal range of fluctuations can only be determined
by detailed study, we can apply the Great Lakes model to hypothesize a desirable
range. On the Great Lakes, it was concluded that the minimum range of fluctuation
should encompass the "exceeded 10% and 90% range." Figure 4-1
presents this model as applied to Sebago Lake. In evaluating this figure,
it becomes immediately apparent that the hypothesized optimal range of water
level fluctuations far exceeds the current operational strategy mediated
by the Maine DEP, although maximum target ranges fairly closely approximate
the 10% exceeded curve. This is particularly true in the spring, summer
and fall when minimum target levels are consistently 2-3 feet higher than
assumed desirable levels. From a wetlands perspective, one must tentatively
conclude that continued management of Sebago Lake water levels within the
MeDEP target ranges may result in long-term negative impacts to associated
wetlands."
Normandeau Associates (1994) offered the following recommendations:
"3. At a minimum, Sebago Lake water level fluctuations should be within
the historic 'exceeded 10% and 90% range to maximize wetland values.'
4. Both the 10% and 90% levels should be achieved at least once every 10-15
years, and probably in all seasons."
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