Ecology of Red Maple Swamps in the Glaciated Northeast: A ...

Fig. 24. Red maple swamp in the groundwater slope hydrologic class. This swamp is located on a
hillside over till deposits; the boulders are glacial erratics.
most commonly found at the bases of hills where
groundwater running downslope over bedmck or
dense till layers discharged at the surface during
early spring. By late August, water levels had
dropped as much as 60 cm. Valley swamps appear
to be intermediate between groundwater slope and
groundwater depression wetlands. They occurred
in level or gradually sloping valley bottoms composed
of till or, less mmmonl~ glaciofluvial deposits.
They received large amounts of both surface
runoff and groundwater from adjacent till slopes.
As a result, some valley swamps held a meter or
more of surface water during early spring and still
had water levels within 10 cm of the surface in early
July While water levels were blow the surface for
more than half the growing season, they did not
drop as far as in the perched swamps. Valley
swamps were commonly drained by shxims.
Hydrologic Budgets in Red
Maple Swamps
logic setting of each wetland determines how many
of the possible components are in its water budget
and how large each component is. Over one or more
years, the input-output equation can be expected
to balance; during any given year, inputs generally
equal or exceed outputs during the dormant season,
while outputs (primarily evapotranspiration) predominate
during the growing season. Hence, in
northeastern red maple swamps, water levels are
normally highest during the winter and spring, and
lowest during late summer or early fall.
O'Brien (1977) developed the most detailed
water budget analysis for red maple swamps in the
glaciated Northeast. Although his data were gathered
h m only two wetlands during a single relatively
dry year (annual precipitation 20,! below normal),
the study provides valuable information on relative
inflows and OUMOWS in different geologic settings,
and it describes seasonal changes characteristic of a
large pmprtion of &e red mp]e swamps in ~ i r
region. The two red maple forested wetlands studied
by CYBrien were located 1.6 km apart, about 22 Ian
The possible avenues of water inflow and outflow northwest of Bosbn, Mass. Smd streams arose
in a red maple swamp are summarized in Fig. 2.5. witbin, and drained, each wetland, but neither site
As shown in the previous paragraphs, the hydro- had streams entering (i.e., both were groundwater